Luminaire for indirect lighting

The luminaire includes a source of light in an opaque housing which extends beneath the source and upwardly about the sides of the source to hide the source from direct view from a horizontal line of sight even with the source. A lens is mounted to the housing above the source and extending around to join with the upper edge of the housing. The lens includes an upper light-dispersing portion which diverges one portion and only displaces another portion of the light from the source to provide an even distribution of luminance to a ceiling above the source. The lens also includes a lateral light-bending portion which receives light from the source and fans it out laterally over the side of the housing to continue the uniform illumination pattern of the ceiling and to illuminate vertical surfaces in the vicinity of the luminaire. A reflector beneath the source directs light onto the lateral light-bending portion of the lens to at least partly compensate for the fact that the light passing through the lateral portion of the lens normally travels farther to the surface it is illuminating and also strikes any horizontal surface at an increased angle of incidence. The lens and housing cooperate to enclose the source of light to prevent dust from entering, and the lateral portion of the lens provides a visible source of light to a person in the room being illuminated.

BACKGROUND AND SUMMARY 
The present invention relates to a luminaire (i.e., the complete lighting 
unit); and more particularly, it relates to a luminaire which may be used 
for indirect lighting particularly in large open areas such as are 
commonplace in modern offices. As will be further explained below, one of 
the advantages of the invention is that its use is not limited only to 
open office areas, but rather, it can be carried through to the lighting 
of hallways, executive suites or conference rooms. However, the invention 
is particularly suited to provide illumination for typical office 
situations with efficient use of energy while having those characteristics 
which recent research has shown to be desirable from a psychological 
viewpoint. 
Modern offices are characterized by large open spaces having a ceiling 
height normally about eight feet, but which may extend to nine feet. The 
space may be sectioned for privacy by movable wall partitions. These 
partitions normally have a height of about five to seven feet. 
In considering the lighting requirements for an office, among the more 
important considerations are the need for individual task lighting, for 
example, for surfaces approximately two and half feet above the floor, and 
the need to provide some ambient lighting. The latter is desirable both 
from a safety standpoint and for psychological reasons, as will be 
discussed below. 
Direct lighting as a source of lighting for offices provides high luminance 
for task areas, but in general, the quality of lighting is not good in 
terms of visibility and visual comfort of a person. 
Lenses have been used in luminaires employing fluorescent lamps for direct 
lighting. One type of lens employs individual conical or spherical lenses 
in a repeating pattern. Another uses parabolic reflectors to direct light 
downwardly. In both of these systems, a light transmission pattern is 
created in which the light is directed downwardly and generally confined 
within an angle of about 45 degrees from the vertical. Further, neither of 
these systems provides ambient lighting for vertical surfaces which has 
been found to be a distinct preference and produces feelings of 
spaciousness and comfort. 
Indirect lighting obviates the problem of glare perceived by an observer, 
but most indirect lighting systems have the disadvantage of collecting 
dust which gathers on the lamps and any reflectors beneath the lamps, and 
this is a major source of reduced luminance. Another disadvantage of most 
indirect lighting systems is a psychological one. Research has shown that 
human beings have a distinct preference for lighter rooms which are 
uniformly illuminated. In other words, a person may comfortably perform a 
task in an area at a relatively low luminance level provided there is a 
minimum of light available and the luminance pattern does not change 
substantially within his field of view. If the luminance level is 
substantially lower than that of the area from which a person enters, 
there will be a period of adaptation, but once the adjustment has been 
effected, there is little difficulty in performing tasks if the 
illumination meets the minimum requirements for the task. Further, people 
prefer to be able to see the source of light. It provides a sense of 
perspective and has been found to be a factor to be considered in 
providing office lighting. As indicated, most indirect lighting systems 
have as a principal object the generation of light while masking 
completely the origin of the light. 
Lenses have in the past been placed above a source of light. Some of these 
lenses do not generate a pattern of illuminance above the luminaire which 
is uniform. Either a very bright spot is created above the luminaire (the 
more common characteristic), or a dark area is generated. In either case, 
the substantial variation in the illumination pattern on the ceiling is 
easily perceived and is undesirable. Further, in the case of the bright 
spot, inefficiency results because most of the light is reflected back to 
the luminaire rather than being used to light the room. 
If a dark area is created on the ceiling, it is undesirable from an 
aesthetic as well as a psychological viewpoint because of the preferences 
mentioned above. 
