Prismatic Light Louver

Abstract

A light transmitting louver for use as a ceiling panel in a luminous ceiling or as a lens in a lighting fixture. The louver has a planar member adapted to be positioned adjacent a light source and a plurality of walls extending from the member on the side opposite the light source to define a symmetrical closed cell system. Within the peripheral extent of each cell and on a surface of the planar member are prisms which extend generally symmetrical to the cell axis and with the cell wall. The individual prisms are asymmetrical in cross-section, i.e., the angular slope of the respective surfaces of each prism is different.

Description

BACKGROUND OF THE INVENTION

In the lighting industry it has been previously suggested that certain advantages are present in the use of a closed cell translucent panel. Positioning such a panel subjacent the light source generally conceals the plenum and shields the light source from direct vision, with the solid membrane or top wall thereof serving as a diffuser to reduce reflected glare and the cell walls shadowed to reduce direct glare. Lighting panels of this general nature are described, for example, in Schwartz et al. U.S. Pat. No. 3,368,070. Notwithstanding advantages inherent in such a closed cell system, certain shortcomings are also present. Primarily, it is found that if sufficient light is transmitted through the panel or lighting louver to provide adequate illumination on the work surface or for general lighting requirements, undesirable high level brightness is also present. In other words, when a person views such an overhead horizontally disposed panel at a high angle from the vertical, the overall ceiling effect produces a relatively harsh glare.

It has also been suggested in the industry to utilize a prismatic sheet underlying a light source. While the use of a conventional prismatic surface will provide good light diffusion and good shielding qualities, a combination of problems have been encountered, including a substantial lowering of efficiency and/or an undesirable high level brightness. By way of example, if the prisms are formed of a relatively deep configuration, i.e. with the opposed prism surfaces defining small acute angles with the vertical, good shielding is provided at high angles, but due to the large amount of refraction, poor light efficiency results. On the other hand, if the prisms are formed of a relatively shallow configuration, i.e. with the opposed prism surfaces defining large acute angles with the vertical, better light efficiency results, but at the sacrifice of having poor shielding against high level brightness.

SUMMARY OF THE INVENTION

In broad terms the present invention is directed towards a closed cell louver system which is modified so as to produce a maximum of light at low angles from the vertical, i.e., for maximum illumination at a work surface, and a minimum of light at high angles from the vertical so as to reduce the overall glare effect accompanying high level brightness.

More particularly, the invention includes the use of prisms for each cell which are so arranged that maximum light transmission efficiency is obtained while high level brightness is minimized. As will be later described in more detail, the cross-sectional configuration of the respective prisms is asymmetrical or possesses a saw-tooth shape, with the prisms extending concentric or parallel to the cell wall. The overall effect of such a prismatic light louver is the provision of a high efficiency lens which cuts out high level brightness, as will be hereinafter discussed in more detail.

DRAWING

FIG. 1 is a plan view of a portion of a prismatic light louver of the present invention;

FIG. 2 is a plan view on an enlarged scale showing four adjacent cells of the louver;

FIG. 3 is a cross-sectional view of one cell on a further enlarged scale, taken substantially in the plane indicated by line 3--3 of FIG. 2;

FIG. 4 is a further enlarged view of a portion of the prism structure shown in FIG. 3; and

FIG. 5 is a plan view of a single cell of a modified form of cell and prism arrangement.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The panel or louver of the present invention, generally indicated by the numeral 10, is of generally planar configuration and adapted to be positioned adjacent a light source. The panel can be of any desired length, width or planar shape, and where used as the lens of a lighting fixture will usually be formed as a single integral piece. However, when used as a luminous ceiling, a plurality of separate panels may be interconnected to provide an overlapping and interlocking continuous appearing modular ceiling in the manner disclosed in the aforesaid U.S. Pat. No. 3,368,070. Since the manner of interconnecting adjacent panels forms no part of the present invention, the edges of the panels are not illustrated nor described herein.

The panel 10 is formed of a suitable plastic material, such as acrylic, by injection molding or the like, and includes a flat rigid and form retaining planar membrane or wall 12 having an upper surface 14 and a lower surface 16. As the terms "upper" and "lower" are used herein, it is assuming that a plenum or light source is disposed in overlying relation to the upper surface 14 and a person within a room would see the lower surface 16.

