Dear Reader:

If you were to read the literature, it seems the industry throws around two terms almost as if they were interchangeable – efficacy and efficiency – when, in fact, they mean two very different things.

Efficacy is the measure of the overall lighting fixture, simply the amount of work it provides (lumens) divided by its input wattage. It is similar to the miles per gallon measurement in the auto industry, whereby both the miles, and gallons, relate to the output and input of the entire vehicle. Lumens per watt for LED fixtures are now upwards of 150 typically, and with some – more expensive products – they can be north of 200.

Efficiency is the measure of what percentage of the lumens generated by the lumenaire actually exits the fixture, to be delivered to the workspace.

Any of a number of things can impact a fixture’s efficiency, including its housing design, materials selected, the...