Luminous Efficacy (LE)
The ratio of visible light transmission to the shading coefficient. This value is determined by dividing the visible light transmission by the shading coefficient. For example, if a film has a visible light transmission of 70%, and a shading coefficient of .50, it would have a luminous efficacy of 1.40. The higher this number, the better the glazing system blocks the transmission of radiant heat rather than merely visible light. This ratio is used to determine "spectral selectivity." Any product with a luminous efficacy above 1.00 is considered "Spectrally Selective".