Light is optical energy. It is an electromagnetic wave that has an electric field that changes periodically with time and creates an orthogonal magnetic field. The wave is self-propagating and can travel through vacuum.
The color of light is intrinsically related to its wavelength. The ultra-violet (UV) spectrum takes over from x-rays at wavelengths of few nanometers, moving into the visible spectrum with violet, which has a short wavelength (~380nm). Moving along the visible spectrum through green, yellow, orange and red the wavelength gets longer. The longest visible red wavelength is ~750nm, and beyond this is the infrared (IR) spectrum. Near-infrared (N-IR) continues from the visible up to the mid-infrared (mid-IR) at about 2000nm, with the far infrared (far-IR) beyond this to ~1mm.
Related Terms: Color, Decibel Scales, Power, White Light