Infrared radiation - (n.)

Infrared radiation is in all respects similar to visible light, except that the wave length of the electromagnetic radiation is longer than that of light. Infrared radiation is also called "heat radiation." Our eyes cannot detect infrared radiation, although at high intensity they can get damaged by it. It is however readily sensed when holding your hand or face some distance from a hot object. Your hand or face feels warm even if the air between the skin and the hot object is quite cold. By employing special instruments, infrared radiation can be used for "seeing" in the dark. Many snakes use infrared sensors for hunting small mammals. (An interesting aside: pound for pound, mammals radiate much more energy in the infrared than the Sun does in visible light!)