U.S. patent application number 09/865430 was filed with the patent office on 2001-11-08 for high efficiency reflector for directing collimated light into light guides.
Invention is credited to Whitehead, Lorne A..
Application Number | 20010038736 09/865430 |
Document ID | / |
Family ID | 25345495 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010038736 |
Kind Code |
A1 |
Whitehead, Lorne A. |
November 8, 2001 |
High efficiency reflector for directing collimated light into light
guides
Abstract
A reflector for reflecting light from an elongate light source
into the input end of a light guide having a diameter "D". The
light source is inserted through the narrow end of a collimating
reflector which has a wide end with a diameter exceeding "D"
through which light is emitted into the guide. The wide end of an
output reflector circumferentially surrounds the collimating
reflector's wide end. The output reflector's narrow end
circumferentially surrounds the light guide's input end. The wide
end of an input reflector circumferentially surrounds the
collimating reflector's narrow end. The reflectors are
cylindrically symmetrical about a common axis. Light passing from
the light source to the collimating reflector is reflected,
producing an output beam whose width varies as a function of
distance along the axis. The light guide's input end is positioned
along the axis to minimize the width of the output light beam.
Inventors: |
Whitehead, Lorne A.;
(Vancouver, CA) |
Correspondence
Address: |
Chernoff, Vilhauer, McClung & Stenzel
1600 ODS Tower
601 S.W. Second Ave.
Portland
OR
97204-3157
US
|
Family ID: |
25345495 |
Appl. No.: |
09/865430 |
Filed: |
May 29, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09865430 |
May 29, 2001 |
|
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09264247 |
Mar 8, 1999 |
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Current U.S.
Class: |
385/31 |
Current CPC
Class: |
G02B 6/4298 20130101;
G02B 6/0006 20130101 |
Class at
Publication: |
385/31 |
International
Class: |
G02B 006/26 |
Claims
What is claimed is:
1. A reflector for reflecting light emitted by an elongate light
source into an input end of a light guide having a light guide
diameter "D", said reflector comprising: (a) a collimating
reflector having: (i) a narrow apertured end for insertable
positioning of said light source within said collimating reflector;
(ii) a wide apertured end for emitting light into said light guide,
said wide apertured end of said collimating reflector having a
diameter exceeding said light guide diameter "D"; (b) an output end
annular reflector having: (i) a wide apertured end
circumferentially surrounding said collimating reflector near said
wide apertured end of said collimating reflector; (ii) a narrow
apertured end circumferentially surrounding said input end of said
light guide; wherein: (1) said reflectors are cylindrically
symmetrical about a common longitudinal axis; (2) light rays
emitted by said light source which pass to said collimating
reflector are reflected by said collimating reflector and produce
an output light beam having a beam width which varies as a function
of distance along said axis; and, (3) said light guide input end is
positioned at a selected distance along said axis at which said
output light beam has a minimum beam width value.
2. A reflector for reflecting light emitted by a light source into
an input end of a light guide having a light guide diameter "D",
said reflector comprising: (a) a collimating reflector having: (i)
a narrow apertured end for insertable positioning of said light
source within said collimating reflector; (ii) a wide apertured end
for emitting light into said light guide, said wide apertured end
of said collimating reflector having a diameter exceeding said
light guide diameter "D"; (b) an input end annular reflector
having: (i) a narrow apertured end for insertable positioning of
said light source through said input end annular reflector; (ii) a
wide apertured end circumferentially surrounding said collimating
reflector near said narrow apertured end of said collimating
reflector; (c) an output end annular reflector having: (i) a wide
apertured end circumferentially surrounding said collimating
reflector near said wide apertured end of said collimating
reflector; and, (ii) a narrow apertured end circumferentially
surrounding said input end of said light guide; wherein said
reflectors are cylindrically symmetrical about a common
longitudinal axis.
3. A reflector as defined in claim 1, wherein said collimating
reflector is an off-axis paraboloidal cross-section, cylindrically
symmetrical reflector.
4. A reflector as defined in claim 2, wherein said collimating
reflector is an off-axis paraboloidal cross-section, cylindrically
symmetrical reflector.
