Note: Descriptions are shown in the official language in which they were submitted.
CA 02499535 2005-03-07
Light Pipe with Directional Side-Light Extraction
Field of the Invention
The present invention relates to a light pipe used for side-light illumination
purposes.
More particularly, the invention relates to directional extraction of side
light from a light pipe.
Background of the Invention
Light pipe is used in two main ways. In an end-light application, the light
pipe is
optimized to carry light along its length, and transmit it at the output face
of the light pipe. In
to a side-light application, light is extracted out the side of the light pipe
and provides
illumination along its length. The present invention relates to applying light-
extraction means
over only a part of the circumference, or cross-sectional perimeter, a light
pipe, less than
360 degrees, in order to extract light in a directional manner rather than
over the full 360
degrees around the light pipe.
Often, light extracted from the side of a light pipe over the full 360 degrees
around
the light pipe is undesirable because a reflector would be needed to redirect
a significant
portion of the light towards the intended area to be illuminated. Some of the
redirected light
impinges on the light pipe and may be either absorbed into the light pipe so
as to reduce
side-light output, or is scattered into unintended directions. This is the
same drawback
2o associated with fluorescent lighting and results in an inefficient fixture
for delivering light onto
the target surface.
It would thus be desirable to eliminate the inefficient fixture and reflector
combination
for use with a light pipe by extracting the light only in the desired
direction, towards the
intended target to be illuminated.
It would be further desirable to obtain uniformity in light output along a
section of light
pipe in which side light is extracted.
Summary of the invention
One embodiment of the invention provides a light pipe with directional side-
light
3o extraction comprising a light pipe and light-extraction means applied to
the light pipe over
only a part of the cross-sectional perimeter of the light pipe and over an
active section of the
length of the light pipe in which directional side lighting is desired. The
light-extraction
means comprises any of (i) material, other than a light-carrying portion of
the light pipe or
CA 02499535 2005-03-07
any fluoropolymer cladding on the light-carrying portion, including light-
scattering material,
(ii) surfaces treated to have light-scattering properties, and (iii) material
with a reflective
property.
The foregoing light pipe eliminates the need for using a reflector, as with
fluorescent
lamps, by extracting the light only in the desired direction, towards a target
area to be
illuminated.
Other embodiments of the invention promote uniformity in side light emission
from a
light pipe.
1o Brief Description of the Drawings
Fig. 1 is a simplified, schematic side view of a sidelight illumination system
according
to the present invention.
Figs. 2a-2c are isometric views of light pipes, with Figs. 2a and 2b showing
prior art
light pipes, while Fig. 3c shows a light pipe according to the present
invention.
is Figs. 3-12 are side plan views of light pipes showing preferred geometries
of light-
extraction means, Fig. 5 being a cross sectional view taken at Lines 5-5 in
Fig. 4.
Fig. 13a is a side plan view of a light pipe, and Fig. 13b is a cross-
sectional view of
the light pipe of Fig. 13a, in which a light-extraction means comprises light-
reflective means.
Figs. 14a and 14b are cross-sectional views of a light pipe with a core and
clad and a
20 light pipe with a core but no clad, respectively.
Figs. 15 and 16 are simplified, isometric views, partially cutaway, of a co-
extrusion
die for inserting different types of light-extraction means between a core and
a clad of a light
pipe.
Figs. 17a-17b show fragmentary, partial cross sections of light pipes having
different
25 light-extraction means.
Detailed Description of the Invention
This description describes the three areas of (1) general principles of the
invention,
(2) preferred geometries of light-extraction means, and (3) methods of
manufacturing the
3o geometries of the light-extraction means.
1. General Principles of the Invention
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Fig. 1 shows a sidelight illumination system 10 according to the present
invention.
System 10 includes a light source 12, a light pipe 14, and a target surface 16
to be
illuminated. Arrows 18 show directional illumination of target surface 16 from
a section 20 of
light pipe 14, referred to herein as the "active section." Section 20 may
comprise either a
fraction of the length of light pipe 14, or the entire length of light pipe
14.
