Hot mirrors are heat-reflecting mirrors/filters designed to transmit visible wavelengths while reflecting near-infrared, heat-generating wavelengths. Cold mirrors are heat-transmitting mirrors/filters designed to reflect visible wavelengths while transmitting near-infrared wavelengths. These filters can be used to remove heat from an optical system. Hot mirrors are offered for 0° angle of incidence, while cold mirrors are available for 45° angle of incidence. They are both available in 25.4 mm diameter and 50.8 mm square sizes.