The Solar Reflectance Index(SRI) is a measure of a surface’s ability to reflect solar heat, as shown by a small temperature rise. It is defined so that a standard black surface (absorptance 0.95, emittance 0.90) is 0, and a standard white surface (absorptance 0.20, emittance 0.90) is 100. SRI is calculated according to the ASTM E1980-11 standard.

The SRI calculation can be used to estimate the surface temperature of a product under prescribed conditions. To calculate SRI, download the SRI Calculator and enter the solar absorptance value (α) and the thermal emittance value (ε) as decimals, then click on “Calculate”.

In order to calculate using solar reflectance (R), subtract 1 from the reflectance value to get the solar absorptance (α).

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