Note: Descriptions are shown in the official language in which they were submitted.
~059483
This invention relates primarily to luminaires for
ceiling mounting, whether on the ceiling surface, suspended
therefrom or recessed therein. It also relates to units emit-
ting luminouq flux upward for the purpose of reflecting light
off a surface above.
For optimum lighting efficiency and architecturally
~I pleasing appearance, lighting fixtures mounted in or on the
ceiling have most often been utilized, especially when the
area to be lighted i8 large. Such areas include open spaces
in business offices, department store~, grocery stores, class-
rooms, warehouses, corridors, and the like. While luminaires
incorporating one or more parabolic reflecting surfaces have
been used to reflect or redirect light in order to provide
efficient distribution of light flux, photometrically illu-
strated as half bat-wing or full bat-wing shaped areas defined
by photometric curves showing relative candlepower distribu-
tion, their efficiency has not been fully utilized due to veil-
ing reflections and direct discomfort glare especially result-
ing when the light source includes a light diffusing envelope
encloaing a light emitter (i.e., phosphor coated lamps such
as, but not limited to, mercury, fluorescent or metal halide.)
Veiling reflections are the reflections of a light
source in the visual task, ~e.g. the printed page) that cause
a reduction in luminance contrast (e.g., between the print and
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its backgrou*d). Since the normal sightline of a worker, in
performing a desk-type visual task, is downward in a-line about
25 to the worker's side of a line perpendicular to the plane
of the task, a light source which is positioned approximately
in a line 25 behind the line perpendicular to the plane of
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the task, will be reflected by the task into the eyes of the
worker. The black part of a visual task (such as print)
approaches the brightness of the white part (such as paper)
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and thus a reduction of luminance contrast results, reducing
; visibility. The reflections therefore act as a veil placed
on the visual task, hence, the term, veiling reflections.
The deficiency results especially from improper
distribution of light flux in the work surface zone, that is,
the zone of about 0 to about 25 above nadir. m is zone is
the normal sitting viewing zone of an office worker at his
desk. Even though existing ceiling fixtures utilize one or
more parabolic reflectors for more efficient candlepower
distribution and minimization of veiling reflections, some
veiling reflections nevertheless are apparent from a task in
the 0 - 25 zone when the light source has a light diffusing
envelope.
Study of the problem has revealed that the veiling
reflections and direct glare (at normal viewing angles 45 -
90 from nadir) result from either improper placement of the
parabolic reflectors or surface relative to the light source,
or the light source having light diffusing envelopes which
prov~de light emanations from near tangential on all surfaces
of the light diffusing envelope of the light source. Accord-
ingly, a significant improvement in the utilization of para-
bolic reflectors in ceiling lighting fixtures will result if
the parabolic reflector~ can be arranged, and other means
provided, to eliminate the effects of the nearly tangential
light emanations in the zone of about 45 to 90 and 0 to
about 25 above nadir.
Comparable considerations apply to the mounting of
a luminaire inverted to illuminate the ceiling from a position
below standing eye level or from a higher position (whèn
desired) in order that the brightness of the ceiling directly
over the luminaire, which might otherwise be excessive, may be
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- ameliorated by the control inherent in this new design.
~References herein to "a~ove nadir" should be read as "below
zenith" when referring to the luminaire in inverted position).
An object of the invention therefore is to provide a
new and improved luminaire which is architecturally pleasing
and which provides controlled illumination of work areas with
minimum direct discomfort glare.
Another object of the invention is to provide a new
and improved luminaire for mounting on, in or below the ceiling
whereby veiling reflections in the zone of about 0 to about
25 above nadir are ~ub~tantially eliminated.
