AskDefine | Define albedo

Dictionary Definition

albedo n : the ratio of reflected to incident light [syn: reflective power]

User Contributed Dictionary



  1. In the context of "physics|meteorology|astronomy": The fraction of incident light or radiation reflected by a surface or body, commonly expressed as percentage.
  2. In the context of "biology": The whitish inner portion of the rind of citrus fruits that is a source of pectin.

Usage notes

Albedo is to be distinguished from reflectivity, which refers to one specific wavelength (monochromatic radiation).


Extensive Definition

The albedo of an object is the extent to which it diffusely reflects light from the sun. It is therefore a more specific form of the term reflectivity. Albedo is defined as the ratio of diffusely reflected to incident electromagnetic radiation. It is a unitless measure indicative of a surface's or body's diffuse reflectivity. The word is derived from Latin albedo "whiteness", in turn from albus "white". The range of possible values is from 0 (dark) to 1 (bright).
The albedo is an important concept in climatology and astronomy. In climatology it is sometimes expressed as a percentage. Its value depends on the frequency of radiation considered: unqualified, it usually refers to some appropriate average across the spectrum of visible light. In general, the albedo depends on the direction and directional distribution of incoming radiation. Exceptions are Lambertian surfaces, which scatter radiation in all directions in a cosine function, so their albedo does not depend on the incoming distribution. In realistic cases, a bidirectional reflectance distribution function (BRDF) is required to characterize the scattering properties of a surface accurately, although albedos are a very useful first approximation.

Terrestrial albedo

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