A new type of electrically controlled optical filter to heighten the color temperature of incident light has been developed that is comprised of guest-host mode liquid-crystal devices containing dichroic dyes. The transmission spectrum of the filter was designed as the ratio of different radiation spectra based on the black body radiation theory. The absorption for long-wavelength visible light is varied according to the liquid crystal alignment change for voltage applied to the filter. When white light with a color temperature of 5700K was incident on a filter fabricated with 6μm-thick liquid-crystal layers, the color temperature of light transmitted from the filter could continuously be changed from 6000K to 11000K by voltage control of less than 10 Vrms. The electrooptic response time was as fast as 50 ms. This liquid crystal optical filter is widely applicable to color-image input/output technologies, including the image sensing, display, and illumination fields.
