Watts to lux calculator
Estimate illuminance in lux (lx) based on power consumption in watts (W). Perfect for assessing the level of illumination provided by a light source. Obtain an estimation of lux from watts using this convenient online tool.
* the predefined luminous efficacy values are typical / average values.
What is Watts to lux
Converting watts (W) to lux (lx) is not a straightforward conversion because lux measures illuminance, which is the amount of light falling on a surface, while watts measure power consumption or the amount of electrical power used by a device.
The illuminance or lux level depends on various factors such as the distance from the light source, the distribution of light, and the properties of the surface being illuminated. Therefore, converting watts to lux requires additional information about the specific lighting setup.
To estimate the illuminance in lux based on the power consumption in watts, you would need to consider the efficiency or efficacy of the light source, the beam angle, and the distance between the light source and the surface.
Generally, the formula for calculating illuminance in lux is:
Lux (lx) = (Luminous Flux in Lumens) / (Area in square meters)
The luminous flux, measured in lumens, represents the total amount of visible light emitted by the light source. The area refers to the surface being illuminated.
To get accurate results, it is recommended to consult the manufacturer's specifications for the light source, which may provide information about the efficacy, beam angle, and other relevant factors. Additionally, considering [Network Error]
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 (ft^{2}):
E_{v(lx)} = 10.76391 × Φ_{V(lm)} / A_{(ft}2_{)}
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 (ft^{2}):
E_{v(lx)} = 10.76391 × P_{(W)} × η_{(lm/W)} / A_{(ft}2_{)}
So
lux = 10.76391 × watts × (lumens per watt) / (square feet)
or
lx = 10.76391 × W × (lm/W) / ft^{2}
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 ft^{2} = 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 (m^{2}):
E_{v(lx)} = Φ_{V(lm)} / A_{(m}2_{)}
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 (m^{2}):
E_{v(lx)} = P_{(W)} × η_{(lm/W)} / A_{(m}2_{)}
So
lux = watts × (lumens per watt) / (square meters)
or
lx = W × (lm/W) / m^{2}
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 m^{2} = 50 lx
Luminous efficacy table
Light type  Typical luminous efficacy (lumens/watt) 

Tungsten incandescent light bulb  12.517.5 lm/W 
Halogen lamp  1624 lm/W 
Fluorescent lamp  4575 lm/W 
LED lamp  80100 lm/W 
Metal halide lamp  75100 lm/W 
High pressure sodium vapor lamp  85150 lm/W 
Low pressure sodium vapor lamp  100200 lm/W 
Mercury vapor lamp  3565 lm/W 
Energy saving lamps have high luminous efficacy (more lumens per watt).
Watts to lux calculator Example
Let's say you have a light source with a power consumption of 60 Watts (W) and you want to calculate the illuminance in Lux (lx) at a certain distance.

Find out the luminous efficacy of the light source. Let's assume it is 80 lumens per Watt (lm/W).

Determine the luminous flux (lm) of the light source by multiplying the power consumption (60 W) by the luminous efficacy (80 lm/W): Luminous Flux (lm) = Power Consumption (W) × Luminous Efficacy (lm/W) Luminous Flux (lm) = 60 W × 80 lm/W = 4800 lm

Measure the distance (in meters) between the light source and the surface where you want to calculate the illuminance. Let's assume it is 3 meters (m).

Calculate the illuminance (lx) using the formula: Illuminance (lx) = Luminous Flux (lm) / (Distance (m))^2 Illuminance (lx) = 4800 lm / (3 m)^2 = 4800 lm / 9 m^2 ≈ 533.33 lx
Therefore, at a distance of 3 meters from the light source, the illuminance would be approximately 533.33 lux.
Keep in mind that the actual illuminance may vary based on various factors such as beam angle, light distribution, and environmental conditions. The given example assumes a point light source and does not consider any losses due to factors like reflection or absorption.