Radiant energy from the sun having a wavelength range of 300 to 4000 nm, which includes UV (300 to 380 nm), visible light (380 to 780 nm) and near infrared energy (780 nm to 4000 nm).
- % Reflectance Out = percentage of incident solar energy directly reflected from the glass back outdoors
- % Absorbance = percentage of incident solar energy absorbed into the glass
- % Transmittance = percentage of incident solar energy directly transmitted through the glass
The sum of percent reflectance out + absorbance out + transmittance = 100%. This is commonly referred to as the RAT equation.
An additional consideration is emission, or emissivity. This refers to the irradiation of absorbed energy that can be emitted toward both the exterior and interior of the building.
Emissivity is controlled through the use of low-emissivity, or low-E coatings.