U.S. patent application number 13/710930 was filed with the patent office on 2013-04-25 for internal collecting reflector optics for leds.
This patent application is currently assigned to RAMBUS INTERNATIONAL LTD.. The applicant listed for this patent is RAMBUS INTERNATIONAL LTD.. Invention is credited to Brian Edward Richardson.
Application Number | 20130100664 13/710930 |
Document ID | / |
Family ID | 44011192 |
Filed Date | 2013-04-25 |
United States Patent
Application |
20130100664 |
Kind Code |
A1 |
Richardson; Brian Edward |
April 25, 2013 |
INTERNAL COLLECTING REFLECTOR OPTICS FOR LEDS
Abstract
An optical system is disclosed that uses an LED light source.
The light output is coupled to an optic element formed from a
material with a high refractive index. The coupling of the light to
the high index material significantly reduces the cone angle of the
light. The system is very efficient in that nearly all the light
generated by the LED is directed to the intended subject.
Inventors: |
Richardson; Brian Edward;
(Los Gatos, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
RAMBUS INTERNATIONAL LTD.; |
Grand Cayman |
|
KY |
|
|
Assignee: |
RAMBUS INTERNATIONAL LTD.
Grand Cayman
KY
|
Family ID: |
44011192 |
Appl. No.: |
13/710930 |
Filed: |
December 11, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12949642 |
Nov 18, 2010 |
|
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13710930 |
|
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61281544 |
Nov 18, 2009 |
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Current U.S.
Class: |
362/235 ;
362/308 |
Current CPC
Class: |
F21Y 2115/10 20160801;
G02B 19/0028 20130101; F21S 2/005 20130101; F21V 7/08 20130101;
F21L 4/02 20130101; G02B 19/0061 20130101; F21V 5/02 20130101; F21V
7/06 20130101; H01L 33/58 20130101; F21V 7/04 20130101; H01L 33/60
20130101; F21V 13/04 20130101 |
Class at
Publication: |
362/235 ;
362/308 |
International
Class: |
F21V 7/04 20060101
F21V007/04; F21V 7/08 20060101 F21V007/08; F21V 13/04 20060101
F21V013/04; F21V 7/06 20060101 F21V007/06 |
Claims
1-23. (canceled)
24. An optical system with a directed output, the optical system
comprising: a light-transmissive solid optic element comprising a
light output surface and, opposite the light output surface, a
reflective surface shaped to create an internal reflection effect;
and an LED light source at the light output surface to direct light
towards the reflective surface, wherein the light from the light
source is reflected by the reflective surface to form an output
light beam that exits the solid optic element through the light
output surface.
25. The optical system of claim 24, wherein the light source is
located substantially at the center of the light output
surface.
26. The optical system of claim 24, wherein: the solid optic
element comprises a facet adjacent an edge of, and non-parallel to,
the light output surface; and the light source is mounted in
optical contact with the facet.
27. The optical system of claim 26, wherein the solid optic element
is configured such that an angle between the centerline of the
light output by the light source and a centerline of light
reflected from the reflective surface is no more than 60
degrees.
28. The optical system of claim 26, in which an angle between a
normal to the facet and a normal to the light output surface is no
more than 60 degrees.
29. The optical system of claim 26, wherein the reflective surface
is sized, angled relative to the light output surface, and offset
from the light output surface such that positive and negative rays
of a cone of light output by the light source are incident thereon
adjacent an edge thereof.
30. The optical system of claim 24, wherein the reflective surface
is parabolic.
31. The optical system of claim 24, wherein the reflective surface
is elliptical.
32. The optical system of claim 24, wherein the reflective surface
is aspheric.
33. The optical system of claim 24, wherein an index of refraction
of the optic element is no less than 1.3.
34. The optical system of claim 24, wherein the light source
comprises more than one LED die.
35. The optical system of claim 24, wherein the light source is
located adjacent an edge of the light output surface.
36. A lighting system with a directed output, the lighting system
comprising an array of optical systems in accordance with claim 24.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the priority benefit of U.S.
provisional application No. 61/281,544, filed Nov. 18, 2009, the
disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates generally to the collection and
control of light from a light emitting diode (LED). More
specifically, the invention is directed to the control of the wide
angular emission of light from an LED to create a highly controlled
beam of light.
[0004] 2. Background Art
[0005] Numerous products require efficient collection and control
of light from a light source. A high degree of control is required
to create a collimated beam of the type needed for searchlights
used for live performances, special events, and illuminating tall
structures. The searchlights use a xenon arc type lamp as a light
source and a deep parabolic reflector to collect and control the
light direction and beam angle. This method has been used for many
years, even before the invention of the light bulb.
