Light as a stream of particles
Albert Einstein (1879 - 1955) did an experiment on the photoelectric effect in 1905 that showed light as a stream of particles (photons). These particles were massless and each had an energy given by:
Note: Planck's constant, h, is 6.626 x 10(-34) joule-sec and it comes from an important experiment on black body radiation performed in 1900 by Max Planck (1858 - 1947).
Thus the dual nature of light; it can be modeled as a wave (Young's experiment) or a particle (Einstein's experiment).