An LED Lesson: Efficacy

What is efficacy? Do I need to know this term when I purchase an LED fixture? Is it unique to LED? Do all colour temperatures produce the same efficacy?

When you measure the light output against the amount of consumption, you will find efficacy of a product. Here’s an example: A light source such as a light bulb, has an efficacy of output lumens divided by wattage. If it has 100 lumens output and 20 watts of consumption, your efficacy equals 5 Lumens per Watt or LPW. 100/20 = 5LPW.

Every type of electrical lighting products regardless of shape, size, or the source of light (CFL, MH, halogen, filament, or LED) uses the same equation to measure LPW.

In the LED world, knowing efficacy will allow you to purchase a product which has greater efficiency in terms of its output. But don’t count efficacy as your only reason to choose a light fixture. It is only a measurement to know the actual consumption vs lumens output.

In today’s LED market, you could find an average of 100 LPW for residential products and about 120-130 for commercial and industrial products. There is an important factor in measuring the LPW for every light fixture and that is knowing LPW of bulbs, tubes, or chips vs the consumption of the whole lighting system (such as a one or more fixture). Yes, you still need to add the power consumption of ballast, transformers, or drivers into your calculations!

Please consider system efficacy when you are calculating your LPW of a fixture which includes the light source and all the other ballasts or drivers that are needed to power up the fixture. Remember, it is only a measurement tool and there are other important considerations when choosing a new light fixture.

LPW is different for different colour temperatures. For instance, if a 100 Watts 5000 Kelvin (cool White) with 110 LPW makes 11,000 total lumens (100W * 110LPW = 11,000 total lumens) then it would most likely produce approx. 10% less lumens output. It would be about 10,000 lumens. Note that maximum lumens output does not always work in your benefit.

The above information is provided to you by our team at Kastor Energy. If you require greater clarification then leave a comment below or email us at

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