[0006] This type of prior art searchlight generally requires a
reflector that is much larger than its arc gap. A 1000-watt xenon
lamp generates most of its light within a sphere 1 mm in diameter.
To create a highly collimated beam, a reflector with a diameter of
20 inches is typically used. Although xenon light sources create an
enormous amount of light in a small area, efficiency of these types
of lamps is poor. A 1000-watt lamp may only produce 35 lumens per
watt of electrical energy. Another drawback with these lamps is the
length of their life, which is only a few thousand hours. Finally,
xenon light sources are filled with gas at a high pressure. Persons
replacing xenon lamps need to wear protective clothing and a face
shield when they are servicing searchlights.
[0007] Another disadvantage of the xenon light systems is the
reduction in performance as a result of the collection of dirt on
the optical surfaces. This collection is compounded by the fact
that the lights typically require forced-air cooling. A xenon
system has at least four surfaces where dirt can collect and reduce
the output. The first of these surfaces is the surface of the lamp
itself. The second is the surface of the reflector. The third and
fourth are the inside and outside of the window. Only a small
amount of dirt on any of these four surfaces significantly reduces
the light output of the system
[0008] The use of a deep parabolic reflector by searchlight
manufacturers adds to the poor efficiency of the overall system. A
lot of the light generated from the lamp exits the front of the
open end of the parabolic reflector and doesn't contribute to the
collimated beam created by the light that does strike the
reflector.
[0009] Manufacturers of searchlights would like to use LEDs as the
light sources for their searchlights. LEDs don't create light with
as high intensity as the xenon light sources. The low intensity of
LED light leads to the requirement of a much larger reflector for
the same output as a xenon system. In some cases using an LED would
require a reflector ten times the size of the reflector used by a
system with a xenon light source. In summary, the main
disadvantages of current xenon based light systems are their short
life, the dangers of servicing the systems, and their low
efficiency.
[0010] Optics systems to collect and control light from LEDs
commonly combine a conventional reflector and refractive optics. A
typical example of this type of system is shown in FIG. 1. Although
this type of system is efficient in collecting all of the light
from the LED, the ability to control the output is limited. The
light that is collected by the reflector portion of the system has
a generally uniform cone angle as it leaves the reflector. In this
example the cone angle ranges from 3.9 degrees to 4.5 degrees. The
refractive optics (i.e. the light transmitted through the lens) has
a much greater cone angle, 41 degrees. Therefore, in searchlight
systems, the light from the refractive optics does not contribute
to the searchlight beam and creates spill light.
[0011] Another drawback inherent to the prior art system of FIG. 1
is that the output light comes from two sources, a lens and a
reflector. The nature of the light from the lens is quite different
from that from the reflector. It is therefore very difficult to
optimize the output from both sources simultaneously. Output
controlling measures that have a positive effect on the light
output from the lens tend to have a negative effect on the light
output from the reflector, and vice versa.
[0012] Another variation of conventional reflector optics is a lamp
that locates an LED at the focal point of a parabolic reflector.
The output normal to the surface of the LED is directed along the
axis of the parabola. Light from the LED is emitted in a
semispherical direction, + and -90 degrees from normal. The
parabola collects all of the emitted light and directs most of the
light in the intended direction. The LED and its mounting absorb
some of the light that would, if not obstructed, go in the intended
direction. This absorption occurs because the LED is in the output
path of the light reflected by the parabola.
[0013] Electricity must be supplied to the LED to generate the
light, which creates heat. To cool the LED, a heat pipe is used to
conduct heat from the LED to a heat sink behind the reflector.
These components also absorb some of the light, thereby reducing
the efficiency of the lighting system even further.
[0014] The reflector in an LED light system needs to be large to
collect the semispherical, .+-.90 degree output from the LED. If
the cone angle could be reduced to less than .+-.45 the reflector
could be much smaller. The output beam angle of the reflector of
prior art products varies greatly as a function of the distance
from the center of the reflector to the rim of the reflector. The
variation in beam angle requires the reflector to be larger than
would be required if the variation in beam angle over the diameter
of the reflector was reduced.
[0015] There is therefore a need for a lighting system that is
highly efficient, that is not as sensitive to dirt and dust, that
provides a high degree of control of the output beam angle, and
that is contained in a compact package.
SUMMARY OF THE CLAIMED INVENTION
[0016] Various embodiments of the present invention disclose an
optical system with a directed output. The system includes at least
one LED that provides a light source. The system further includes
an optic element that reduces the cone angle of a light output of
the light source. The light reflects off a reflective surface at an
acute angle. The reflected light then forms an output light
beam.