Extending outwardly from surface 16 and normal to the plane of membrane 12 are a plurality of adjacent cells 18. As best illustrated in FIGS. 1 through 3 of the drawing, each cell 18 consists of an annular wall 20 which, with the adjacent portion of surface 16, defines a downwardly directed cell area 22. Such a structure is conventional in the art, and no claim is made thereto in the present application. It might also be noted that with the exception of the outermost edge cells in the panel, the wall 20 of each cell is common with the adjacent wall of four adjacent cells and where the cells are circular in shape, generally diamond shaped portions 24 are provided on membrane 12 defined by four adjacent arcuate cell wall portions 26. These interstice portions 24 will be hereinafter discussed in connection with another feature of the invention.

The membrane area defined by each cell is provided with prisms, generally indicated at 28. As here illustrated, such prisms are provided on lower surface 16 of membrane 12, but it is possible that the same could be disposed on the upper surface 14. In practice, however, it has been found that it is easier to polish the prisms when disposed within the cell rather than on the continuous upper surface of the panel. It will be noted that the prisms are located only within the peripheral confines of each cell, the interstice portions 24 being preferably non-prismatic.

The configuration of the prisms and their relationship to the cell walls 20 constitute an important feature of the present invention. Basically, what is desired is a light distribution pattern through the prisms so that a maximum amount of light is directed downwardly between each cell wall 20, and a minimum amount of light will be directed past and under the bottom edge 34 of the cell wall at a small acute angle with the plane of the panel. With such an arrangement, the prisms will provide a shield against direct glare for a person looking directly upwardly towards the panel and a shielding of the plenum chamber and light source. Further, the prisms, in combination with the cell walls, minimize high level brightness. Finally, and as will be shortly explained, these desirable features are attained with maximum lighting efficiency for a prismatic light control system.

As previously explained, a conventional prismatic panel will not produce the desired results since both shallow or steep prism surfaces have certain drawbacks. In accordance with the teachings of the present invention, the prisms 28 are of a sawtooth or asymmetrical cross-sectional configuration as best seen in FIGS. 3 and 4, but the length of the prisms are symmetrical relative to the shielding means, i.e., the cell wall 20, as best illustrated in FIG. 2 of the drawing. As further shown in said latter view, six continuous prisms are provided in each cell, designated as P1, P2, P3, P4, P5 and P6, each concentric about the cell axis and parallel to the cell wall 20. The exact number of prisms is not critical, but the spacing between adjacent prisms results in a substantially continuous prismatic surface, and as here illustrated, such spacing approximates the thickness of membrane 12. The prisms are relatively shallow in depth and preferably have a depth dimension slightly less than the aforesaid spacing. If the prisms are made too deep, they become inefficient, since light will be reflected back and will not readily leave the prisms.

With reference to the asymmetrical configuration of the individual prisms, and to maintain the desired light distribution pattern with maximum efficiency, the inner prism surface 38 defines a larger included angle with the vertical than does the angle defined by the outer prism surface 40 with the vertical line being taken at the intersection of the respective prism surfaces with the lower surface 16 of panel 10. A particularly effective arrangement has been produced where the inner surface 38 defines an angle of about 50.degree. with the vertical and the outer surface defines an angle of about 10.degree. with the vertical. The term "inner prism surface" is used herein to define the prism surface facing the axial center line of the cell, while the term "outer prism surface" refers to the other prism surface or the one facing the interior of its cell wall 20. Thus, since the cell wall is parallel to the cell axis, the prism surfaces 40 facing such wall are only offset by about 10.degree. from being parallel therewith, while the prism surfaces 38 form a substantial angle thereto. It will be noted that the respective surfaces 38 and 40 of each prism intersect and terminate along a lower circular line 41, and the innermost surfaces of surfaces 38 and 40 of adjacent prisms terminate and intersect along an upper circular line 42 on the lower surface 16 of the panel. Thus, with respect to each prism, it might be said that it comprises an acute irregular triangle in cross-section defined by surfaces 38 and 40 and the adjacent portion of membrane surface 16, but extends lineally in the symmetrical pattern above described.

