ABSTRACT
The energy from a light source can be considered as a stream of discrete particles – photons – or as a continuous stream of energy along a ray or wave. Both theories are equally valid, and together they form the ‘duality of light’ hypothesis. The concept of the photon is useful when considering light in terms of quantum physics, as used in the investigation of the origin of light and how light interacts with matter. Generally, the concept of the propagation of waves of light gives useful insight into classical optical phenomena and underpins the majority of visual optics.