Still another object of the invention is to provide
a new and improved luminaire utilizing a light source having a -;
light diffusing envelope such as a phosphor coated mercury
lamp, a metal halide coated lamp, a fluorescent lamp or a
frosted incandescent lamp so as to provide maximum candlepower
distribution in the 25 to about 45 zone above nadir, but
with minimum veiling reflections.
j A further object of the invention is to provide a
new and improved lwminaire adapted to be mounted in a position
to direct luminou~ flux upward, with controlled distribution.
A still further object of the invention i9 to provide
certain improvements in the form, construction, arrangement and
materials of the luminaire whereby the above named and other
objects may effectively be attain,ed.
These and other objects, features and advantages of
the invention will be apparent from the specification which
! follow~.
In brief outline, the objects of the invention are
achieved by utilizing at least one pair of parabolic reflectors
or a single reflector that is a parabolic surface of revolution
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positioned in specific orientations about a light source having
a light diffusing envelope, in combination with a plurality of
light absorbing surfaces also positioned at specific orient-
ations relative to the light source, light envelope and para-
bolic reflectors. The parabolic reflectors or reflector are
oriented with re~pect to the light source so that their focal
points substantially coincide, and the light emitter within the
light diffusing envelope is positioned at such coincident foci.
The reflectors also are positioned such that reflections there-
from provide maximum candlepower in the zones of about 25 toabout 45 above nadir, thereby to form the familiar full bat-
wing configuration when the light flux of the luminaire is
analyzed and plotted photometrically. Veiling reflections are
thereby substantially eliminated in thé important wor~ zone.
The light absorbing surfaces are positioned between the -
reflectors so as to absorb substantially all light emanating
nearly tangentially from the light source envelope into the
reflectors that would reflect into the 45 to about 90 above
nadir zone, thereby minimizing the direct discomfort glare
which otherwise would result.
In accordance with one aspect of the present invention,
there i8 provided in a luminaire, the combination of: a light
source in an envelope: parabolic reflecting surfaces disposed
on at least two opposite sides of said light source so that
their focal points substantially coincide, said light source
being positioned approximately at said coincident focal points
and portions of said reflecting surfaces being ~o positioned
that reflections therefrom cross and'provide maximum candle-
power in the zones of about 25 to about 45 above nadir; and
a plurality of light absorbing surfaces positioned between said
reflecting surfaces, close to ~aid envelope and generally
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radially of said light source so as to cut off substantially
all light emanating near tangentially from said envelope which
would otherwise have reflected into the zones of about 45 to
about 90 above nadir: whereby veiling reflections are substan- .
tially eliminated in the zones about 0 to about 25 above
nadir and direct glare is eliminated in the zones above about
45 above nadir.
In accordance with a further aspect of the present :
invention, there is provided in a luminaire, the combination
of: a light source in an envelope, a reflecting surface in
the form of a parabolic surface of revolution disposed about
said light source, said light source being positioned approxi-
mately at the focal point of said surface of revolution and
~ portions of said reflecting surfaces being so positioned that
: reflections therefrom cross and provide maximum candlepower in
the zones of about 25 to about 45 above nadir; and a plurality
of light absorbing surfaces positioned between said reflecting
surface, close to said envelope and generally radially of said
light ~ource so as to cut off 3ubstantially all light emanating
near tangentially from said envelope which would otherwise
have reflected into the zones of about 45 to about 90 above
nadir, whereby veiling reflections are substantially eliminated
in the zones about 0 to about 25 above nadir and direct
glare is eliminated in the zones above about 45 above nadir.
v~ The invention accordingly comprises the features of
construction, combination of elements, and arrangement of parts
which will be exemplified in the constructions hereinafter set
forth, and the scope of the invention will be indicated in the
claims.
