Selectivity Index

Selectivity Index (IS) or Light to Solar gain (LGC) is the ratio of the visible light transmittance to the Solar Factor (FS). IS=Transmittance(Tvis)/FS

A higher LSG ratio means sunlight entering the room is more efficient for daylighting, especially for summer conditions where more light is desired with less solar gain. This ratio is the measurement used to determine whether the glazing is “spectrally selective.”