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Percentage of diffusely reflected sunlight in relation to various surface conditions

Albedo ({{#invoke:IPAc-en|main}}), or reflection coefficient, derived from Latin albedo "whiteness" (or reflected sunlight) in turn from albus "white", is the diffuse reflectivity or reflecting power of a surface.

It is the ratio of reflected radiation from the surface to incident radiation upon it. Its dimensionless nature lets it be expressed as a percentage and is measured on a scale from zero for no reflection of a perfectly black surface to 1 for perfect reflection of a white surface.

Albedo depends on the frequency of the radiation. When quoted unqualified, it usually refers to some appropriate average across the spectrum of visible light. In general, the albedo depends on the directional distribution of incident radiation, except for Lambertian surfaces, which scatter radiation in all directions according to a cosine function and therefore have an albedo that is independent of the incident distribution. In practice, a bidirectional reflectance distribution function (BRDF) may be required to accurately characterize the scattering properties of a surface, but albedo is very useful as a first approximation.

The albedo is an important concept in climatology, astronomy, and calculating reflectivity of surfaces in LEED sustainable-rating systems for buildings. The average overall albedo of Earth, its planetary albedo, is 30 to 35% because of cloud cover, but widely varies locally across the surface because of different geological and environmental features.<ref>Environmental Encyclopedia, 3rd ed., Thompson Gale, 2003, ISBN 0-7876-5486-8</ref>

The term was introduced into optics by Johann Heinrich Lambert in his 1760 work Photometria.

Albedo sections
Intro  Terrestrial albedo  Astronomical albedo  Examples of terrestrial albedo effects  Other types of albedo  See also  References  External links  

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