Lumens to Watts / Lux to Footcandles Converter
Convert lumens to watts, watts to lumens, lux to footcandles, and calculate illuminance from area.
Compare LED, CFL, halogen, and incandescent bulb efficiency.
Lighting Measurements — What Each Unit Means
Understanding lighting requires distinguishing between how much light is produced and how much falls on a surface.
Luminous Flux (Lumens) Lumens (lm) measure the total amount of visible light emitted by a source in all directions. A candle produces about 12 lumens. A 60W incandescent bulb produces about 800 lumens.
Power (Watts) Watts measure electrical energy consumed per second. Comparing lumens to watts gives you the luminous efficacy — how efficiently the bulb converts electricity to light.
Luminous Efficacy Efficacy (lm/W) = Lumens ÷ Watts. Higher is better:
- Incandescent: 10–15 lm/W (most energy becomes heat)
- Halogen: 15–20 lm/W
- Compact Fluorescent (CFL): 45–75 lm/W
- LED: 80–120 lm/W (typical modern LED)
- High-Efficiency LED: up to 200 lm/W (laboratory conditions)
- HID (High Intensity Discharge): 80–150 lm/W
Illuminance — Lux and Footcandles Illuminance measures how much light actually falls on a surface.
- Lux (lx): lumens per square meter. The SI unit.
- Footcandles (fc): lumens per square foot. Used primarily in the United States.
- Conversion: 1 footcandle = 10.764 lux (exactly).
Lumens from Area Illuminance (lux) = Luminous flux (lumens) ÷ Area (m²) Rearranging: Lumens = Lux × Area (m²)
Inverse Square Law For a point source of light: Illuminance = Luminous Intensity / distance². Doubling the distance reduces illuminance to one quarter.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.