Light is a form of energy called electromagnetic radiation when a wavelength which can be detected by the human eye. Light is made up of tiny energy particles, smaller than an atom, called photons. Light travels at 299,792 kilometers per second.


A diagram showing the full spectrum of light and the components of light.Credit to Victor Blacus

Light shows properties of both waves and particles. Each wave has a wavelength or frequency. The human eye sees each wavelength as a different color. Rainbows show the entire spectrum of visible light. The separate colors, moving in from the outer edges, are usually listed as red, orange, yellow, green, blue, indigo and violet. They are always in that order because red has the longest wavelength, and violet has the shortest. Other colors can be seen only with special cameras or instruments: The types of electromagnetic radiation below the frequency of red are infrared, microwave, and radio waves, and higher than violet are called ultraviolet, X-rays, and gamma rays.