Lighting, LEDs & Electrical Fixtures worked example

Luminous Efficacy with fixture lumen output of 6,000 lm: a worked example

Suppose fixture lumen output falls to 6,000 lm. This page works the full calculation at that level so you can see exactly which result moves and by how much. Calculate luminous efficacy in lumens per watt for an LED fixture or light source. Compare efficacy to DLC, ENERGY STAR, or internal specification targets to evaluate energy performance and product qualification readiness.

The inputs for this scenario

  • Fixture lumen output: 6,000 lm (the input this scenario stresses; the baseline uses 12,000)
  • Fixture input power: 100 W (held at the documented default)
  • Efficacy scale factor: 1 x (held at the documented default)

Working through the calculation

  • The calculation starts from the formula this tool documents: Luminous efficacy = fixture lumen output / fixture input power x scale factor.
  • Luminous efficacy (lm/W) works out to 60 lm/W at these inputs, and this is the headline figure for the scenario.
  • Lm/W before scale factor works out to 60 value at these inputs.
  • Conversion factor works out to 1 x at these inputs.
  • Fixture input power (W) works out to 100 value at these inputs.

How this compares with the baseline

  • Against the tool's baseline example, where fixture lumen output sits at 12,000 lm and the headline result is 120 lm/W, this scenario comes in 50% below the baseline at 60 lm/W.
  • It computes fixture luminous efficacy in lumens per watt from rated lumen output and input power, with an optional scale factor. When the numbers land here, the stressed input is the lever to work; the walkthrough above shows exactly how much each output recovers as it climbs back toward the baseline.

Results at a glance

  • Luminous efficacy (lm/W): 60 lm/W (headline result)
  • Lm/W before scale factor: 60 value
  • Conversion factor: 1 x
  • Fixture input power (W): 100 value

Run it with your numbers

  • To rerun this with your own numbers, open the live Luminous Efficacy calculator, set fixture lumen output to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.