Note: Descriptions are shown in the official language in which they were submitted.
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METHODS AND APPARATUS FOR PROVIDING LUMINANCE
COMPENSATION
Field of the Disclosure
[0001] The present disclosure relates generally to the generation of variable
color or
variable color temperature light, wherein compensation is provided for the
natural
phenomenon of perceived different brightness for different colors or color
temperatures
having the same luminance.
Backeround
[0002] A well-known phenomenon of human vision is that humans have different
sensitivities to different colors. The sensors or receptors in the human eye
are not equally
sensitive to all wavelengths of light, and different receptors are more
sensitive than others
during periods of low light levels versus periods of relatively higher light
levels. These
receptor behaviors commonly are referred to as "scotopic" response (low light
conditions),
and "photopic" response (high liglit conditions). In the relevant literature,
the scotopic
response of human vision as a function of wavelength k often is denoted as
W(k) whereas
the photopic response often is denoted as V(X); both of these funetions
represent a
normalized response of human vision to different wavelengths X of light over
the visible
spectrum (i.e., wavelengths from approximately 400 nanometers to 700
nanometers). For
purposes of the present disclosure, human vision is discussed primarily in
terms of lighting
conditions that give rise to the photopic response, which is maximum for light
having a
wavelength of approximately 555 nanometers.
[0003] A visual stimulus corresponding to a perceivable color can be described
in terms
of the energy emission of a light source that gives rise to the visual
stimulus. A "spectral
power distribution" (SPD) of the energy emission from a light source often is
expressed as
a function of wavelength X, and provides an indication of an amount of radiant
power per
small constant-width wavelength interval that is present in the energy
emission throughout
the visible spectrum. The SPD of energy emission from a light source may be
measured via
spectroradiometer, spectrophotometer or other suitable instrument. A given
visual stimulus
may be thought of generally in terms of its overall perceived strength and
color, both of
which relate to its SPD.
[0004] One measure of describing the perceived strength of a visual stimulus,
based on
the energy emitted from a light source that gives rise to the visual stimulus,
is referred to as
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"luminous intensity," for which the unit of "candela" is defined.
Specifically, the unit of
candela is defined such that a monochromatic light source having a wavelength
of 555
nanometers (to which the human eye is most sensitive) radiating 1/683 Watts of
power in
one steradian has a luminous intensity of 1 candela (a steradian is the cone
of light
spreading out from the source that would illuminate one square meter of the
inner surface
of a sphere of 1 meter radius around the source). The luminous intensity of a
light source in
candelas therefore represents a particular direction of light emission (i.e.,
a light source can
be emitting with a luminous intensity of one candela in each of multiple
directions, or one
candela in merely one relatively narrow beam in a given direction).
[0005] From the definition above, it may be appreciated that the luminous
intensity of a
light source is independent of the distance at which the light emission
ultimately is
observed and, hence, the apparent size of the source to an observer.
Accordingly, luminous
intensity in candelas itself is not necessarily representative of the
perceived strength of the
visual stimulus. For example, if a source appears very small at a given
distance (e.g., a
tiny quartz halogen bulb), the perceived strength of energy emission from the
source is
relatively more intense as compared to a source that appears somewhat larger
at the same
distance (e.g., a candle), even if both sources have a luminous intensity of 1
candela in the
direction of observation. In view of the foregoing, a measure of the perceived
strength of a
visual stimulus, that takes into consideration the apparent area of a source
from which light
is eniitted in a given direction, is referred to as "luminance," having units
of candelas per
square meter (cd/m2). The human eye can detect luminances from as little as
one millionth
of a cd/mZ up to approximately one million cd/m2 before damage to the eye may
occur.
[0006] The luminance of a visual stimulus also takes into account the photopic
(or
scotopic) response of human vision. Recall from the definition of candela
above that
radiant power is given in terms of a reference wavelength of 555 nanometers.
Accordingly,
to account for the response of human vision to wavelengths other than 555
nanometers, the
luminance of the stimulus (assuming photopic conditions) typically is
determined by
applying the photopic response V(X) to the spectral power distribution (SPD)
of the light
source giving rise to the stimulus. For example, the luminance L of a given
visual stimulus
under photopic conditions may be given by:
), (1)
L = K(P,V, +P2Vz +P3V3 +......
where Pi, P2, P3, etc., are points on the SPD indicating the arnount of power
per small
constant-width wavelength interval throughout the visible spectrum, Vl, V2,
and V3, etc., are
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the values of the V(X) function at the central wavelength of each interval,
and K is a
constant. If K is set to a value of 683 and P is the radiance in watts per
steradian per square
meter, then L represents luminance in units of candelas per square meter
(cd/m2).
[0007] The "chromaticity" of a given visual stimulus refers generally to the
perceived
color of the stimulus. A "spectral" color is often considered as a perceived
color that can be
correlated with a specific wavelength of light. The perception of a visual
stimulus having
multiple wavelengths, however, generally is more complicated; for example, in
human
vision it is found that many different combinations of light wavelengths can
produce the
same perception of color.
[0008] Chromaticity is sometimes described in terms of two properties, namely,
"hue"
and "saturation." Hue generally refers to the overall category of perceivable
color of the
stimulus (e.g., purple, blue, green, yellow, orange, red), whereas saturation
generally refers
to the degree of white which is mixed with a perceivable color. For example,
pink may be
thought of as having the same hue as red, but being less saturated. Stated
differently, a
fully saturated hue is one with no mixture of white. Accordingly, a "spectral
hue"
(consisting of only one wavelength, e.g., spectral red or spectral blue) by
definition is fully
saturated. However, one can have a fully saturated hue without having a
spectral hue
(consider a fully saturated magenta, which is a coinbination of two spectral
hues, i.e., red
and blue).
[0009] A "color model" that describes a given visual stimulus may be defined
in terms
based on, or related to, luminance (perceived strength or brightness) and
chromaticity (hue
and saturation). Color models (sometimes referred to alternatively as color
systems or color
spaces) can be described in a variety of manners to provide a construct for
categorizing
visual stimuli; some examples of conventional color models employed in the
relevant arts
include the RGB (red, green, blue) model, the CMY (cyan, magenta, yellow)
model, the
HSI (hue, saturation, intensity) model, the YIQ (luminance, in-phase,
quadrature) model,
the Munsell system, the Natural Color System (NCS), the DIN system, the
Coloroid
System, the Optical Society of America (OSA) system, the Hunter Lab system,
the Ostwald
system, and various CIE coordinate systems in two and three dimensions (e.g.,
CIE x,y;
C1E u',v'; CIELUV, CIELAB). For purposes of illustrating an exemplary color
system, the
CIE x,y coordinate system is discussed in detail below. It should be
appreciated, however,
that the concepts disclosed herein generally are applicable to any of a
variety of color
models, spaces, or systems.
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[0010] One example of a commonly used model for expressing color is
illustrated by
the CIE chromaticity diagram shown in Fig. 1, and is based on the CIE color
system. In
one implementation, the CIE system characterizes a given visual stimulus by a
luminance
parameter Y and two chromaticity coordinates x and y that specify a particular
point on the
chromaticity diagram shown in Fig. 1. The CIE system parameters Y, x and y are
based on
the SPD of the stimulus, and also take into consideration various color
sensitivity functions
which correlate generally with the response of the huinan eye.
[0011] More specifically, colors perceived during photopic response
essentially are a
function of three variables, corresponding generally to the three different
types of cone
receptors in the human eye. Hence, the evaluation of color from SPD may employ
three
different spectral weighting functions, each generally corresponding to one of
the three
different types of cone receptors. These three functions are referred to
commonly as "color
matching functions," and in the CIE systems these color matching functions
typically are
denoted as x(A), y(A), z(,Z) . Each of the color matching functions x(A),
y(A), f(A) may be
applied individually to the SPD of a visual stimulus in question, in a manner
similar to that
discussed above in Eq. (1) above (in which the respective components Vl, V2,
V3.... of
V(X) are substituted by corresponding components of a given color matching
function), to
generate three corresponding CIE "primaries" or "tristimulus values," commonly
denoted
as X, Y, and Z.
[0012] As mentioned above, the tristimulus value Y is taken to represent
luminance in
the CIE system and hence is commonly referred to as the luminance parameter
(the color
matching function y(/I) is intentionally defined to match the photopic
response function
V(X), such that the CIE tristimulus value Y = L, pursuant to Eq. (1) above).
Although the
value Y correlates with luminance, the CIE tristimulus values X and Z do not
substantially
correlate with any perceivable attributes of the stimulus. However, in the CIE
system,
important color attributes are related to the relative magnitudes of the
tristimulus values,
which are transformed into "chromaticity coordinates" x, y, and z based on
normalization
of the tristimulus values as follows:
X=X/(X+Y+Z)
y=Y/(X+Y+Z)
z=Z/(X+Y+Z),
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Based on the normalization above, clearly x + y + z = 1, so that only two of
the
chromaticity coordinates are actually required to specify the results of
mapping an SPD to
the CIE system.
[0013] In the CIE chromaticity diagram shown in Fig. 1, the chromaticity
coordinate x
is plotted along the horizontal axis, while the chromaticity coordinate y is
plotted along the
vertical axis. The chromaticity coordinates x and y depend only on hue and
saturation, and
are independent of the amount of luminous energy in the stimulus; stated
differently,
perceived colors with the same chromaticity, but different luminance, all map
to the same
point x,y on the CIE chromaticity diagram. The curved line 50 in the diagram
of Fig. 1
serving as the upper perimeter of the enclosed area indicates all of the
spectral colors (pure
wavelengths) and is often referred to as the "spectral locus" (the wavelengths
along the
curve are indicated in nanometers). Again, the colors falling on the line 50
are by definition
fully saturated colors. The straight line 52 at the bottom of the enclosed
area in the
diagram, connecting the blue (approximately 420 nanometers) and red
(approximately 700
nanometers) ends, is referred to as the "purple boundary" or the "line of
purples." This line
represents colors that cannot be produced by any single wavelength of light;
however, a
point along the purple boundary nonetheless may be considered to represent a
fully
saturated color.
[0014] In Fig. 1, an "achromatic point" E is indicated at the coordinates x =
y= 1/3,
representing full spectrum white. Hence, colors generally are deemed to become
less
saturated as one moves from the boundaries of the enclosed area toward the
point E. Fig. 2
provides another illustration of the chromaticity diagram shown in Fig. 1, in
which
approximate color regions are indicated for general reference, including a
region around the
achromatic point E corresponding to generally perceived white light.
