| Summary: | A prototype of a prism light guide using a new variable extraction technique is
discussed. Prism light guides are hollow structures that pipe light by means of total
internal reflection (TIR). High efficiency and uniform illumination can be achieved
using a uniform extraction technique along the prism light guides. However, the shapes
of extractors used for uniform extraction have to be designed specifically for different
geometries of conventional light guides. Another limitation of the conventional systems
is that the level of extraction along the guides cannot be controlled once the extractors
have been built into the light guides.
Motivated to generalize the shape of the extractor and to enable the control of the
extraction/illumination level along the light guide, a new variable extraction technique
has been developed. This extraction technique is based on frustration of TIR,
electrophoresis, and photon scattering. A rectangular variable extractor based on the
new technique has been made with highly scattering silica particles in a fluorinert
suspension contained between two transparent conducting films. By changing the
polarity of the electrical potential applied across the conducting films, the charged silica
particles can be moved to prevent, or "frustrate," TIR (through interaction with light in
the very thin evanescent wave region near the TIR interface inside the light guide) and
cause scattering in which light gets extracted, whereas the opposite polarity will not
affect TIR. As a result, by changing the strength of the applied potential the level of
scattering or extraction can be varied for each extractor independently along the light
guide.
A Monte Carlo ray tracing analysis of the light guide using the new extraction technique
has been performed, and the results are promising. Based on the ray tracing model, a
scale prototype of the variable extractor light guide has been constructed.
The prototype consists of a prism light guide with a rectangular cross section and eight
variable extractors. To test it the light guide was then mounted on a model o f a series of
eight offices with two light sources at each end of the guide, such that each extractor
controls the illumination level in each office. A simulation algorithm was developed to
predict the extraction or illumination level for different settings of the applied potential in each office, and the performance of the actual prototype was compared and agrees
with the model prediction. A control algorithm was then programmed to adjust the
level of extraction in each office according to the needs of the users, and the algorithm
was successfully applied to the actual prototype. === Science, Faculty of === Physics and Astronomy, Department of === Graduate
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