Noun

(en noun)

(particle) The quantum of light and other electromagnetic energy, regarded as a discrete particle having zero rest mass, no electric charge, and an indefinitely long lifetime. It is a gauge boson.

* {{quote-magazine, year=2013, month=July-August, author= Fenella Saunders

, title= Tiny Lenses See the Big Picture, magazine=(American Scientist) , passage=The single-imaging optic of the mammalian eye offers some distinct visual advantages. Such lenses can take in photons from a wide range of angles, increasing light sensitivity. They also have high spatial resolution, resolving incoming images in minute detail.}}

Noun

(-)

(physics) Used attributively to describe a form of photoemission in which an electron in a metal is excited by a photon and subsequently tunnels out of the surface