How do you calculate luminous efficacy?

Divide fixture lumen output by input power in watts, then apply any scale factor. A 12,000 lm fixture drawing 100 W has an efficacy of 120 lm/W.

What is a good lm/W for an LED fixture?

DLC Premium minimums generally run 100-160 lm/W depending on category. At 120 lm/W, this fixture clears most Premium thresholds and far exceeds legacy HID at 60-90 lm/W.

What's the difference between fixture and LED chip efficacy?

Chip efficacy is measured at the diode; fixture efficacy accounts for driver losses and optics, so it's always lower. Always spec on fixture (luminaire) efficacy for accurate comparisons.

Why does my fixture's real efficacy drop over time?

LEDs depreciate, often quoted as L70 (70% of initial output at end of life), and heat reduces output. This calculator uses rated initial values, so derate for field and end-of-life planning.

How does efficacy compare across light sources?

Incandescent sits near 15 lm/W, HID 60-90, fluorescent 80-100, and modern LED 100-180+. The 120 lm/W here represents a solid current-generation LED fixture.

What is the scale factor for?

It applies a multiplier for unit conversions or to adjust rated output to a field-corrected value. Leave it at 1 to report the straight rated efficacy.

Lighting, LEDs & Electrical Fixtures calculator

Luminous Efficacy (Lumens Per Watt) Calculator

Luminous efficacy measures how efficiently a fixture turns electrical watts into usable lumens, expressed in lumens per watt. Lighting designers, spec engineers, and procurement teams use it to compare fixtures, qualify products against DLC and ENERGY STAR thresholds, and predict the energy savings of a retrofit. A higher lm/W means more light for the same wattage, which is the single number that drives both rebate eligibility and lifetime operating cost. The scale factor lets you adjust for test-vs-field conditions or unit conversions without redoing the math.

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.
It computes fixture luminous efficacy in lumens per watt from rated lumen output and input power, with an optional scale factor.

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:
Fixture input power:
Efficacy scale factor:

How to use the result

Use it to compare fixtures, check DLC Premium or ENERGY STAR qualification, or estimate the efficiency gain of a retrofit.
It uses rated output, so it doesn't account for in-fixture optical losses, thermal derating over time, or LED lumen depreciation across the product's life.

Current U.S. benchmarks

The producer price index for copper and brass mill shapes stands at 559.593 (BLS, May 2026), up 76.8% from a year earlier. Quotes priced off last quarter's material cost miss this move. Global copper trades at $13,484 per tonne (IMF via FRED, May 2026).
Industrial electricity averages 8.66 cents per kWh across the U.S. (EIA, Apr 2026), up 5.5% from a year earlier. Energy-intensive steps carry this directly into unit cost.
The U.S. has 5,397 electrical equipment and appliances establishments employing about 369,437 workers (Census County Business Patterns, 2023).

Common questions

How do you calculate luminous efficacy? Divide fixture lumen output by input power in watts, then apply any scale factor. A 12,000 lm fixture drawing 100 W has an efficacy of 120 lm/W.
What is a good lm/W for an LED fixture? DLC Premium minimums generally run 100-160 lm/W depending on category. At 120 lm/W, this fixture clears most Premium thresholds and far exceeds legacy HID at 60-90 lm/W.
What's the difference between fixture and LED chip efficacy? Chip efficacy is measured at the diode; fixture efficacy accounts for driver losses and optics, so it's always lower. Always spec on fixture (luminaire) efficacy for accurate comparisons.
Why does my fixture's real efficacy drop over time? LEDs depreciate, often quoted as L70 (70% of initial output at end of life), and heat reduces output. This calculator uses rated initial values, so derate for field and end-of-life planning.
How does efficacy compare across light sources? Incandescent sits near 15 lm/W, HID 60-90, fluorescent 80-100, and modern LED 100-180+. The 120 lm/W here represents a solid current-generation LED fixture.

Last reviewed 2026-05-12.