A peculiar property of light is that it behaves both as a wave and a particle. One light particle is referred to as a "photon", but each photon can also be described as a bundle of waves. When thinking about light as a particle, each photon of light can be described by the amount of energy it carries. Alternatively, if you think of light as a wave, you can describe a photon by the wavelength of the wave (the distance between two peaks or two valleys of the wave) or its frequency (the number of peaks that pass by a given point per second). Higher energy photons have shorter wavelengths, and they appear blue. Lower energy photons have longer wavelengths and appear red.

The light from most light sources (the Sun or a lightbulb, for example) includes photons of many different colors. So at any given second the lightbulb you are looking at is giving off red, orange, yellow, green, blue, and violet light, but when all of those photons hit your eye at once, the light will appear white.