Emulsions made with special sensitizing dyes can respond to radiation at wavelengths up to 1200 nanometers, though the most common infrared films exhibit little sensitivity beyond 900 nm. One specialized colour film incorporates a layer sensitive in the 700–900-nm region and is developed to false colours to show infrared-reflecting subjects as bright red.
Photographs can thus be made of subjects, which radiate in the near-infrared, such as stars, certain lasers and light-emitting diodes, and hot objects with surface temperatures greater than 500°F 260°C). Infrared films are more commonly used to photograph subjects, which selectively transmit or reflect near-infrared radiation, especially in a manner different from visible radiation. Infrared photographs are taken from long distances or high altitudes usually show improved clarity of detail because atmospheric scatter haze is diminished with increasing wavelength and because the contrast of ground objects may be higher as a result of their different reflectance in the near-infrared. Grass and foliage appear white because chlorophyll is transparent in the near-infrared, while water is rendered black because it is an efficient absorber of infrared radiation.
