This approximation captures essence of the [[Radiative transfer|radiative transport]] in light scattering atmosphere.<ref name=meador80a>W.E. Meador and W.R. Weaver, 1980, Two-Stream Approximations to Radiative Transfer in Planetary Atmospheres: A Unified Description of Existing Methods and a New Improvement, 37, Journal of the Atmospheric Sciences, 630–643
http://amsjournals.allenpressametsoc.comorg/archivedoi/1520-0469pdf/3710.1175/3/pdf/i15201520-0469-37-3-630%281980%29037%3C0630%3ATSATRT%3E2.pdf0.CO%3B2</ref> Two-stream approximation is commonly used in parameterizations of radiative transport in [[Global climate model|global circulation models]] and in weather forecasting models such as [[Weather Research and Forecasting model|WRF]]. There is a surprisingly large number of applications of the two-stream approximations, including variants such as [[Kubelka-Munk approximation]]. The two-stream approximation is the simplest approximation which can be used to explain common observation inexplicable by single-scattering arguments, such as the brightness and color of the clear sky, the brightness of clouds, the whiteness of a glass of milk, the darkening of sand upon wetting.<ref>Bohren, Craig F., 1987, Multiple scattering of light and some of its observable consequences, American Journal of Physics, 55, 524-533.</ref> The two-stream approximation comes in many variants, including [[Radiative_transfer#The_Eddington_approximation|Eddington approximation]], Modified Eddington, Quadrature, Hemispheric constant models.<ref name=meador80a/> Modern mathematical description of the two-stream approximation is given in several books.<ref>{{cite book|author=G. E. Thomas and K. Stamnes|title=Radiative Transfer in the Atmosphere and Ocean|publisher=Cambridge University Press.|year=1999|isbn=0-521-40124-0}}</ref>
<ref>{{cite book|title=A First Course In Atmospheric Radiation (2nd Ed.)|author=Grant W. Petty|publisher=Sundog Publishing, Madison, Wisconsin|year=2006|ISBN=10: 0-9729033-1-3}}</ref>
