US 2737577 A
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March 6, 1956 R. e. M PHAIL DIRECT LIGHTING FIXTURES Filed Jan. 25. 1951 IN VEN TOR.
5055/97 6'. A/c/ /m/A United States PatentO 2,737,577 DIRECT LIGHTING FIXTURES Robert G. McPhail, Newark, Ohio, assignor to Holophane Company, Inc., New York, N. Y., a corporation of Delaware Application January 25, 1951, Serial No. 207,789 11 Claims. (Cl. 240-5111) The present invention relates to direct lighting fixtures and is more particularly directed toward direct lighting fixtures for general lighting, using rectilinear fluorescent lamps adapted for use close up to the ceiling line.
Such lighting equipment is intended to deliver the entire light output downwardly and laterally and often is in the glare zone, so that screening of the lamps against direct observation is necessary if excessive glare is to be avoided.
Where the devices interposed between the lamps and points of observation to provide suitable light screening and redirection are made of transparent or translucent light transmitting material, the lighting equipment presents elongatedoften continuous-sources of luminosity at various angles of observation in the glare zone.
According to the present invention, the lighting equipment is symmetrical on opposite sides of a central median plane, the lamp or lamps on each side of the median plane are at a common level and close to the ceiling. A reflector is employed above the lamps to return light into useful directions and light transmitting covers are provided about the lamps, these covers being close to the lamps and extending nearly to the ceiling line. The width of the luminous area from underneath the fixture,
. or when viewed lengthwise from underneath, is substantially the entire width of the fixture. By making the fixture as shallow as possible and yet have the lamps enclosed, the depth of the fixture may be reduced to a minimum and the subtended angle of the luminous area when one views the fixture from the side at various locations remote from the nadir is also the minimum possible.
Inasmuch as the fixtures are intended to be mounted against the ceiling, the fixtures are provided with a prewired unit including a suitable wireway, ballast housing, and lamp supports, which can be secured to the ceiling. This prewired unit, which is shown and claimed in concurrently filed application of Vearl S. Wince, Serial No. 207,803, now Patent No. 2,596,634, dated May 13, 1952, supports a second unit which includes a pan or reflector which covers the wireway and ballast and extends above the lamps, and a light transmitting closure about the lamps. The closure means about the lamps includes frames supported from the reflector margins and the central portion of the pan or reflector. preferably hinged at the outer edges and held in place by releasable catches or the like at the center.
In order to allow the light from the lamps and the downwardly reflected light from the reflector to be delivered in useful directions, the light transmitting cover should interfere as little as possible with light output in the more useful directions which, in general, are below about 60 from the nadir, and, in order to reduce brightness of the luminaire when viewed at angles higher than about 60 from the nadir, should divert the light away from the line of sight. Inasmuch as it is desirable to obtain ceiling illumination from the side portions of the luminaire, it is also desirable to direct light in angles above the horizontal in an amount to satisfactorily illuminate the upper side walls and the ceiling. According to the present invention, the light transmitting cover the purposes mentioned.
These frames were Patented Mar. 6, 1956 According to the present invention, the cover has underneath the light sources generally fiat portions which are provided with prismatically acting light screening means which discriminate against emission of light at horizontal angles higher than a predetermined angle from the nadir so that this relatively large horizontal area of the cover has low brightness at angles further from the nadir than said angle. While this action may take place in longitudinal directions only, it is preferable to employ prismatic elements which act in all azimuths. The cover also extends upwardly'outside of and past the light source to reach nearly to the ceiling, and this upper portion has prismatic light discriminating means which discriminates against longitudinal emission of light within substantially the same predetermined angles to the general direction of the fixture.
According to the present invention, the inner or light incident surfaces of the upwardly extending portions of the prismatic cover are provided with light splitting prismatic ribs, each rib having a face which acts in cooperation with the opposed outer surface of the cover to confine the emitted light within the optimum limiting angle.
from the nadir, while the other face of the rib in cooperation with the opposed outer surface of the cover acts to confine the emitted light to regions above the horizontal for ceiling illumination. As a result of this ray splitting, very little light is sent laterally in generally horizontal directions.
Other and further objects of the invention will appear as the description proceeds.
The accompanying drawings show, for purposes of illustrating the present invention, one embodiment in which the invention may take form, together with a modification, it being understood that the drawings are i1lustrative of the invention rather than limiting the same.