For a fuller understanding of the nature and objects
of the invention, reference is had to the following description
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taken in conjunction with the accompanying drawings, in which:
FIG. 1 is an approximate photometric curve showing
relative candlepower in a vertical plane through light flux
from a luminaire of the invention;
FIG. 2 is a partially diagrammatic, perspective view
from below one embodiment of a luminaire of the invention,
FIG. 3 is a detailed,sectional and side elevational
. view of a portion of the luminaire shown in FIG. 2;
, FIG 4 is a diagrammatic view of the emanations and
reflection, of the luminaire of FIG. 2,
FIG. 5 is a perspective view of another embodiment
of luminaire of the invention,
FIG. 6 is an end view of the luminaire of FIG. 5; and
:~ FIG. 7 is a vertical sectional view of another embodi-
~: ment of the luminaire of the invention.
With reference to FIG. 1, the area under the photo-
metric (relative candlepower) curve 11 by virtue of its full
- bat-wing configuration indicates that luminaires of the
invention provide near ideal light flux distribution from a
~, 20 ceiling mounted light source 12. Maximum candlepower is shown
to be in the zone of about 25 to about 45 above nadir, both
to right and left of nadir~ subtending the angle A. Prefer-
~ ably, the maximum candlepower is within the 35 - 45 zone~,
b with cut-off of emanations and reflections at 45. In addition,
it is a frequent occurrence that a person is so positioned that
the light ~ource 12 i8 in front of and above his eyes shown
diagrammatically at 13. This diagram defines a zone B of about
0 to about 25 from nadir which includes in most desk-type
~ applications the area of the task on a horizontal surface 14.
:. 30 The luminaire of the invention thus distributes light emanations
with maximum efficiency throughout the entire area to be lighted
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(work surface as well as background); as will become evident
from the discussion following, luminaires of the invention sub-
stantially reduce veiling reflections in the work zone.
In the underside view of a luminaire 15 of the
invention, illu~trated in FIG. 2, the luminaire can include a -
housing or frame 16 wherein the lower edge 17 of the frame can
coincide with the plane of a ceiling. The luminaire is thus
recessed, this being a frequently desired arrangement from an
architectural standpoint. Surface mounting of the lwminaire
on the ceiling or pendant mounting can also be effected, if
desired. Within the housing 16 is at least one pair of oppos-
ing parabolic reflectors 18 and 19 and preferably a second pair
of opposing parabolic reflectors 21 and 22 mounted adjacent ~-
the first pair of reflectors so as to form a shell abGut a
light source 23. An opening 24 serving as an air vent may be
positioned above the reflectors, if the light source is of a
type generating considerable heat. It might also serve to
allow light to be emanated upward if mounted as shown, or
downward if the unit is inverted.
Positioned between the parabolic reflectors (or the
parabolic surface, as the case may be) and below the light
source 23 is a plurality of light absorbing surfaces 25. The
light absorbing surface~ 2S are shown as elongated planes held
together by struts 26 and suspended from upper portions of the
parabolic reflectors by rods 27. However, the absorbers may
have other geometrical configurations. The absorbers are formed
of any suitable light-absorbing medium, ~uch as matte black
paint on metal surfaces or the like. A significant spatial
relationship is maintained between the parabolic reflectors,
the light absorbing surfaces and the ligh source 23. This
relationship is best understood by consideration of FIG. 4.
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With reference to FIG, 4, the lightsource 23 is shown
in end view and is positioned between the parabolic reflectors
shown in section, such as reflectors 21 and 22, The parabolic
reflectors (or the parabolic surface of revolution reflector)
21 and 22 are positioned such that their foci substantially
coincide, the coincident foci also being coincident with the
center of the light ~ource 12, However, the axes of the para-
bolic reflectors are set such that the reflections therefrom
cross and provide maximum candlepower distribution in the zone
of about 25 to about 45 above nadir, preferably 35 to 45,
and on both sides of nadir so as to define the familiar full
bat-wing photometric curve.
While the total reflecting surface may be parabolic,
it is preferred to insert general reflecting surfaces 28 and 29
in place of the upper portions of the parabolic reflectors so
that the light emanations higher than about 135~ above nadir
will be reflected downwardly as shown by reflections 32, rather
than back into the light source.
