U.S. patent number 3,668,381 [Application Number 05/007,950] was granted by the patent office on 1972-06-06 for prismatic light louver.
Invention is credited to Rodney P. Osterberg, Robert A. D. Schwartz.
United States Patent |
3,668,381 |
Schwartz , et al. |
June 6, 1972 |
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.
Inventors: |
Schwartz; Robert A. D.
(Oakland, CA), Osterberg; Rodney P. (Oakland, CA) |
Family
ID: |
21728993 |
Appl.
No.: |
05/007,950 |
Filed: |
February 2, 1970 |
Current U.S.
Class: |
362/339; 362/330;
359/831; 362/355 |
Current CPC
Class: |
F21V
3/00 (20130101); F21V 5/02 (20130101); F21Y
2103/00 (20130101) |
Current International
Class: |
F21V
5/00 (20060101); F21V 3/00 (20060101); F21V
5/02 (20060101); F21v 005/00 () |
Field of
Search: |
;350/204,211,286,287,162P ;240/9,106.1,106 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Schonberg; David
Assistant Examiner: Tokar; Michael J.
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.
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.
* * * * *