[0017] Other embodiments of the present invention may disclose a
lighting system with a directed output including an array of
optical systems. Each of the optical systems includes at least one
LED that provides a light source and an optic element that reduces
the cone angle of a light output of the light source. The light
contacts a reflective surface, and the light is reflected from the
reflective surface at an acute angle. The reflected light then
forms an output light beam. The light beams of the array of optical
systems are combined to form a lighting system output beam.
[0018] Still other embodiments of the present invention disclose an
optical system with a directed output including at least one LED
that provides a light source. The light source is positioned in an
output light path of the system. An optic element reduces the cone
angle of a light output of the light source. A reflective surface
reflects light form the light source at an acute angle. The
reflected light forms an output light beam of the system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a side sectional view of prior art.
[0020] FIG. 2 is an isometric view of an exemplary optical
system.
[0021] FIG. 3 is a side sectional view of an exemplary optical
system.
[0022] FIG. 4 is a side sectional view of an exemplary optical
system showing light rays.
[0023] FIG. 5 is a side view of another exemplary optical
system.
[0024] FIG. 6 is an isometric view of an exemplary array of optical
systems.
DETAILED DESCRIPTION OF THE INVENTION
[0025] Various embodiments of the present invention disclose
systems that control the direction and angle of a light output. The
output of the systems reduces power consumption by directing a very
high percentage of light generated by one or more LEDs specifically
to the object designated to be lighted.
[0026] Referring first to FIGS. 2 and 3, an optical system 200
includes an LED assembly 210 that is coupled to a light pipe 220.
It will be understood by those skilled in the art that the type and
size of the LED assembly 210 may vary with the particular optical
system to be used in a given application. The LED assembly 210 is
shown with a heat sink plate 230 that conducts heat from an LED die
310 (see FIG. 3).
[0027] While the LED die 310 is generally depicted in the several
figures of the drawing as a single element, the LED die 310 may be
formed from multiple dies. When multiple dies are used to form the
LED die 310, the multiple dies may be bonded together.
[0028] Light pipe 220 may be implemented at least in part as a tube
lined with a reflective material, an optical fiber, a hollow light
guide, a fluorescence based system, and/or another device suitable
for transporting light. The light pipe 220 may be coupled to the
LED die 310, which may in turn be coupled to the heat sink plate
230. The light pipe 220 may be optically coupled to the emitting
surface of the LED die 310. When the light pipe 220 and the
emitting surface of the LED die 310 are optically coupled with
either a gel or an adhesive, reflection losses from the body of the
LED die 310 are reduced, as are the reflection losses at the mating
surface of the light pipe 220 and the LED die 310. If reflection
losses are not deemed critical, the LED assembly 210 may be
constructed so that there is a narrow air gap between the LED die
310 and a first end of the light pipe 220.
[0029] A second end of the light pipe 220 may be optically coupled
to an optic element 240. The optic element 240 may be cylindrical
in cross section. The optical coupling of the light pipe 220 with
the LED die 310 and the optic element 240 reduces light losses at
the ends of the light pipe 220.
[0030] Light traveling within the light pipe 220 may travel within
a range from approximately +42 degrees to approximately -42 degrees
relative to the centerline of the light pipe 220. The actual angle
of the light travel will depend on the index of refraction of the
light pipe 220 and the specific output of the LED die 310.
[0031] The light pipe 220 conducts light to the optic element 240.
The optic element 240 may be cylindrical in cross section, but
other shapes may also be utilized. The optic element 240 may or may
not have the same index of refraction as the light pipe 220. The
optic element 240 may have a much greater index of refraction than
the index of refraction of air, which is very close to 1. The index
of refraction for acrylic is approximately 1.49 and for
polycarbonate it is approximately 1.58. Some plastics have a higher
refractive index, and glass materials may have much higher indexes
of refraction. The higher the index of refraction of the material
used to form the optic element 240, the narrower the cone angle of
the light relative to a light pipe centerline 410 (see FIG. 4). For
an optic element formed from a polycarbonate, the cone angle would
be approximately .+-.39 degrees.
[0032] Referring now to FIG. 4, light from the LED assembly 210
that is directed along the light pipe centerline 410 will continue
in that same direction when the light enters the optic element 240.
Within the optic element 240, the light will eventually intersect
an internal reflective surface 250. For a collimated beam the
reflective surface 250 would be parabolic.
[0033] The shape of the internal reflective surface 250 may be
varied according to the desired characteristics of the output beam.
The output beam may be collimated, but different types of output
beams may be desired. The reflective surface 250 may be ellipsoidal
or aspheric to provide different effects for the output beam.
