A novel LED recycling scheme using double prisms is presented. Two identical triangular prisms with square bases, one cross-stacked on top of the other, are tight-fit into a mirrored light tunnel. The whole prism/light tunnel assembly is then mounted on top of a square LED source, whose emitting area is the same as that of the base plane of the said prism/light tunnel assembly. Each prism acts as a tapered-down light guide in one dimension, which selectively retro-reflects high angle light along that direction. The outer light tunnel serves as a mirrored wall that folds back any light that escapes outside the two prisms. For a given collection cone angle, the height of the two prisms is optimized using ASAP, a commercial ray-tracing software. Simulation and experimental results show promise in significantly increasing the brightness of the LED sources within the collection cone. Specifically for a 4x recycling ratio a 70% recycling gain in center illuminance has been achieved (i.e., illuminance measured in the forward direction). This scheme has advantages over previous recycling configurations due to its compactness and ease of mounting. For example, compared to Wavien's spherical reflector approach that has been previously published, the current recycling configuration is much smaller in size because instead of fitting a much larger mirrored reflector on top of the LED source, this time we're using a structure that has the same lateral dimensions as those of the LED source itself. Further improvement is also possible if optimization of various system parameters is carried out.
Two novel LED recycling schemes using either recycling light pipes or recycling "collars" show promise in significantly
increasing the brightness of the LED sources. Preliminary experimental data show significant brightness enhancement,
especially with a relatively high chip reflectivity and/or high mirror blockage factor. Further improvement may be
expected when various system parameters are optimized.
An etendue efficient, prism-based LED color mixing scheme is presented in this paper. The prisms have dichroic
coatings deposited on their diagonal surfaces and serve as beam splitters which selectively pass or reflect light of
different wavelengths. Light confinement within the prisms is achieved through waveguiding, which is first explained in
theory, and then verified by some preliminary experimental results. The compact size of this device makes it especially
attractive for miniaturized projector systems.
A general theory on light-pipe/tunnel-based recycling schemes, along with some experimental data obtained from LED illuminators, is presented in this paper. Light recycling is classified as angular, spatial, or mixed based on the angular filtering characteristics of the recycling process. The principles behind the three schemes are analyzed and some experimental results are presented at the end.
Wavien patented dual paraboloid reflector (DPR) system, while optimal in maximizing image brightness (equivalent to minimizing the image aberration) at the input of its light pipe, does not produce maximal lumen throughput at its output. The overall lumen throughput depends in large part on three factors: Fresnel losses and image aberration, both defined at the input face of the light pipe, and the light pipe's input dimensions. Fresnel losses can be reduced by narrowing the cone angles of the light cone incident on the light pipe, which in turn can be achieved by increasing the size and/or focal length of the second paraboloid reflector. Smaller cone angles also mean reduced tapering of the light pipe which translates into larger input sizes (as its output dimensions are fixed) and higher coupling efficiency. Unfortunately this gain in coupling efficiency comes at the expense of breaking the system symmetry, which destroys 1:1 imaging and leads to increased aberration and reduced brightness. Using a ray-tracing software an optimal point of operation can be reached and it is found that at least 10% increase in lumen throughput over the symmetric DPR system is achievable.
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