Hybrid solar and electrically controlled transmission of light filters

The investigations show that it is possible to develop hybrid light filters which could be switched by solar as well as by electrical energy. The light filters are based on thermotropic gels changing their transmission depending on the concentration of the cross-linker from 60% to 80% to ⩽1% in the temperature range 29–36°C. Detailed investigations of the electrical switching process show that the switching times significantly decrease with increasing thickness of the tin-doped indium oxide (ITO) used as transparent electrodes. The switching times could be varied from 3 to over 50 min. Furthermore the required wattage for the switching process significantly decreases with increasing thickness of the ITO-layers. A gel layer having a thickness of 2 mm is quite enough to realize changes in the transmission from about 62% to ⩽1%. Comparable results were obtained for light filters having a size of either 25 or 180 cm2, respectively. Therefore, it should be possible to transfer these results to light filters having a size of 0.5-1 m2.