5. A reflector for reflecting light emitted by a light source into
an input end of a light guide, said reflector comprising: (a) a
collimating reflector having: (i) a narrow apertured end for
insertable positioning of said light source within said collimating
reflector; (ii) a wide apertured end for emitting light into said
light guide; (b) an input end annular reflector having: (i) a
narrow apertured end for insertable positioning of said light
source through said input end annular reflector; and, (ii) a wide
apertured end circumferentially surrounding said collimating
reflector near said narrow apertured end of said collimating
reflector; wherein said reflectors are cylindrically symmetrical
about a common longitudinal axis, (c) said input end annular
reflector further comprising a curved surface, wherein, in any
cross-sectional plane containing said axis, said curved surface
defines: (i) a first arc on one side of said axis, said first arc
having a first center of curvature located on said one side of said
axis, and located within a cylinder which is symmetrical about said
axis and which has a diameter not greater than the diameter of said
narrow apertured end of said collimating reflector; and, (ii) a
second arc on an opposed side of said axis, said second arc having
a second center of curvature located on said opposed side of said
axis, and located within said cylinder.
6. A reflector as defined in claim 3, said input end annular
reflector further comprising a curved surface, wherein in any
cross-sectional plane containing said axis, said curved surface
defines: (i) a first arc on one side of said axis, said first arc
having a first center of curvature located on said one side of said
axis, and located within a cylinder which is symmetrical about said
axis and which has a diameter not greater than the diameter of said
narrow apertured end of said collimating reflector; and, (ii) a
second arc on an opposed side of said axis, said second arc having
a second center of curvature located on said opposed side of said
axis, and located within said cylinder.
7. A reflector as defined in claim 1, wherein: (a) said collimating
reflector has a focal point f, and, (b) said output end annular
reflector further comprises a spherical arc section having a center
of curvature near said focal point f.
8. A reflector as defined in claim 2, wherein: (a) said collimating
reflector has a focal point f; and, (b) said output end annular
reflector further comprises a spherical arc section having a center
of curvature near said focal point f.
9. A reflector as defined in claim 3, wherein said light source is
a metal halide light bulb having an elongate light emitting
arc.
10. A reflector as defined in claim 9, wherein said light emitting
arc has one end near said focal point f and an opposed end near
said narrow apertured end of said collimating reflector.
11. A reflector as defined in claim 2, wherein: (a) light rays
emitted by said light source which pass to said collimating
reflector are reflected by said collimating reflector and produce
an output light beam having a beam width which varies as a function
of distance along said axis; and, (b) said light guide input end is
positioned at a selected distance along said axis at which said
output light beam has a minimum beam width value.
12. A reflector as defined in claim 4, wherein: (a) light rays
emitted by said light source which pass to said collimating
reflector are reflected by said collimating reflector and produce
an output light beam having a beam width which varies as a function
of distance along said axis; and, (b) said light guide input end is
positioned at a selected distance along said axis at which said
output light beam has a minimum beam width value.
13. A reflector as defined in claim 5, wherein: (a) light rays
emitted by said light source which pass to said collimating
reflector are reflected by said collimating reflector and produce
an output light beam having a beam width which varies as a function
of distance along said axis; and, (b) said light guide input end is
positioned at a selected distance along said axis at which said
output light beam has a minimum beam width value.
Description
REFERENCE TO RELATED APPLICATION
[0001] This is a continuation-in-part of U.S. patent application
Ser. No. 09/264,247 filed Mar. 8, 1999.
TECHNICAL FIELD
[0002] This invention pertains to efficient reflective coupling of
collimated light into the input end of a light guide.
BACKGROUND
[0003] FIG. 1 schematically depicts the way in which light is
conventionally emitted into the input end of a light guide of the
type disclosed in, U.S. Pat. Nos. 4,615,579; 4,750,798; 4,787,708;
4,834,495; or, 4,850,665. An elongate (i.e. non-point) light source
such as an arc-type metal halide light bulb 10 mounted in a socket
12 is slidably inserted through an aperture 14 in a paraboloidal
collimator 16. The circumferential rim at the wide end of
collimator 16 is flanged as shown at 18. A mating circumferential
flange 20 is provided around the input end of hollow prism light
guide 22. Flanges 18, 20 are connected together to mechanically
couple collimator 16 to the input end of light guide 22. When light
bulb 10 is energized, light rays emitted by the bulb's arc portion
24 are reflected and collimated by collimator 16 toward the input
end of light guide 22 which confines the rays and distributes them
uniformly along the light guide.
