What is light?

Light is electromagnetic (EM) radiation. In physics it is a form of oscillating electric and magnetic fields that propagates as waves. Visible light is just one band (≈380–700 nm) of the EM spectrum. However, all wavelengths of EM radiation are "light" in the general sense. Quantum-mechanically, light also consists of photons – massless particles carrying quanta of EM energy (E=hf) that travel at speed c. Thus light has a dual wave-particle nature. In practical terms, light carries energy and information; it is how we see (visible photons hitting our eyes) and how stars, lamps and screens transmit images. It travels in straight lines in empty space and can be reflected, refracted, or absorbed by matter.