Definitions
Visible light transmittance - The percent of visible light that passes through a glazing system
Ultraviolet (UV) rejection - The percent of total ultraviolet light that is rejected from passing through a glazing system
Visible light reflectance - The percent of total visible light that is reflected by a glazing system

Percent of total solar energy rejected - The percent of incident solar energy (heat) rejected by a glazing system. Equals solar reflectance plus the part of solar absorption which is re-radiated
Total solar reflectance - The percent of incident solar radiation that is reflected by a glazing system
Total solar absorptance - The percent of incident solar radiation that is absorbed through a glazing system
Total solar transmittance - The percent of incident solar radiation that passes directly through a glazing system
Shading coefficient - The ratio of the solar heat gain to that of a single double pane glass.
Solar heat gain coefficient - The ratio of the solar heat gain entering the space through the glazing system to the incident solar radiation. Solar heat gain includes directly transmitted solar heat and absorbed solar radiation which is then re-radiated, conducted, or convected into the space
U-factor - The overall coefficient of heat transfer by conduction. Equals the reciprocal of the R-value. The lower the U-factor, the better the insulating qualities of the glazing system.
Emissivity - A measure of the ability of a product to reflect long wave radiant energy. The lower the emissivity, the better the insulating qualities of the glazing system
Luminous Efficacy - The ratio of daylight transmission to solar heat transmission which passes through a glazing system. This is determined by dividing the visible light transmittance by the shading coefficient. It indicates how much of the transmitted solar energy is useful visible light rather than heat.