Discrete bundle of light energy. Light of a given energy (frequency) cannot be broken up indefinitely. Rather for a given frequency it comes in discrete bundles with energy (h = Planck’s constant and ν= frequency):
It is often useful to think of light as a bunch of particle photons; whereas, at other times it is useful to think of light as a Propagating disturbance which transmits energy from one point to another without physically transporting the oscillating quantity. A wave is characterized by wavelength and frequency.. This is termed the “Principle of quantum mechanics implying that light (and, indeed, all other subatomic particles) sometimes acts like a wave, and sometime acts like a particle, depending on the experiment being performed. For instance, low frequency electromagnetic radiation tends to act more like a wave than a particle; high frequency electromagnetic radiation.” The idea of the photon was advanced by Albert Einstein in his theory of the photoelectric effect.
Some or all content above used with permission from J. H. Wittke.