Efficiency vs Efficacy

When deciding on what fixture to use, it is critically important to understand the difference between “efficiency” and “efficacy”.

• “Efficiency” is the percentage of light emitted from a light fixture and light source when energized.
• “Efficacy” is the amount of useable light from a source per unit of electrical measure, or Lumens/Watt.

Fixtures are designed for a variety of purposes and in a variety of ways; aesthetics, installation, unique application, and/or performance, but fixture efficiency is not always at the top of the list.

You could select a product whose efficacy is high, but which has a low efficiency, totally missing the light level target.  Or pick a highly efficient product whose available lumens are low and again, miss the light level target.

When choosing a lighting product, it is important to select one with the necessary lumens/watt and whose “efficiency” will work in concert to render the light levels you need on the work surface and or in the ambient.