[0004] Prism light guides work best when the input light is
collimated within a half angle of about 30.degree.. This
requirement limits the range of suitable light sources, because the
efficiency with which light can be emitted into the input end of
the light guide decreases rapidly as the size of the light bulb
increases. Arc-type metal halide light bulbs of the type shown in
FIG. 1 are reasonably practical light sources for illuminating
light guides, due to their high efficiency, compact size and
reasonably long lamp life.
[0005] The maximum efficiency with which prior art paraboloidal
collimator 16 can couple collimated light into light guide 22
depends on the ratio of the light guide's diameter "D", to the
length "L" of the light bulb's arc. For a typical prior art D:L
ratio of about 6:1, reflector efficiencies of about 70% can be
achieved. Thus, about 30% of the light emitted by light bulb 10 is
typically lost, in the sense that it does not enter the input end
of light guide 22. It is desirable to reduce the ratio D:L, since
this would enable the use of larger, higher output, more efficient
metal halide arc lamps. But, even modest reductions in the ratio
D:L substantially reduce the efficiency with which light emitted by
the light bulb can be collimated and coupled into the input end of
the light guide. For example, a D:L ratio of about 4:1 typically
yields a light guide input coupling efficiency of only about 50%,
meaning that about 50% of the light emitted by the light bulb is
lost, in the sense that it does not enter the input end of the
light guide as collimated light.
[0006] This invention overcomes the coupling efficiency problems
associated with conventional light guide systems. For example, the
invention permits efficient collimation and coupling of light
emitted by a one kW metal halide light bulb having a 12,000 hour
rated life into a 25 cm diameter light guide. Such systems are
advantageous in general lighting situations in which high
efficiency linear lighting is required and in which maintenance of
multiple point source or fluorescent fixtures is problematic.
SUMMARY OF INVENTION
[0007] The invention provides a reflector for reflecting light
emitted by an elongate light source into the input end of a light
guide having a light guide diameter "D". All embodiments of the
invention incorporate a collimating reflector having a narrow
apertured end through which the light source is insertably
positionable; and, a wide apertured end having a diameter exceeding
"D", through which light is emitted into the light guide. All
embodiments of the invention also incorporate an "output end"
annular reflector, or an "input end annular reflector, or both.
[0008] The output end annular reflector has a wide apertured end
which circumferentially surrounds the collimating reflector near
its wide apertured end, and a narrow apertured end which
circumferentially surrounds the input end of the light guide. The
input end annular reflector has a narrow apertured end through
which the light source is insertably positionable, and a wide
apertured end which circumferentially surrounds the collimating
reflector near its narrow apertured end. All of the reflectors are
cylindrically symmetrical about a common longitudinal axis. Light
rays emitted by the light source which pass to the collimating
reflector are reflected by the collimating reflector and produce an
output light beam having a beam width which varies as a function of
distance along the aforementioned axis. The light guide's input end
is positioned at a selected distance along the axis at which the
output light beam has a minimum beam width value.
[0009] Advantageously, the input end annular reflector further has
a curved surface, such that, in any cross-sectional plane
containing the aforementioned axis, the curved surface defines a
first arc on one side of the axis, and, a second arc on an opposed
side of the axis. The first arc has a first center of curvature
located on the one side of the axis, and further located within a
cylinder which is symmetrical about the axis and which has a
diameter not greater than the diameter of the collimating
reflector's narrow apertured end. The second arc has a second
center of curvature located on the opposed side of the axis and
further located within the aforementioned cylinder.
[0010] The collimating reflector is preferably an off-axis
paraboloidal cross-section, cylindrically symmetrical reflector
having a focal point f. The output end annular reflector preferably
forms a spherical arc section having a center of curvature near the
collimating reflector's focal point f The light source is typically
a metal halide light bulb having a light emitting arc having one
end near the focal point f and an opposed end near the narrow
apertured end of the collimating reflector.
BRIEF DESCRIPTION OF DRAWINGS
[0011] FIG. 1 is a schematic side elevation view of a prior art
paraboloidal collimator mounted to reflect light emitted by an
arc-type metal halide light bulb into the input end of a light
guide.
[0012] FIG. 2 is similar to FIG. 1, except that the light guide
diameter "D" is less than the diameter of the outward end of the
paraboloidal collimator.
[0013] FIG. 3 is a schematic side elevation view of a reflector
constructed in accordance with the invention.
[0014] FIG. 4 is similar to FIG. 3, but shows a longer portion of
the light guide.
[0015] FIG. 5 is a schematic fragmented cross-section showing the
geometric characteristics of the preferred off-axis paraboloidal
collimator.
