Double slit experiment. Light from a light bulb (left) is shone towards a plate (centre) containing two slits. The light that passes through the slits is observed on a screen behind the plate. This experiment shows that light exhibits the characteristics of both a wave and a particle, a phenomenon known as wave-particle duality. Each photon of light travels through one of the slits, as would be expected of a particle, but light from the two slits interfere, as expected of a wave.