[0015] VWhite light often is discussed in terms of "color temperature" rather
than
"color;" the term "color temperature" essentially refers to a particular
subtle color content
or shade (e.g., reddish, bluish) of white light. The color temperature of a
given white light
visual stimulus conventionally is characterized according to the temperature
in degrees
Kelvin (K) of a black body radiator that radiates essentially the same
spectrum as the white
light visual stimulus in question. Black body radiator color temperatures fall
within a range
of from approximately 700 degrees K (generally considered the first visible to
the human
eye) to over 10,000 degrees K; white light typically is perceived at color
temperatures
above 1500-2000 degrees K. Lower color temperatures generally indicate white
light
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having a more significant red component or a"warmer feel," while higher color
temperatures generally indicate white light having a more significant blue
component or a
"cooler feel."
[0016] Fig. 3 shows a lower portion of the chromaticity diagram of Fig. 2,
onto which is
mapped a "white light/black body curve" 54, illustrating representative CIE
coordinates of
a black body radiator and the corresponding color temperatures. As can be seen
in Fig. 3, a
significant portion of the white liglit/black body curve 54 (from about 2800
degrees K to
well above 10,000 degrees K) falls within the region of the CIE diagram
generally
identified as corresponding to white light (the achromatic point E corresponds
approximately to a color temperature of 5500 degrees K). As discussed above,
color
temperatures below about 2800 degrees K fall into regions of the CIE diagram
that typically
are associated with "warmer" white light (i.e., moving from yellow to orange
to red).
[0017] One anomaly of human visual perception is that different colors or
color
temperatures (i.e., having different CIE chromaticity coordinates x and y)
having a same
luminance (i.e., a same CIE luminance parameter Y) actually may be perceived
to have
different brightnesses, even if perceived under the same photopic viewing
conditions. This
phenomenon is referred to in the relevant literature as the "Helmholtz-
Kohlrausch" effect
(hereinafter referred to as the HK effect). A variety of efforts have been
made to model the
HK effect (e.g., based on empirical data), and some exemplary discussions may
be found in
Nakano et al., "A Simple Formula to Calculate Brightness Equivalent
Luminance," CIE No.
133, CIE 24th Session, Warsaw, V.1, Part 1, pages 33-37, 1999; Natayani et
al., "Perceived
Lightness of Chromatic Object Color Including Highly Saturated Colors," Color
Res.
Appl., 1, pages 127-141, 1992; Hunt, RWG, "Revised Colour-appearance model for
related
and unrelated colors," Color Research Appl., 16, pages 146-165, and Natayani,
Y., "A
Colorimetric Explanation of the Helm.holtz-Kohlrausch Effect," Color Research
Appl., Vol.
23, No. 6, 1998, each of which is incorporated herein by reference.
[0018] In general, according to the HK effect, saturated colors are perceived
to be
brighter than less saturated colors even when equal in luminance. Thus, if a
white light and
a saturated red light of the same luminance are compared side by side under
the same
viewing conditions, the red light looks brighter than the white to most
observers. Similarly,
if a white light and a saturated blue-green light of the same luminance are
compared side by
side, the blue-green light looks brighter than the white.
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[0019] If, however, the saturated red and blue-green lights above are then
added
together and compared with the additive mixture of the two white lights above,
the
respective perceived brightnesses of the two mixtures are now similar; in this
situation, the
luminance of both mixtures is the same, and the perceived brightness of the
mixtures also is
the same. This arises because the mixture of the saturated red and blue-green
light results
in a whitish color, and the additional perceived brightness associated with
the individual
saturated colors has disappeared in the mixture. In view of the foregoing,
while the
luminance for different colors is additive, the perceived brightnesses of two
different colors
may not be additive.
[0020] An empirical formula has been developed (Kaiser, P.K., CIE Journal 5,
57
(1986)) that makes it possible to identify color stimuli which, on average,
may be expected
to be perceived as equally bright. First, a factor F is evaluated from the CIE
chromaticity
coordinates x and y corresponding to a given stimulus as follows:
F = 0.256 - 0.184y - 2.527xy + 4.656x3y + 4.657xy4 . (2)
Then, if two stimuli have respective luminances Yl and Y2, and factors Fl and
F2, the two
stimuli are perceived with equal brightness if:
log(Y, ) + F, =1og(YZ ) + F2. (3)
If the left and right sides of Eq. (3) above are not equal, then whichever is
greater indicates
the stimulus having the greater perceived briglltness. Similarly, it may be
appreciated from
Eq. (3) that, given equal luminance values Yl and Y2 for two different
stimuli, they will
appear equally as bright to an observer if Fl equals F2.
[0021] Fig. 4 illustrates the CIE chromaticity diagram of Fig. 1, on which
loci or
"contours"' 70A, 70B, 70C, etc., of equal values of F are shown based on Eq.
(2) above.
Again, two different colors falling into the same loci or contour appear
equally as bright at
the same luminance; hence, each contour indicated in Fig. 4 may be
conceptually thought of
as an "isobrightness" contour. The collection of isobrightness contours
establishes the
variation in perceived brightness across all chromaticity coordinates. The
numbered values
in Fig. 4 are given in terms of 10F for each contour. It may be observed by
comparing Figs.
2 and 4 that the nadir 70 of the contours (minimum value of 10F= 0.836) occurs
in a
generally yellowish region of the CIE chromaticity diagram. From Fig. 4, it
also may be
appreciated that, pursuant to the HK effect, 10F generally tends to increase
with increased
saturation (i.e., as one moves from the yellowish region around the nadir 70
toward the
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spectral locus 50 or the purple boundary 52 of the diagram), especially in the
direction of
saturated reds, greens, and blues (refer again to Fig. 2).
[0022] Considering both sides of Eq. (3) as base-10 exponents, and re-writing
Eq. (3) in
terms of the values 10F, provides the relationships:
Y10F. =YZlOF2
10 (4)
Y=10F2Y,.
The relationships in Eq. (4) illustrate that the numeric values assigned to
the contours in
Fig. 4 provide factors by which the luminance of a first stimulus having a
chromaticity
lying in one of the contours may be adjusted (increased or decreased) relative
to the
luminance of a second stimulus having a chromaticity lying in a different
contour, so that
both stimuli appear to have the same brightness when seen under the same
viewing
conditions.
[0023] Accordingly, the collection of isobrightness contours given by Eq. (2)
and the
corresponding relationships in Eq. (4) establish the variation in perceived
brightness across
all chromaticity coordinates. For example, consider a first stimulus having a
luminance Yl
and chromaticity coordinates that fall in the contour 70B corresponding to 10F
= 1, and a
second stimulus having a luminance Y2 and chromaticity coordinates that fall
in the contour
70G corresponding to 10F = 1.5. For these two stimuli to be perceived as
having the same
brightness, according to Eq. (4) the luminance Y2 needs to be (1/1.5)
or.667Y1.
Summary
[0024] In view of the foregoing, Applicants have recognized and appreciated
that
lighting apparatus configured to generate multi-colored light, including
apparatus based on
LED sources, maybe prone to the "Helmholtz-Kohlrausch" (HK) effect. More
specifically,
lighting apparatus configured to generate multi-color or multi-color
temperature light may
generate different colors or color temperatures of light that are actually
perceived to have
significantly different brightnesses, notwithstanding identical luminances for
the different
colors or color temperatures. Accordingly, various embodiments of the present
disclosure
are directed to methods and apparatus for providing luminance compensation to
lighting
apparatus so as to mitigate, at least in part, the HK effect.
[0025] For example, one embodiment of the present disclosure is directed to a
method,
comprising an act of generating at least two different colors or color
temperatures of light,
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over a significant range of different saturations or different color
temperatures, with an
essentially constant perceived brightness.
[00261 Another embodiment is directed to an apparatus, comprising at least one
LED
configured to generate at least two different colors or color temperatures of
light over a
significant range of different saturations or different color temperatures,
and at least one
controller to control the at least one LED so as to generate the at least two
different colors
or color temperatures of the light with an essentially constant perceived
brightness.
[00271 Another embodiment is directed to a method, comprising acts of: A)
mapping a
lighting command to a reference frame in relation to which at least one model
for the
Helmholtz-Kohlrausch effect is defined, the lighting command specifying at
least a color or
a color temperature of light to be generated; and B) applying a luminance
compensation
factor to the lighting command, based on the at least one model for the
Helmholtz-
Kohlrausch effect and the mapped lighting command, to provide an adjusted
lighting
command.
[00281 Another embodiment is directed to an apparatus, comprising at least one
LED,
and at least one controller to control the at least one LED based at least in
part on a lighting
command that specifies at least first color or a first color temperature of
light to be
generated by the at least one LED. The at least one controller is configured
to map the
lighting command to a reference frame in relation to which at least one model
for the
Helmholtz-Kohlrausch effect is defined. The at least one controller further is
configured to
apply a luminance compensation factor to the lighting command, based on the at
least one
model for the Helmholtz-Kohlrausch effect and the mapped lighting command, to
provide
an adjusted lighting command.
[0029] As used herein for purposes of the present disclosure, the term "LED"
should be
understood to include any electroluminescent diode or other type of carrier
injection/junction-based system that is capable of generating radiation in
response to an
electric signal. Thus, the term LED includes, but is not limited to, various
semiconductor-
based structures that einit light in response to current, light emitting
polymers,
electroluminescent strips, and the like.
[0030] In particular, the term LED refers to light emitting diodes of all
types (including
semi-conductor and organic light emitting diodes) that may be configured to
generate
radiation in one or more of the infrared spectrum, ultraviolet spectrum, and
various portions
of the visible spectrum (generally including radiation wavelengths from
approximately 400
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nanometers to approximately 700 nanometers). Some examples of LEDs include,
but are
not limited to, various types of infrared LEDs, ultraviolet LEDs, red LEDs,
blue LEDs,
green LEDs, yellow LEDs, amber LEDs, orange LEDs, and white LEDs (discussed
further
below). It also should be appreciated that LEDs may be configured and/or
controlled to
generate radiation having various bandwidths (e.g., full widths at half
maximum, or
FWHIVI) for a given spectrum (e.g., narrow bandwidth, broad bandwidth), and a
variety of
dominant wavelengths within a given general color categorization.
[0031] For example, one implementation of an LED configured to generate
essentially
white light (e.g., a white LED) may include a number of dies which
respectively emit
different spectra of electroluminescence that, in combination, mix to form
essentially white
light. In another implementation, a white light LED may be associated with a
phosphor
material that converts electroluminescence having a first spectrum to a
different second
spectrum. hi one example of this implementation, electroluminescence having a
relatively
short wavelength and narrow bandwidth spectrum "pumps" the phosphor material,
which in
turn radiates longer wavelength radiation having a somewhat broader spectrum.
