Editing Optics (section)

{{Short description|Branch of physics that studies light}}
{{About|the branch of physics|the book by Sir Isaac Newton|Opticks|other uses}}
[[File:ANDY7187.jpg|thumb|A researcher working on an optical system|300x300px]]
{{TopicTOC-Physics}}

'''Optics''' is the branch of [[physics]] that studies the behaviour and properties of [[light]], including its interactions with [[matter]] and the construction of [[optical instruments|instruments]] that use or [[Photodetector|detect]] it.<ref name=McGrawHill>{{cite book|title=McGraw-Hill Encyclopedia of Science and Technology|edition=5th|publisher=McGraw-Hill|year=1993}}</ref> Optics usually describes the behaviour of [[visible light|visible]], [[ultraviolet]], and [[infrared]] light. Light is a type of [[electromagnetic radiation]], and other forms of electromagnetic radiation such as [[X-ray]]s, [[microwave]]s, and [[radio wave]]s exhibit similar properties.<ref name=McGrawHill />

Most optical phenomena can be accounted for by using the [[Classical electromagnetism|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. The most common of these, [[geometric optics]], treats light as a collection of [[Ray (optics)|rays]] that travel in straight lines and bend when they pass through or reflect from surfaces. [[Physical optics]] is a more comprehensive model of light, which includes [[wave]] effects such as [[diffraction]] and [[Interference (optics)|interference]] that cannot be accounted for in geometric optics. Historically, the ray-based model of light was developed first, followed by the wave model of light. Progress in electromagnetic theory in the 19th century led to the discovery that light waves were in fact electromagnetic radiation.

Some phenomena depend on light having both [[wave–particle duality|wave-like and particle-like properties]]. Explanation of these effects requires [[quantum mechanics]]. When considering light's particle-like properties, the light is modelled as a collection of particles called "[[photon]]s". [[Quantum optics]] deals with the application of quantum mechanics to optical systems.

Optical science is relevant to and studied in many related disciplines including [[astronomy]], various [[engineering]] fields, [[photography]], and [[medicine]] (particularly [[ophthalmology]] and [[optometry]], in which it is called physiological optics). Practical applications of optics are found in a variety of technologies and everyday objects, including [[mirror]]s, [[Lens (optics)|lenses]], [[optical telescope|telescopes]], [[microscope]]s, [[laser]]s, and [[fibre optics]].