[0016] FIG. 6 is a schematic side elevation view of a reflector
constructed in accordance with the invention, showing how the
paraboloidal collimator reflects into the light guide substantially
all light rays which pass directly from the center "C" of the light
source to the paraboloidal collimator.
[0017] FIG. 7 is a schematic side elevation view showing how the
paraboloidal collimator reflects light rays which pass through the
center, rearward (left) end, and forward (right) end of the light
source.
[0018] FIG. 8 graphically depicts the variation of the width of the
output beam produced at the wide apertured end of the reflector as
a function of distance d along the reflector's longitudinal
axis.
DESCRIPTION
[0019] As shown in FIGS. 3 and 4, reflectors constructed in
accordance with the invention include a collimating reflector such
as conventional paraboloidal collimator 16 A, which is preferably
an off-axis paraboloidal cross-section cylindrically symmetric
reflector. Arc-type metal halide light bulb 10A mounted in socket
12 A is slidably inserted through aperture 14 A in the narrow end
of paraboloidal collimator 16 A, as in the case of prior art
reflector 16 described above. Unlike prior art reflectors,
reflectors constructed in accordance with the invention include not
only paraboloidal collimator 16 A, but also annular reflectors 26
and 28.
[0020] As seen in FIG. 1, the diameter of prior art paraboloidal
collimator 16 at its wide end (i.e. the end bearing circumferential
flange 18) is substantially equal to the diameter D of light guide
22. However, the wide end diameter of paraboloidal collimator 16 A
shown in FIGS. 3 and 4 exceeds the diameter D of light guide 22 A.
This facilitates collimation of light emitted by a metal halide
light bulb 10 A which is larger than light bulb 10, assuming light
guides 22, 22 A to be of equal diameter.
[0021] If a larger light bulb were used in a prior art reflector
system like that of FIG. 1, the diameter of aperture 14 in the
narrow end of paraboloidal collimator 16 would have to be increased
to facilitate insertion of the larger bulb. Increasing the diameter
of aperture 14 increases the amount of light which is lost due to
rearward emission (i.e. to the left, as viewed in the drawings)
outside paraboloidal collimator 16 and away from light guide 22.
This problem is solved by the provision of annular reflector 26, as
hereinafter explained. Increasing the wide end diameter of the
paraboloidal collimator would also cause a problem in a prior art
reflector system. Specifically, light rays which encounter the
annular region of overlap 25 (FIG. 2) between paraboloidal
collimator 16 and light guide 22 are lost, in that they do not
enter the input end of light guide 22. This problem is solved by
the provision of another annular reflector 28, as hereinafter
explained.
[0022] Input end" annular reflector 26 is an aspherical arc section
reflector having a wide apertured end 30 (FIG. 3) which
circumferentially surrounds paraboloidal collimator 16A, near the
narrow apertured (i.e. "input") end of paraboloidal collimator 16A.
(Reflector 26 is "annular" in the sense that it forms a ring around
axis 27 when viewed from the right along axis 27.) Light bulb 10A
is slidably inserted through the narrow apertured end 32 of annular
reflector 26. Annular reflector 26 intercepts much of the light
which is emitted rearwardly (i.e. to the left, as viewed in the
drawings) by light bulb arc 24A and reflects a substantial portion
of such rearwardly emitted light back through aperture 14A and
light bulb 10A for further reflection by paraboloidal collimator
16A into light guide 22A.
[0023] The aspherical characteristic of reflector 26 (i.e. the
shape of reflector 26 deviates slightly from a perfectly spherical
shape) ensures that most light rays reflected by reflector 26 are
unlikely to pass through arc 24A, thus avoiding reabsorption of
such rays by arc 24A. More particularly, reflector 26 is preferably
toroidal in the sense that, when viewed in cross-section as shown
in FIGS. 3 and 4, curved portions 26A and 26B of reflector 26 form
circular arcs having centers which lie slightly off the
longitudinal axis 27 about which paraboloidal collimator 16A, light
guide 22A, reflectors 26, 28 and light bulb 10A are respectively
cylindrically symmetrical. Thus, the circular arc formed by curved
reflector portion 26A has a center C1 which is located above axis
27, within the diameter of aperture 14A at the narrow (i.e.