[0032] It should also be understood that the term LED does not limit the
physical and/or
electrical package type of an LED. For example, as discussed above, an LED may
refer to
a single light emitting device having multiple dies that are configured to
respectively emit
different spectra of radiation (e.g., that may or may not be individually
controllable). Also,
an LED may be associated with a phosphor that is considered as an integral
part of the LED
(e.g., some types of white LEDs). In general, the term LED may refer to
packaged LEDs,
non-packaged LEDs, surface mount LEDs, chip-on-board LEDs, T-package mount
LEDs,
radial package LEDs, power package LEDs, LEDs including some type of
encasement
and/or optical element (e.g., a diffusing lens), etc.
[0033] The term "light source" should be understood to refer to any one or
more of a
variety of radiation sources, including, but not limited to, LED-based sources
(including
one or more LEDs as defined above), incandescent sources (e.g., filament
lamps, halogen
lamps), fluorescent sources, phosphorescent sources, high-intensity discharge
sources (e.g.,
sodium vapor, mercury vapor, and metal halide lamps), lasers, other types of
electroluminescent sources, pyro-luminescent sources (e.g., flames), candle-
luminescent
sources (e.g., gas mantles, carbon arc radiation sources), photo-luminescent
sources (e.g.,
gaseous discharge sources), cathode luminescent sources using electronic
satiation,
galvano-luminescent sources, crystallo-luminescent sources, kine-luminescent
sources,
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thermo-luminescent sources, triboluminescent sources , sonoluminescent
sources,
radioluminescent sources, and luminescent polymers.
[0034] A given light source may be configured to generate electromagnetic
radiation
within the visible spectrum, outside the visible spectrum, or a combination of
both. Hence,
the terms "light" and "radiation" are used interchangeably herein.
Additionally, a light
source may include as an integral component one or more filters (e.g., color
filters), lenses,
or other optical components. Also, it should be understood that light sources
may be
configured for a variety of applications, including, but not limited to,
indication, display,
and/or illumination. An "illumination source" is a light source that is
particularly
configured to generate radiation having a sufficient intensity to effectively
illuminate an
interior or exterior space. In this context, "sufficient intensity" refers to
sufficient radiant
power in the visible spectruin generated in the space or environment (the unit
"lumens"
often is employed to represent the total light output from a light source in
all directions, in
terms of radiant power or "luminous flux") to provide ambient illumination
(i.e., light that
may be perceived indirectly and that may be, for example, reflected off of one
or more of a
variety of intervening surfaces before being perceived in whole or part).
[0035] The term "spectrum" should be understood to refer to any one or more
frequencies (or wavelengtlls) of radiation produced by one or more light
sources.
Accordingly, the tenn "spectrum" refers to frequencies (or wavelengths) not
only in the
visible range, but also frequencies (or wavelengths) in the infrared,
ultraviolet, and other
areas of the overall electromagnetic spectrum. Also, a given spectrum may have
a
relatively narrow bandwidth (e.g., a FWHM having essentially few frequency or
wavelength components) or a relatively wide bandwidth (several frequency or
wavelength
components having various relative strengths). It should also be appreciated
that a given
spectrum may be the result of a mixing of two or more other spectra (e.g.,
mixing radiation
respectively emitted from multiple light sources).
[0036] For purposes of this disclosure, the term "color" is used
interchangeably with
the term "spectrum." However, the term "color" generally is used to refer
primarily to a
property of radiation that is perceivable by an observer (although this usage
is not intended
to limit the scope of this term). Accordingly, the terms "different colors"
implicitly refer to
multiple spectra having different wavelength components and/or bandwidths. It
also should
be appreciated that the term "color" may be used in connection with both white
and non-
white light.
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[0037] The term "color temperature" generally is used herein in connection
with white
light, although this usage is not intended to limit the scope of this term.
Color temperature
essentially refers to a particular color content or shade (e.g., reddish,
bluish) of white light.
The color temperature of a given radiation sample conventionally is
characterized
according to the temperature in degrees Kelvin (K) of a black body radiator
that radiates
essentially the same spectrum as the radiation sample in question. Black body
radiator
color temperatures generally fall within a range of from approximately 700
degrees K
(typically considered the first visible to the human eye) to over 10,000
degrees K; white
light generally is perceived at color temperatures above 1500-2000 degrees K.
[0038] Lower color temperatures generally indicate white light having a more
significant red component or a "wanner feel," while higher color temperatures
generally
indicate white light having a more significant blue component or a "cooler
feel." By way
of example, fire has a color teinperature of approximately 1,800 degrees K, a
conventional
incandescent bulb has a color temperature of approximately 2848 degrees K,
early morning
daylight has a color temperature of approximately 3,000 degrees K, and
overcast midday
skies have a color temperature of approximately 10,000 degrees K. A color
image viewed
under white light having a color temperature of approximately 3,000 degree K
has a
relatively reddish tone, whereas the same color image viewed under white light
having a
color temperature of approximately 10,000 degrees K has a relatively bluish
tone.
[0039] The terms "lighting unit" and "lighting fixture" are used
interchangeably herein
to refer to an apparatus including one or more light sources of same or
different types. A
given lighting unit may have any one of a variety of mounting arrangements for
the light
source(s), enclosure/housing arrangements and shapes, and/or electrical and
mechanical
connection configurations. Additionally, a given lighting unit optionally may
be associated
with (e.g., include, be coupled to and/or packaged together with) various
other components
(e.g., control circuitry) relating to the operation of the light source(s). An
"LED-based
lighting unit" refers to a lighting unit that includes one or more LED-based
light sources as
discussed above, alone or in combination with other non LED-based light
sources.
[0040] The terms "processor" or "controller" are used herein interchangeably
to
describe various apparatus relating to the operation of one or more light
sources. A
processor or controller can be implemented in numerous ways, such as with
dedicated
hardware, using one or more microprocessors that are programmed using software
(e.g.,
microcode) to perform the various functions discussed herein, or as a
combination of
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dedicated hardware to perform some functions and programmed microprocessors
and
associated circuitry to perform other functions. Examples of processor or
controller
components that may be employed in various embodiments of the present
invention
include, but are not limited to, conventional microprocessors, application
specific integrated
circuits (ASICs), and field-programmable gate arrays (FPGAs).
[0041] In various implementations, a processor or controller may be associated
with
one or more storage media (generically referred to herein as "memory," e.g.,
volatile and
non-volatile computer memory such as RAM, PROM, EPROM, and EEPROM, floppy
disks, compact disks, optical disks, magnetic tape, etc.). In some
implementations, the
storage media may be encoded with one or more programs that, when executed on
one or
more processors and/or controllers, perform at least some of the functions
discussed herein.
Various storage media may be fixed within a processor or controller or may be
transportable, such that the one or more programs stored thereon can be loaded
into a
processor or controller so as to implement various aspects of the present
invention
discussed herein. The terms "program" or "computer program" are used herein in
a generic
sense to refer to any type of computer code (e.g., software or microcode) that
can be
employed to program one or more processors or controllers.
[0042] The term "addressable" is used herein to refer to a device (e.g., a
light source in
general, a lighting unit or fixture, a controller or processor associated with
one or more light
sources or lighting units, other non-lighting related devices, etc.) that is
configured to
receive infonnation (e.g., data) intended for multiple devices, including
itself, and to
selectively respond to particular information intended for it. The term
"addressable" often
is used in connection with a networked environment (or a "network," discussed
further
below), in which multiple devices are coupled together via some communications
medium
or media.
[0043] In one network implementation, one or more devices coupled to a network
may
serve as a controller for one or more other devices coupled to the network
(e.g., in a
master/slave relationship). In another implementation, a networked environment
may
include one or more dedicated controllers that are configured to control one
or more of the
devices coupled to the network. Generally, multiple devices coupled to the
network each
may have access to data that is present on the communications medium or media;
however,
a given device may be "addressable" in that it is configured to selectively
exchange data
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with (i.e., receive data from and/or transmit data to) the network, based, for
example, on
one or more particular identifiers (e.g., "addresses") assigned to it.
[0044] The term "network" as used herein refers to any interconnection of two
or more
devices (including controllers or processors) that facilitates the transport
of information
(e.g. for device control, data storage, data exchange, etc.) between any two
or more devices
and/or among multiple devices coupled to the network. As should be readily
appreciated,
various implementations of networks suitable for interconnecting multiple
devices may
include any of a variety of network topologies and employ any of a variety of
communication protocols. Additionally, in various networks according to the
present
invention, any one connection between two devices may represent a dedicated
connection
between the two systems, or alternatively a non-dedicated connection. In
addition to
carrying information intended for the two devices, such a non-dedicated
connection may
carry information not necessarily intended for either of the two devices
(e.g., an open
network connection). Furthermore, it should be readily appreciated that
various networks
of devices as discussed herein may employ one or more wireless, wire/cable,
and/or fiber
optic links to facilitate information transport throughout the network.
[0045] The term "user interface" as used herein refers to an interface between
a human
user or operator and one or more devices that enables communication between
the user and
the device(s). Examples of user interfaces that may be employed in various
implementations of the present invention include, but are not limited to,
switches,
potentiometers, buttons, dials, sliders, a mouse, keyboard, keypad, various
types of game
controllers (e.g., joysticks), track balls, display screens, various types of
graphical user
interfaces (GUIs), touch screens, microphones and other types of sensors that
may receive
some form of human-generated stimulus and generate a signal in response
thereto.
