Low-Emittance (Low-E) is a term used for a surface that radiates, or emits, low levels of radiant energy. Emittance refers to the ability of a materials surface to emit radiant energy. All materials absorb, reflect and emit radiant energy. Emissivity is the value given to materials based on the ratio of heat emitted compared to a blackbody, on a scale of 0 to 1. A blackbody would have an emissivity of 1 and a perfect reflector would have a value of 0. Reflectivity is inversely related to emissivity and when added together their total should equal 1. Therefore, if asphalt has an emissivity value of 0.90 its reflectance value would be 0.10. This means that it absorbs and emits 90% of radiant energy and reflects only 10%.
Conversely, a low-e coating such as Laser Gold has an emissivity value of 0.03 and a reflectance value of 0.97, meaning it reflects 97% of radiant energy and emits only 3%.