In absorption, the frequency of the incoming light wave is at or near the energy levels of the electrons in the matter. The electrons will absorb the energy of the light wave and change their energy state.
There are several options that could happen next, either the electron returns to the ground state emitting the photon of light or the energy is retained by the matter and the light is absorbed. If the photon is immediately re-emitted, the photon is effectively reflected or scattered. If the photon energy is absorbed, the energy from the photon typically manifests itself as heating the matter up.
The absorption of light makes an object dark or opaque to the wavelengths or colors of the incoming wave:
Wood is opaque to visible light.
Some materials are opaque to some wavelengths of light, but transparent to others. Glass and water are opaque to ultraviolet light, but transparent to visible light.
By which wavelengths of light are absorbed by a material, the material composition and properties can be understood.
Light Absorption: Colour
Another manner in which the absorption of light is apparent is by their colour. If a material or matter absorbs light of certain wavelengths or colours of the spectrum, an observer will not see these colours in the reflected light. On the other hand, if certain wavelengths of colours are reflected from the material, an observer will see them and see the material in those colours. For example, the leaves of green plants contain a pigment called chlorophyll, which absorbs the blue and red colors of the spectrum and reflects the green - leaves therefore appear green.