"input") end of paraboloidal collimator 16A. Similarly, the center
C2 of the circular arc formed by curved reflector portion 26B is
beneath axis 27, within the diameter of aperture 14A. Centers C1,
C2 need not lie on lines which are diameters of aperture 14A,
although such positioning is preferred, as shown in FIG. 3.
Generally, it is sufficient to locate centers C1, C2 within a
cylinder which is symmetric about axis 27 and which has a diameter
equal to the diameter of aperture 14A. The inner reflecting surface
of reflector 26 is preferably slightly diffuse (i.e. non-specular)
to further reduce possible reabsorption by are 24A of light rays
reflected by reflector 26.
[0024] As shown in FIG. 3, the end of arc 24A closest to the wide
end of paraboloidal collimator 16A is positioned to coincide with,
or at least be located near to the focal point f of paraboloidal
collimator 16A. Light rays emitted by arc 24A near focal point f
which reach paraboloidal collimator 16A are reflected by
paraboloidal collimator 16A through a range of angles toward the
input end of light guide 22A. If the input end of light guide 22A
were moved away from the output end of paraboloidal collimator 16A
(i.e. moved to the right, as viewed in the drawings) then more of
the light rays reflected by paraboloidal collimator 16A could be
coupled into the input end of light guide 22A. However, this would
again leave an annular region or gap through which light rays
passing directly from arc 24A would be lost. Annular reflector 28
solves this problem as well as the aforementioned problem
respecting loss of light rays at annular region 25.
[0025] "Output end" annular reflector 28 is a spherical arc section
reflector having a center coinciding with focal point f More
particularly, reflector 28 has a wide apertured end 34 (FIG. 4)
which circumferentially surrounds paraboloidal collimator 16A near
the wide apertured (i.e. "output") end of paraboloidal collimator
16A. Reflector 28 also has a narrow apertured end 36 which
circumferentially surrounds the input end of light guide 22A.
(Reflector 28 is "annular" in the sense that it forms a ring around
axis 27 when viewed from the left along axis 27.) Light rays which
would otherwise be lost through annular region 25 as aforesaid are
reflected by reflector 28 for possible re-reflection by
paraboloidal collimator 16A into light guide 22A. The efficiency
with which reflector 28 reflects light is not particularly high due
to a number of factors. In particular, some rays may be lost due to
absorption by reflector 28 itself (collimator 16A and reflector 26
are also absorptive to some degree); some rays may be lost due to
reflection onto and reabsorption by arc 24A; some rays may be lost
due to reflection through aperture 14A; and, in general, efficiency
is reduced whenever multiple reflections occur, such as reflection
by reflector 28 followed by further reflection by paraboloidal
collimator 16A. However, only a relatively small portion of the
light rays emitted by arc 24A reach reflector 28, so losses
inherent in its comparative reduced efficiency are acceptable. The
inner reflecting surface of reflector 28 may be made slightly
diffuse (i.e. non-specular) to further reduce possible reabsorption
by arc 24A of light rays reflected by reflector 28, although this
is not essential.
[0026] FIG. 5 illustrates the preferred geometric characteristics
of off-axis paraboloidal collimator 16A. As shown in FIG. 6, these
characteristics enable collimator 16A to direct into the input end
of light guide 22A, as collimated light, substantially all light
rays which pass directly from arc 24A to paraboloidal collimator
16A. Persons skilled in the art conventionally use the term
"collimated", as does this application, to describe a light beam
containing light rays which trace paths defining a limited range of
directions, as opposed to a non-collimated light beam containing
rays which trace paths in all directions. Thus, persons skilled in
the art will understand that paraboloidal collimator 16A is a
"collimating" reflector and that light rays 40 depicted in FIG. 6
are "collimated", even though rays 40 do not represent
theoretically perfect collimation. "Perfect" collimation in which
light rays propagate in parallel relationship without any crossing
or intersection of the rays' paths, can never be attained in
practice, as is well known to persons skilled in the art. See for
example The Photonics Dictionary, 45th ed., 1999, Laurin Publ. Co.
Inc., Pittsfield, which defines collimated radiation as follows
"Radiation in which every ray from any given object point can be
considered to be parallel to every other. This is never completely
the case: The light from a star is really diverging, and all
collimators have aberrations."
[0027] Paraboloidal collimator 16A consists of two parabolic
sections located on opposite sides of axis 27 (i.e. the upper and
lower sides of axis 27, as viewed in the drawings). The upper
parabolic section is formed by rotating a parabola 16A-1 through a
180.degree. arc about and above axis 27, as viewed in FIG. 5.
