Solar Reflective Index (SRI)

What Does Solar Reflective Index (SRI) Mean?

The solar reflective index (SRI) is a measure of the solar radiation that is reflected back by a rooftop surface (or any other surface in question) and the emissivity of the surface. It is an indicator of how hot the surface will become when the sun's radiation falls directly on it.

The heat absorbed by the surface is inversely proportional to the SRI, so a material with a lower SRI is likely to become hotter in the sun (i.e., it absorbs more heat and has a low reflecting power). Conversely, we can say that the reflectivity of a material is directly proportional to its SRI. The SRI of any material is measured on a scale of 0 to 100.

A solar reflective index is a specific case of the more general term refractive index.

Corrosionpedia Explains Solar Reflective Index (SRI)

In the construction industry and process industries (e.g., power plants, oil refineries, petrochemical plants) where equipment is exposed to the sunlight and other environmental conditions, it is desirable for the coatings on buildings and equipment to reflect the sun's infrared radiation to keep the temperature of the building or equipment at an acceptable level.

Coating materials with a high solar reflective index (SRI) value keep the surface cooler. Spectrophotometric instruments are used to measure the solar reflectance of a material.