This velocity is so nearly that of light, that it seems we have strong reason to conclude that light itself (including radiant heat, and other radiations if any) is an electromagnetic disturbance in the form of waves propagated through the electromagnetic field according to electromagnetic laws.

James Clerck Maxwell, A Dynamical Theory of the Electromagnetic Field (1864), §20

UNESCO declared 2015 the International Year of Light. The opening ceremony will be in held in Paris on January 19th and 20th. The website has a very interesting overview of applications, basic definitions and much more!