Definition: Absorption of light; Absorb; Absorbing surface; Black card

Definition: Absorption of light; Absorb; Absorbing surface; Black card | Glossary entry

Absorption of light; Absorb; Absorbing surface

The absorption of light occurs when a ray of light strikes a surface. The energy from the light is transferred to the surface material. The transfer creates heat (usually small amounts). An absorbing surface prevents reflection or diffusion of light striking on the surface. In practice, perfect absorption does not exist. However, the surface of photographic absorbers are normally of low reflectivity as a result of texture and colour.

A highly absorbing surface, like the matt black of a blackboard, has a higher transfer of light to energy at the surface. Consequently the board will become warmer or hotter than the ambient temperature in strong direct sunlight. Equally a mirror with a very high reflection level will absorb very little energy and will remain close to the ambient temperature.

In photography absorbing boards, or matt black card sheets, are used to dampen the light in the region of a photographic subject. As the black surface does not reflect any light striking the surface, the card will dampen stray light preventing it relighting the immediate area. In photography this type of non-reflector is used for a variety of reasons. Black reflectors provide black outlines when photographing glass, intensifying the darker areas of a photograph and to prevent diffusion in a local area where lighting is used. This type of use of absorbing material is important mainly in studio or still life photography since any effects are extremely localised. However, in studios many pieces of photographic equipment are painted with matt black finish to prevent them affecting the local light conditions by causing erroneous reflection/diffusion which might be difficult to control.