US 3591798 A
Description (OCR text may contain errors)
United States Patent Inventor Noel S. Florence Cranlord, NJ. Appl. No, 772,903 Filed Nov. 4, I968 Patented July 6, I971 Assignee Lightolier Incorporated Jersey City, NJ.
LIGHTING FIXTURE 5 Claims, 8 Drawing Figs.
US. Cl 240/S1.11, 240/41 .35 Int. Cl H05b 33/02 Field of Search .1 240/9, 9 A, 51.1 1, 41.35,41.37
References-Cited UNITED STATES PATENTS 240/5l.ll
Doane 2,436,635 2/1948 De Bishop, Jr. 240/5l.11 2,591,661 4/1952 McCandless 240/5l.ll 3,246,138 4/1966 Florence 240/5 1 .1 1
Primary Examiner l0hn M. Horan Assistant Examiner-Richard M. Sheer Attorney-Arthur B. Colvin ABSTRACT: A lighting fixture comprising a pair of parallel vertically aligned fluorescent lamps positioned midway between two elongated specular reflecting surfaces each of which is substantially parabolic in curvature. The reflecting surfaces are arranged with respect to the lamps so that the major portion of the illumination provided by the fixture will be projected therefrom at an angle greater than 30 with respect to the vertical so as to minimize the veiling reflections effect to a viewer whose working surface is illuminated by such fixture.
IXVIW'IUR. NOEL S. FLORENCE SHEET 1 [IF 1 PATENTEU JUL 6 I971 NY MN ATTORNEY PATENTEU JUL 6 l9?! SHEET 3 OF 4 Ell l.\ Vlz'fvl UR. NOEL 5. FLORENCE ATTORNEY PATENTEU JUL 6 mm SHEET 4 [1F 4 ATTORNEY LIGHTING FIXTURE As conducive to an understanding of the invention, it is noted that the normal viewing angle of a person sitting at a desk, is from to 30 from the vertical. As a result, where the ,light from a source of illumination strikes the working surface at an angle such that it will be reflected from the working surface at an angle of from 0 to 30, it is apparent that such reflected light will be within the normal viewing range and hence may be reflected directly into the eyes of the viewer. As a result of such reflection, known as "veiling reflection, contrast between say black printed type on a paper and the white that no rays due to specular reflections of the luminaires in the task will emanate from the task in'the direction of the eyes of the worker.
However, since in most cases work is performed in rooms or chambers with a multiplicity of regularly spaced lighting fixtures or luminaires, it is likely that one or more of the luminaires will be in a location which will cause veiling reflections.
It is accordingly among the objects of the invention to provide a luminaire which may be readily fabricated at relatively low cost, which will be of substantially standard size, using standard available fluorescent lamps and which will control the light emitted therefrom in such manner that only a relatively small portion of the total available illumination therefrom will be emitted at angles which could produce veiling reflections, regardless of the position of the worker in the room in which the luminaires are installed.
Another object of the invention is to provide a lighting fixture with very low brightness at normal viewing angles and from which more than 60 of the total light output will be emitted at angles of from 30 to 60 from the vertical.
Another object is to provide a lighting fixture which may form part of an installation of a plurality of identical fixtures for use in a room or chamber and which installation will provide an overall illumination of desired intensity for offlce work in,all areas of the room with minimum veiling reflection effect being experienced by the workers in any portion thereof.
According to the invention, these objects are accomplished by providing a lighting fixture consisting of two elongated juxtaposed fluorescent lamps extending parallel to each other in vertical alignment, in association with specular reflectors so arranged that the majority of the light emitted by said lamps will be reflected by said reflectors at an angle greater than 30. More. particularly, the specular reflectors are positioned on each side of the longitudinally extending lamps and extend parallel thereto, each of said specular reflectors having substantially a parabolic curved surface having its focus at a point substantially midway between the two lamps and midway between a line tangent to the outer surfaces of the juxtaposed lamps and a line extending through the axes of said lamps with the axis of each of said parabolas being at an angle of between 25f and 45.