The luminaire of the present invention has as a principal object the 
provision of indirect lighting of large open office systems by achieving a 
uniform distribution of light (i.e. illumination pattern) on a ceiling 
over the luminaire as well as by fanning the light out laterally to extend 
the uniform luminance on the ceiling to adjacent areas not directly above 
the luminaire. Further, due to the reinforcement and bending of lateral 
rays, vertical surfaces are illuminated even at a substantial distance 
from the unit. 
The luminaire includes an opaque housing beneath the source of light which 
preferably includes two or three fluorescent lamps placed side by side. 
The length of the lamps helps to distribute the light along the length of 
the housing. 
A lens is mounted to the housing above the source, and in the illustrated 
embodiment, it includes a generally flat upper portion and lateral 
portions which curve downwardly and join to the housing to enclose the 
lamps. The upper portion of the lens includes a flat upper surface and a 
series of light-diverging prisms on the lower surface, facing the source 
of light. Adjacent prisms are spaced by a flat portion. The function of 
the prisms is to refract and diverge incident light, and the function of 
the flats is to permit incident light to pass between the prisms. The 
prisms and flats cooperate to provide a uniform pattern of luminance on a 
ceiling above the luminaire which normally has a high reflectance to 
provide good indirect lighting qualities. This uniformity is effective 
when the ceiling is placed about two to three feet above the upper surface 
of the lens and the effect persists even though the spacing is reduced to 
one foot. 
A reflector is located beneath the light sources in the housing to direct 
light from the sources out to the lateral portions of the lens. Some of 
the reflected light is transmitted upwardly to the upper portion of the 
lens. In the illustrated embodiment there are two lateral lens portions, 
but only one is necessary, for example, if the luminaire is designed for 
placement directly on the side of a vertical wall. The lateral lens 
portion or portions are curved downwardly from the top lens portion to the 
upper edge of the housing, and they contain a plurality of external prisms 
extending the length of the lens. 
The placement of the source of light in the housing is such that it cannot 
be seen directly by an observer having an eye level the same height as or 
slightly above the source. Further, because of the interposition of the 
lens, the light source cannot be seen directly from any elevation. The 
lateral lens portions bend the light from the source as well as the light 
from the reflectors toward the horizontal to "fan" the incident light and 
thereby extend the uniform pattern of luminance onto portions of the 
ceiling not directly above the luminaire. A pattern of luminance having 
substantial uniformity is thus achieved on the ceiling directly over-head 
and extending a few feet either side of the lens without creating bright 
spots which cause glare or dark areas on the ceiling, as characterized by 
some prior luminaires used for indirect lighting. Thus, luminaires of the 
present invention may be spaced at relatively wide distances if they are 
associated, for example, with movable wall panels since adjacent 
luminaires will both exhibit this fanning effect and achieve a luminance 
for indirect lighting which not only provides uniform ambient lighting but 
also more than adequate task lighting at the same time. 
The fact that the light flux density diminishes as the distance between the 
luminaire and the point being illuminated increases as well as the fact 
that the flux density is reduced because the flux density in a plane 
perpendicular to the source is spread over an extended area for large 
angles of incidence (i.e. the angle relative to the normal), as is the 
case for areas not directly above the luminaire, are compensated by the 
effect of the reflector which routes most of the light from the bottom of 
the source toward the lateral lens portions, although some is transmitted 
to the top lens portion because of the size of the lamps. This, as well as 
the particular prism designs, disclosed below, cooperates to achieve a 
pattern of substantially uniform luminance which is highly desirable from 
a psychological standpoint and which achieves uniform task light as well 
as ambient lighting while reducing the amount of electricity to accomplish 
this in a large open office area. 
The lateral lens portions of the luminaire transmit direct and reflected 
light from the source to illuminate vertical surfaces such as walls and 
provide a brighter ambient lighting. 
Further, because the prisms on the curved lateral portion of the lens are 
on the exterior surface of the lens, they act to segment the incident 
light and provide a series of softly glowing lines of light which are 
perceptible to a person standing to the side of the luminaire, but without 
transmitting a direct image of the source. Thus, persons in a space 
illuminated by the present invention have the psychological benefit of 
knowing where the light is coming from, yet they do not experience the 
discomfort of glare which accompanies normal direct lighting. When the 
luminaire of the present invention is mounted to the top of a movable wall 
panel at a height of 72 to 84 inches, the light source is out of the 
direct line of sight of a person less than about seven feet tall. 
