Light as a fundamental particle

Arguments are provided in favour of treating electrodynamics and optics on the basis of a photon as one of elementary particles possessing specific quantum numbers - unit spin and zero mass. On the other hand it is shown that a reverse approach is more fruitful, which assumes gauge invariance to be a fundamental symmetry of the Nature. An idea of the generalized gauge invariance involving electromagnetic, weak, and, possibly, strong interactions is discussed. Under the approach a photon is treated as a member of a corresponding vector field set