Light has a dual nature.
It behaves as particles sometimes, as shown by the phenomena of Black Body Radiation and Photo Electric Effect, the experiments by J.J. Thompson and Mullikan and the scintillation produced when an electron strikes a ZnS screen.
It also behaves as a particle and shown by Davisson and Germer's Experiments of electron diffraction using a nickel crystal, and Goldstein's electron diffraction using a gold foil.
This might also be interesting: from http://www.thespectroscopynet.com/Educational/wave_particle_duality.htm
Is light a wave or a particle? The apparent dual nature of light is easily demonstrated:
1. Stand outside in the sun. The shadow your body makes in sunlight suggests that light travels in straight lines from the sun and is blocked by your body. In this, light behaves like a collection of particles fired from the sun.
2. Place two sheets of glass together with a little water between them. With care, you will see fringes. These are formed by the interference of waves.
In 1925, our understanding of light seemed to have come to an impasse. Particle theory could explain reflection and refraction, and recent experiments in radiation (such as the radiation from hot bodies and the Compton experiment with X-rays). And wave theory could explain the interference and polarization of light which particle theory could not. Thus simple and sophisticated experiments both indicated that light could be a particle sometimes and a wave at others.
Albert Einstein (1924) expressed the dilemma:
There are therefore now two theories of light, both indispensable, and - as one must admit today in spite of twenty years of tremendous effort on the part of theoretical physicists - without any logical connections.(1)
The dilemma prompted Neils Bohr (1928) to offer his 'complementarity principle': that particle theory and wave theory were equally valid. Scientists should simply chose whichever theory worked better in solving their problem. While it got physics out of its immediate hole, coming from someone as important in modern physics as Bohr, it gained a dominance in physics teaching probably never intended.
Over the succeeding years, the currently accepted solution came in the form of the 'quantised electromagnetic field theory', i.e. 'quantum electrodynamics' (QED). The theory merges particle and wave properties into a unified whole. Despite this, the undergraduate physics of light is still often taught as separate chapters on particles and waves with little or no attempt to give an overall understanding of how this can be so. The complementarity principle is still used in books on optics to justify the use of wave theory to explain interference, polarization, diffraction, etc. The student is then left with the impression either that we do not really understand the true nature of light or that physics is simply a collection of tools for solving problems.