Electromagnetic radiation that can be perceived by the human eye. It is made up of electromagnetic waves with wavelengths between 4 × 10-7 and 7 × 10-7 meters. Light, and all other electromagnetic radiation, travels at a speed of about 299,728 km (185,831 mi) per second in a vacuum. See also photon.
Electromagnetic energy of a wavelength just outside the range the human eye can detect, such as infrared light and ultraviolet light. See Note at electromagnetic radiation.