Light travels as waves of energy. Waves of light have different wavelengths (the distance between the top of one wave and the top of the next). Different colors of light have different wavelengths. Purple and blue light waves have short wavelengths. Red light has a longer wavelength. This picture shows the lengths of the waves of different colors of light. The longest red waves are about 700 nanometers long. The shortest purple waves are 400 nanometers long. Light waves with short wavelengths carry more energy than ones with long wavelengths. "Light" waves shorter than 400 nm are called "ultraviolet" or "UV" light. "Light" waves longer than 700 nm are called "infrared" or "IR" light. Some people use a distance unit called an Ångström to measure light waves. There are 10 Ångströms in one nanometer. Green light has a wavelength of 5,500 Ångströms, which is the same as 550 nanometers.
Original Windows to the Universe artwork by Randy Russell.