Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
1998-12-14
2001-01-23
Day, Michael H. (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S499000, C313S110000, C362S800000, C362S339000
Reexamination Certificate
active
06177761
ABSTRACT:
This invention concerns efficient extraction of light from solid transparent media, and more particularly by the use of pyramidal structure.
Light produced inside a high index of refraction material may be trapped by total internal reflection. This is particularly true in a geometry of high symmetry, say a cube or parallelepiped. This poses a problem for light emitting diodes (LED's) where the index of refraction is very high, i.e. greater than three, so that only a small fraction of the light emerges. There is need for a means to enable a very large fraction of the light to emerge from LED associated transmission media, in order to significantly increase the efficiency of light transmission from LED's.
Various means have been suggested or actually used, to extract light by geometric means, but these are not particularly efficient. For example:
a) The LED can be embedded in a sphere of the same high index material. This is possible only for a point source at the emitter center and not for a finite size emitter. In addition, emerging light has large Fresnel reflection at the interface, [(n−1)/(n+1)]
2
which is ≈25% for n=3.
b) An aplanatic lens, which is a hemisphere of radius r with conjugates at r
and nr, has been used to collimate the light within the Brewster Angle in an attempt to reduce Fresnel reflections. Typically, the material has index n≈1.5, so that much of the light, i.e. over 16%, remains trapped in the aplanatic lens, because of its high (rotational) symmetry. By keeping all reflections at angles inside the Brewster's Angle, losses are relatively small, but the tradeoff is a much greater system size than the actual LED.
SUMMARY OF THE INVENTION
It is a major object of the invention to provide an improved LED light extraction means embodying a pyramidal configuration. Basically, the extraction means comprises:
a) a cylindrical body consisting of light transmitting material, the body having a cylindrical outer wall,
b) a pyramidal body having at least three planar sides and consisting of light transmitting material, the pyramidal body located longitudinally endwise of the cylindrical body, to expose the three or more sides, the planar sides defining planes which intersect the cylindrical body outer wall at curved edges, the cylindrical outer wall terminating at such curved edges,
c) LED means located in spaced relation to the pyramidal body, and oriented to transmit light in the cylindrical body and toward the pyramidal body.
Such a device can attain efficiencies in excess of 90% in transferring light from a higher index of refraction material into air. Also, such a device is much more compact than the aplanatic device.
Comparison of the two systems shows that the monochrome LED aplanat system is somewhat larger in diameter and has no ability to mix together light from an RGB LED triad, because the aplanat system is an imaging system whereas the LED pyramidal extractor is non-imaging and therefore a good RGB mixer. The new three-sided pyramidal extractor disclosed herein has almost no losses due to Fresnel reflections, which are themselves extracted. While a 3-sided pyramidal structure is a preferred configuration, one with more than 3 sides is also effective. Additionally, an RGB (red, green, blue) extractor system that varies its color balance can be made very compactly. Three LEDs, each emitting at a specific wavelength or color, can be combined into one extractor system that can change color output by independently varying the emission of each LED. In this regard, the aplanat system of prior art requires a system diameter at least twice the diameter of the pyramidal extractor. Also, the present pyramidal system design is independent of the index of refraction within the extractor.
A further object of the invention is to provide an improved apparatus to extract light from multiple LEDs. The apparatus comprises:
a) a transparent body having a first region in which the LED's are at least partly received,
b) the body having a second region in the paths of light transmission from the LEDs, and acting to mix such light transmission,
c) the body having a third region in the path of light transmission from the second region, the third region being of reduced volume from which mixed light is transmitted,
d) the second region having cylindrical surface shape between surface areas which are continuations of planes defined by sides of said third pyramid region.
As referred to above, the third region may preferably have pyramidal shape, the second region may have conical shape, and the first region may have cylindrical shape. In this regard, the second region typically has surfaces that are continuations of planes defined by the sides of the third pyramid region. Three LED's may be employed, in a cluster, and may, for example, respectively be red, green and blue light emitting, and there may be means for controlling the relative emissions from the LEDs, for color control of the mixed light transmitted from the third region.
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Parkyn, Jr. William A.
Pelka David G.
Winston Roland
Day Michael H.
Haefliger William W.
Teledyne Lighting and Display Products, Inc.
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