Hot mirrors are constructed by applying a thin dielectric film coating to a substrate so that it reflects IR radiation and transmits visible light while cold mirrors do the opposite. Both Hot and Cold Mirrors are designed specifically for an angle of incidence ranging from 0 to 45 degrees and can be manufactured from multi-layer dielectric coatings or thin films. Cold mirrors can be utilized as dichroic beam splitters with laser systems to reflect visible light while transmitting IR. Hot mirrors are also now utilized for incandescent bulbs thereby increasing its efficiency by redirecting unwanted infrared frequencies back to the filament while transmitting the useful visible radiation.