Light is a form of electromagnetic radiation. It travels as waves that pass freely through space, even in the absence of air. Like other forms of electromagnetic radiation, light waves have a wavelength, and light is the visible part of these waves.
The actual wavelength of the electromagnetic radiation determines the colour of the light. Long wavelengths produce red colours, and very long wavelengths produce infrared light, which we cannot see. Shorter wavelengths produce blue light, or ultraviolet radiation. Strangely, light can also be considered as a form of particle, called a photon, which travels in a straight line. Both descriptions — wave and particle — are correct, and both mean that light is a form of energy.
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