Nevertheless, he is capable of seeing light emanating from the exit 
surfaces of the prisms on the curved lateral portions of the lens. A small 
amount of light also emanates from the riser surfaces of the prisms 
through internal reflection, and this light is greatly diminished in 
luminance, but it extends downwardly from the luminaire, thereby providing 
a visual image of the source of light even to a person sitting at a work 
surface mounted to the same or adjacent wall panel to which the luminaire 
is mounted. 
Another advantage to the present invention is that the lens provides a dust 
cover for the lamps, and the smooth exterior surface of the upper portion 
of the lens facilitates cleaning. That is, there are no crevices in which 
dust can gather. Thus, a major source of reduction of luminance in 
indirect lighting is obviated, namely, the collection of dust on the lens 
or lamps. 
Other features and advantages of the invention will be apparent to persons 
skilled in the art from the following detailed description of a preferred 
embodiment accompanied by the attached drawing wherein identical reference 
numerals will refer to like parts in the various views.

DETAILED DESCRIPTION 
Referring first to FIG. 1, reference numeral 10 generally designates a 
movable wall panel at the top of which a luminaire generally designated 11 
is mounted by means of an upright mount 12 extending from the top of the 
panel 10. The amount 12 may take the form of a pair of upright arms 
enclosed in a sheet metal casing. 
To illustrate the type of task lighting to which the present invention is 
directed, a cabinet generally designated 13 may be mounted to the wall 
panel 10, and a work surface 14 may be provided beneath the cabinet 13. 
Turning now to FIG. 2, the fixture 10 is seen to include a housing 15, 
first and second end caps 17, 18, and an upper lens 19. 
As best seen in FIG. 3, the housing 15 includes a generally flat bottom 
wall 21 and upwardly curved side walls 22, 23. The housing 15 may be 
formed by extruded aluminum since its cross section is uniform throughout. 
It is then cut to the desired length. 
On the side wall portion 22, there is formed a screw mount 25, and a 
similar screw mount 26 is formed on the inner surface of the side wall 23. 
First and second inwardly extending lips 27, 28 are formed at the upper 
edges of the side walls 22, 23 respectively. 
A reflector generally designated 30 is mounted in the housing 15 by screws 
31 secured in the screw mounts 25, 26. The reflector 30 is symmetrical 
about a vertical plane P extending through the longitudinal center of the 
luminaire to form side halves 33, 34. Thus, the side 33 includes a flat 
portion 35 beneath a first lamp L1; and to the side of the lamp L1, the 
reflector is smoothly curved upwardly to form a portion 36, the edge of 
which is formed into a mounting flange 37. The central portion of the 
reflector is turned upwardly as at 39. The surface of the reflector may 
vary according to the effect desired, but for general office use, a 
specular surface may be used. 
The illustrated embodiment includes a second lamp L2 located within the 
housing 22. Both lamps are mounted between a pair of conventional lamp 
holders, one of which is shown in FIG. 3 at 39 mounted to a first 
intermediate wall 40. A third lamp may be used by moving the two lamps 
shown further apart and inserting a third lamp between them. The center 
lamp would be raised slightly. The luminaire may also be used with only a 
single lamp or with a switch for illuminating one, two or three lamps, as 
desired. 
A lens generally designated 41 is mounted to the housing 15 by means of 
first and second elongated fittings 44, 45 which releasably couple 
respectively to the inwardly extending lips 27, 28 of the housing 15. 
Thus, the lens is mounted in such a manner that it can be removed easily, 
simply by pressing the sides, yet it prevents dust and dirt from entering 
the interior of the luminaire. The end seals will be described in 
connection with FIG. 4. 
The lens 41 includes an upper lens portion 48, and first and second curved 
lateral portions 49, 50. The lens 41 is also symmetrical about the plane 
P. Because both side halves of the fixture operate in a similar manner, 
the features and advantages of the invention can be achieved simply be 
extending the housing along the plane P for a luminaire adapted to mount 
to the vertical surface of a wall, such as in a hall or conference room, 
as distinguished from the botton-mounted luminaire shown. 
