US2640148A - Reflector for controlling at a predetermined angle direct and indirect rays from a light source - Google Patents

Description

May 26, 1953 MccAN 555 2,640,148

LLING A PREDETERMINED ANGLE REFLECTOR FOR CONTRO DIRECT AND INDIRECT R OM A LIGHT SOURCE Filed Mar m C i I I INVENT OR. M. EY 40 W E A TTORNEY Patented May 26, 1953 2,640,148 REFLECTOR FOR CONTROLLING AT A PRE- DETERMINED ANGLE DIRECT AND IN- DIRECT RAYS FROM A LIGHT SOURCE Stanley McCandless, Hamden, Conn., assignor to Century Lighting, Inc., New York, N. Y., a corporation of New York Application March 12, 1949, Serial No. 81,161

4 Claims. 1

This invention relates to electric lighting fixtures. More particularly my invention pertains to that type of electric lighting fixture known as a downlight, this being a fixture which is set into a ceiling to illuminate the floor or an object beneath the fixture. Even more specifically my invention is. concerned with a downlight of the character which employs as a source of illumination a general service lamp, i. e., a lamp without a built-in reflector, so that the fixture itself must supply a reflecting surface.

It is an object of my invention to provide a downlight of the character described which is comparatively inexpensive to manufacture, is relatively efiicient and is unobtrusive.

It is another object of my invention to provide a downlight of the character described having a highly compact structure and a relatively small height.

It is another object of my invention to provide a downlight of the character described having-a specular surface which has a low surface brightness in the normal viewing angle so that distraction of attention and visual discomfort is avoided.

It is another object of my invention to provide a downlight of the character described whose visible internal surfaces within the normal viewing angle are of about the same brightness as the ceiling, that is to say, Whose visible internal surfaces with the viewing angle are neither very brightly illuminated so as to cause an unpleasant glare nor are markedly under-illuminated so as to resemble a black spot.

It is another object of my invention to provide a downlight of the character described which affords easy access to the lamp bulb and which is so designed that it will direct a maximum percentage of light downwardly at angles exceeding the normal angle of vision.

It is another object of my invention to provide a downlight of the character described in which the light at the working plane is distributed more evenly than in conventional downlights using similar sources of illumination.

Other objects of my invention will in part be obvious and in part will be pointed out hereinafter.

My invention accordingly consists in the features of construction, combinations of elements and arrangements of parts which will be exemplified in the construction hereinafter described and of which the scope of application will be indicated in the appended claims.

In the accompanying drawings in which is t shown one of the various possible embodiments of my invention,

Fig. 1 is a vertical axial section through a downlight made'in accordance with my invention;

Fig. 2 is a bottom view of the downlight .with the left hand side of the escutcheon plate broken away better to illustrate the construction of the downlight; and

Fig. 3 is a fragmentary sectional view through .the rim of the downlight as the same appears prior to mounting the reflector. Referring now in detail to the drawings, the reference numeral H] denotes a downlight embodying my invention and comprising a plaster ring 12, a reflector l4 and a splice box I6- The plaster ring is designed to be mounted in a ceiling C and comprises an open-ended tubular stub sleeve Il' having an outturned integral flange :8 extending from its lower edge. Said ring is located in an opening in the ceiling with the lower surface of the flange l8 flush with the exposed ceiling surface. To secure the ring in place, a plurality of mounting tabs 20 are provided which are adapted to be bent back to lie against the concealed upper surface of the ceiling. Wire or other suitable anchoring meansimbedded in the plaster of the ceiling may be threaded through openings 22 in the tabs, as shown, for example in my copending application, Serial No. 675,845, filed June 11, 1946, for Electric Light Fixtures, issued as United States Letters Patent No. 2,465,248 on the 22nd day of March, .1949.

The plaster ring supports an escutcheon plate 24 by means of fiat headed screws 26 countersunk in said plate and threaded in tubes 2'! welded to the flange I8. The escutcheon plate is slightly lower than the ceiling, being spaced therefrom by a chamfered rim 28 which touches the ceiling. S'aid escutcheon plate has a large central opening 30 concentric with the axis of symmetry of the plaster ring.

The plaster ring also includes a plurality, e. g. four, reflector mounting clips 32 constituting strips of a malleable metal, whereby they can be deformed readily by hand, but when thus deformed are capable of supporting the weight of the reflector and splice box. By way of example, said clips may be made from light gauge, e. g. 22 gauge, sheet iron which can be coated with zinc, tin or lead to prevent corrosion. One end of the strip is secured to the inner surface of the plaster ring in some suitable fashion, e. g. by welding, leaving the balance of the strip free. The portion of the strip next to the weld is formed with an inwardly directed indentation 34. Prior to mounting, the free end of the strip extends downwardly as shown in full lines in Fig. 3.

