reflectance, ρ

Fraction of incident radiation reflected by a surface or discontinuity, $ρ λ = P λ refl P λ 0$ , where $P λ 0$ and $P λ refl$ are, respectively, the incident and reflected spectral radiant power.

Note:

The reflectance for a beam of light normally incident on a surface separating two materials of refractive indices $n 1$ and $n 2$ is given by

$ρ λ = ( n 1 − n 2 ) 2 ( n 1 + n 2 ) 2$

Reflectance increases as the angle of incidence decreases from 90 degrees.

Source:

PAC, 2007, 79, 293 (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 413

reflectance, $ρ$

Also contains definitions of: reflectance factor, reflectivity