Oscillating electric and magnetic fields travelling together through space at a speed of nearly 300 000 kps. Visible light is composed of electromagnetic waves. The electromagnetic spectrum is a family of waves that includes radio waves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays. All electromagnetic waves are transverse waves. They can be reflected, refracted, diffracted, and polarized.

Radio and television waves lie at the long wavelength–low frequency end of the spectrum, with wavelengths longer than 10^–4 m. Infrared radiation has wavelengths between 10^–4 m and 7 × 10^–7 m. Visible light has yet shorter wavelengths from 7 × 10^–7 m to 4 × 10^–7 m. Ultraviolet radiation is near the short wavelength–high frequency end of the spectrum, with wavelengths between 4 × 10^–7 m and 10^–8 m. X-rays have wavelengths from 10^–8 m to 10^–12 m. Gamma radiation has the shortest wavelengths (less than 10^–10 m). The different wavelengths and frequencies lend specific properties to electromagnetic waves. While visible light is diffracted by a diffraction grating, X-rays can only be diffracted by crystals. Radio waves are refracted by the atmosphere; visible light is refracted by glass or water.