# 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:

 Enter power in watts: W Select light source -- select light source -- Tungsten incandescent light bulb Halogen lamp Fluorescent lamp LED lamp Metal halide lamp High pressure sodium vapor lamp Low pressure sodium vapor lamp Mercury vapor lamp Or enter luminous efficacy in lumens per watt: lm/W Enter surface area: ft² m² Or enter spherical radius: ft m Illuminance result in lux: lx

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

Related

### Watts to lux calculation with area in square feet

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

ΦV(lm) = P(W) × η(lm/W)

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

Ev(lx) = 10.76391 × ΦV(lm) / A(ft2)

So the illuminance Ev 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):

Ev(lx) = 10.76391 × P(W) × η(lm/W) / A(ft2)

So

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

or

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?

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

### Watts to lux calculation with area in square meters

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

ΦV(lm) = P(W) × η(lm/W)

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

Ev(lx) = ΦV(lm) / A(m2)

So the illuminance Ev 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):

Ev(lx) = P(W) × η(lm/W) / A(m2)

So

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

or

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?

ΦV = 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).