In the accompanying drawings:
Figure 1 is a perspective view of the luminaire attached to the ceiling;
Figure 2 is a diagrammatic cross-sectional view through one side of the luminaire illustrating the optical action of lamps, reflector and cover;
Figure 3 is a fragmentary longitudinal section through the bottom of the plate taken for example on the line 3-3 of Figure 2;
Figure 4 is a similar view toward the side of the plate taken on the line 4-4 of Figure 2;
FiguresS, 6 and 7 are enlarged sectional views at the regions marked with corresponding numbered areas in Figure 2;
Figure 8 is a photometric curve showing light distri-' bution of the luminaire across the axis; and
Figure 9 is a fragmentary view illustrating a modified form of plate.
Figure 1 shows a single lamp length fixture for use with two 100 watt lamps or four T-l2 lamps. The overall width of the fixture is approximately 18 inches and the depth to the bottom of the glass cover approximately 4 inches. These dimensions determine the area of luminosity of the fixture and the angles subtended at any particular point of observation. The reflecting, pan 30 as shown in Figure 2 has the central channel-like portion 31 with side walls 31a which extend from about 10 below the horizontal through the midpoint 23:: below the lamps 23, see line 23b upwardly past the nearer of the lamps 23, the flat portion 32, the rib 34, reflecting surfaces 35 and 36, extending about 60 from the zenith,
as shown by the line 230 and relatively inactive surfaces 1 37 and 3s.
The prismatic cover 70 is in the form of pressed glass plates of suitable width to fit the frames and of suitable length, usually one foot. Each plate of the glass cover 70 has a horizontal portion 71 underneath the lamps 23,
23 and extending toward the median plane CL of the fixture as indicated. This flat portion 71 of the cover is smooth on top and on the lower surface is provided with light discriminating means, preferably in the form of cones or pyramids 72 with their sides making angles of from to with the horizontal as stated in McPhail Patent No. 2,474,317. The portion 73 of the plate, which is generally concave inwardly and which extends up to the upper flange 74, is provided on the outer surface with vertical ribs 75, also of the angle 30 to 35 with the general direction of the plate surface and for similar reasons. The cones (or pyramids) 72 and vertical ribs 75 act as shown in Figures 3 and 4 to discriminate against longitudinal emission of light at angles of greater than 60 from the nadir, or the general direction of the surface of the plate. The cones (or pyramids) 72 also discriminate against emission of light in all azimuths at angles beyond 60 from the nadir. The inner surface of the upwardly extending portion 73 of the plate is provided with longitudinal prismatic ribs 76 of varying angle, as shown in Figures 2, 5 and 6.
The slopes of these upper surfaces vary from rib to rib depending upon the elevation of the prismatic rib above the bottom of the plate. The upper faces 77 of these ribs intercept direct light from the adjacent lamp to the left of the normal in wedge-shaped ridges of varying angular width and slope as indicated in Figures 2, 5 and 6, refractively transmit this light in downward directions toward the opposed lower surfaces, as indicated at 78, 79 (Figures 5 and 6), where it is refractively transmitted as indicated at 80 in these figures. The angular relations between the surfaces 77 and the profile of the opposite surface of the plate is such that the highest emitted rays such as 800 are approximately 60 from the nadir. The spread of light in the 0-60 zone from nadir will depend upon the position of the corresponding refracting surface 77.
The intermediate surfaces 81 between the surfaces 77 are properly disposed to receive similar, but lower wedges of light from the light sources above the normals and to refract them as indicated at 82, 82 so that they fall on the outer surface at much different angles from the bundles of rays indicated at 79. So much of this light as falls on the outer surface beyond the critical angle is totally reflected as indicated at 83, 83. The remainder is transmitted refractively as indicated at 84 to form an indirect component with the lowest angle of the refraeted light horizontal as indicated by the ray 84a, Figure 2.
The light splitting prisms 76 extend up along the side of the plate to an elevation preferably slightly higher than the top of the lamp and, above these light splitting ribs, the plate is provided with diffusing flutes 85, which intercept upwardly proceeding direct light for transmission in upwardly direct diffused beam indicated at 86.
The relatively steep sloping reflector surface 35 above the outer lamp reflects light upwardly and outwardly so that comparatively small amount of light so reflected is returned in downward directions. The light from portion 35 of the reflector falls principally on the diffusing flutes 85. This action avoids high brightness of the upper, outer part of the plate.
In order to illuminate the frame member 55 employed with the light controlling plate, it is provided with the sloping surface 57 and the inner marginal portion of the plate is provided with external longitudinal prismatic ribs 90, shown in detail in Figure 7. These ribs receive refracted light as indicated at 91, 91 and refractively transmit it downwardly as indicated at 92 into the useful 060 zone, or upwardly as indicated at 93 to fall on the sloping surface 57.