It will thus be noted that the emanations and
reflection9 from the light source 23 are of several varieties.
The first is the parallel reflections 34 from each of the para-
bolic reflectors 21 and 22, which cross over and are directed
to provide the full bat-wing candlepower distribution photo-
metrically illustrated in FIG. 1. The second variety is the
downward reflections 32 from the general reflecting Qurfaces
28 and 29. The third variety comprises the light rays 35 which
emanate directly and near tangentially from the light diffu~ing
envelope 33. The tangential emanations from the top half of ,~
the lamp are reflected as rays 36 and therefore cause no direct
glare from a normal viewing angle.
The light absorbing surfaces 25 are positioned to
provide effective cut-off of tangential light emanations in
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the zone between about 45 and 120 above nadir. If such light
emanations had been allowed to reach the reflector, they would
have reflected out of the luminaire in the zone of 45 above
nadir to 90 above nadir, thereby causing direct discomfort
glare. Preferably the absorbing surfaces 25 are planar and
are set at angles other than tangential to the light diffusing
envelope 33, such as angles radial to the center of the light
source or emitter 12. The light absorbing surfaces 25 may
extend around the entire lower half of the envelope 33 or they
may be separated into several, spaced-apart sets, as shown.
The light source 23 and its light diffusing envelope
33 may have any suitable geometric form, although generally the
form will be spherical, globular or tubular, for example. Among
suitable lamps may be mentioned phosphor-coated mercury, coated
metal halide, fluorescent, and frosted incandescent.
In another embodiment of the invention, with reference
to FIGS. 5 and 6, the light source may be an elongated tube
such a~ the fluorescent tube 37. A single pair of longitudin-
ally elongated parabolic reflectors 38 and 39 generally will
be sUffiCient in this embodiment, preferably in combination
with a pair of general reflectors 41 and 42 corresponding in
position to reflectors 28 and 29 of FIG., 4. The reflecting
surface~ are positioned relative to the fluorescent tube 37
and its envelope 43 substantially as described with respect to
the first embodiment of the invention, as illustrated in FIGS.
1-4. A plurality of light absorbing surfaces 44 extend longi-
tudinally of the tube 37 and are positioned for cut-off of
tanqential light emanations from envelope 43 that would other-
wise have reflected into the 45 to 90 zone above nadir, sub-
stantially as described with respect to the embodiment ofFIGS. 1-4.
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However, since the elongated nature of tube 37 would
cause light emanating at high angles to result in direct glare
into the eyes of a viewer, a plurality of light absorbers 45
are mounted transversely of the absorbers 44 so that the tube
37 cannot be viewed directly from either end thereof at normal
viewing angles. Accordingly, the luminaire of FIGS. 5 and 6
also provides illumination producing minimum veiling reflections
and direct glare from substantially any normal viewing angle.
As an alternative to the pair or pairs of parabolic
reflectors shown in FIGS, 2, 4, 5 and 6 the reflector may be a
parabolic surface of revolution, as shown at 50 in FIG. 7, this
reflector being circular in plan or horizontal section and being
modified to include a general reflecting area 51 adjacent its
apex comparable to the areas 28, 29, 41 and 42. m e light
source 52 is located at the focal point of the parabolic
reflector and has its long axis disposed vertically. A plural-
ity of light absorbers 53 are mounted adjacent the lower part
of the light source in positions to cut off tangential light
emanations from the envelope of the source 52 in the manner
indicated by FIGS. 4 and 6. The light distribution in this
case will show the full bat-wing configuration along any verti-
cal plane through the light source, the entire configuration
being in the form of a conical bat-wing, with advantages in
illumination as described above.
While the invention has been illustrated and des-
cribed in what are considered to be the most practical and
preferred embodiments, it will be recognized that many vari-
ations are possible and come within the scope thereof, the
appended claims therefore being entitled to a full range of
equivalents.
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