In a preferred embodiment of the invention there is associated with said fluorescent lamps and positioned above the uppermost lamp an elongated reflector, arcuate in cross section having as its focus the longitudinal axis of the lowermost lamp, whereby light rays emitted by said lamps will be substantially directed back into said lamps to reinforce the brightness thereof, particularly at the foci of said parabolic reflectors.
In the accompanying drawings in which is shown one or more of various possible embodiments of the several features ofthe invention,
FIG. I is a longitudinal sectional view taken along line 1-1 of FIG. 2;
FIG. 2 is a transverse sectional view taken along line 2-2 of FIG. I;
FIG. 3 is a perspective view of a baffle member used in the embodimentof FIGSJ and 2;
FIGS. 4, 5 and 6 are diagrammatic views illustrating the angles of light rays from the lamps of the embodiment shown;
FIG. 7 is a diagrammatic view of an installation using a plurality of lighting fixtures according-to the invention, and
FIG. 8 is a diagrammatic view of another embodiment of the invention.
Referring now to the drawings, as shown in FIGS. 1 and 2, the lighting fixture, according to the invention, comprises an elongated, inverted troughlike housing 11 having end walls-12 to each of which is secured a pair of vertically aligned sockets 13 to mount the ends of a pair of elongated fluorescent lamps I4 and 15, said lamp thus extending longitudinally of the housing 11 parallel to each other and in juxtaposed vertical alignment.
The longitudinal edges of the housing adjacent its mouth 16 are bent outwardly as shown at l7'to permit mounting of the fixture in conventional manner in a suitable rectangular opening provided by ceiling members 18 in a ceiling 19.
Preferably, the housing 11 is designed tofit in a standard 1 foot by 4 foot opening and the fixture is designed to carry two standard 40 watt fluorescent lamps.
The housing illustratively has secured to one of the end walls 12 thereof a container 21 in which a conventional ballast is positioned.
As the electricalconnections for the fixture are'conventional, they will not be further described.
As is shown in the drawings, and particularly FIG. 2 thereof, the housing in cross section has a flat top wall 22 with two outwardly inclined sidewalls 23, the lower ends of the latter hav ing outwardly extending flanges 24 from which depend sidewalls 25. Positioned in the portion of the housing between the lower sidewalls 25 thereof is a baffle member 26 which is designed to be readily displaceable to permit relamping of the fixture.
As shown in FIG. 3, for example, the baffle member 26 comprises a pair of parallel curved specular reflector sidewalls 27 between which extend a plurality of spaced parallel louvers 28.
Each of the louvers 28, as is clearly shown in FIG. 1, has a wide top surface-29 and a narrow bottom edge 31 with the opposed faces 32 of each louver formed as a substantially parabolic specular reflector.
As shown in FIGS. 2 and 3, a hinge member 33 is provided at the-end of the lower edge of each of the sidewalls 27 of the bafflemember 26. Each hinge illustratively comprises an L- shaped member having one leg 33 slidably mounted in a suitable support 34 carried by the sidewalls 27. To mount the baflle member in the housing, it is merely necessary to position the baffle member between the sidewalls 25 of the housing and move the hinge members outwardly. so that the slidable legs 33' thereof will enter the corresponding opening in the end walls 12 of the housing. For purposes of relamping, it is merely necessary to retract the legs 33 carried by one of the sidewalls 27 of the baffle member, so that the latter will pivot downwardly, being supported by the legs 33' on the other sidewall 27.
According to the invention there is positioned between the sidewalls 23 of the housing 11 a pair of elongated curved specular reflector members 41. The reflector members 41' preferably extend theentire length of the housing and are secured at their upper and lower longitudinal edges as at 43, 44 to the top wall 22 and the flanges 24 in any suitable manner such as by screwing, welding or the like.
Positioned directly over the upper fluorescent lamp 14 is an elongated specular reflector 45 which is secured to the top wall of the housing as at 46 in any suitable manner.