The splice box IE which is of conventional construction provides a connection for an armored conduit 36 inside of which are the electric wires 38 for the fixture. The box 16 is secured in any suitable fashion, e. g. by screws 44, to an inturned flange 46 forming the top of the reflector l4. Said box houses a standard electric light socket 40 which is adapted to receive a general service lamp 42 having its axis of symmetry vertical and its base uppermost. The illustrated lamp is an A-shaped lamp of a 75 or 100 watt size, the reflector being specially designed for the size and shape of lamp envelope.

To prevent the insertion of overly large lamps in the socket 4!! I employ a stop 48 which is fitted into a neck 50 comprising the upper end of the reflector. Said lamp stop is secured in place by small screws 52 and provides within the neck of the reflector a partition 54 having an opening 56 large enough to admit the stem of general service lamps no larger than 150 watts.

In accordance with my invention the general service lamp 42 has no reflector, and its envelope is translucent, i. e. difiusing, being rendered. so in any conventional fashion, for example by frosting or silica spraying.

Further in accordance with my invention, the

reflector M is symmetrical about the axis of symmetry of the envelope of the lamps and has a specular, i. e. a mirror-like, inner surface. The reflector is of special design to obtain a certain distribution of illumination. Said design is sirnifcrence that, whereas in said co-pending application the reflector is symmetrical with respect to a plane passing through the longitudinal axis of an elongated diffuse envelope of a fluorescent tube, in the present application the reflector is symmetrical with respect to the single axis of symmetry of a diffuse lamp envelope which constitutes a surface of revolution. More particularly, the reflector has a zone ab which is of such configuration that all light rays, issuing from the lamp tangential to the envelope there of and impinging on the reflector in this zone, will be reflected at approximately a constant angle, hereinafter referred to as the cut oil'" angle. Said angle preferably is equal to or slightly in excess of the normal angle of vision, which is about 45, so that the reflected angle of all such incident light rays is about 45.

The manner in which these tangential light rays arereflected is clearly seen in Fig. 1 wherein the reference numerals 5B, 60, 62, 64, 66, denote light rays issuing tangential to the envelope of the lamp 42 and incident upon the reflector in the zone ab. The reflected paths of these rays are denoted by reference numerals 68, 10. 12, 14,16. All of the reflected rays are substantially parallel to one another and are oriented at an angle of about 45, this being the cut off angle of the fixture,

, To obtain the foregoin results, the curvature of the reflector in the zone a-b is neither ellipsoidal nor paraboloidal. It can be laid out empirically or on a drafting board with ease simply by applying the controlling criterion of obtaining similar orientation of reflected tangential rays. For example, an empirical method constitutes shining a narrow beam of light in the direction of tangential beams emanating from the surface of the lamp envelope and impinging these beams on a flexible flat specular strip. The configuration of the strip is varied over its length until the desired similar orientation of reflected rays is obtained and the shape of the strip will be the desired curve for generating the reflector zone a-b. The drafting board method simply consists in laying out on paper several small contiguous flat lines of different angularity which secure the desired constant angle of reflection (see my aforesaid copending application Serial No. 732,995), drawing a smooth curve tangent to these lines and using the curve as a generatrix.

The point a at the uppermost edge of the zone just described, is the point at which a light ray issuing tangential to the diffusing envelope of the lamp at the cut off angle will be incident upon the reflector. Above this point the reflector has a paraboloidal configuration (except for the opening at the neck). The focus of the paraboioid is located slightly above the filament, i. e., closer to the reflector than to the filament. With this arrangement, light rays emanating from the center of the light source within the lamp, and exemplified by the light rays (8, 80, 32, upon striking the paraboloidal portion will be reflected downwardly at a steep angle to the horizontal and tend to converge slightly toward the axis of symmetry of the reflector. Due to the specified configuration of the zone (Ir-b, light rays, exemplified by the rays 84, 86, 8B, 90, emanating from the center of the light source and striking said zone will be directed downwardly at an angle between the cut off angle and the angle of rays reflected from the paraboloidal portion.

With a reflector of the foregoing configuration, the intensity of light on the Working plane near the normally under-illuminated edges of the illuminated area will be built up since the reflector directs to such parts of the area the rays of light issuing tangential to the envelope. Other rays striking the zone a-b in general also are directed outwardly toward near the edges 01 the illuminated area although at steeper angles than the tangential rays. The central portion of the illuminated area in the workin plane receives direct rays of light issuing from the bulb supplemented by reflection from the parabololdal part of the reflector.

