Interaction of light with matter, microscopic particles of which matter is essentially composed of photons, or absorb radiation at the same time to change the condition of their sports performance.

Microscopic particles has a specific set of energy levels (usually) of these energy levels are discrete. Any moment particle only in correspond to a certain level

The law of the interaction between matter and light

State (or simply expressed as at a certain level). Interact with photons, the particles from one energy level transition to another level, and accordingly the photons or absorb radiation. Photon energy for this two level of energy difference delta E, frequency of argument = delta E/h (h is Planck's constant)