[0046] The following patents and patent applications are hereby incorporated
herein by
reference:
[0047] U.S. Patent No. 6,016,038, issued January 18, 2000, entitled
"Multicolored LED
Lighting Method and Apparatus;"
[0048] U.S. Patent No. 6,211,626, issued April 3, 2001, entitled "Illumination
Components,"
[0049] U.S. Patent No. 6,608,453, issued August 19, 2003, entitled "Methods
and
Apparatus for Controlling Devices in a Networked Lighting System;"
[0050] U.S. Patent No. 6,548,967, issued April 15, 2003, entitled "Universal
Lighting
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Network Methods and Systems;"
[0051] U.S. Patent Application Serial No. 09/886,958, filed June 21, 2001,
entitled
Method and Apparatus for Controlling a Lighting System in Response to an Audio
Input;"
[0052] U.S. Patent Application Serial No. 10/078,221, filed February 19, 2002,
entitled
"Systems and Methods for Programming Illumination Devices;"
[0053] U.S. Patent Application Serial No. 09/344,699, filed June 25, 1999,
entitled
"Method for Software Driven Generation of Multiple Simultaneous High Speed
Pulse
Width Modulated Signals;"
[0054] U.S. Patent Application Serial No. 09/805,368, filed March 13, 2001,
entitled
"Light-Einitting Diode Based Products;"
[0055] U.S. Patent Application Serial No. 09/716,819, filed November 20, 2000,
entitled "Systems and Methods for Generating and Modulating Illumination
Conditions;"
[0056] U.S. Patent Application Serial No. 09/675,419, filed September 29,
2000,
entitled "Systems and Methods for Calibrating Light Output by Light-Emitting
Diodes;"
[0057] U.S. Patent Application Serial No. 09/870,418, filed May 30, 2001,
entitled "A
Method and Apparatus for Authoring and Playing Back Lighting Sequences;"
[0058] U.S. Patent Application Serial No. 10/045,604, filed March 27, 2003,
entitled
"Systems and Methods for Digital Entertainment;"
[0059] U.S. Patent Application Serial No. 10/045,629, filed October 25, 2001,
entitled
"Methods and Apparatus for Controlling Illumination;"
[0060] U.S. Patent Application Serial No. 09/989,677, filed November 20, 2001,
entitled "Information Systems;"
[0061] U.S. Patent Application Serial No. 10/158,579, filed May 30, 2002,
entitled
"Methods and Apparatus for Controlling Devices in a Networked Lighting
System;"
[0062] U.S. Patent Application Serial No. 10/163,085, filed June 5, 2002,
entitled
"Systems and Methods for Controlling Programmable Lighting Systems;"
[0063] U.S. Patent Application Serial No. 10/174,499, filed June 17, 2002,
entitled
"Systems and Methods for Controlling Illumination Sources;"
[0064] U.S. Patent Application Serial No. 10/245,788, filed September 17,
2002,
entitled "Methods and Apparatus for Generating and Modulating White Light
Illumination
Conditions;"
[0065] U.S. Patent Application Serial No. 10/245,786, filed September 17,
2002,
entitled "Light Emitting Diode Based Products;"
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[0066] U.S. Patent Application Serial No. 10/325,635, filed December 19, 2002,
entitled "Controlled Lighting Methods and Apparatus;"
[0067] U.S. Patent Application Serial No. 10/360,594, filed February 6, 2003,
entitled
"Controlled Lighting Methods and Apparatus;"
[0068] U.S. Patent Application Serial No. 10/435,687, filed May 9, 2003,
entitled
"Methods and Apparatus for Providing Power to Lighting Devices;"
[0069] U.S. Patent Application Serial No. 10/828,933, filed Apri121, 2004,
entitled
"Tile Lighting Methods and Systems;"
[0070] U.S. Patent Application Serial No. 10/839,765, filed May 5, 2004,
entitled
"Lighting Methods and Systems;"
[0071] U.S. Patent Application Serial No. 11/010,840, filed December 13, 2004,
entitled "Thermal Management Methods and Apparatus for Lighting Devices;"
[0072] U.S. Patent Application Serial No. 11/079,904, filed March 14, 2005,
entitled
"LED Power Control Methods and Apparatus;"
[0073] U.S. Patent Application Serial No. 11/081,020, filed on March 15, 2005,
entitled
"Methods and Systems for Providing Lighting Systems;"
[0074] U.S. Patent Application Serial No. 11/178,214, filed July 8, 2005,
entitled "LED
Package Methods and Systems;"
[0075] U.S. Patent Application Serial No. 11/225,377, filed September 12,
2005,
entitled "Power Control Methods and Apparatus for Variable Loads;" and
[0076] U.S. Patent Application Serial No. 11/224,683, filed September 12,
2005,
entitled "Lighting Zone Control Methods and Systems."
[0077] It should be appreciated that all combinations of the foregoing
concepts and
additional concepts discussed in greater detail below are contemplated as
being part of the
inventive subject matter disclosed herein. In particular, all combinations of
claimed
subject matter appearing at the end of this disclosure are contemplated as
being part of the
inventive subject matter disclosed herein.
Brief Description of the Drawings
[0078] Fig. 1 illustrates the conventional CIE Chromaticity Diagram.
[0079] Fig. 2 illustrates the diagram of Fig. 1, with approximate color
categorizations
indicated thereon.
[0080] Fig. 3 illustrates a portion of the diagram of Fig. 2, onto which is
mapped a
white light/black body curve representing color temperatures of white light.
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[0081] Fig. 4 illustrates the diagram of Fig. 1, onto which are mapped
contours of
constant perceived brightness pursuant to the "Helmholtz-Kohlrausch" effect.
[0082] Fig. 5 is a diagram illustrating a lighting unit according to one
embodiment of
the disclosure.
[0083] Fig. 6 is a diagram illustrating a networked lighting system according
to one
embodiment of the disclosure.
[0084] Fig. 7 is a flow chart illustrating a metliod according to one
embodiment of the
disclosure for providing luminance compensation, for example, in one or more
lighting
units similar to those shown in Figs. 5 and 6.
[0085] Fig. 8 illustrates the diagram of Fig. 1, onto which is mapped a color
gamut
based on red, green and blue LED-based light sources of the lighting unit of
Fig. 5,
according to one embodiment of the disclosure.
Detailed Description
[0086] Various embodiments of the present disclosure are described below,
including
certain embodiments relating particularly to LED-based light sources. It
should be
appreciated, however, that the present disclosure is not limited to any
particular manner of
implementation, and that the various embodiments discussed explicitly herein
are primarily
for purposes of illustration. For example, the various concepts discussed
herein may be
suitably implemented in a variety of environments involving LED-based light
sources,
other types of light sources not including LEDs, environments that involve
both LEDs and
other types of light sources in combination, and environments that involve non-
lighting-
related devices alone or in combination with various types of light sources.
[0087] Applicants have recognized and appreciated that lighting apparatus
configured
to generate multi-colored light, including apparatus based on LED sources, may
be prone to
the "Helmholtz-Kohlrausch" (HK) effect and hence generate different colors (or
color
temperatures) of light that may be perceived to have significantly different
brightnesses,
notwithstanding identical luminances for the different colors. Accordingly,
various
embodiinents of the present disclosure aire directed to methods and apparatus
for providing
luminance compensation to lighting apparatus so as to mitigate, at least in
part, the HK
effect.
[0088] To create multi-colored or white light based on additive color mixing
principles,
often multiple different color light sources are employed, for example red
light, blue light
and green light, to represent the primary colors. These three primary colors
roughly
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represent the respective spectral sensitivities typical of the three different
types of cone
receptors in the human eye (having peak sensitivities at approximately 650
nanometers for
red, 530 nanometers for green, and 425 nanometers for blue) under photopic
conditions.
Much research has shown that additive mixtures of primary colors in different
proportions
can create a wide range of colors discernible to humans. This is the well-
known principle
on which many color displays are based, in which a red light emitter, a blue
light emitter,
and a green light emitter are energized in different proportions to create a
wide variety of
perceivably different colors, as well as white light, based on additive mixing
of the primary
colors.
[0089] Solid-state lighting devices (e.g., light emitting diodes, or LEDs) are
employed
in many ligliting applications. In one exemplary implementation, to create
multi-colored or
white light, multiple different color LEDs may be employed to represent the
primary colors
(e.g., red LEDs, blue LEDs and green LEDs). Although not completely
monochromatic,
the radiation generated by many "colored" LEDs (i.e., non-white LEDs)
characteristically
has a very narrow bandwidth spectrum (e.g., a full-width at half maximum, or
FWHM, on
the order of approximately 5-10 nanometers). Exemplary approximate dominant
wavelengths for commonly available red, green and blue LEDs include 615-635
nanometers for red LEDs, 515-535 nanometers for green LEDs, and 460-475
nanometers
for blue LEDs. Exemplary variable-color and white light generating devices
based on LED
light sources are discussed below in connection with Figs. 5 and 6. It should
be appreciated
that while some exemplary devices are discussed herein in terms of red, green
and blue
LED sources, the present disclosure is not limited in this respect; namely,
light generating
devices according to various embodiments of the present disclosure may include
LEDs
having any of a variety of dominant wavelengths and overall spectrums (e.g.,
red LEDs,
green LEDs, blue LEDs, cyan LEDs, yellow LEDs, amber LEDs, orange LEDs,
broader
spectrum white LEDs having various color temperatures, etc.)
[0090] Fig. 5 illustrates one example of a lighting unit 100 that may be
configured
according to one embodiment of the present disclosure to provide luminance-
compensated
variable color or variable color temperature light. Some examples of LED-based
lighting
units similar to those that are described below in connection with Fig. 5 may
be found, for
example, in U.S. Patent No. 6,016,038, issued January 18, 2000 to Mueller et
al., entitled
"Multicolored LED Lighting Method and Apparatus," and U.S. Patent No.
6,211,626,
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issued April 3, 2001 to Lys et al, entitled "Illumination Components," which
patents are
both hereby incorporated herein by reference.
[0091] In various embodiments of the present disclosure, the lighting unit 100
shown in
Fig. 5 may be used alone or together with other similar lighting units in a
system of lighting
units (e.g., as discussed further below in connection with Fig. 6). Used alone
or in
combination with other lighting units, the lighting unit 100 may be employed
in a variety of
applications including, but not limited to, interior or exterior space (e.g.,
architectural)
illumination in general, direct or indirect illumination of objects or spaces,
theatrical or
other entertainment-based/special effects ligllting, decorative lighting,
safety-oriented
lighting, vehicular lighting, illuinination of displays and/or merchandise
(e.g. for
advertising and/or in retail/consumer environments), combined illumination and
communication systems, etc., as well as for various indication, display and
informational
purposes.
[0092] Additionally, one or more lighting units similar to that described in
connection
with Fig. 5 may be implemented in a variety of products including, but not
limited to,
various forms of light modules or bulbs having various shapes and
electrical/mechanical
coupling arrangements (including replacement or "retrofit" modules or bulbs
adapted for
use in conventional sockets or fixtures), as well as a variety of consumer
and/or household
products (e.g., night lights, toys, games or game components, entertainment
components or
systems, utensils, appliances, kitchen aids, cleaning products, etc.) and
architectural
components (e.g., lighted panels for walls, floors, ceilings, lighted trim and
ornamentation
components, etc.).