[0034] The reflective surface 250 creates an internal reflection
effect in the optic element 240. Reflective surface 250 may be
formed by coating the surface of the optic element 240 with a high
reflectance material. The high reflectance material may be, for
example, silver, aluminum, or a high performance interference
coating. The selection of the specific material for the coating
appropriate to the application is an engineering decision that
takes into account the requirements of a particular application and
the budget constraints of the project.
[0035] The intersection of the light pipe centerline 410 with the
reflective surface 250 may be near the midpoint of the reflective
surface 250. Constructing the system 200 so that the centerline 410
is near the midpoint of reflective surface 250 maximizes the amount
of light that impinges on the reflective surface 250.
[0036] It may be noted that if the optic element used in the system
is not formed from a high refractive index material, the cone angle
of the light exiting the light pipe would be in the range .+-.90
degrees. The large cone angle would be a result of light being
refracted at an output surface of the light pipe. A large cone
angle would also result if the light pipe was made of acrylic and
the non-high refractive index optic element was a hollow element
filled with air.
[0037] The geometry of the optical system 200 may be such that the
light enters the optic element 240 near where light exits the optic
element 240. By locating the inlet near the outlet, the angle
between an output centerline 430 and the light pipe centerline 410
may be minimal. The smaller the angle between the two centerlines
410, 430, the less difference there is between the length of a
positive internal ray 440, a ray with a positive angle from the
light pipe centerline 410, and the length of a negative internal
ray 450, a ray with a negative angle from the light pipe centerline
410.
[0038] The length and geometry of the rays 440, 450 determine the
output beam cone angle by their geometry. Reducing the angle
between the light pipe centerline 410 and the output centerline 430
may reduce the size of the system 200. The greater the angle
between the light pipe centerline 410 and the output centerline
430, the larger the system 200 may be to achieve the same output
beam cone angle.
[0039] In the system depicted in FIG. 4, the optical lengths may
vary from nominal approximately .+-.30%. If the angle between the
two centerlines 410, 430 were much greater, for example 60 degrees,
the differences in the nominal lengths would be closer to
approximately .+-.60%. To maintain the same output beam cone angle
the reflector would need to be much larger in overall size. In
summary, the higher the index of refraction of the optic element
240, the more compact the system 200 may be. Further, the smaller
the angle between the centerlines 410, 430, the more compact the
system 200 may be.
[0040] Those skilled in the art will note that the light exiting
the high refractive index optic element 240 at the output surface
420 may be refracted so that the light past the output surface 420
may have a greater cone angle than light within the optic element
240.
[0041] The output surface 420 may be flat. The output surface 420
may also have other geometries. The geometry of the output surface
420 may be selected based on the overall system requirements and
the lighting effect desired. Other optic elements may be added to
the system 200 downstream of the output surface 420.
[0042] If desired for a given installation, the light pipe 220 may
be eliminated from the optical system 200. In this case, the LED
assembly 210 may be directly optically coupled to the optic element
240. The optical performance of the system 200 may be maintained by
reducing the size of the heat sink plate 230, or reconfiguring the
heat sink plate 230. If the light pipe 230 is used, the length of
the light pipe 220 is dependent on the size of the LED assembly 210
and its heat sink plate 230.
[0043] FIG. 5 illustrates a side view of another exemplary optical
system 500. In optical system 500, the LED die 510 is located
within an output light path. In this configuration, the centerlines
of the input light path and the output light path are coincident,
and the angle between them is zero. This configuration therefore
may yield a system 500 of minimal size. Electricity and heat must
be conducted to and from the LED 510. If the conducting components
are large, they can absorb a significant amount of light.
Therefore, high power systems might generally not be configured
with LEDs in the output path.
[0044] FIG. 6 illustrates an isometric view of an exemplary array
600 of optical systems 200. The array 600 may be used for systems
in which a large amount of light is required, such as a high
powered searchlight. By using an array of optical systems 200, heat
dissipation may be made simpler. By utilizing an array of smaller
optical modules as opposed to a single large LED, the heat
generated is spread over a larger area and is therefore easier to
dissipate. The depth of an array 600 of optical systems 200 may be
less than that required for an equivalent system using a single
large LED or optic element. It will be recognized by those skilled
in the art that the array 600 may be implemented in any of the
configurations described herein.
[0045] The above disclosure is not intended as limiting. Those
skilled in the art will readily observe that numerous modifications
and alterations of the device may be made while retaining the
teachings of the invention. Accordingly, the above disclosure
should be construed as limited only by the restrictions of the
appended claims.
* * * * *