反照率（albedo）通常是指物体反射太阳辐射与该物体表面接收太阳总辐射的两者比率或分数度量，也就是指反射辐射与入射总辐射的比值。

反照率 (英语发音：/ælˈbiːdoʊ/)或反射系数，是从拉丁文的“白反照”（"albedo whiteness"），或“反射的阳光”衍伸出来的，意思是漫反射或是表面反射的能力。

它是从表面反射辐射与入射辐射的比率，是无量纲量。其性质以百分比来表示，度量上从完全黑的表面反照率为0，至表面完美的白色反照率为1。

注解：因为它是以全部的反射辐射对入射辐射，所以包括漫反射和镜面反射。射辐射对入射辐射的它将包括弥漫性和镜面反射辐射反映。它们共同承担表面的反射，然而我们通常假设只有完全漫射或只有完全的镜面反射，以简化计算。

Albedo (/ælˈbiːdoʊ/) 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. NOTE: Since it is the ratio of all reflected radiation to incident radiation it will include the diffuse AND the specular radiation reflected. It is, however, common to assume a surface reflects in either a totally specular manner or a totally diffuse manner, as this can simplify calculations.