The reflector 30 is disposed relative to the lamps to intercept substantially all the light between a line 94, approximately from the nadir from the top of the left lamp,'and'line 95, approximately 45 above the horizontal and measured from the bottom of the right-hand lamp. This reflected light is returned in generally downward directions and away from the median plane CL through the unit. This reflected light (after multiple reflections) falls on the light transmitting closure plates in generally the same direction as the direct light, and is emitted in directions determined by the prismatic configuration of these plates. A single large lamp such as 23 may be used instead of two lamps, if desired.
The overall performance of the plates 70 is such that low brightnesses are produced in all directions of observation at points beyond about 60 from the nadir. A portion of the light is directed upwardly from the upper side portions of the plates so as to illuminate ceiling and upper side wall regions of the room.
Candle power distribution is illustrated in Figure 8 wherein the full line photometric curve 100 indicates relative candle power values of the complete unit in transverse planes and the dotted line 101 the values for the lamps and reflector alone. It will be noted that almost all the light output is within 60 from the nadir. A very small amount is emitted above the nadir, and in regions near 90 the output is very small. It is very much less than at angles slightly above 90 where light is directed toward the ceiling.
While the cone or pyramid prisms indicated at 72 in Figure 3 are preferred because they provide light control in all azimuths, it is, however, possible to secure excellent longitudinal control by extending the V-shaped ribs across the bottom of the plate as indicated at 75:: in Figure 9.
Owing to the very shallow depth of the luminous cover for the lamps, the subtended angle of the fixture at locations further than 60 from the nadir laterally is very small. This small angle, together with the low brightness in such directions materially reduces the total amount of light flux in the field of view from such points of observation.
Since it is obvious that the invention may be embodied in other forms and constructions within the scope of the claims, I wish it to be understood that the particular form shown is but one of these forms, and various modifications and changes being possible, I do not otherwise limit myself in any way with respect thereto.
What is claimed is:
1. A direct lighting luminaire having an elongated light source of substantial width and depth and a light refracting and transmitting plate of uniform profile parallel with the source and having a lower substantially horizontal portion below and close to the source and which extends laterally of the source to one side thereof and an upper outwardly flaring portion which extends from a region below the other side of the source to a region above and laterally beyond the source so as to intercept light from the source at corresponding transverse and longitudinal angles, the lower portion of the plate having prismatically acting light screening means which discriminate against emission of light at longitudinal angles higher than a predetermined angle from the nadir, the upper portions of the plate having prismatic light discriminating means which discriminate against longitudinal emission of light within like predetermined angles to the general direction of the plate, whereby the sources are completely screened from below and from the side having the upwardly flaring portion of the plate, and light is suppressed at angles of observation in longitudinal directions higher from the nadir than said predetermined angles.
2. A luminaire such as claimed in claim 1, wherein the light discriminating means on the bottom of the plate acts similarly in all azimuths, and the inner surface of the upwardly flaring portion has prismatic ridges each with a surface which refracts light upwardly for further refraction upwardly by the outer surface and a surface which refracts light downwardly for transmission by the outer surface into downward directions whereby in transverse and oblique directions light is suppressed at angles from the nadir higher than the said predetermined angles.
3. A direct lighting luminaire such as claimed in claim 1, wherein the upwardly and outwardly flaring portions are inwardly concave.
4. A direct lighting luminaire such as claimed in claim 1, wherein the light discriminating means on the bottom of the plate is in the form of pointed lenticulations with apex angle of from 30 to 35, and the light discriminating means at the upwardly flaring portion is in the form of vertical V-shaped ribs of apex angle of from 30 to 35 5. A direct lighting luminaire having on the opposite sides of a vertical longitudinal median plane and spaced therefrom a pair of rectilinear light sources side by side, and a rectilinear light refracting and transmitting cover having downwardly and inwardly converging side portions extending from regions substantially above the sources and more widely spaced than the outermost sources to regions close to and beneath said outermost sources, and substantially flat portions between the side portions to intercept all downwardly and laterally emitted light, the side portions having external vertical light discriminating ribs which discriminate against emission of light within a predetermined angle from the general direction of the cover, the flat portion having light discriminating means which discriminates against longitudinal emission of light at longitudinal angles above a predetermined angle from the nadir whereby longitudinal spread of light is substantially confined within said angles and brightnesses at higher longitudinal angles suppressed.
6. A direct lighting luminaire such as claimed in claim 5, wherein the light discriminating means in the flat portion acts similarly in all azimuths and the side portions have internal light splitting prismatic ribs which in cooperation with the opposed external surfaces divide the emitted light into beams directed above the horizontal and into beams directed below substantially the same predetermined angles below the horizontal to provide in transverse and oblique directions below the horizontal low brightness at high angles above the nadir.
