Different colors of light have different wavelengths. Shades of purple have the shortest wavelengths, as low as 400 nanometers (or the equivalent 4,000 Ångströms). Red light has the longest wavelength, up to 700 nm (7,000 Å). Short wavelengths correspond to higher frequencies and higher energies, while longer waves oscillate at lower frequencies and carry less energy. Electromagnetic waves with wavelengths below 400 nm are in the ultraviolet (UV) portion of the electromagnetic spectrum, while waves longer than 700 nm are in the infrared (IR) region of the spectrum.
Original Windows to the Universe artwork by Randy Russell.