The Nature of Light Light behaves both as a wave phenomenon and as discrete particles of energy called photons . Different wavelengths of light have different characteristic energies and properties. Light can also travel at various speeds in different media, producing a frequency at which the wave travels. The energy contained in a wave of light is related to its frequency.
Short wavelengths have high energies and long wavelengths have lower energies.
Molecules, when struck by a wave or photon of light, reflect some of its energy back out, or it can absorb the energy, and thus enter into a higher energy or excited state. Each molecule absorbs or reflects its own characteristic wavelengths of light. Molecules that have evolved to absorb wavelengths in the visible region of the spectrum very well are called pigments . An absorption spectrum for a particular pigment describes the wavelengths at which it can absorb light and enter into an excited state. And action spectrum closely follows an absorption spectrum for a particular pigment because the molecule has to be able to absorb light to enter into its excited state and pass the energy along.