Photoconductive cells are semiconductor-based cells with bandgaps. These relate to the photon energies to be perceived. Such cells can be found in exposure metres and automatic street lamp switches that operate in the visible spectrum. Cadmium sulphide is used to make them. Infrared detectors, such as night-vision sensors, are instances of this. Mercury cadmium telluride or sulphur cadmium telluride are used to make them.