As a component of our cost-effective core daylighting research program, we have developed a hollow light guide that can be used to distribute sunlight collected by a heliostat device, and can also operate as an efficient fluorescent light fixture when the sunlight is insufficient to illuminate the workspace. This dual-function prism light guide structure has a cross-section that is similar to standard commercial fluorescent light fixtures, but with an increased depth in order to pipe the sunlight. The bottom surface of the guide is lined with a thin polycarbonate film having prismatic surface features, while the top and sides are lined with a highly-reflective multilayer optical film having a luminous reflectance greater than 98 percent. The angular constraints of the concentrated sunlight, combined with the high reflectance of the surfaces, enable the sunlight to be efficiently transported within the guide along a distance of greater than 10 m. The guide can also illuminate the room using electric sources, since the light from the lamps strikes the prismatic bottom surface at angles for which it is an efficient transmitter. Photometric characterization of the new dual-function guide has been performed, resulting in illuminance levels, uniformity and efficiency values well within recommended standards. The dual-function design approach has yielded a daylighting system that can be cost-effectively incorporated into standard office building construction.
The building industry recognizes the importance of incorporating daylighting into the illumination of buildings to improve energy performance and lighting quality. There are several well-known methods that building designers use to increase the daylighting level in buildings, including windows and skylights. However, these methods are usually not capable of illuminating the core of the building, and may increase the energy usage of the building due to reduced insulation. There are other systems designed for illuminating the core of buildings with daylighting, but all have some limitations that have impeded widespread adoption. An alternate daylighting system described here offers a novel approach to illuminating the core of buildings. This system consists of active and passive optical components that capture sunlight outside multi-floor buildings and transfer it to the dark core. Active sunlight redirectors, mounted at roof level on the edge of the building, track the sun throughout the day and redirect the sunlight towards building façades at a certain angle. Passive concentrator elements mounted on the façades of the building capture and concentrate the light and direct it into light guides. The sunlight is then distributed within the building via interior light guides to efficiently illuminate the building.
We present an experimental demonstration of two new methods for electronically modulating diffractive structures. The first involves the creation of periodic displacement of a liquid-air interface by application of a spatially modulated electric field produced by an array of electrodes. The second method also uses an electrode array but creates a diffraction grating by selectively attracting and repelling electrophoretic particles in a dielectric fluid. Potential areas of application of these techniques include controllable holography and wavelength division multiplexing.
This paper begins by "re-introducing" the phenomenon of total internal reflection and the associated critical angle, including a careful discussion of the extent to which the "total" in TIR is truly total, and the "critical" in critical angle is truly critical. Although in one sense these points are largely of theoretical interest, they also have an applied aspect in relation to controlling TIR. From this perspective, two practical applications of TIR are discussed. The first involves illuminating engineering applications with prism light guides, and the second concerns electronic image displays employing frustrated TIR. In both cases the unique attributes of TIR play a key role in the efficiency and practicality of these applications.
In this paper, we present a method for determining the force due to hysteresis in an elastomer to which a series of displacements has been applied. Beginning with the Preisach hysteresis model, we develop a method which is more general, but also computationally efficient, in order to predict the hysteretic force resulting from the past displacements applied to the elastomer. The model was tested by measuring the residual displacement of the midpoint of a silicone elastomer fiber following various applied displacements and comparing them to the value predicted by this model. The predicted results were found to be in reasonable agreement with the observed residual displacements.
Abstract We present a reflective color display technique using a configuration of subtractive color filtering regions to control total internal reflection (TIR) in prismatic microstructures. The ability of the prismatic surface to efficiently redirect ambient light rays toward the viewer and the use of subtractive color filters result in a bright, easily legible, low power color image which has a four‐fold improvement in reflectivity over conventional RGB reflective LCD displays. A key advantage of this technique is the ability to switch between the highly reflective and intensely colored states with only about a half‐micron movement of the controllable subtractive color filter.
