He proposed that light was emitted only in tiny bundles. Planck was trying to explain the way certain substances give off light.
Light is the movement of energy through space in the form of electromagnetic waves.
These electromagnetic waves, of which light is but one type, are caused by certain motions of tiny, negatively charged particles called electrons, which generally surround the dense core, or nucleus, of an atom. Only whole quanta can be given off, never a fraction of a quantum. The energy of these quanta varies directly with the frequency of the light. Energetic light of higher frequency, such as violet or ultraviolet light, consists of higher-energy quanta than does light of lower frequency, such as red or infrared light. Planck made some calculations of the relation between energy and frequency of a light quantum.