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 studies the behaviour of visible, ultraviolet, and infrared light.
  • The observation and study of optical phenomena offer many clues as to the nature of light.
  • Optics explains how rainbows exist, how light reflects off mirrors, how light refracts through glass or water, and what splits light shining through a prism.
  • In addition to visible light in the standard “spectrum” of red, orange, yellow, green, blue, indigo, and violet, optics also deals with invisible parts of the whole electromagnetic spectrum of which visible light is but a small part.
  • Optics is both a science and an area of engineering. It has been used to make many useful things, including eyeglasses, cameras, telescopes, and microscopes. Many of these things are based on lenses, which focus light and can make images of things that are bigger or smaller than the original.
  • While optics is an old science, new things are still being discovered about it. Scientists have learned how to make light travel through a thin optical fibre made of glass or plastic. Light can go long distances in a fibre. Fibres are used to carry phone calls and the Internet between cities.

Geometrical optics, or ray optics, is a model of optics that describes light propagation in terms of rays. A ray in geometric optics is an abstraction useful for approximating the paths along which light propagates under certain circumstances.

  • The simplifying assumptions of geometrical optics include that light rays:
  • Propagate in straight-line paths as they travel in a homogeneous medium
  • Bend, and in particular circumstances may split in two, at the interface between two dissimilar media
  • Follow curved paths in a medium in which the refractive index changes
  • May be absorbed or reflected.
  • Geometrical optics does not account for certain optical effects such as diffraction and interference. This simplification is useful in practice; it is an excellent approximation when the wavelength is small compared to the size of structures with which the light interacts. The techniques are particularly useful in describing geometrical aspects of imaging, including optical aberrations.