The reflectors 41 which are symmetrically disposed on each side of the lamps l4 and 15 are substantially parabolic in curvature, each having its focus at point P which is substantially midway between the lamps 14, 15 and midway between a line that is tangent to the outer surface of the lamps and a line extending through the axes of said lamps.
The axis of each parabolic reflector 41 is at an angle of between 25 and 45 from the vertical and preferably at an angle of 35. Thus, each of the parabolic reflectors 41 will reflect light originating at the focus F in a direction parallel to the axis of each reflector and hence at an angle of 35 in the preferred embodiment herein described. However, it is within the scope of the invention to utilize reflectors having optical curves that lie between two parabolic curves having axes of 25 and 45 respectively with each of said parabolic curves having its focus at a point positioned substantially midway between said lamps.
The sidewalls 27 of the baffle 26 also have a curvature which is substantially parabolic and forms a continuation of the parabolic curve of the reflectors 41.
The reflector 45 is radially curved, having its origin or focus at the longitudinal axis C of the lower lamp 15.
As the result of the provision of the curved reflector 45, since the light from the lower lamp 14 tends to be reflected back by the reflector 45, there is an increased surface brightness at the region adjacent the focus F of each of the parabolic reflectors 41 which will be projected against the opposed reflectors 41 for subsequent reflection thereby.
With the arrangement above described, and referring to FIGS. 4, and 6, for example, it is apparent that the light emanating from the focus F will be reflected from say the lower portion of the parabolic reflector (FIG. 4) defined by the sidewall 27 at an angle of 35 as at 1 (since the axis of the parabola is at 35) and from the outer edges of the upper and lower lamps 14 and at angles of say 30 and at 50 as at ll and Ill.
Referring to FIG. 5, the light emanating from the focus F will be reflected from the lower portion of reflectors 41 at an angle of 35 as at l and from the outer edges of the lamps 14 and 15 at angles ofsay 24 and 55 as at II and 1".
Referring to FIG. 6, the light emanating from the focus F will be reflected from the upper portion of reflectors 41 at an angle of 35 as at I" and the light emanating from the lower lamp 15 will be reflected first by reflector 41 to the lower reflector 27 and then reflected at an angle of say 51 as at 111". It is apparent that the major portion of the light transmitted by the parabolic reflectors 41 and 27 will be between the angles of 24 and 55 with most of the light being at an angle greater than 30 but less than 60.
As a result of photometric distribution tests of a typical fixture of the type above described, the following has been found.
In the 0 to 30 zone measured from the vertical there is emitted approximately 37 percent of the total light emitted by the fixture. In the 30 to 60 zone there is emitted approximately 61 percent of the total light emitted by the fixture and in the 60 to 90 zone there is emitted approximately 2 percent of the total light emitted by the fixture.
As previously noted, it has been found that conventionally a worker sitting at desk views the work surface at angles between 0 and 30 with respect to the vertical. Where the work surface is illuminated by rays of light that are within this region of from 0 to 30, veiling reflections may be created, i.e., there may be reflections of one or more luminaires in the viewing task. This causes the contrast between the detail in the task, a printed letter, for example, and the white background of the paper to be reduced, making it much harder to read and tiring the eyes of the viewer.
It is apparent from the foregoing description of the lighting fixture herein, that with respect to each fixture the maximum portion of the light produced by the fixture will be emitted at an angle from vertical of between 30 and 60, i.e., at an angle greater than the normal task viewing angle of from 0 to 30. Hence, with respect to the total light emitted from any one fixture, only a relatively small portion of such light, i.e., approximately 37 percent thereof; as above illustratively described,
will be illuminating the task at angles likely to cause veiling reflections.
The fixture according to the present invention, is designed for use in a relatively large area in which a plurality of the fixtures will be used. A typical installation is diagrammatically shown in FIG. 7.
Thus, for example, a room or chamber may contain four fixtures 11a, 1 lb, 11c and 11d. Referring to the fixtures 11b and 1 1:, for example, the regions R of light from each of such fixtures will have approximately 37 percent of the total light emitted by the associated fixture.