To put the sidelight illumination system of Fig. 1 into perspective, Figs. 2a
and 2b
show prior art light pipes of two different types. Fig. 2a shows a prior art
light pipe 22
designed to receive light 24 at one end, transport it through the light pipe
with minimum
attenuation, and provide illumination 25 at the other end. Light pipe 24
includes a core 26
1o and a cladding 28 having a lower index of refraction relative to the core.
Fig. 2b shows a length of prior art light pipe 30 constructed for sidelight
emission,
which is designed to extract light along its length and around its entire
circumference. Thus,
light 32 entering one end of light pipe 30 is extracted as sidelight 34 around
the entire
circumference of the light pipe. Residual light 35 passes through the other
end of the light
pipe. Similar to Fig. 2a, light pipe 30 has a core 32 and cladding 36.
In accordance with the invention, Fig. 2c shows one example of a light pipe 40
in
which light is extracted in a manner that favors one side of the pipe. Thus,
light 42 entering
core 44 of the light pipe is extracted from the side of the pipe in strip-like
region 46 of
cladding 48. Light pipe 40 of Fig. 2c provides directional side-light
extraction, and so can be
2o used as light pipe 14 of Fig. 1.
2. Preferred Geometries of Light-extraction means
Figs. 3-12 show preferred geometries of light-extraction means according to
the
invention. In all these figures, the light pipes may have a fluoropolymer
cladding over a core
as shown in Fig. 14a, for instance, or may be free of a fluoropolymer cladding
as shown in
Fig. 14b, for instance.
Fig. 3 shows an active section of a light pipe 50 that receives light 52 at
one end,
extracts light 54 from the side of the pipe along a strip 56 of uniform width
that contains light-
extraction means (described in the next section). Any light not extracted then
exits the other
end of the light pipe as light 58.
3o As can be seen in Fig. 3, a greater density of light rays 54 are extracted
near input
light 52 than near output light 58. This would result from having a uniform
density of light-
extraction means along the length of strip 56, and also from the fact that
less light is
available in the light pipe as the distance from input light 52 increases. To
counteract this
phenomenon, the light-extraction means could have a differential strength
along the light
pipe, with more light-extraction capability in the pipe the further away from
input light 52.
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This phenomenon is illustrated in Fig. 4, in which extracted side-light rays
54a from light pipe
50a along strip 56a are uniform in density along the entire length of light
pipe shown. As
used herein, "uniformity" in side-light emission means that the lumen output
as between inlet
and outlet portions of a side-light emitting section of the light pipe is
within plus or minus 20
percent of the average value of each other. More uniformity than this may also
be desirable
in some circumstances.
One way to increase the light-extraction strength along a light pipe to
achieve
uniform side-light extraction is shown in Fig. 5. Thus, in Fig. 5, a light
pipe 50b having a
core 60 and a cladding 62 includes a strip 56b of light-extraction means-such
as a
to substrate with light-scattering material-interposed between the core and
cladding. Strip
56b increases in thickness from input light 52 to output light 58. This
achieves a uniform
distribution of side-light 54b extracted from the light pipe. As used herein,
"light-scattering
material" includes material that scatters light by reflection, material that
scatters light by
refraction, or material that scatters light by a combination of refraction and
reflection.
Rather than increasing the density of light-extraction means along the length
of a
light pipe-or in addition to such increase in density, Fig. 6 shows a light
pipe 50c in which a
strip 56c increases in width along the length of the light pipe. This
increases light-extraction
efficiency as the strip widens. Thus, the side-light rays 54c are uniform
along the length of
light pipe shown.
2o Fig. 7 shows a light pipe 50d having a strip 56d, whose width increases in
the
direction from input light 52 to output light 58. Strip 56d is similar to
strip 56c of Fig. 6,
although strip 56d exists only in active section 70; that is, a section of the
light pipe for side-
light extraction. This configuration allows the maximum amount of light to be
delivered to a
remote area and then be extracted through use of light-extraction means at the
desired area
to be illuminated.