It is important to note that the asymmetrical orientation of the prism surfaces is that as above described, i.e., with the more vertical prism surface 40 directed towards or facing the cell wall. With this arrangement, brightness at high angles is shielded by the adjacent cell wall. If such surface 40 was reversed, as the surface became brighter at high angles, the more distant cell wall would not be as efficient in producing the desired shielding.

By way of example only, a satisfactory prismatic louver has been tested in which the following dimensional proportions were present. The cell diameter was 1 inch; the cell depth from lower surface 16 was one-quarter inch; the prism depth was 0.055 inch; the prism spacing was 0.65 inch, as was the thickness of membrane 12. The angular disposition of the prism surfaces was as indicated in FIG. 4 of the drawing.

In FIG. 5 a modified form of cell structure is illustrated which in place of the circular cell wall 20 is of square configuration having side walls 44, 46, 48 and 50. The depth of such walls would correspond to the depth of wall 20. Here, again, a plurality of prisms P7, P8, P9, P10, P11 and P 12 are provided, each prism being symmetrical about the central axis of the cell and having four lineally extending sides parallel to the respective cell walls. The saw tooth prism construction is the same as previously described, and a cross-section taken through the center of the cell would be identical to the cross-sectional view of FIG. 3.

Referring back to the secondary feature of the present invention, the louver above described lends itself to the production of a unique and ornamental two-color design. By way of example, the cell walls 20 and the interstice portions 24 may be frosted. By adding a color tint to the plastic during the molding thereof, the polished prism will appear bright, while the cell walls and interstice portion, particularly when frosted, will pick up the color. Since substantially all of the usable light passes through the prisms, the tinting of the plastic will not materially reduce the light transmission efficiency.

It is also preferred to have the cell walls frosted for better shielding irrespective of any addition of color tint to the plastic, and in the case of the interstices 24 between adjacent cells, to likewise frost the same.

It might also be pointed out that while the asymmetrical prisms give optimum results, a louver superior to those of the prior art can be obtained with symmetrical prisms disposed in symmetrical relationship with the closed cell arrangement. The cell walls will reduce high-level brightness, but not to the extent provided for by the saw tooth prism construction described above.

Claims

1. A light louver including a generally planar rigid membrane, wall means formed integrally with said membrane and extending normal from one surface of said membrane and defining a plurality of adjacent cells, each of said cells being generally symmetrical about the central axis thereof, a surface of said membrane being provided with a plurality of prisms disposed within the peripheral confines of the respective cells, said prismatic portion of said membrane being polished, said wall means being frosted to thereby define a lusterless surface compared to said polished prismatic surface, said prisms extending lineally symmetrically about each cell axis and symmetrically with the wall means defining the respective cell, and said prisms extending uniformly across substantially the entire

2. A louver as set forth in claim 1 in which each of said prisms has a pair

3. A louver as set forth in claim 1 in which each of said cells is

4. A louver as set forth in claim 1 in which each of said cells is square.

5. A louver as set forth in claim 1 in which said prisms are provided on the surface of said membrane from which said wall means extend, and each

6. A louver as set forth in claim 2 in which the prism surface facing said cell axis has a greater slope relative to said axis than the other prism

7. A louver as set forth in claim 3 in which a plurality of said prisms are defined in adjacent concentric relation within each cell, and each of said prisms has a pair of asymmetrical surfaces extending from the surface of

8. A louver as set forth in claim 7 in which one of each of said prism surfaces faces the central axis of said cell and the other of each of said prism surfaces faces said wall means, each of said latter surfaces defining a lesser angle with said axis than said first mentioned surfaces.

9. A louver as set forth in claim 8 in which said lesser angle is about 10.degree. and the first mentioned surface defines an angle of about

10. A louver as set forth in claim 2 in which the spacing between adjacent

11. A louver as set forth in claim 5 in which said cells are substantially deeper than the depth of said prisms and extend a substantially greater

12. A louver as set forth in claim 1 in which the portions of said membrane intermediate adjacent cells are frosted.