The total lumens emitted by a light source divided by the total lamp power input, expressed as lumens per watt.
(Light-to-Shading Coefficient Ratio) The visible transmittance of a glazing system divided by the shading coefficient. This ratio is helpful in selecting glazing products for different climates in terms of those that transmit more heat than light and those that transmit more light than heat. Also referred to as the Coolness Factor.
The light output (lumens) of a light source divided by the total power input (watts) to that source. It is expressed in lumens per watt.
Luminous efficacy is a property of light sources, which indicates what portion of the emitted electromagnetic radiation is usable for human vision. It is the ratio of emitted luminous flux to radiant flux. Luminous efficacy is related to the overall efficiency of a light source for illumination, but the overall lighting efficiency also depends on how much of the input energy is converted into electromagnetic waves (whether visible or not).