ASHRAE Terminology

A Comprehensive Glossary of Terms for the Built Environment
ashrae.org/ashraeterms

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reflectance

(1) portion of the incident radiation on a surface that is reflected from the surface. Note: for an opaque surface, the sum of the reflectance and the absorptance is unity at equilibrium. Absorptances and reflectances are of various types, as are emittances. (2) the ratio of the light reflected by a surface to the light incident upon it.