Note: Descriptions are shown in the official language in which they were submitted.
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A LIGHT UNIT
Field of the Invention
This invention relates to light units, particularly for illuminating signs
which display a
message or pattern when illuminated.
Background of the Invention
Dimmick, US Patent 5,151,679, discloses a sign having at least one light pipe
made of
light-transmitting material, the light pipe carrying at least one light source
(LED)
proximate at least one end, the light source directed towards another end of
the light pipe.
A portion of the outer surface of the light pipe is translucent to permit
light to exit
therefrom. The light source is energized and the light pipe or pipes are
mounted in an
array to form a predetermined message or design.
Holmes, Jr., US Patent 5,499,165, proposes a transparent edge-lit rectangular
window
pane for lighting displays through which maps, pictures etc. can be viewed.
The pane
may be tapered in that one of its main surfaces is inclined to the opposite
surface. The
pane may also have a compound double taper on one of its surfaces from its
edges
towards its middle. The surface facing an object to be illuminated is frosted
to make it
translucent One or two linear light sources are disposed at one or both edges
of the pane
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to introduce light into the pane. The light undergoes internal reflection
within the pane,
becomes partially reflected from the top surface and exits due to refraction
through the
bottom, frosted surface to illuminate the object.
Hehr, US Patent 4,277,817 describes a large-area light source which, to
provide for a
uniform output throughout the area of the light source, particularly as an
illuminating
surface for LCD, has a light emitting surface which is formed as a wedge-
shaped body of
transparent material, with light being coupled thereto at the wider side
surface. The
bottom surface of the body has preferably a reflective layer.
1o Hathaway et al, US Patent 5,050,946, discloses a faceted light pipe which
has a planar
front surface and a stairstepped or faceted back surface. A reflector is
located so as to
reflect light escaping from the back surface and to direct it back through the
light pipe to
exit the front surface.
15 A light unit for use in lighted sign assemblies, with illumination provided
by light
emitting diodes, is described also in US Patent 5,365,411 to Rycroft et al.
There is still a need to develop a robust, simple, efficient and easy to
manufacture light
unit suitable for illuminating signs, e.g. exit signs and the like. In a
device of this type,
2o the uniformity of illumination over the area of the device may be
secondary, while the
simplicity of the design and efficiency of the lighting (i.e. having most of
the light
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produced by a light source to be emitted toward the viewer rather than be
returned to the
light source or being trapped in the unit) may be of prime importance.
Summary of the Invention
In accordance with the invention, there is provided a light unit comprising:
a panel having a first surface and an opposite second surface,
a plurality of light pipes of transparent material, each light pipe having a
first end,
a second end and side surfaces extending therebetween, including a bottom side
surface
to and a top side surface, the top and bottom side surfaces being tapered
relative to each
other from the first end to the second end, each light pipe being affixed to
said panel with
the bottom surface, and
a light source mounted at the first end of each light pipe such as to direct a
beam
of light into the light pipe towards the second end of the pipe.
In a preferable embodiment of the invention, the light pipes and the panel are
a
unitary integral structure, e.g. made in a single molding operation, the panel
being of the
same transparent material as the light pipes.
2o The light sources are preferably light emitting diodes (LED). The first
ends of the
light pipes are dimensioned to contain each a LED without undue excess
material.
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The light pipes may be arranged in pairs on a strip-shaped panel such that two
light pipes are aligned, with the second narrower ends are adjacent to each
other, while
the first ends, with the light sources mounted therein, are disposed at the
edges of the
panel.
Preferably, at least the top side surfaces of the light pipes are non-
polished, e.g.
translucent, roughened etc. so as to interrupt the internal reflection of
light passing from
the light source through the pipe towards the second end.
1o Further details of the invention will become more apparent from the
following
detailed description when read in conjunction with accompanying drawings.
Brief Description of the Drawings
In the drawings,
Fig. 1 is a schematic perspective view of an exit sign using the light unit of
the invention,
Fig. 2 is a side view of an embodiment of the light unit,
Fig. 3 is a side view of another embodiment of the unit,
Fig. 4 is an enlarged end view of the light pipe illustrated in Figs 1-3,
2o Fig. 5 is an enlarged end view of another embodiment of the light pipe of
the unit of the
invention, and
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Fig. 6 illustrates another embodiment of the light unit of the invention.
