Lighting, LEDs & Electrical Fixtures calculator

Luminous Efficacy (Lumens Per Watt) Calculator

Calculate the luminous efficacy of an LED fixture or light source in lumens per watt (lm/W). Enter the fixture lumen output from photometric test data (LM-79) and the fixture input power in watts. The result gives efficacy in lm/W, which you can compare to DLC Premium minimums (typically 100 to 160 lm/W depending on product category), ENERGY STAR requirements, or your internal specification target.

What this calculator does

  • 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.
  • Use this when checking whether a fixture meets DLC Premium or ENERGY STAR efficacy thresholds, comparing efficacy across LED chip or driver combinations, evaluating a supplier's performance claims, or selecting between fixture options for a retrofit or new installation.
  • Turns fixture lumen output, fixture input power, efficacy scale factor into a ratio for luminous efficacy in lighting, leds and electrical fixtures.

Formula used

  • Luminous efficacy = fixture lumen output / fixture input power x scale factor
  • Result in lm/W: compare to DLC Premium minimums (typically 100 to 160 lm/W) and ENERGY STAR requirements

Inputs explained

  • Fixture lumen output: Measured total lumen output from the complete luminaire per your LM-79 photometric test report. Not the LED chip or module rating. Typical LED fixture range: 1,500 to 50,000 lm depending on wattage and type.
  • Fixture input power: Total watts consumed by the complete fixture at rated voltage, measured at the input (includes driver losses). Use LM-79 test data, not the nominal LED chip wattage.
  • Efficacy scale factor: Leave at 1 for standard lumens per watt. Set to 0.001 if you entered lumens in thousands (klm) to convert to lm/W correctly.

How to use the result

  • Use it when luminous efficacy in lighting, leds and electrical fixtures is being normalized for comparison.
  • Ratios hide absolute change; pair with the underlying counts when you present.

Common questions

  • How does this luminous efficacy calculator help my lighting, leds and electrical fixtures team? 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. You get a ratio you can defend before quoting, scheduling, or sign-off.
  • Where do I get the inputs for this lighting, leds and electrical fixtures calculator? fixture lumen output, fixture input power, efficacy scale factor usually move the ratio most. Pull from measured lighting, leds and electrical fixtures runs, supplier data, and recent quotes rather than memory.
  • How should I act on the output? Use the ratio in lighting, leds and electrical fixtures reporting or as a normalized score against another period.
  • What can throw the result off? Confirm both inputs are from the same time window and scope before you trust the ratio.

Last reviewed 2026-05-12.