Optics is the branch of physics that studies the behaviour and properties
of light, including its interactions with matter and the construction of
instruments that use or detect it. Optics usually describes the behaviour of
visible, ultraviolet, and infrared light. Because light is an electromagnetic
wave, other forms of electromagnetic radiation such as X-rays, microwaves, and
radio waves exhibit similar properties.
Most optical phenomena can be accounted for by using the classical
electromagnetic description of light, however complete electromagnetic
descriptions of light are often difficult to apply in practice. Practical
optics is usually done using simplified models.