Editing Light (section)

===Electromagnetic theory===
{{Main|Electromagnetic radiation}}
[[File:Onde electromagnetique.svg|thumb|upright=1.8|A [[linear polarization|linearly polarized]] electromagnetic wave traveling along the z-axis, with E denoting the [[electric field]] and perpendicular B denoting [[magnetic field]]|400x400px]]

In 1845, [[Michael Faraday]] discovered that the plane of polarization of linearly polarized light is rotated when the light rays travel along the [[magnetic field]] direction in the presence of a transparent [[dielectric]], an effect now known as [[Faraday rotation]].<ref name="LongairMalcolm">{{cite book |last=Longair |first=Malcolm |title=Theoretical Concepts in Physics |url=https://archive.org/details/theoreticalconce00mslo |url-access=limited |year=2003 |page=[https://archive.org/details/theoreticalconce00mslo/page/n106 87]}}</ref> This was the first evidence that light was related to [[electromagnetism]]. In 1846 he speculated that light might be some form of disturbance propagating along magnetic field lines.<ref name="LongairMalcolm" /> Faraday proposed in 1847 that light was a high-frequency electromagnetic vibration, which could propagate even in the absence of a medium such as the ether.<ref>{{Cite book|title=Understanding Physics|last=Cassidy|first=D|publisher=Springer Verlag New York|year=2002}}</ref>

Faraday's work inspired [[James Clerk Maxwell]] to study electromagnetic radiation and light. Maxwell discovered that self-propagating electromagnetic waves would travel through space at a constant speed, which happened to be equal to the previously measured speed of light. From this, Maxwell concluded that light was a form of electromagnetic radiation: he first stated this result in 1862 in ''On Physical Lines of Force''. In 1873, he published ''[[A Treatise on Electricity and Magnetism]]'', which contained a full mathematical description of the behavior of electric and magnetic fields, still known as [[Maxwell's equations]]. Soon after, [[Heinrich Hertz]] confirmed Maxwell's theory experimentally by generating and detecting radio waves in the laboratory and demonstrating that these waves behaved exactly like visible light, exhibiting properties such as reflection, refraction, diffraction and [[Wave interference|interference]]. Maxwell's theory and Hertz's experiments led directly to the development of modern radio, radar, television, electromagnetic imaging and wireless communications.

In the quantum theory, photons are seen as [[wave packet]]s of the waves described in the classical theory of Maxwell. The quantum theory was needed to explain effects even with visual light that Maxwell's classical theory could not (such as [[spectral line]]s).