SRI (Solar Reflectance Index)
We can provide you the SRI of your coatings from albedo and emissivity measurements
The SRI (Solar Reflectance Index) is an index to classify coatings (paints, coatings, …) according to their ability not to heat up under solar radiation.
ASTM E1980 is the standard method for calculating the Solar Reflectance Index (SRI) from albedo and emissivity.
The calculated SRI thus concerns the horizontal opaque surfaces with weak slope under standard conditions (sunshine, wind, …).
The method is intended to calculate SRI for surfaces with an emissivity greater than 0.1.
The principle is to classify from 0 to 100 the coatings.
The theoretical equilibrium temperature of a black paint is calculated with an index of 0 and a white paint with an index of 100.
The SRI is a grading proportional to the temperature of the coating under the same conditions.
The white paint of reference is an albedo painting equal to 80% (the albedo is the proportion of the solar flux reflected by the coating) and emissivity of 0.9.
The black paint of reference is an albedo painting equal to 5% and emissivity of 0.9.
To calculate the SRI must therefore know the albedo which is the solar reflection factor (calculated according to ASTM E903 for example) and the thermal emissivity, property that conditions radiation heat exchange.
WARNING ! The SRI can exceed the value of 100 for more reflective paints than the standard white paint, and can even be negative for black coatings or very low emissivity (such as metals for example).