[0093] In one embodiment, the lighting unit 100 shown in Fig. 5 may include
one or
more light sources 104A, 104B, and 104C (shown collectively as 104), wherein
one or
more of the light sources may be an LED-based light source that includes one
or more light
emitting diodes (LEDs). In one aspect of this embodiment, any two or more of
the light
sources 104A, 104B, and 104C may be adapted to generate radiation of different
colors
(e.g. red, green, and blue, respectively). Although Fig. 5 shows three light
sources 104A,
104B, and 104C, it should be appreciated that the lighting unit is not limited
in this respect,
as different numbers and various types of light sources (all LED-based light
sources, LED-
based and non-LED-based light sources in combination, etc.) adapted to
generate radiation
of a variety of different colors, including essentially white light, may be
employed in the
lighting unit 100, as discussed further below.
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[0094] As shown in Fig. 5, the lighting unit 100 also may include a processor
102 that
is configured to output one or more control signals to drive the light sources
104A, 104B,
and 104C so as to generate various intensities of light from the light
sources. For example,
in one implementation, the processor 102 may be configured to output at least
one control
signal for each light source so as to independently control the intensity of
light (e.g., radiant
power in lumens) generated by each light source. Some examples of control
signals that
may be generated by the processor to control the light sources include, but
are not limited
to, pulse modulated signals, pulse width modulated signals (PWM), pulse
amplitude
modulated signals (PAM), pulse code modulated signals (PCM) analog control
signals
(e.g., current control signals, voltage control signals), combinations and/or
modulations of
the foregoing signals, or other control signals. In one aspect, one or more
modulation
techniques provide for variable control using a fixed current level applied to
one or more
LEDs, so as to mitigate potential undesirable or unpredictable variations in
LED output that
may arise if a variable LED drive current were employed. In another aspect,
the processor
102 may control other dedicated circuitry (not shown in Fig. 5) which in turn
controls the
light sources so as to vary their respective intensities.
[0095] In one embodiment of the lighting unit 100, one or more of the light
sources
104A, 104B, and 104C shown in Fig. 5 may include a group of multiple LEDs or
other
types of light sources (e.g., various parallel and/or serial connections of
LEDs or other
types of light sources) that are controlled together by the processor 102.
Additionally, it
should be appreciated that one or more of the light sources 104A, 104B, and
104C may
include one or more LEDs that are adapted to generate radiation having any of
a variety of
spectra (i.e., wavelengths or wavelength bands), including, but not limited
to, various
visible colors (including essentially white liglit), various color
temperatures of white light,
ultraviolet, or infrared. LEDs having a variety of spectral bandwidths (e.g.,
narrow band,
broader band) may be employed in various implementations of the lighting unit
100.
[0096] In another aspect of the lighting unit 100 shown in Fig. 5, the
lighting unit 100
may be constructed and arranged to produce a wide range of variable color
radiation. For
example, the lighting unit 100 may be particularly arranged such that the
processor-
controlled variable intensity (i.e., variable radiant power) light generated
by two or more of
the light sources combines to produce a mixed colored light (including
essentially white
light having a variety of color temperatures). In particular, the color (or
color temperature)
of the mixed colored light may be varied by varying one or more of the
respective
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intensities (output radiant power) of the light sources (e.g., in response to
one or more
control signals output by the processor 102). Furthermore, the processor 102
may be
particularly configured (e.g., programmed) to provide control signals to one
or more of the
light sources so as to generate a variety of static or time-varying (dynamic)
multi-color (or
multi-color temperature) lighting effects.
[0097] Thus, the lighting unit 100 may include a wide variety of colors of
LEDs in
various combinations, including two or more of red, green, and blue LEDs to
produce a
color mix, as well as one or more other LEDs to create varying colors and
color
temperatures of white light. For example, red, green and blue can be mixed
with amber,
white, UV, orange, IR or other colors of LEDs. As discussed above in
connection with
Figs. 1-4, such combinations of differently colored LEDs in the lighting unit
100 can
facilitate accurate reproduction of a host of desirable spectrums of lighting
conditions,
examples of which include, but are not limited to, a variety of outside
daylight equivalents
at different times of the day, various interior lighting conditions, lighting
conditions to
simulate a complex multicolored background, and the like. Other desirable
lighting
conditions can be created by removing particular pieces of spectrum that may
be
specifically absorbed, attenuated or reflected in certain environments. Water,
for example
tends to absorb and attenuate most non-blue and non-green colors of light, so
underwater
applications may benefit from lighting conditions that are tailored to
emphasize or attenuate
some spectral elements relative to others.
[0098] As shown in Fig. 5, the lighting unit 100 also may include a memory 114
to
store various information. For example, the memory 114 may be employed to
store one or
more lighting programs for execution by the processor 102 (e.g., to generate
one or more
control signals for the light sources), as well as various types of data
useful for generating
variable color radiation (e.g., calibration information, discussed further
below). The
memory 114 also may store one or more particular identifiers (e.g., a serial
number, an
address, etc.) that may be used either locally or on a system level to
identify the lighting
unit 100. In various embodiments, such identifiers may be pre-programmed by a
manufacturer, for example, and may be either alterable or non-alterable
thereafter (e.g., via
some type of user interface located on the lighting unit, via one or more data
or control
signals received by the lighting unit, etc.). Alternatively, such identifiers
may be
determined at the time of initial use of the lighting unit in the field, and
again may be
alterable or non-alterable thereafter.
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[0099] One issue that may arise in connection with controlling multiple light
sources in
the lighting unit 100 of Fig. 5, and controlling multiple lighting units 100
in a lighting
system (e.g., as discussed below in connection with Fig. 6), relates to
potentially perceptible
differences in light output between substantially similar light sources. For
example, given
two virtually identical light sources being driven by respective identical
control signals, the
actual intensity of light (e.g., radiant power in lumens) output by each light
source may be
measurably different. Such a difference in light output may be attributed to
various factors
including, for example, slight manufacturing differences between the light
sources, normal
wear and tear over time of the light sources that may differently alter the
respective
spectrums of the generated radiation, etc. For purposes of the present
discussion, light
sources for which a particular relationship between a control signal and
resulting output
radiant power are not known are referred to as "uncalibrated" light sources.
[00100] The use of one or more uncalibrated light sources in the lighting unit
100 shown
in Fig. 5 may result in generation of light having an unpredictable, or
"uncalibrated," color
or color temperature. For example, consider a first lighting unit including a
first
uncalibrated red light source and a first uncalibrated blue light source, each
controlled by a
corresponding control signal having an adjustable parameter in a range of from
zero to 255
(0-255), wherein the maximum value of 255 represents the maximum radiant power
available from the light source. For purposes of this example, if the red
control signal is set
to zero and the blue control signal is non-zero, blue light is generated,
whereas if the blue
control signal is set to zero and the red control signal is non-zero, red
light is generated.
However, if both control signals are varied from non-zero values, a variety of
perceptibly
different colors may be produced (e.g., in this example, at very least, many
different shades
of purple are possible). In particular, perhaps a particular desired color
(e.g., lavender) is
given by a red control signal having a value of 125 and a blue control signal
having a value
of 200.
[00101] Now consider a second lighting unit including a second uncalibrated
red light
source substantially similar to the first uncalibrated red light source of the
first lighting unit,
and a second uncalibrated blue light source substantially similar to the first
uncalibrated
blue light source of the first lighting unit. As discussed above, even if both
of the
uncalibrated red light sources are driven by respective identical control
signals, the actual
intensity of light (e.g., radiant power in lumens) output by each red light
source may be
measurably different. Similarly, even if both of the uncalibrated blue light
sources are
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driven by respective identical control signals, the actual light output by
each blue light
source may be measurably different.
[00102] With the foregoing in mind, it should be appreciated that if multiple
uncalibrated
light sources are used in combination in lighting units to produce a mixed
colored light as
discussed above, the observed color (or color temperature) of light produced
by different
lighting units under identical control conditions may be perceivably
different. Specifically,
consider again the "lavender" example above; the "first lavender" produced by
the first
lighting unit with a red control signal having a value of 125 and a blue
control signal having
a value of 200 indeed may be perceivably different than a "second lavender"
produced by
the second lighting unit with a red control signal having a value of 125 and a
blue control
signal having a value of 200. More generally, the first and second lighting
units generate
uncalibrated colors by virtue of their uncalibrated light sources.
[00103] In view of the foregoing, in one embodiment of the present disclosure,
the
lighting unit 100 includes calibration means to facilitate the generation of
light having a
calibrated (e.g., predictable, reproducible) color at any given time. In one
aspect, the
calibration means is configured to adjust (e.g., scale) the light output of at
least some light
sources of the lighting unit so as to compensate for perceptible differences
between similar
light sources used in different lighting units.
[00104] For example, in one embodiment, the processor 102 of the lighting unit
100 is
configured to control one or more of the light sources 104A, 104B, and 104C so
as to
output radiation at a calibrated intensity that substantially corresponds in a
predetermined
manner to a control signal for the light source(s). As a result of mixing
radiation having
different spectra and respective calibrated intensities, a calibrated color is
produced. In one
aspect of this embodiment, at least one calibration value for each light
source is stored in
the memory 114, and the processor is programmed to apply the respective
calibration
values to the control signals for the corresponding light sources so as to
generate the
calibrated intensities.
[00105] In one aspect of this embodiment, one or more calibration values may
be
determined once (e.g., during a lighting unit manufacturing/testing phase) and
stored in the
memory 114 for use by the processor 102. In another aspect, the processor 102
may be
configured to derive one or more calibration values dynamically (e.g. from
time to time)
with the aid of one or more photosensors, for example. In various embodiments,
the
photosensor(s) may be one or more external components coupled to the lighting
unit, or
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alternatively may be integrated as part of the lighting unit itself. A
photosensor is one
example of a signal source that may be integrated or otherwise associated with
the lighting
unit 100, and monitored by the processor 102 in connection with the operation
of the
lighting unit. Other examples of such signal sources are discussed further
below, in
connection with the signal source 124 shown in Fig. 5.
[00106] One exemplary method that may be implemented by the processor 102 to
derive
one or more calibration values includes applying a reference control signal to
a light source
(e.g., corresponding to maximum output radiant power), and measuring (e.g.,
via one or
more photosensors) an intensity of radiation (e.g., radiant power falling on
the photosensor)
tlius generated by the light source. The processor may be programmed to then
make a
comparison of the measured intensity and at least one reference value (e.g.,
representing an
intensity that nominally would be expected in response to the reference
control signal).
Based on such a comparison, the processor may determine one or more
calibration values
(e.g., scaling factors) for the light source. In particular, the processor may
derive a
calibration value such that, when applied to the reference control signal, the
light source
outputs radiation having an intensity that corresponds to the reference value
(i.e., an
"expected" intensity, e.g., expected radiant power in lumens).