It already has been pointed out how, by shaping the reflector in the foregoing manner, no reflected rays of light issue from the fixture at an angle less than the cut off angle of 45 although reflection extends up to substantially that angle. Issuance of direct rays of light at less than the cut off angle is prevented by the escutcheon plate 34 whose central openin 30 is so dimensioned with respect to its distance downwardly from the lamp envelope that a line drawn from an edge of the opening tangent to the lamp envelope in a plane including the axis of symmetry of the lamp will be inclined at an angle equal to or slightly in excess of the cut oi! angle. It may be mentioned that the escutcheon plate can be eliminated insofar as its cut-oil function is concerned, by having the point D low enough p rform this function. However, by employing said plate a shallower fixture can be used, with but a small loss of lighting efficiency It now will be apparent that all light, whether direct or reflected, which issues from the fixture will do so at an angle greater than the angle of normal vision so that a person will not be distracted by a bright glare of light radiating from the fixture unless that person deliberately looks at the lamp. It also is pointed out that, because the reflector has a specular surface, as observed Within the normal. angle of vision, it is dully illuminated has a gray appearance, its intensity of illumination being in the order of the intensity of illumination of a ceiling so that the fixture will not seem to be a black spot on the ceiling.

Due to the fact that the central opening in the escutcheon plate is Smaller than the maximum diameter of the reflector, the lower portion b-c of the reflector is not effective, it being remembered that no light rays are to be reflected at less than the cut-off angle of 45. Accordingly this lower portion b-c need not be specular and, if desired can be left unfinished. Said portion is covered by a tubular masking ring 92 having a black velvet finish. It will be noticed that the top edge of the masking ring at the point b is slightly higher than necessary. I have found this desirable in order to prevent highly uneven illumination which might occur should too much of the reflector be eflective.

The masking ring also serves to conceal the mounting clips 32 which otherwise would be visible within the normal line of vision and would appear as small areas of intense illumination,

It may be noted that by imparting a black velvet finishd to the masking ring the same, which is directly illuminated by strong light rays, will have a grayish appearance of approximately the same order of intensity of illumination as the specular surface of the reflector so that this part of the fixture likewise will be of approximately the same order of illumination as the ceiling and therefore will be noticeable neither as a glare nor as a black spot.

The reflector is located with its lower beaded edge within the plaster ring and at about the same level as the lower edge of said ring. After being inserted in the plaster ring, the reflector is held in place by the mounting clips 32 whose free ends are bent over to the dot-and-dash line position illustrated in Fig. 3 wherein they fold about the beaded edge of the reflector and are located within the reflector. Subsequent to mounting of the reflector, the masking ring is thrust into the reflector. This ring has an outside diameter less than the inside diameter of the reflector by an amount barely exceeding the thickness of the clips Thus, when the maskillg ring is slipped into place, it will be held in position by frictional engagement with the clips. The escutcheon plate 24 is bolted in place after the reflector and masking ring have been positioned.

It thus will be seen that I have provided an electric lighting fixture which achieves the several objects of my invention and is well adapted to meet the conditions of practical use.

As various possible embodiments might be made of the above invention and as various changes might be made in the embodiment above set forth, it is to be understood that all matter herein described or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

Having thus described my invention, I claim as new and desire to secure by Letters Patent:

1. An electric lighting fixture comprising a. socket for holding a lamp having a d ffuse envelope symmetrical about a single a and a specular reflector symmetrical about a single axis and within which the lamp envelope is arranged to be disposed, said reflector having its axis of symmetry coincident with the axis of symmetry of the lamp envelope, said reflector being so shaped and located with respect to said lamp envelope that all light rays emanating tangential to said. envelope within approximately a predetermined angle of cut off and incident upon the reflector will be reflected at substantially the cut off angle, the shape of said reflector in a plane including the axi of symmetry of the reflector bein that of a smooth curve tangent to small contiguous straight lines of progressively varying angularity from which light rays issuing tangential to said lamp envelope within approximately the cut of? angle are reflected substantially parallel to said angle, the shape of said reflector in said plane including a portion on each side of the axis of symmetry of the reflector, each said portion having an upper boundary in a line which is tangent to the lamp envelope at a point on the envelope located on the same side of the axis of symmetry of the lamp envelope as said portion, said tangent line extending upwardly from the lamp envelope to the upper boundary of said portion, the small straight line at the upper boundary of each portion being disposed perpendicular to the tangent line extending upwardly from. the lamp envelope to said upper boundary.

2. An electric lighting fixture as set forth in claim 1 wherein means is provided to block rays of li ht issuing from the envelope at all angles less than the cut off angle.

3. A lighting fixture as set forth in claim 2 wherein the blocking means comprises a plate below the reflector, said plate having an opening concentric with the axis of symmetry of the reflector, said opening being of such diameter that a line through any point of its circumference and tangent to the envelope in a plane including the axis of symmetry of the reflector is at substantially the cut off angle.

4. A lighting fixture as set forth in claim 3 wherein a masking ring is provided in the form of a sleeve with a black velvet finish within the fixture above the plate, said ring constituting the innermost portion of the fixture in the region where it is located.

STANLEY MCCAN'DLESS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,869,823 Reader Aug. 2, 1932 2,032,622 Le Guillou Mar. 3, 1936 2,138,635 I-Ioeveler Nov. 29, 1938 2,179,161 Rambusch et al. Nov. 7, 1939 2,297,124 Anderson Sept. 29, 1942 2,337,437 Allen Dec. 21, 1943

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