But I thought light was a particle ?
Light is both a particle and a wave, but it cannot be both simultaneously. Light reveals wave characteristics when we test for light as a wave.
Light exhibits particle characteristics when employed in demonstrating the photoelectric effect. This demonstration involves high frequency, high energy light ejecting electrons from a charged surface. This only occurs when high frequency light is employed. If light were a wave the continuous energy of any frequency of light would eventually eject the electron but this is not the case. Only high energy particles , therefore, could eject the electrons.