7. A direct lighting luminaire such as claimed in claim 5, wherein the light transmitting cover is composed of opposite pairs of plates, and having supporting frames extending along the edges of the plates, the central portions of the frames extending downwardly below the plates, the adjacent edges of the plates having refracting prism-s which elevate light to provide illumination for the lower surfaces of the adjacent frame portions.
8. For use with an elongated light source having a substantial vertical cross section, an elongated refractor of uniform profile in vertical transverse planes through the source and adapted to be disposed relative to the source to intercept light from a lower region below and close to the source to a lateral region above and more remote from the source whereby each portion of the inner surface of the refractor intercepts a converging bundle of light rays of substantial angular width in said vertical plane and varying vertical angle, the inner surface of the lateral portion of the refractor having alternate light depressing surfaces and light elevating surfaces forming prismatic ribs, the light elevating surfaces being mutually optically cooperative with the outer surface to refractively transmit light in directions only above the horizontal, the light depressing surfaces being mutually optically cooperative with the lower surface to transmit light only below a predetermined angle below the horizontal, whereby light transmission into the intervening region is substantially completely suppressed.
9. A refractor such as claimed in claim 8, wherein the outer surface has vertical, V-shaped ribs with apex angle of from 30 to 35 to suppress light longitudinally at angles of less than the corresponding angle from the general direction of the refractor.
10. For use with a rectilinear light source having a substantial vertical cross section, a refractor parallel with the source and of uniform profile in vertical transverse planes through the source and adapted to be disposed relative to the source to intercept light from a lower region below and close to the source to a lateral region above and more remote from the source whereby each portion of the inner surface of the refractor intercepts a converging wedge of light rays of substantial angular width in said vertical plane and varying vertical angle, the inner surface of the lateral portion of the refractor having alternate light depressing surfaces and light elevating surfaces extending longitudinally and forming prismatic ribs, the light elevating surfaces being mutually optically cooperative with the outer surface to refractively transmit light in directions only above the horizontal, the light depressing surfaces being mutually optically cooperative with the lower surface to transmit light only below a predetermined angle below the horizontal, whereby light transmission into the intervening region is substantially completely suppressed.
11. A luminaire adapted for mounting close to the ceiling and having a rectilinear fluorescent light source of substantial horizontal width and vertical depth, a transversely uninterrupted light retracting and transmitting cover underneath the source corresponding in length with the source and extending generally horizontally to one side of the source in an amount to intercept light from the top of that side of the source out to substantially 45 from the nadir and upwardly about the other side of the source to intercept light from the bottom of the source up to about 45 from the zenith and light from the entire adjacent side of the source, and a reflector intercepting light outside said region and returning it toward the source and transmitting plate whereby the entire output, less reflection and transmission losses, is emitted from the elongated luminous cover as a secondary light source of corresponding width and depth, the generally horizontal regions of the cover having lenticulations which transmit light within predetermined angles from the nadir in all azimuths and substantially suppress transmission at higher angles from the nadir, the upwardly extending portions of the cover having internal alternately disposed longitudinal refracting surfaces which are mutually cooperative with the opposed external surfaces of the cover to transmit direct rays either above the horizontal or within the same predetermined angle from the nadir as the lenticulations in the horizontal region, the upwardly extending portions also having external vertical ribs which transmit light within predetermined longitudinal angles and substantially suppress transmission at greater longitudinal angles, whereby, the prismatic cover presents longitudinally, obliquely and transversely a continuous luminous source, with substantially less brightness in all azimuths at angles of observation beyond said predetermined angles from the nadir than within said angles.
References (Iitetl in the file of this patent UNITED STATES PATENTS 2,022,078 Dorey Nov. 26, 1935 2,170,912 Rolph Aug. 29, 1939 2,246,320 Rolph June 17, 1941 2,258,354 Doane Oct. 7, 1941 2,280,160 Rolph Apr. 21, 1942 2,352,804 Schepmoes July 4, 1944 2,372,874 Zimmerman Apr. 3, 1945 2,428,827 Beck Oct. 14, 1947 2,434,049 Nordquist Jan. 6, 1948 2,465,141 Wakefield Mar. 22, 1949 2,474,317 McPhail June 28, 1949 2,474,341 Wince June 28, 1949 2,523,581 Margolis Sept. 26, 1950 2,526,074 Guth Oct. 17, 1950 2,587,807 Arenberg et al. Mar. 4, 1952 FOREIGN PATENTS 921,846 France Jan. 20, 1947 OTHER REFERENCES Holophane Cat. C1-1-5M-48, page 14.