Absorption describes how the light incident on a surface is totally or partially absorbed depending on the absorption factor of the given material. In the construction of luminaires absorption is primarily used for shielding light sources; in this regard it is essential for visual comfort. In principle, however, absorption is not desirable since it does not direct but rather wastes light, thereby reducing the light output ratio of the luminaire. Typical absorbing elements on a luminaire are black multigroove baffles, anti-dazzle cylinders, barn doors or louvres of various shapes and sizes.