Referring now to FIG. 4, the end cap 17 is seen in detail. It is received 
on and held to an intermediate wall 53 which serves to mount the lamps and 
also to support a ballast B in the manner illustrated. Thus, the end cap 
17 cooperates with the intermediate wall 53 to provide a housing for the 
ballast B which may be mounted by means of a flexible grommet 55 to a 
platform 56 cantilevered from the intermediate wall 53 to reduce noise 
transmission from the ballast B. 
In FIG. 4, there is also shown a gasket 58 which seals the left edge of the 
lens 41 against the entry of dust into the interior of the luminaire. A 
similar gasket is provided on the other intermediate wall 40. 
Turning now to FIG. 5, which illustrates the structure of one side of the 
lens 41 in relation to the center of lamp L1, designated 60 in FIG. 5, the 
top portion 48 of the lens has a flat upper surface designated 61. This 
facilitates dusting of the fixture and provides no crevices for collecting 
dust or dirt. The under surface of the top portion 48 of the lens 41 is 
formed into a plurality of equilateral prisms 62 which extend the length 
of the lens, and are separated by flat portions or simply "flats" 
designated 63. 
The principal function of the prisms 62 is to cause incident light to 
diverge through refraction. Consider, for example, parallel incident rays 
65, 66 which are incident respectively on the surfaces 62A and 62B. The 
ray 65 is refracted and travels along the path 67 through the transparent 
material of the lens to the upper exit surface 61 thereof where it is 
again refracted ray 66 follows the path 69 in the lens and emerges along 
the path 70 from the exit surface 61. Thus, the light which is incident on 
the surfaces of the prisms 62 is widely dispersed and diverged through 
refraction. 
Light which is incident on one of the flats 63, on the other hand, is 
simply displaced but remains parallel to the path of the original incident 
ray. Consider, for example, the ray 72 which is incident on a land 
designated 63A. It travels along a path 73 within the lens material, but 
emerges from the exit surface 61 to travel along a path 74 which is 
parallel to the path of the original ray 72. Because of the size, 
configuration and spacing of the prisms, the light emerging from the exit 
surface 61 is diverged in such a manner that the resulting pattern of 
luminance on a horizontal surface above the luminaire for as close a 
spacing as one foot is substantially uniform without either bright or dark 
areas. 
In a preferred embodiment, the angle of each of the prisms 62 is 60 
degrees; and the height h' is 30 mils. The spacing d' of the prisms is 62 
mils, and the thickness of the lens 41 between the exit surface 61 and the 
flats 63 is 130 mils. These dimensions can be changed without any 
appreciable change in the results. If the proportion of prisms height to 
spacing remains the same, the results will be the same. The material of 
the lens preferably is clear virgin acrylic, although other materials such 
as Lexon may also be used. 
Turning now to the lateral portion 50 of the lens, its principal function 
is to bend incident light from the source and to "fan" the light out 
laterally so that it is spread to the side of the fixture on a ceiling and 
may also be used to illuminate any vertical surfaces in the neighboring 
vicinity. Because of the reduction in intensity due to the greater 
distance traveled by the light passing through the lateral portion 50 as 
well as the fact that the flux will be spread over a greater area of any 
illuminated horizontal surface due to the increased angle of incidence, a 
principal function of the reflector 30 and particularly the curvature of 
the portion 36 is to direct light from the source L1 toward the lateral 
portion 50 of the lens. 
The lateral lens portion 50 of the lens has a uniformly curved, smooth 
interior surface 80 which has a radius of curvature R centered at 81. The 
outer surface of the lateral portion 50 of the lens is formed into a 
plurality of prisms, the points of which are designated respectively 
P1-P21 for convenience. 
Each of the prisms P1-P21 includes an active or emitting surface such as 
that designated 84 for the prisms P3 from which light incident on the 
inner surface 80 wll emerge, and a second surface 85 referred to as a 
riser or return surface. The structure of the prisms P1-P21 is illustrated 
in Table I where the angles RHS, LHS, LHS-1 and LHS-2 are defined in FIG. 
5. The dimension "h" is the height of a prism. The nominal thickness of 
the lateral portion 50 from the uniformly curved surface 80 to the 
intersection between an adjacent riser 85 of one prism and the active 
surface of the adjacent prism is 125 mils. Further, the center 60 of the 
light source is approximately 0.625 inches below the center 81 of the 
radius of curvature of the surface 80, and approximately two inches to the 
left of it. It will also be observed that the center 81 is in 
approximately the same horizontal plane as the upper extension of the 
curved side 22 of the opaque housing 15. Thus, the light sources cannot be 
seen directly by an observer whose eye level is the same height as the 
source. 
