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.