How is Luminous Efficacy used?
Incandescent light bulb manufacturers use luminous efficacy as an alternative to efficiency. Efficiency is a unitless ratio of input to output. Thus, efficiency for an incandescent light bulb can be calculated by dividing the output radiated radiometric energy in watts, by the electrical input energy. However, this does not give a good indication of how effective the incandescent bulb is at converting energy into visible light. Therefore, they define luminous efficacy as photometric light output in lumens divided by electrical input in watts. LED manufacturers use luminous efficacy to convert photometric lumens to radiometric watts. This conversion is necessary for all of our customers who don’t use the human eye as their detector, for example, blood analysis equipment, erase bars for copiers, fiber optic communications. An alternate would be to measure LED’s radiometrically. However, it is impractical to have two different measures for intensity. Therefore, because the majority of our