Because the luminaires are preferably mounted at a height of six to seven 
feet above the floor (that is, the height to the top of the side wall 22 
of the housing 15), a person who is less than about seven feet tall will 
have a line of sight which will be above the lamps. However, as will be 
explained presently, he will perceive where the light is coming from. 
Still referring to FIG. 5, three light rays are designated 90, 91 and 92; 
and for purposes of illustration, they are shown as emanating from the 
center 60 which is an idealized point. In the medium of the lens, the rays 
take the respective paths 90A, 91A and 92A; and when they exit from the 
associated active surfaces of the prisms as illustrated, they travel along 
the paths 90B, 91B and 92B respectively. It can thus be seen that the 
light from the source is spread out in an increasing pattern from the top 
to the side edge of the lateral portion 50 of the lens. Further, it is 
segmented in the sense that an observer viewing the lens from the side at 
normal angles will see a series of softly glowing horizontal lines and 
therefore perceive where the light is emanating from. Not illustrated in 
FIG. 5 for clarity are the rays of light emanating from the source L1 
which are reflected by the reflector 30 and directed toward the lateral 
portion 50 of the lens. As indicated, these rays reinforce the direct rays 
from the source so that the pattern of luminance on a horizontal surface 
above the fixture will be substantially uniform and without glare spots or 
dark areas not only directly above the luminaire but also for a distance 
of several feet to the side thereof. By providing uniform ambient 
lighting, as mentioned above, the overall luminance can be maintained at a 
relatively low level and yet provide adequate task lighting. By bending 
the light and fanning it out laterally through the lateral portions of the 
lens, the luminaires can be placed at relatively greater distances than 
would otherwise be required to achieve complete illumination coverage and 
uniform luminance. Vertical surfaces in a room employing these luminaires 
are also illuminated in a substantially uniform manner even at eye level 
and above, because of light directed from the lateral lens portions and 
reflected off the ceiling. As mentioned, human perception of whether a 
room is adequately lighted depends to some extent on whether the vertical 
surfaces are visibly illuminated. 
Still further, it will be appreciated that the lens acts as a dust cover to 
prevent dust and dirt from reducing the luminance emanating from the 
source, and because of the upper surface of the top portion of the lens is 
flat, it facilitates cleaning. It will be observed that at least some 
light emanates from the riser surfaces of the prisms on the lateral 
portion of the lens, and this light is directed downwardly below the 
horizontal. It may not be enough light to provide adequate task lighting 
but it nevertheless provides a visual image to an observer seated at a 
work area so that he can see where the light is coming from. 
Having thus described in detail a preferred embodiment of the invention, 
persons skilled in the art will be able to modify certain of the structure 
which has been illustrated and substitute equivalent elements for those 
disclosed while continuing to practice the principle of the invention. For 
example, the dimensions of the lens may be altered without substantially 
changing the photometric properties of the luminaire, particularly, if the 
height-to-spacing proportions of the various prisms is maintained. 
Further, although flourescent lamps are preferred, other lamps may also be 
used; and lamps not yet developed may have equal or better results. 
Finally, the number of lamps or type of ballast are not critical to 
achieving the overall desired results. It is, therefore, intended that all 
such modifications and substitutions be covered as they are embraced 
within the spirit and scope of the appended claims. 
TABLE I 
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POINT 1 2 3 4 5 6 7 
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RHS 0 0 0 0 0 0 0 
LHS 63.9 65.2 66.4 67.6 68.8 70.0 71.1 
h .070 .067 .063 .060 .057 .054 .066 
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POINT 8 9 10 11 12 13 14 
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LHS-1 24.1 33.3 33.3 33.3 33.3 12.1 9.8 
LHS-2 69.0 69.0 69.0 69.0 67.8 70.4 73.0 
h .082 .082 .082 .082 .070 .058 .047 
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POINT 15 16 17 18 19 20 21 
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RHS 0 0 0 0 -- 87.2 82.5 
LHS 70.0 74.3 78.8 83.4 -- 0 1.25 
h .054 .044 .034 .017 -- .017 .025 
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