Note: Descriptions are shown in the official language in which they were submitted.
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60557-3738
The present invention relates to thin light fixtures.
In various situations thin light fixtures are desirable.
For example, back-lit flat panel displays normally should he kept
as thin as possible. When they are thinner they tend to be
llghter in weight and more compact, both desirable properties when
they are used in applications such as portable computers.
Automobile taillights and brake lights also should be kept compact
where possible. This is because space used by such lights comes
at the expense of luggage space in the vehicle's trunk.
Various designs for thin panel lighting have been
proposed. For example, our United States Patent 4,789,921
describes a Fresnel-type reflector lying on a conic surface.
Typically the Fresnel-type structures of that refle~tor are
designed to mimic the performance of a parabolic reflector. The
conic Fresnel provides a hlghly efficient compact light source,
but suffers from the same disadvantage as other parabolic
reflectors. That disadvantage is a lack of uniformity in
intensity of light output. As may be expected, regions closer to
the light source will be more brightly illuminated than those more
distant from the light source.
Other designs have been proposed for use when uniform
illuminatlon is desirable. One such proposal ls described ln our
copendlng Canadian Patent Appll~ation Serial No. 562,153, filed
March 23, 1988. That design utilizes a film known as rlght angle
fllm. The use of right angle film in a light flxture allows the
outpuk optical window to be very evenly llluminated, but requlres
the separate construction of the right angle film and the
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60557-3738
insertion of that film into the light fixture. In some situations
it would be desirable to construct a light fixture having a
performance similar to that of the fixture using right angle film,
without the requirement of the insertion of a separate film into
the fixture.
Summary of the Invention
According to the invention a housing defines an optical
cavity having an optical window. A source of partially collimated
light having an axis of collimation is located inside the optical
cavity. A structured surface having a plurality of prisms thereon
is positioned within the optical cavity such that the prisms
reflect light through the optical window. The peaks of the prisms
define a surface at least a portion of which makes an acute angle
with the axis of collimation.
Brief Description of the Drawinq~
Flgure 1 is a view of a first embodiment of a light
fixture according to the invention;
Eigure 2 is a view of a second embodiment of a light
fixture according to the invention;
Figure 3 is a view of a third embodiment of a light
fixture according to the invention; and
Figure 4 is a view of a light fixture according to the
lnvention having two light sources.
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Detailed Description
Figure 1 illustrates a first embodiment of the
invention. In the embodiment of Figure l a housing
including walls 10 and 12 defines an optical cavity. The
optical ~avity has an optical window with a light
transmitting member 14, therein. Light transmitting member
14 may be of a transparent or translucent material. If
desired, light transmitting member 14 could include
structures such as pillow optics or Fresnel prisms.
A source of partially collimated light 16 is
positioned inside the optical cavity and adjacent side 10
of the housing. Light source 16 may be any source of
partially collimated light such as a fluorescent tube or
other gas discharge lighting element with an appropriate
reflector or an incandescent light with a reflector.
Alternatively light source 16 could include a plurality of
light emitting diodes (LEDs).
Side 22 of wall 12 is a structured surface having
a plurality of, preferably triangular, prisms, 24, thereon.
In a preferred embodiment, prisms 24 are linear prisms.
Prisms 24 are rendered specularly reflective, typically by
aluminum vapor coating. It is only necessary that prisms
24 be specularly reflective on the side adjacent light
source 16, but it is typically easier to vapor coat both
sides. Such prisms reflect light from light source 16 in a
predetermined direction. Typically the predetermined
direction will be perpendicular to transparent or
translucent material 14.
Light source 16 emits a beam of substantially
collimated light having an axis of collimation 18. Line 20
is drawn parallel to collimation axis 18. As may be seen,
the peaks of prisms 24 define a planar surface that makes
an acute angle ~ with line 2~, and thus with collimation
axis 18. As a result side 22 of wall 12 cuts through the
beam of light emitted by light source 16. Because
structured surface 22 so cuts through the beam of light
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emitted by light source 16, the entire aperture of the
optical window is illuminated.
The structure of the present invention may be
advantageously formed directly on the rear wall of the
light fixture. Such a structure could be formed by
injection molding. Alternatively a separate film having
the structured surface described above could be placed in
the light fixture.
Figure 2 shows an alternative embodiment to that
of Figure 1. In the embodiment of Figure 2 structured
surface 22' is curved. Thus the surface defined by the
peaks of prisms 24 is curved rather than planar. As a
result, that surface is parallel or nearly parallel to the
axis of collimation in the region closest to light source
16, but forms a variety of acute angles with it in regions
more distant from light source 16. This has the effect of
causing prisms more distant from light source 16 to
intercept a greater portion of the beam than those closer
to light source 16. ~ecause the light beam will naturally
expand as it progresses to locations distant from the
source, the curvature helps to maintain uniformity of
illumination.
Figure 3 illustrates an alternative embodiment
wherein a housing 30 including walls 32, 34, 36 and 38
defines an optical cavity having an optical window. ~
transparent or translucent cover 40 lies in the optical
window. Light from two partially coIlimated light sources
is directed from light sources 42 and 44 to structured
surface 46. The peaks of the prisms of structured surface
46 may define a planar surface lying at an angle to the
axis of collimation of the light sources, similar to the
embodiment of Figure 1 or may define a curved surface
cutting through the beams of light as in the embodiment of
Figure 2.
Figure 4 illustrates another embodiment of the
invention wherein light source 14' includes a light emitter
50 and a structured surface 52. Structured surface 52 acts
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in a manner similar to structured surface 22 to take light
from a compact source 50 and provide a linear beam. The
embodiment of Figure 4 then acts similarly to the
embodiment of Figure 1 with surface 52 acting as a light
source for structured surface 54.
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