Detailed Description of the Invention
Fig. 1 illustrates the use of the light unit of the invention. The unit,
generally designated
as 10, is placed adjacent to a perforated plate 12, the perforations spelling
the desired
message. The plate and the unit are mounted in a casing, not shown in the
drawings. The
unit has a panel 14 which is integral with a number of light pipes 16. Each
light pipe, as
shown in Fig. 2 and 3, has a tapered shape, wherein one end 18 of the pipe 16
protrudes
to more from the panel than the opposite end 20 of the pipe. Each light pipe
defines a
bottom surface 22 and an opposite top surface 24 which form a wedge.
The panel and the pipes are moulded from a transparent plastic e.g.
polystyrene or
polymethyl acrylate. In Fig. 1, the light pipes are arranged in aligned pairs
but they may
be arranged in a different pattern. It is however advantageous that the larger
ends 18 of
all the pipes be disposed at the edges of the panel 14 for the ease of
electrical connections
to the light sources, illustrated schematically in Figs. 2-5.
As shown in Figs. 2 and 3, the light pipes 16 are generally tapered in shape
from the first
2o end 18 to the second end 20. The upper surface 24 may be flat as shown in
Fig. 2 or it
may be curved (e.g. semicircular or parabolic in cross-section) as shown in
Fig. 3. The
first ends 18 of the pipes 16 are dimensioned to accommodate a LCD in a manner
as
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283
explained in the LrS patent 5,1x1,&79. Also, the LCDs are connected to a
source of electric
energy in a manner known in the prior art, e.g. via two strip electrodes (not
illustrated
herein) running along the edges of the plate 14.
In the embodiments of Fig. 2 and 3, the narrower second ends 20 of the
opposite pipes 16
do not contact each other. It is however feasible to design the unit such that
the pipes
contact each other thus forming a composite double wedge.
As shown in Fig. 4, wherein a single light pipe is illustrated as seen from
the first erld 18
(at 90 degrees relative to the view of Fig. 2), the light pipes are foxxned
integrally with the
paxlel 14, e.g. by injection molding such that the bottom surface 22 of each
light pipe is
imaginary only_ The material of the panel and the pipes is preferably a
transparent
plastic e.g. acrylic (polymethyl acrylate) or equivalent.
Alternatively, the light pipes may be formed separately and attached (e.g.
glued) to a
panel to Form a unit 10 as shown by example in Fig. 1.
As illustrated in pig. 4, the LEIas 26 can be mounted in the unit such that
they extend, as
illustrated by the circular cross-section, into the panel 14.
As known in the art, the light pipes are dimerlsionad to inject light provided
by the LEDs
into the body of the light pipe toward the apposite end. If all surfaces of
the light pipe
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were transparent (polished), very little light would egress the light pipe
towards the
viewer, most of light being reflected internally within the pipe. Therefore,
it is important that at least the top surface 24 as shown in Figs 2 - 5 is
translucent to a
degree to be able to interrupt the internal reflection and enable the light to
be transmitted
out of the pipes from the top surface 24 towards the viewer. The translucency
may be
achieved in a manner known in the art, e.g. by etching with solvents,
roughening,
deliberate imperfections of the mold etc.
Depending on the design of the light sign utilizing the light unit of the
present invention,
to other surfaces of the unit may also be made translucent. The bottom surface
28 of the
panel 14 may be translucent at least in areas corresponding to the placement
of the light
panels on the opposite surface of the panel 14. This will cause the light
emitted by the
LEDs 26 to egress not only from the translucent (roughened) top surface 24 but
also from
the opposite side of the panel 14.
As illustrated in Fig. 5, the top surface does not have to be a continuous
surface. It is
conceivable that the top surface is a faceted surface 28, its configuration
still enabling the
transmission of light from within the pipe towards the viewer through the
surface 28.
2o Another embodiment of the invention is schematically presented in Fig. 6,
wherein the
wedge-shaped light pipes are formed, or installed, on both surfaces of the
panel 14. The
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LED 26 may be mounted symmetrically by providing an opening therefor in the
panel 14
in the respective position where the light pipes are placed.
It is an advantage of the invention that a self supported light unit is
provided which
contains relatively few structural parts while maximizing the lighting
efficiency of a LED
source compared to straight light pipes to Dimmick design of US 5,151,679.
It is another advantage of the invention that the light unit uses relatively
less material than
comparable backlighting wedge-shaped panels such as that of US Patent
4,277,817 to
1o Hehr or of US Patent 5,050,946 to Hathaway et al.
