Watts to Lux Calculator

Find illuminance from electrical power and luminous efficacy.

Power (W)

Luminous efficacy (lm/W)

Illuminated area

Illuminance (lx) 160

Luminous flux (lm) 800

Formula: lux = watts · efficacy ÷ area

Step-by-step with your numbers:

1. Values used:

2. Power = 10 W

3. Luminous efficacy = 80 lm/W

4. Illuminated area = 5

6. Power x Luminous efficacy = 10 x 80 = 800

7. Illuminance = (Power x Luminous efficacy) / Illuminated area = 800 / 5 = 160lx

8. Luminous flux = Power x Luminous efficacy = 10 x 80 = 800lm

Did we solve your problem today?

Convert a light's electrical power to illuminance using its efficiency.

The math behind it

Lumens = watts × efficacy; lux = lumens ÷ area. LED efficacy is typically 80–120 lm/W.

10 W LED at 80 lm/W over 5 m² → 160 lux.

What is luminous efficacy?

Visible light output per watt — higher means a more efficient lamp.