As an alternative to providing a single strip of light-extracting material 56
in Fig. 3,
Fig. 8 shows a light pipe 50e in which a series of rectangular strips 56e of
light-scattering
means are placed along the light pipe. Using a series of constant-width strips
decreases the
light extraction along a section of light pipe relative to using a single
strip of material with the
3o same light-extraction strength per unit area. Fig. 9 shows a similar series
of strips 56f of
light-extraction means, but with a higher density the further the distance
from input light 52.
Similar to Fig. 8, Fig. 10 shows round configurations of light-scattering
means 56g
along the length of a light pipe 50g.
Somewhat similar to Fig. 9, Fig. 11 shows round configurations of light-
extraction
means 56h at a higher density the further the distance from input light 52.
Light-extraction
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means 56h, however, are bunched together in groups of differing sizes to
achieve a higher
density the further the distance from input light 52.
Fig. 12 shows another pattern of light-extraction means 56i for a light pipe
50i
comprising a series of progressively larger triangular shapes. This
illustrates that the
shapes can be the same, but simply increase in size.
From the various approaches illustrated herein for achieving an increase the
strength
of light-extraction the further away from input light, a person of ordinary
skill in the art will
find combinations of various approaches to be obvious.
Fig. 13a shows a light pipe 50j incorporating light-extraction means 56j
comprising
io reflective material. Suitable reflective materials include barium sulfate,
titanium dioxide,
calcium carbonate, zinc oxide or a metallic foil. As shown in Fig. 13b, light
rays 72 are
extracted from light pipe 50j by reflection from light reflective material
50j, shown greatly
enlarged. This occurs when the angle of incidence of light (not shown)
propagating down a
light pipe and striking the reflective surface is high enough to cause the
light to be extracted
1s from the opposite side of the light pipe.
The various geometries of light-extraction means described in connection with
Figs.
3-4 and 6-12 also apply to the embodiment of Figs. 13a-13b.
Unless otherwise noted, the various geometries of light-extraction means
described
in connection with Figs. 3-13 apply to construction of a light pipes having a
core with or
2o without a fluoropolymer clad. Thus, Fig. 14a shows a light pipe 73 having a
core 74 and
fluoropolymer clad 76, while Fig. 14b shows a light pipe 75 having a core 76
but no
fluoropolymer clad. Whether to include a fluoropolymer clad or not depends on
the
composition of the core and the type of light-extraction means used, which
means are
discussed under point (3) below.
25 To summarize some of the foregoing considerations under this point (2) on
preferred
geometries of light-scattering means-without referring to the drawings-, by
applying a strip
of light-scattering material along one side of a light pipe, light can be
extracted where the
material is located in a directed manner. A uniform piece of constant width
and thickness
would be the easiest to manufacture. However, over a long length of light
pipe, such
3o construction would be difficult to achieve even illumination along the
length of the light pipe.
As the distance along a light pipe from the light input increases, there is
less and less
light available for extraction. However, by making the light-extraction
efficiency in the light
pipe increasingly higher, the further the distance from the light input, the
number of raw (i.e.,
non-adjusted) lumens per unit length extracted from the side of the light pipe
remains
3s substantially constant along the length and produces uniform illumination.
One way to
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increase light-extraction efficiency is by tapering a strip containing light-
scattering material,
so that at increasing distances from the light input, the strip increasingly
widens to increase
its extraction efficiency. Alternate methods of achieving increased extraction
efficiency are
to vary the density of light-scattering material present within the strip, or
to vary the thickness
s of the strip. A combination of all three of the foregoing approaches may
provide the
optimum design for a particular application.
This light scattering strip does not need to cover the entire length of the
light pipe. If
made from a longer piece of light pipe, the first section can be optimized to
transmit light,
such as end-light, and then the scattering material could be placed so that it
extracts light at
to the far end of the light pipe. This would produce an integrated light pipe
with a section of
light pipe optimized to transport light, and a section optimized to extract
light towards a
target area. Several pieces of the light-scattering material could be placed
along the length
of a light pipe to produce more than one area of side illumination along the
length of a long
light pipe.
