#There are some kinds of photons that we cannot see – for example heat radiation, X rays, infra-red and ultra-violet rays. We say that light travels as a wave and different coloured lights have different wave-length associated with them. | #There are some kinds of photons that we cannot see – for example heat radiation, X rays, infra-red and ultra-violet rays. We say that light travels as a wave and different coloured lights have different wave-length associated with them. |