[00107] In various aspects, one calibration value may be derived for an entire
range of
control signal/output intensities for a given light source. Alternatively,
inultiple calibration
values maybe derived for a given light source (i.e., a number of calibration
value
"samples" may be obtained) that are respectively applied over different
control
signal/output intensity ranges, to approximate a nonlinear calibration
function in a
piecewise linear manner.
[00108] In another aspect, as also shown in Fig. 5, the lighting unit 100
optionally may
include one or more user interfaces 118 that are provided to facilitate any of
a number of
user-selectable settings or functions (e.g., generally controlling the light
output of the
lighting unit 100, changing and/or selecting various pre-programmed lighting
effects to be
generated by the lighting unit, changing and/or selecting various paranzeters
of selected
lighting effects, setting particular identifiers such as addresses or serial
numbers for the
lighting unit, etc.). In various embodiments, the communication between the
user interface
118 and the lighting unit may be accomplished through wire or cable, or
wireless
transmission.
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[00109] In one implementation, the processor 102 of the lighting unit monitors
the user
interface 118 and controls one or more of the light sources 104A, 104B, and
104C based at
least in part on a user's operation of the interface. For example, the
processor 102 may be
configured to respond to operation of the user interface by originating one or
more control
signals for controlling one or more of the light sources. Alternatively, the
processor 102
may be configured to respond by selecting one or more pre-programmed control
signals
stored in memory, modifying control signals generated by executing a lighting
program,
selecting and executing a new lighting program from memory, or otherwise
affecting the
radiation generated by one or more of the light sources.
[00110] In particular, in one implementation, the user interface 118 may
constitute one
or more switches (e.g., a standard wall switcli) that interrupt power to the
processor 102. In
one aspect of this implementation, the processor 102 is configured to monitor
the power as
controlled by the user interface, and in turn control one or more of the light
sources 104A,
104B, and 104C based at least in part on a duration of a power interruption
caused by
operation of the user interface. As discussed above, the processor may be
particularly
configured to respond to a predetermined duration of a power interruption by,
for example,
selecting one or more pre-programmed control signals stored in memory,
modifying control
signals generated by executing a lighting program, selecting and executing a
new lighting
program from memory, or othet-wise affecting the radiation generated by one or
more of the
ligllt sources.
[00111] Fig. 5 also illustrates that the lighting unit 100 may be configured
to receive one
or more signals 122 from one or more otlier signal sources 124. In one
implementation, the
processor 102 of the lighting unit may use the signal(s) 122, either alone or
in combination
with other control signals (e.g., signals generated by executing a lighting
program, one or
more outputs from a user interface, etc.), so as to control one or more of the
light sources
104A, 104B and 104C in a manner similar to that discussed above in connection
with the
user interface.
[00112] Examples of the signal(s) 122 that may be received and processed by
the
processor 102 include, but are not limited to, one or more audio signals,
video signals,
power signals, various types of data signals, signals representing information
obtained from
a network (e.g., the Internet), signals representing one or more
detectable/sensed conditions,
signals from lighting units, signals consisting of modulated light, etc. In
various
implementations, the signal source(s) 124 may be located remotely from the
lighting unit
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100, or included as a component of the lighting unit. For example, in one
embodiment, a
signal from one lighting unit 100 could be sent over a network to another
lighting unit 100.
[00113] Some examples of a signal source 124 that may be employed in, or used
in
connection with, the lighting unit 100 of Fig. 5 include any of a variety of
sensors or
transducers that generate one or more signals 122 in response to some
stimulus. Examples
of such sensors include, but are not limited to, various types of
environmental condition
sensors, such as thermally sensitive (e.g., temperature, infrared) sensors,
humidity sensors,
motion sensors, photosensors/light sensors (e.g., sensors that are sensitive
to one or more
particular spectra of electroinagnetic radiation), various types of cameras,
sound or
vibration sensors or other pressure/force transducers (e.g., microphones,
piezoelectric
devices), and the like.
[00114] Additional examples of a signal source 124 include various
metering/detection
devices that monitor electrical signals or characteristics (e.g., voltage,
current, power,
resistance, capacitance, inductance, etc.) or chemical/biological
characteristics (e.g., acidity,
a presence of one or more particular chemical or biological agents, bacteria,
etc.) and
provide one or more signals 122 based on measured values of the signals or
characteristics.
Yet other examples of a signal source 124 include various types of scanners,
image
recognition systems, voice or other sound recognition systems,
artificial.intelligence and
robotics systems, and the like. A signal source 124 could also be a lighting
unit 100, a
processor 102, or any one of many available signal generating devices, such as
media
players, MP3 players, computers, DVD players, CD players, television signal
sources,
camera signal sources, microphones, speakers, telephones, cellular phones,
instant
messenger devices, SMS devices, wireless devices, personal organizer devices,
and many
others.
[00115] In one embodiment, the lighting unit 100 shown in Fig. 5 also may
include one
or more optical elements 130 to optically process the radiation generated by
the light
sources 104A, 104B, and 104C. For example, one or more optical elements may be
configured so as to change one or both of a spatial distribution and a
propagation direction
of the generated radiation. In particular, one or more optical elements may be
configured to
change a diffusion angle of the generated radiation. In one aspect of this
embodiment, one
or more optical elements 130 may be particularly configured to variably change
one or both
of a spatial distribution and a propagation direction of the generated
radiation (e.g., in
response to some electrical and/or mechanical stimulus). Examples of optical
elements that
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may be included in the lighting unit 100 include, but are not limited to,
reflective materials,
refractive materials, translucent materials, filters, lenses, mirrors, and
fiber optics. The
optical element 130 also may include a phosphorescent material, luminescent
material, or
other material capable of responding to or interacting with the generated
radiation.
[00116] As also shown in Fig. 5, the lighting unit 100 may include one or more
communication ports 120 to facilitate coupling of the lighting unit 100 to any
of a variety of
other devices. For example, one or more communication ports 120 may facilitate
coupling
multiple lighting units together as a networked lighting system, in which at
least some of
the lighting units are addressable (e.g., have particular identifiers or
addresses) and are
responsive to particular data transported across the network.
[00117] In particular, in a networked lighting system environment, as
discussed in
greater detail further below (e.g., in connection with Fig. 6), as data is
communicated via
the network, the processor 102 of each lighting unit coupled to the network
may be
configured to be responsive to particular data (e.g., lighting control
commands) that pertain
to it (e.g., in some cases, as dictated by the respective identifiers of the
networked lighting
units). Once a given processor identifies particular data intended for it, it
may read the data
and, for example, change the lighting conditions produced by its light sources
according to
the received data (e.g., by generating appropriate control signals to the
light sources). In
one aspect, the memory 114 of each lighting unit coupled to the network maybe
loaded, for
example, with a table of lighting control signals that correspond with data
the processor 102
receives. Once the processor 102 receives data from the network, the processor
may
consult the table to select the control signals that correspond to the
received data, and
control the light sources of the lighting unit accordingly.
[00118] In one aspect of this embodiment, the processor 102 of a given
lighting unit,
whether or not coupled to a network, may be configured to interpret lighting
instructions/data that are received in a DMX protocol (as discussed, for
example, in U.S.
Patents 6,016,038 and 6,211,626), which is a lighting command protocol
conventionally
employed in the lighting industry for some programmable lighting applications.
For
example, in one aspect, a lighting command in DMX protocol may specify each of
a red
channel control signal, a green channel control signal, and a blue channel
control signal as
an eight-bit digital signal representing a number from 0 to 255, wherein the
maximum value
of 255 for any one of the color channels instructs the processor 102 to
control the
corresponding light source(s) to generate the maximum available radiant power
for that
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color. Hence, a command of the format [R, G, B] = [255, 255, 255] would cause
the
lighting unit to generate maximum radiant power for each of red, green and
blue light
(thereby creating white light). It should be appreciated, however, that
lighting units suitable
for purposes of the present disclosure are not limited to a DMX command
format, as
lighting units according to various embodiments may be configured to be
responsive to
other types of communication protocols so as to control their respective light
sources.
1001191 In one embodiment, the lighting unit 100 of Fig. 5 may include and/or
be
coupled to one or more power sources 108. In various aspects, examples of
power
source(s) 108 include, but are not limited to, AC power sources, DC power
sources,
batteries, solar-based power sources, thermoelectric or mechanical-based power
sources
and the like. Additionally, in one aspect, the power source(s) 108 may include
or be
associated with one or more power conversion devices that convert power
received by an
external power source to a form suitable for operation of the lighting unit
100.
[00120] While not shown explicitly in Fig. 5, the lighting unit 100 may be
implemented
in any one of several different structural configurations according to various
embodiments
of the present disclosure. Examples of such configurations include, but are
not limited to,
an essentially linear or curvilinear configuration, a circular configuration,
an oval
configuration, a rectangular configuration, combinations of the foregoing,
various other
geometrically shaped configurations, various two or three dimensional
configurations, and
the like.
[00121] A given lighting unit also may have any one of a variety of mounting
arrangements for the light source(s), enclosure/housing arrangements and
shapes to
partially or fully enclose the light sources, and/or electrical and mechanical
connection
configurations. In particular, a lighting unit may be configured as a
replacement or
"retrofit" to engage electrically and mechanically in a conventional socket or
fixture
arrangement (e.g., an Edison-type screw socket, a halogen fixture arrangement,
a
fluorescent fixture arrangement, etc.).
[00122] Additionally, one or more optical elements as discussed above may be
partially
or fully integrated with an enclosure/housing arrangement for the lighting
unit.
Furtliermore, a given lighting unit optionally may be associated with (e.g.,
include, be
coupled to and/or packaged together with) various other components (e.g.,
control circuitry
such as the processor and/or memory, one or more sensors/transducers/signal
sources, user
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interfaces, displays, power sources, power conversion devices, etc.) relating
to the operation
of the light source(s).
[00123] Fig. 6 illustrates an example of a networked lighting system 200
according to
one embodiment of the present disclosure. In the embodiment of Fig. 6, a
number of
lighting units 100, similar to those discussed above in connection with Fig.
5, are coupled
together to form the networked lighting system. It should be appreciated,
however, that the
particular configuration and arrangement of lighting units shown in Fig. 6 is
for purposes of
illustration only, and that the disclosure is not limited to the particular
system topology
shown in Fig. 6.
[00124] Additionally, while not shown explicitly in Fig. 6, it should be
appreciated that
the networked lighting system 200 may be configured flexibly to include one or
more user
interfaces, as well as one or more signal sources such as sensors/transducers.
