What is lighting Efficacy?

Efficacy is a measure of how much light a light source produces for the energy put in to it. This is normally expressed in lm/W (lumens per watt). With LED sources, efficacy is advancing at a rate of roughly double every 3 years although (as with lumen degradation) this varies with drive current and temperature. Like most markets, there is a wide variety of quality and cost - efficacy is one of the most important parameters in selecting an LED light fitting. High end products can reach around 150 lm/W or even higher whereas typically the budget end of the market can be as low as 70 or 80 lm/W, meaning that they are around half the efficiency of their premium counterparts!