Lux to Watts Calculator
Enter target illuminance, illuminated area, and the light source efficacy. The estimate uses P = E × A ÷ η.
Estimated power: W
Formula: P = E × A ÷ η
Estimate only; assumes uniform illuminance and includes the entered system efficacy.
A QUICK WALKTHROUGH
How to use this tool
- Enter target illuminance in lux (lx).
- Enter the illuminated area in square metres.
- Enter luminous efficacy in lumens per watt (lm/W), then calculate estimated watts.
A direct lux-to-watts conversion needs assumptions
Lux measures illuminance on a surface, while watts measure electrical power. Area and luminous efficacy are required to connect them; there is no fixed unit-only conversion.
Idealized lighting estimate
This calculator assumes the target illuminance is uniform across the entered area and that the entered luminous efficacy represents the complete lighting system. It does not model beam distribution, mounting height, reflectance, maintenance factor, control gear, or standby losses.
Formula
P = E × A ÷ η, where P is estimated electrical power in watts, E is illuminance in lux, A is illuminated area in square metres, and η is luminous efficacy in lumens per watt.
GOOD TO KNOW
Common questions
Why do I need luminous efficacy?
Luminous efficacy relates visible luminous flux to electrical power. Different lamps and complete fixtures produce different lumens per watt, so the result depends on the value you enter.
Does this predict my fixture wattage?
It is a planning estimate for the stated area and target lux. Real installations can require more power because of optical, room, control, and maintenance losses.