For example,
one or more user interfaces and/or one or more signal sources such as
sensors/transducers
(as discussed above in connection with Fig. 5) may be associated with any one
or more of
the lighting units of the networked lighting system 200. Alternatively (or in
addition to the
foregoing), one or more user interfaces and/or one or more signal sources may
be
implemented as "stand alone" components in the networked lighting system 200.
Whether
stand alone components or particularly associated with one or more lighting
units 100, these
devices may be "shared" by the lighting uiuts of the networked lighting
system. Stated
differently, one or more user interfaces and/or one or more signal sources
such as
sensors/transducers may constitute "shared resources" in the networked
lighting system that
may be used in connection with controlling any one or more of the lighting
units of the
system.
[00125] As shown in the embodiment of Fig. 6, the lighting system 200 may
include one
or more lighting unit controllers (hereinafter "LUCs") 208A, 208B, 208C, and
208D,
wherein each LUC is responsible for communicating with and generally
controlling one or
more lighting units 100 coupled to it. Although Fig. 6 illustrates one
lighting unit 100
coupled to each LUC, it should be appreciated that the disclosure is not
limited in this
respect, as different numbers of lighting units 100 may be coupled to a given
LUC in a
variety of different configurations (serially connections, parallel
connections, combinations
of serial and parallel connections, etc.) using a variety of different
communication media
and protocols.
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[00126] In the system of Fig. 6, each LUC in turn may be coupled to a central
controller
202 that is configured to communicate with one or more LUCs. Although Fig. 6
shows
four LUCs coupled to the central controller 202 via a generic connection 204
(which may
include any number of a variety of conventional coupling, switching and/or
networking
devices), it should be appreciated that according to various embodiments,
different numbers
of LUCs may be coupled to the central controller 202. Additionally, according
to various
embodiments of the present disclosure, the LUCs and the central controller may
be coupled
together in a variety of configurations using a variety of different
communication media
and protocols to form the networked lighting system 200. Moreover, it should
be
appreciated that the interconnection of LUCs and the central controller, and
the
interconnection of lighting units to respective LUCs, may be accomplished in
different
mamiers (e.g., using different configurations, communication media, and
protocols).
[00127] For example, according to one embodiment of the present disclosure,
the central
controller 202 shown in Fig. 6 may by configured to implement Ethernet-based
communications with the LUCs, and in turn the LUCs may be configured to
implement
DMX-based communications with the ligliting units 100. In particular, in one
aspect of this
embodiment, each LUC may be configured as an addressable Ethenlet-based
controller and
accordingly may be identifiable to the central controller 202 via a particular
unique address
(or a unique group of addresses) using an Ethernet-based protocol. In this
manner, the
central controller 202 may be configured to support Ethernet communications
throughout
the network of coupled LUCs, and each LUC may respond to those communications
intended for it. In turn, each LUC may communicate lighting control
information to one or
more lighting units coupled to it, for example, via a DMX protocol, based on
the Ethernet
communications with the central controller 202.
[00128] More specifically, according to one embodiment, the LUCs 208A, 208B,
and
208C shown in Fig. 6 may be configured to be "intelligent" in that the central
controller
202 may be configured to communicate higher level commands to the LUCs that
need to be
interpreted by the LUCs before lighting control information can be forwarded
to the
lighting units 100. For example, a lighting system operator may want to
generate a color
changing effect that varies colors from lighting unit to lighting unit in such
a way as to
generate the appearance of a propagating rainbow of colors ("rainbow chase"),
given a
particular placement of lighting units with respect to one another. In this
example, the
operator may provide a simple instruction to the central controller 202 to
accomplish this,
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and in turn the central controller may communicate to one or more LUCs using
an Ethernet-
based protocol high level command to generate a "rainbow chase." The command
may
contain timing, intensity, hue, saturation or other relevant infonnation, for
example. When
a given LUC receives such a command, it may then interpret the command and
communicate further commands to one or more lighting units using a DMX
protocol, in
response to which the respective sources of the lighting units are controlled
via any of a
variety of signaling techniques (e.g., PWM).
[00129] It should again be appreciated that the foregoing example of using
multiple
different communication implementations (e.g., Ethernet/DMX) in a lighting
system
according to one embodiment of the present disclosure is for purposes of
illustration only,
and that the disclosure is not limited to this particular example.
[00130] From the foregoing, it may be appreciated that one or more lighting
units as
discussed above are capable of generating highly controllable variable color
light over a
wide range of colors, as well as variable color temperature white light over a
wide range of
color temperatures. For some applications involving dynamic changes in light
output, it is
desirable that transitions between different colors or color temperatures
occur in a
predictable, "smooth," or visually pleasing manner. Applicants have
appreciated and
recognized, however, that in some instances the human vision phenomenon of
perceiving
saturated colors more brightly than unsaturated colors, pursuant to the
"Helmholtz-
Kohlrausch" (HK) effect, may adversely impact the perception of a desired
lighting effect
(e.g., a transition from one lighting state to another).
[00131] In view of the foregoing, one embodiment of the present disclosure is
directed to
methods and apparatus for providing luminance compensation so as to mitigate
the HK
effect. Fig. 7 is a flow chart illustrating a method according to one
embodiment of the
disclosure for providing such luminance compensation. In one exemplary
implementation,
the processor 102 of one or more lighting units siinilar to those shown in
Figs. 5 and 6 may
be appropriately configured (e.g., programmed) to implement the method
outlined in Fig. 7.
[00132] According to one aspect of the embodiment illustrated in Fig. 7, to
facilitate a
determination of appropriate luminance compensation for a given color or color
temperature generated by the lighting unit, first a spectral power
distribution (SPD) may be
measured or estimated for each of the different source colors of a given
lighting unit 100.
For purposes of the discussion immediately below, an exemplary lighting unit
100 is
considered having one or more red LEDs, one or more green LEDs, and one or
more blue
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LEDs. With the foregoing in mind, as indicated in block 80 of Fig. 7, an SPD
may be
measured (by an appropriate measuring instrument) for a red LED (or a group of
red LEDs
energized together), a green LED (or a group of green LEDs energized
together), and a blue
LED (or a group of blue LEDs energized together); alternatively, an SPD may be
assumed
5' for a given color LED source or group of sources energized together, based
on an
expected/approximate dominant wavelength, FWHM, and radiant power. In one
aspect of
this embodiment, the SPDs are measured (or estimated) at maximum available
radiant
powers for the respective source colors.
[00133] For some applications, whether the SPDs are measured or estimated, it
may be
desirable to take into account one or more intervening surfaces between the
generated light
and an anticipated point of perception of the light. For example, consider an
application in
wliich a given lighting unit is positioned so as to illuminate one or more
walls of a room,
and the light generated by the lighting unit generally is perceived in the
room after the light
has reflected off of the wall(s). Based on the physical properties of the
material constituting
the wall(s), including possible wall coverings such as paints, wallpapers,
etc., the light
reflected from the wall(s) and ultimately perceived may have an appreciably
different SPD
than the light impinging on the wall(s). More specifically, the wall(s) (or
any other
intervening surface) may absorb/reflect each of the source spectrums (e.g.,
the red, green
and blue light) somewhat differently. In view of the foregoing, in one
embodiment some or
all of the SPDs may be measured, estimated, or specifically modeled to include
the effects
of one or more intervening surfaces that may be present in a given
application, so as to take
into account light-surface interactions in the determination of luminance
compensation.
[00134] As indicated in block 82 of Fig. 7, the measured or estimated SPDs
subsequently
may be mapped to some color model or color space serving as a frame of
reference for
categorizing color. As discussed above in connection with Fig. 1, the CIE
color system
provides one conventional example of a useful reference frame for categorizing
color, via
the CIE chromaticity diagram for example. While the discussion below focuses
on the CIE
color system (and, in particular, the CIE chromaticity diagram) as a frame of
reference,
again it should be appreciated that the concepts disclosed herein generally
are applicable to
any of a variety of constructs used to describe a color model, space, or
system that may be
employed to facilitate a determination of luminance compensation.
[00135] In view of the foregoing, in one exemplary implementation of the
embodiment
outlined in Fig. 7, CIE chromaticity coordinates x,y may be calculated in the
manner
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described above in connection with Fig. 1 and plotted on the CIE chromaticity
diagram for
each different color source (or group of sources) of the lighting unit 100.
Depending on
several factors including, but not limited to, dominant wavelength, spectral
changes due to
LED drive current and/or temperature, manufacturing differences and the like,
approximate
but illustrative values for typical chromaticity-coordinates for the different
LED colors are
indicated in Table 1 below. As indicated earlier, exemplary approximate
dominant
wavelengths for commonly available red, green and blue LEDs include 615-635
nanometers for red LEDs, 515-535 nanometers for green LEDs, and 460-475
nanometers
for blue LEDs.
LED Color x-coordinate y-coordinate
Red 0.7 0.3
Green 0.17 0.68
Blue 0.115 0.14
Table 1
Fig. 8 illustrates the CIE chromaticity diagram of Fig. 1, onto which are
mapped the x,y
chromaticity coordinates from Table 1 generally representative of red, green
and blue LED
sources that may be employed in the lighting unit 100. The resulting three
points 60R, 60G
and 60B form an enclosed area referred to as a color gamut 60, representing
the colors that
may be generated by the lighting unit 100 using the red, green and blue
sources based on
additive mixing. In Fig. 8, the white light/black body curve 54 and the
achromatic point E
also are illustrated; as can be seen, a significant portion of the curve 54
falls within the
gamut 60.
[00136] Once the SPDs are mapped to the color space serving as a reference
frame (e.g.,
the CIE chromaticity diagram), a transfonnation may be determined to
subsequently map to
the color space lighting commands representing arbitrary combinations of the
red, green
and blue source colors of the lighting unit 100, as indicated in block 84 of
Fig. 7. In an
implementation employing the CIE color system, this process relates
significantly to the
CIE tristimulus values determined for each of the different source colors of
the lighting unit
100.