With respect to any work being performed at a desk in said room, say one directly beneath the fixture 11b, it is apparent that there will be illumination provided within the region R from fixture 11b which will strike the desk at an angle of from 0 to 30. Hence, such illumination may produce veiling reflections. However, there will also be illumination from the adjacent fixtures 11a and Us which will strike the desk beneath fixture 11b at an angle greater than 30 so that there will be no veiling reflections, caused by the light from the adjacent fixtures, on such desk.
Due to the fact that a greater proportion of the illumination falling on the desk of the viewer will be at angles which will not cause veiling reflections, such reflections will be minimized, thus increasing the task contrast ratios and thereby providing a much more effective type of illumination.
It is further to be noted that since only a small portion of the light emanating from each of the fixtures is at an angle greater than 60, a person standing or seated in the room will not be subjected to direct glare when viewing the fixture in direction at right angles to its length. By reason of the transverse louvers 28 carried by the baffle member, direct light from each fixture to the viewer, longitudinally of the length thereof, will also be minimized in manner common with transverse louvers.
With the relatively simple construction above described, a relatively low cost lighting fixture is provided which may readily form part of a complete installation for a room or chamber and which will provide effective illumination for office viewing tasks in substantially all portions of such chamber with a substantial reduction of veiling reflections, thus increasing the contrast ratio of the tasks and improving visual perception of such tasks throughout the room.
By reason of the use of two elongated fluorescent lamps, the stroboscopic effect caused when only one lamp is used is eliminated. The use of the two vertically superimposed lamps provides the desired overall light intensity required with a bright zone at a desired location to produce the maximum efficiency.
It is within the scope of the invention where further reduction of veiling reflection is desired to provide an arcuate baffle or shield 50 directly beneath the lower lamp 15 as shown in FIG. 8. This shield which illustratively is opaque will substantially reduce direct downward rays and hence further reduce the amount of light in the 0 to 30 zone.
Although such opaque baffle 50 will somewhat decrease the efficiency of each fixture, where there are sufficient fixtures available in a room, such decrease may not be critical and can be balanced against the desirability of having a minimum percentage of the illumination from each fixture within the undesirable range of from 0 to 30.
As many changes could be made in the above constructions, and many apparently widely different embodiments of this invention could be made without departing from the scope of the claims, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:
1. A lighting fixture comprising an elongated inverted trough-shaped housing having two opposed elongated specular reflecting surfaces, means in said housing for supporting a pair of elongated fluorescent lamps to extend longitudinally of said housing parallel to each other and in juxtaposed vertical alignment, said lamps being positioned midway between said pair of specular reflecting surfaces, each of said specular reflecting surfaces being substantially parabolic in curvature, an arcuate reflector positioned over the uppermost lamp and extending substantially the length thereof midway between the two substantially parabolic specular reflecting surfaces, the longitudinal edges of the arcuate reflector being positioned with respect to the curved surfaces of the parabolic reflectors to permit impingement of light rays from the lamps against only that portion of the curved surface of each of the parabolic reflectors which will reflect light therefrom in convergent rays, whereby the greater portion of the total illumination provided by said fixture will be emitted within a 30 to 60 zone with respect to the vertical.
2. The combination set forth in claim 1 in which each of said opposed specular reflecting surfaces has an optical curve that lies between two parabolic curves having axis of 25 and 45 respectively with respect to the vertical, each of said parabolic curves having its focus at a point positioned substantially midway between said lamps.
3. The combination set forth in claim 2 in which each focal point is positioned substantially midway between a line tangent to the outer surface of both of said vertically disposed lamps and a line extending through the axes of said lamps.
4. The combination set forth in claim 1 in which said arcuate reflector has as its focus the longitudinal axis of the lowermost lamp of said pair.
5. The combination set forth in claim 1 in which each of said opposed specular reflecting surfaces has an axis of substantially 35 with respect to the vertical.