IESNA Definition: the ratio of the reflected flux to the incident flux.

Reflectance values express the percentage of light that is reflected back from a surface, the difference having been absorbed or transmitted by the surface. Reflectances of room surfaces are used in determining coefficient of utilization values for luminaires. Reflectance is also commonly used as an evaluation criterion for luminaire reflectors.

The reflectance of this translucent piece of glass is 80%. Note that the angle of the incoming ray is the same as the angle of the reflected ray.

Some typical reflectance values for room surfaces are:

Room Surface Reflectance Value
white acoustic-tiled ceilings 70 to 80%
light-colored walls 40 to 60%
carpeting 15 to 30%

Some typical reflectance values for luminaire reflectors are:

Luminaire Reflector Reflectance Value
high-quality white paint 90%
silver film 95%
highly reflective aluminum 85%
enhanced reflective aluminum 95%

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Glossary Terms: coefficient of utilization, flux, IESNA