Light is electromagnetic radiation detected by the human eye. Within the broad spectrum of electromagnetic radiation is a very narrow band of wavelengths visible to humans. Spectral regions adjacent to this visible band are often referred to as light, infrared at one end and ultraviolet at the other. Optics is the genesis and propagation of light, the changes that it undergoes and produces, and other closely associated phenomena. Physical Optics deals primarily with nature and properties of light itself. Geometrical Optics are the principles governing the image-forming properties of lenses, mirrors, and other devices that make use of light.