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Watts to lux calculator

Electric power in watts (W) to illuminance in lux (lx) calculator and how to calculate.

Enter the power in watts, luminous efficacy in lumens per watt, surface area in square feet / meters or spherical radius in feet / meters and press the Calculate button to get the illuminance in lux:

* the predefined luminous efficacy values are typical / average values.

Watts to lux calculation formula

Watts to lux calculation with area in square feet

The luminous flux Φ_V in lumens (lm) is equal to the power P in watts (W), times the luminous efficacy η in lumens per watt (lm/W):

Φ_V(lm) = P_(W) × η_(lm/W)

The illuminance E_v in lux (lx) is equal to 10.76391 times the luminous flux Φ_V in lumens (lm) divided by the surface area A in square feet (ft²):

E_v(lx) = 10.76391 × Φ_V(lm) / A_(ft2₎

So the illuminance E_v in lux (lx) is equal to 10.76391 times the power P in watts (W), times the luminous efficacy η in lumens per watt (lm/W) divided by the surface area A in square feet (ft²):

E_v(lx) = 10.76391 × P_(W) × η_(lm/W) / A_(ft2₎

lux = 10.76391 × watts × (lumens per watt) / (square feet)

lx = 10.76391 × W × (lm/W) / ft²

Example

What is the illuminance with power consumption of 60 watts, luminous efficacy of 15 lumens per watt and surface area of 200 square feet?

Φ_V = 10.76391 × 60 W × 15 lm/W / 200 ft² = 48.44 lx

Watts to lux calculation with area in square meters

The luminous flux Φ_V in lumens (lm) is equal to the power P in watts (W), times the luminous efficacy η in lumens per watt (lm/W):

Φ_V(lm) = P_(W) × η_(lm/W)

The illuminance E_v in lux (lx) is equal to the luminous flux Φ_V in lumens (lm) divided by the surface area A in square meters (m²):

E_v(lx) = Φ_V(lm) / A_(m2₎

So the illuminance E_v in lux (lx) is equal to the power P in watts (W), times the luminous efficacy η in lumens per watt (lm/W) divided by the surface area A in square meters (m²):

E_v(lx) = P_(W) × η_(lm/W) / A_(m2₎

lux = watts × (lumens per watt) / (square meters)

lx = W × (lm/W) / m²

Example

What is the illuminance with power consumption of 60 watts, luminous efficacy of 15 lumens per watt and surface area of 18 square meters?

Φ_V = 60 W × 15 lm/W / 18 m² = 50 lx

Luminous efficacy table

Light type	Typical luminous efficacy (lumens/watt)
Tungsten incandescent light bulb	12.5-17.5 lm/W
Halogen lamp	16-24 lm/W
Fluorescent lamp	45-75 lm/W
LED lamp	80-100 lm/W
Metal halide lamp	75-100 lm/W
High pressure sodium vapor lamp	85-150 lm/W
Low pressure sodium vapor lamp	100-200 lm/W
Mercury vapor lamp	35-65 lm/W

Energy saving lamps have high luminous efficacy (more lumens per watt).

Enter power in watts:
	W
Select light source

Or enter luminous efficacy in lumens per watt:
	lm/W
Enter surface area:

Or enter spherical radius:



Illuminance result in lux:
	lx

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