[00137] In particular, in calculating the x,y chromaticity coordinates for the
respective
primary color LED sources, as discussed above in connection with Fig. 1 each
source is
associated (via the color matching functions x(A), y(A), z(A) ) with a
corresponding set of
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CIE tristimulus values X, Y, and Z. According to one aspect of the embodiment
of Fig. 7, a
matrix transformation may be derived, based on the three sets of tristimulus
values, to map
an arbitrary R-G-B ratio representing a desired color or color temperature to
a
corresponding set of tristimulus values according to:
XR Xc XB R X
Y R Y G Y B GY . (5)
ZR ZG ZB B Z
[00138] In Eq. (5), the R-G-B column vector represents relative amounts of the
respective sources according to some predetermined scale (zero to some maximum
value
representing maximum available output radiant power for each source). For
example, in
one embodiment, a lighting command may specify each of the R, G, and B values
in the
column vector as a number varying from 0 to 255, wherein lighting commands are
processed by the lighting unit according to the DMX protocol (in which eight
bits are
employed to specify the relative strength of each different color source). It
should be
appreciated, however, that virtually any scale may be employed, in any of a
variety of
lighting cominand fonnats, to specify the relative amounts of the respective
sources.
[00139] In Eq. (5), each column of the three-by-three transformation matrix
represents
the tristimulus values for one of the primary colors at its maximum possible
value in the R-
G-B colunm vector (e.g., XR, YR, and ZR represent the tristimulus values for
the red primary
source at maximum available output radiant power, wherein YR represents the
maximum
luminance from the red source). Finally, the column vector X-Y-Z in Eq. (5)
represents the
resulting CIE tristimulus values of the desired color corresponding to the
arbitrary ratio
specified in the R-G-B column vector, wherein Y represents the luminance of
the desired
color. Hence, according to the transformation given in Eq. (5) above, any
arbitrary
combination of light generated by the red, green and blue LED sources (i.e.,
relative
proportions of red, green and blue, indicated by the R-G-B column vector in
Eq. (5)) may
be mapped to the CIE tristimulus values, which in turn are normalized and
mapped to the
chromaticity diagram, falling within or along the perimeter of the gamut 60
shown in Fig. 8.
[00140] Once a lighting command can be mapped to the CIE chromaticity diagram,
a
corresponding luminance compensation factor may be determined for the lighting
command, as indicated in block 86 of Fig. 7. In an exemplary implementation
according to
one embodiment, a luminance compensation factor may be derived based on Eq.
(2) above;
for example, the value F may be calculated based on Eq. (2) utilizing the
chromaticity
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coordinates x,y corresponding to the mapped lighting command. In turn, the
value 10F can
be calculated, thereby associating a relative measure of perceived brightness
with the
lighting command based on the isobrightness contours illustrated in Fig. 4.
[00141] In one aspect, a scaling factor maybe applied to the value 10F to
arrive at a
luminance compensation factor, such that the nadir 70 of the isobrightness
contours shown
in Fig. 4 corresponds to the maximum luminance generated by the lighting unit
100. In this
aspect, lighting commands mapped onto isobrightness contours beyond the nadir
70 are
attenuated by the luminance compensation factor.
[00142] For example, consider a luminance compensation factor (LCF) defined
as:
LCF = ~ aF6 . (6)
Based on Eq. (6) above, a lighting command mapped onto the nadir 70 in Fig. 4
would have
a luminance compensation factor LCF = 1. Lighting commands mapped to any other
portion of the chromaticity diagram would have a luminance compensation factor
less than
one (e.g., between approximately 0.45 near saturated blue to approximately
0.93 around the
nadir 70).
[00143] As indicated in block 88 of Fig. 7, the luminance compensation factor
once
determined can be applied to the lighting command so as to mitigate, at least
in part, the
"Helrnholtz-Kohlrausch" (HK) effect. For example, a luminance coinpensation
factor
according to Eq. (6) above may be applied as an identical multiplier to each
element of the
original R-G-B lighting command (e.g., the R-G-B column vector of Eq. (5)),
after which
the processor 102 processes the modified cominand to provide luminance
compensation for
the resulting color generated by the lighting unit. Since luminance is
additive, and each
source color of the lighting command is scaled identically by the luininance
compensation
factor, the resulting luminance of the additive mix of colors is appropriately
compensated.
[00144] As may be appreciated from Eq. (6) above, the application of a
luminance
compensation factor to a lighting command may significantly reduce the overall
possible
dynamic range of brightness for some colors as compared to others; in essence,
some
dynamic range is sacrificed for more saturated colors. In view of the
foregoing, according
to one embodiment the relationship of Eq. (6) may be modified, or another
relationship
defined, such that only "partial" compensation for the HK effect is provided.
[00145] For example, in one aspect, luminance compensation may be limited in
terms of
the range of colors or color temperatures to which compensation is applied
(e.g., applying
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luminance compensation to only some predetermined portion of the color space,
defining
some minimum LCF to limit the attenuation of more saturated colors, etc.). In
another
aspect, luminance compensation may be scaled, limited, or applied in a piece-
wise linear or
nonlinear fashion over some range of colors or color temperatures. In yet
another aspect,
luminance compensation may be limited by specifying predetermined limited
amounts of
compensation over a predetermined limited range of colors or color
temperatures. In
general, pursuant to the foregoing examples, according to one embodiment the
application
of luminance compensation to lighting commands may take into consideration
some
balance between the luminance compensation and the notion of sacrificing a
dynamic range
of brightness for more saturated colors.
[00146] While the foregoing discussion presented a derivation of a luminance
compensation factor based on the empirical formula for F given in Eq. (2) and
the resulting
contours on the CIE chromaticity diagram shown in Fig. 4, it should be
appreciated that the
teachings of the present disclosure are not limited in this respect. More
generally, any of a
variety of models for the HK effect (e.g., other empirical determinations or
mathematical
models) may be employed to generate a luminance compensation factor based on
mapping
a lighting command to CIE chromaticity coordinates.
[00147] For example, as an alternative to the specific nonlinear relationship
provided by
Eq. (2), a look-up table may be stored (e.g., in the memory 114 of a lighting
unit 100), in
wliich is specified a predetermined luminance compensation factor
corresponding to a
given pair of chromaticity coordinates. The mapping of a luminance
compensation factor
to a pair of chromaticity coordinates in such a look-up table may be based in
part on the
empirical formula given by Eq. (2), or by some other relationship (e.g.,
formula or
algorithm) modeling the HK effect. Additionally, the resolution between
different
luminance compensation factors to be applied to lighting commands may be
determined in
any of a number of ways. For example, in one embodiment, a look-up table may
store
luminance compensation values corresponding to a relatively smaller number of
isobrightness contours than indicated in Fig. 4, and interpolation may be
employed to
determine luminance compensation values intermediate to those actually stored
in the look-
up table. Such interpolation may include, for example, piece-wise, linear or
non-linear (Nth
order) interpolation. The concept of interpolation may be extended to any of a
variety of
luminance compensation models; in one aspect, the use of interpolation may
facilitate a less
memory-intensive implementation of luminance compensation.
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[00148] By providing luminance compensation values according to the various
concepts
discussed above, one or more lighting units 100 may be controlled to provide a
wide variety
of different colors or color temperatures of light while maintaining a
constant level of
perceived brightness. For example, a lighting unit 100 may be configured to
generate a
"rainbow" of light by cycling through a wide variety of saturated and
unsaturated colors at
some predetermined rate and prescribed same luminance for all of the colors,
and maintain
a constant level of perceived brightness for all of the colors according to
the luminance
compensation methods discussed herein. Similarly, a lighting unit may be
configured to
provide white light over a wide range of the white light/black body curve 54
shown in Fig.
3, wherein different color temperatures of white light (spanning different
isobriglitness
contours of Fig. 4) having a same prescribed luminance are perceived with the
same
brightness according to the luminance compensation methods discussed herein.
[00149] It should be appreciated that the concepts discussed above in
connection with
Figs. 7 and 8 may be implemented for each of multiple lighting units 100 of a
lighting
network similar to that shown in Fig. 6, to provide luminance compensation on
a
network/system level.
[00150] Moreover, while the foregoing discussion in connection with Fig. 8
used the
example of a color gamut 60 based on red, green and blue LED sources in the
lighting unit
100, it should be appreciated that, theoretically, any arbitrary gamut may be
envisioned
within (or including a portion of the perimeter of) the CIE chromaticity
diagram spectral
locus 50 and purple boundary 52. For example, any two or more different
chromaticity
points within the enclosed area or on the perimeter of the CIE diagram (e.g.,
any two or
more differently colored LED sources, including two white LEDs having
different
spectrums) may define a gamut. Furthermore, any three or more different
chromaticity
points may form a triangle or other polygon defining a gamut, wherein at least
some or all
of the different chromaticity points serve as respective vertices of the
polygon. More
generally, gamuts having arbitrarily curved shapes, and/or various numbers of
flat sides,
may be mathematically defined. Practically speaking, the points serving as the
vertices of a
polygonal gamut may correspond or relate in some way to an existing source of
light (e.g.,
one or more LEDs) that is employed to generate the various colors or color
temperatures of
the gamut based on additive mixing principles.
[00151] In any case, it should be appreciated that the concepts discussed
herein may be
applied to other multiple-color and white light-generating constructs (e.g.,
lighting units
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similar to those discussed above in connection with Figs. 5 and 6, employing
various
numbers of different primary sources that may or may not include one or more
of the red,
green and blue LED sources discussed above), and any of a variety of defined
gamuts
(based on actual sources or mathematical derivation). Stated differently, in a
colored or
white light generation system based on additive mixing of arbitrary different
sources, a
transformation may be derived (e.g., in a manner similar to that discussed
above in
connection with Eq. (5) above) such that any representation of a visible
stimulus that may
be generated can be mapped to the CIE chromaticity diagram shown in Fig. 1,
and a
luminance compensation factor appropriately determined and applied pursuant to
the
methodology outlined in Fig. 7.
[00152] More generally, according to other embodiments of the present
disclosure, color
models, color systems or color spaces other than the CIE color system and CIE
x,y
chromaticity diagram may be employed as reference frames, in relation to which
some
model for the HK effect is defined. In one aspect of these embodiments, any
arbitrary
lighting command can be mapped onto a given reference frame (again, in a
manner similar
to that discussed above in connection with Eq. (5) above) and, based on an
associated
model for the HK effect, luminance compensation factors may be derived
according to the
various concepts discussed herein.
[00153] Having thus described several illustrative embodiments, it is to be
appreciated
that various alterations, modifications, and improvements will readily occur
to those skilled
in the art. Such alterations, modifications, and improvements are intended to
be part of this
disclosure, and are intended to be within the spirit and scope of this
disclosure. While some
examples presented herein involve specific combinations of functions or
structural
elements, it should be understood that those functions and elements may be
combined in
other ways according to the present invention to accomplish the same or
different
objectives. In particular, acts, elements, and features discussed in
connection with one
embodiment are not intended to be excluded from similar or other roles in
other
embodiments. Accordingly, the foregoing description and attached drawings are
by way of
example only, and are not intended to be limiting.
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