Parabola 16A-1 is an "off-axis" parabola, in that its vertex V is
located above, not on, axis 27. The axis 38 of parabola 16A-1
intersects axis 27 at an angle .THETA., with the parabola's focus f
being at the point of intersection of axes 27, 38. The focal length
f, of parabola 16A-1 is the segment of axis 38 extending between
the parabola's vertex V and focus f. In an embodiment of the
invention in which collimated light is coupled into the input end
of a light guide having a diameter of 25 cm, parabola 16A-1 is
defined by the equation: 1 y = x 2 4 f - f
[0028] where y is measured along axis 38 as shown in FIG. 5; x is
measured along the perpendicular axis 39 passing through the
parabola's focus f .THETA.33.2.degree.; and, f 8.862 cm. The lower
parabolic section of paraboloidal collimator 16A is identical to
the upper parabolic section, except that it is formed by rotating
another off-axis parabola through a 180.degree. arc about and below
axis 27, as viewed in FIG. 5.
[0029] As shown in FIG. 6, the above-described off-axis,
cylindrically symmetric characteristics of paraboloidal collimator
16A ensure that substantially all of the light rays 40 which pass
directly from light bulb arc 24A (more particularly, all light rays
originating or passing through the center "C" of light bulb arc
24A) to paraboloidal collimator 16A are reflected into the input
end of light guide 22A. Accordingly, rays which would otherwise be
lost in annular region 25 (FIG. 2) if a prior art, non off-axis
paraboloidal reflector 16 having an output diameter greater than
the light guide's input diameter were used, are collimated and
directed into the input end of light guide 22A by off-axis
paraboloidal collimator 16A.
[0030] Light bulb arc 24A is elongate and emits light rays along
its entire length "L", not just from its center "C". As previously
explained, this has an important bearing on the efficiency with
which collimated light can be coupled into the light guide. FIG. 7,
which is similar to FIG. 6 but omits reflectors 26, 28 and light
guide 22A, shows not only light rays which originate at the center
"C" of arc 24A, but also light rays which originate near the
rearward (left) and forward (right) ends of arc 24A. As can be
seen, the width of the light beam produced by reflector 16A varies
as a function of distance d along axis 27. More particularly, and
as is graphically depicted in FIG. 8, at the wide apertured end of
reflector 16A the output beam's width is essentially equal to the
diameter Dr of the wide apertured end of reflector 16A. The beam
width then decreases as d increases, eventually reaching a minimum
value D.sub.o(d); and, thereafter, the beam width continues to
increase as d increases. By structuring reflector 16A to produce a
light beam having a minimum beam width equal to the diameter of the
light guide's input end; and, by positioning the light guide's
input end to coincide with the point at which the beam attains such
minimum width, one may ensure that a maximal fraction of the light
rays exiting reflector 16A are directed into the light guide's
input end. Conversely, if the input end of the light guide were
positioned to the left or to the right of the point at which beam
attains its minimum width, then some light rays would be lost.
[0031] As previously explained, as a light guide's D:L ratio
increases, it becomes progressively more difficult to achieve high
efficiency coupling of collimated light from a light source into
the light guide. For light guides having a given D:L ratio, the
invention provides much higher efficiency in coupling of collimated
light into such light guides than can be provided by prior art
reflectors in respect of light guides having the same D:L
ratio.
[0032] As will be apparent to those skilled in the art in the light
of the foregoing disclosure, many alterations and modifications are
possible in the practice of this invention without departing from
the spirit or scope thereof. For example, although the invention
has been described in relation to "prism" light guides, those
skilled in the art will appreciate that the invention can be
applied to any light guide having input collimation requirements
and D:L ratio as described above. As another example, it is not
necessary that the narrow apertured end 36 of output end annular
reflector 28 coincide precisely with the input end of light guide
22A. In some cases, end 36 may project a short distance inside the
input end of the light guide. This construction, which is
convenient if the light guide happens to be out-of-round at its
input end, is still considered to "circumferentially surround" the
input end of the light guide, within the meaning of the claims.
There should not however be a gap between the narrow apertured end
36 of output end reflector 28 and the input end of the light guide,
because this would result in loss of light through the gap. Persons
skilled in the art will also understand that the invention is not
confined to the dimensional or geometrical relationships depicted
in the drawings. The scope of the invention is to be construed in
accordance with the substance defined by the following claims.
* * * * *