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 in¬ vention 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 char¬ acteristics 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 indivi¬ dual task lighting, for example, for surfaces approximately two and a 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 pro¬ vides 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 sperical 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 surfa_-_a-__-____

which has been found to be a distinct preference and produces feelings of spaciousness and comfort.

Indirect lighting obviates the problem of glare perceiv by an observer, but most indirect lighting systems have the di advantge of collecting dust which gathers on the lamps and any reflectors beneath the lamps, arid this is a major source of reduced luminance. Another disadvantge of most indirect light systems is a psychological one. Research has shown that human beings have a distinct preference for lighter rooms which are formaly 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 luminan 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 ada tion, but-once the adjustment has been effected, there is litt difficulty in performing tasks if the illumination meets the m mum requirements for the task. Further, people prefer to be able to see the source of light. It provides a sense of persp tive and has been found to be a factor to be considered in pro viding office lighting. As indicated, most indirect lighting systems have 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 ill nance above the luminaire which is uniform. Either a very bri spot is created above the luminance (the more common character tic) , or a dark area is generated. In either case, the substa tial variation in the illumination pattern on the ceiling is easily perceived and is undesirable.. Further, in the case of t bright spot, inefficiency results because most of the light is reflected back to the luminaire rather than being used to ligh the room.

If a dark area is created on the ceiling, it is undesira from an aesthetic as well as a psychological viewpoint because the preferences mentioned above.

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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. illu¬ mination 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. Adja¬ cent 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 pat¬ tern of luminance on a ceiling above the luminaire which normally has a high reflectance to provide good indirect lighting quali¬ ties. 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 por¬ tions 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 por¬ tion 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 li from the reflectors toward the horizontal to "fan" the inciden 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 overhead and extending a few feet either side of the lens without creating bright spots whic cause glare or dark areas on the ceiling, as characterized by some prior luminaires used for indirect lighting. Thus, lumi- naires of the present invention may be spaced at relatively wid distances-if they are associated, for example, with movable wall panels since adjacent luminaires will both exhibit this f ning 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 are 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 i transmitted to the top lens portion because of the size of the lamps. This, as well as the particular prism designs, disclose below, cooperates to achieve a pattern of substantially uniform luminance which is highly desirable from a psychological stand¬ point 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.

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The lateral lens portions of the luminaire transmit direct and reflected light from the source to illuminate vertical sur¬ faces 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. Nevirtheless, 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 sur¬ face 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 ap¬ parent 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.

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The Drawing

FIG. 1 is a side elevational view of a typical movable panel wall system on which a luminaire constructed according t the present invention is mounted;

FIG. 2 is an upper side perspective view of the luminair Of FIG. 1;

FIG. 3 is a transverse cross sectional view of the lumi¬ naire of FIG. 2;

FIG. 4 is a fragmentary longitudinal vertical cross sec¬ tional view of one end of the luminaire of FIG. 2; and

FIG. 5 is a diagrammatic cross sectional view of the rig side of a lens incorporated into the luminaire of FIG. 2.

Detailed Description

Referring first to FIG. 1, reference numeral 10 generall 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 mount 12 may ta the form of a pair of upright arms enclosed in a sheet metal casing.

To illustrate the type of task lighting to which the pres ent invention is directed, a cabinet generally designated 13 ma be mounted to the wall panel 10, and a work surface 14 may be p vided beneath the cabinet 13.

Turning now to FIG. 2, the fixture 10 is seen to include housing 15, first and second end caps 17, 18 and an upper lens 1

As best seen in FIG. 3, the housing 15 includes a general 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 mou 25, and a similar screw mount 26 is formed on the inner surface the side wall 23. First and second inwardly extending lips 27, are formed at the upper edges of the side walls 22, 23 respecti ly.

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 LI; and to the side of the lamp LI, the re¬ flector 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 30. 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 lumi¬ naire. 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 by 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 dis¬ tinguished from the bottom-mounted luminaire shown.

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OMPI

Referring now to FIG. 4, the end cap 17 is seen in detai It is received on and held to an intermediate wall 53 which ser to mount the lamps and also to support a ballast B in the manne illustrated. Thus, the end cap 17 cooperates with the intermedi ate 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 canti levered from the intermediate wall 53 to reduce noise transmissi from the ballast B.

In FIG. 4, there is also shown a gasket 58 which seals th left edge of the lens 41 against the entry of dust into the inte ior 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 Ll, 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 incide light to diverge through refraction. Consider, for example, par llel 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 refractέ-d and travels along the divergent path 68. Similarly, the ray 66 fol¬ lows 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 s faces 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 63 A. It travels along a path 73 within the lens material, but emerges from the exit

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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 is 30 mils. The spacings 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 prism 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 prin¬ cipal 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 particu¬ larly the curvature of the portion 36 is to direct light from the source Ll toward the lateral portion 50 of the lens.

The lateral portion 50 of the lens has a uniformly curved, smooth interior surface 80 which has a radius of curvature cen¬ tered 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 will emerge, and a second surface 85 referred to as a riser or return surface. The struc¬ ture of the prisms P1-P21 is illustrated in Table I an les RHS LHS LHS-1 and LHS-2 are defined in FIG

but also for a distance of several feet to the side thereof. By providing uniform ambient lighting, as mentioned, above, the over¬ all 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 em¬ ploying these luminaires are also illuminated in a substantially uniform manner even at eye level and above, because of light direct from the lateral lens portions and reflected off the ceil¬ ing. As mentioned, human perception of whether a room is ade¬ quately lighted depends to some extent on whether the vertical surfaces are visibly illuminated.

Still further, it will be appreciated that the lens act as a dust -cover to prevent dust and dirt from reducing the lumi¬ nance emanating from the source , and because 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 substi¬ tute equivalent elements for those disclosed while continuing to practice the principle of the invention. For example, the dimen¬ sions 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 main¬ tained. Further, although fluorescent 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 sub- stitutions be covered as•they are embraced within the spirit and

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TABLE I