Hi Kimya, thank you for your question.

Albedo, or solar reflectance, is a measure of the ability of a surface material to reflect sunlight (visible, infrared and ultraviolet wavelengths) on a scale of 0 to 1, calculated by a ratio of reflected solar energy to incoming solar energy.

Emissivity is the ratio of the radiation emitted by a surface to the radiation emitted by a blackbody both at the same temperature (think back to your physics class).

SRI is the measure of a material’s ability to reject solar heat, as shown by a small temperature rise. Standard black (reflectance 0.05, emittance 0.90) has an SRI of 0 and standard white (reflectance 0.80, emittance 0.90) has an SRI of 100.

A material with high visible reflectance has a low solar reflectance. Because of the way SRI is defined, particularly hot materials can even take slightly negative SRI values, and particularly cool materials can exceed 100 (per the Lawrencey Berkley National Laboratory Cool Roofing Materials Database).

Dark paving materials, like asphalt, generally have low reflectance and low SRI values. Gray or white concrete has a higher reflectance and higher SRI value. Note that it’s important to properly maintain gray or white concrete due to the fact that it will weather over time, and SRI will decrease. Typical pressure washing of cememtitious materials can restore reflectance close to original value. Emissivity, Reflectance and SRI for the standard paving materials discussed above are as follows:

Typical new gray concrete (gravel): Reflectance, 0.35 and SRI, 35.

Typical new white concrete: Reflectance, 0.7 and SRI, 86.

New asphalt: Reflectance, 0.05 and SRI, 0.

Related Advice:

• SRI to Albedo and Back: How do I Convert?