UBC Theses and Dissertations
Pneumatic switching of the optical power of a Fresnel lens for control of solar illumination Watanabe, Eri
A pneumatic-based illumination switch has been developed for use in conjunction with collimated daylighting collection systems that collect sunlight on the façade of a multi-storey building and distribute it throughout the core areas of the building. Daylight collection systems are currently of interest since they have the potential to significantly reduce the need for electrical lighting in workplaces, thus reducing the required electrical energy and associated greenhouse gas emissions. In one particular system, sunlight is distributed by hollow light guides and redirected into light fixtures positioned along the guides. The illumination switch described here can be incorporated into the light guides to control the amount of sunlight that is directed into each fixture. This control device consisted of a Fresnel lens positioned with its structured surface adjacent to a layer of silicone gel that had a similar refractive index value as the lens. In one mode of operation, the gel layer was separated from the lens so that the lens focused incident sunlight into a hollow light guide that carried the sunlight to a fixture. In the second mode of operation, when the index-matching gel layer was pressed into contact with the structured surface of the Fresnel lens, the switch allowed sunlight to pass substantially undeflected through the lens and continued down the guide. The switch was activated by a vacuum pump that adjusted the relative pressure in order to pull the silicone gel into and out of contact with the Fresnel lens. Experimental tests showed that intensity of the light emitted by a fixture can be controllably and reproducibly reduced by about 75 % of the original intensity when the switch was activated.
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