~s It some cases a single run of light-scattering material may extract too
much light too
quickly or in an undesirable distribution. To avoid this, multiple smaller
pieces of light
scattering strips may be applied in various patterns to produce the desired
output
distributions.
These light-scattering materials could be applied to many various types of
light pipes.
20 3. Methods of Manufacturing the above-described Geometries
Light-extraction means of the invention include (i) material inserted between
the core
and clad of a light pipe, (ii) surfaces of the core of a light pipe treated to
have light-scattering
properties.
As to (i) material inserted between the core and clad of a light pipe, co-
extrusion die
25 80 of Fig. 15 could be used. Fig. 15 shows a reservoir 82 for material for
a clad 84 of a light
pipe 86, but omits a reservoir for a core 87 for simplicity. A nozzle for core
87 is shown at
87a. Clad 84 is shown partially cutaway. In a molten state, the clad is shown
at 85, shown
partially cutaway. At this point, molten clad 85 has just been injected from a
nozzle 85a. A
strip 88 of material which may include regions 90 of light-extraction means,
such as light-
3o scattering material, is inserted between core 87 and clad 84 in a co-
extrusion process.
Alternatively, strip 88 could comprise reflective material for the embodiment
described above
in connection with Figs. 13a and 13b.
Fig. 16 shows a co-extrusion die 94 for extruding light-extracting material 96
between
a core 98 and clad 100. In a molten state, the clad is shown at 101, and is
partially cutaway.
35 At this point, molten clad 101 has just been injected from a nozzle 101 a,
and molten core
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material 99 for forming core 98 has just been injected from a nozzle 99a. Fig.
16 shows a
reservoir 82 for material for clad 100, but omits a reservoir for core 98 for
simplicity. Multiple
streams 102 of material form light-extracting material 96, which streams can
be analogized
to the operation of an ink jet printer. Material 96 may comprise, as shown, a
series of strips
of material whose length-and hence density and light-extraction effectiveness-
vary along
the length of the light pipe. More generally, the light-extracting material 96
could be co-
extruded in the desired shape, size, thickness, and/or density between the
core and cladding
material.
Two alternatives for extruding light-scattering material between the cladding
and core
to are, first, that light-scattering material may be extruded as part of the
cladding material. This
can be done using multiple streams (not shown) of clad material, similar to
the multiple
streams of light-extracting material 102 in Fig. 16. In this case co-extrusion
of the core
material is not necessarily needed, as the cladding and sheathing could be
extruded as a
hollow tube with the desired pattern of scattering material in the cladding
already. The core
~5 material could then be poured into the tube and the light pipe would be
cast in the traditional
manner. Second, a strip or strips of material (not shown), similar to strip 88
shown in Fig.
15, with regions 90 of light-scattering means, could be inserted into a
preformed cladding in
tubular form.
For light pipes which do not have a cladding, light-scattering material can be
applied
2o in the proper size and shape with a simple adhesive sticker (not shown)
that is adhered to
the light pipe. Alternatively, the light pipe's surface could be etched (i.e.,
roughened) by
mechanical or chemical means, or even painted to produce the desired pattern
in the
surface of the light pipe. Further, organic solvents in oil-based paints can
chemically etch
the surface of a polymer light pipe to create light scattering, in addition to
any light-scattering
25 properties of the paint itself.
Finally, Figs. 17a-17b show some of the different types of light-extraction
means
discussed in this specification.
Fig. 17a shows a light pipe 120 with an etched, or roughened, surface 122 of a
core
124. Light rays 126 reaching roughened surface 122 are extracted from the side
of the light
3o pipe.
Fig. 17b shows a light pipe 130 with a paint layer 132 on a core 134. Paint
layer 132
contains light-scattering material, such as titanium dioxide or barium
sulfate.
While the invention has been described with respect to specific embodiments by
way
of illustration, many modifications and changes will occur to those of
ordinary skill in the art.
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It is, therefore, to be understood that the appended claims are intended to
cover all such
modifications and changes as fall within the true scope and spirit of the
invention.
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