# Lux to watts calculator

Estimate power consumption (watts) based on illuminance in lux (lx). Ideal for energy efficiency assessments, lighting comparisons, and electrical planning. Obtain an estimation of wattage from lux using this practical online tool.

 Enter illuminance in lux: lx 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 Power  result in watts: W

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

Related

## What is Lux to watts

Converting lux (lx) to watts (W) is not a direct conversion because lux measures illuminance (the amount of light falling on a surface), while watts measure power consumption (the amount of electrical power used by a device).

The relationship between lux and watts depends on various factors, including the efficiency of the light source and the area being illuminated. Different light sources have different levels of efficacy in converting electrical power into visible light.

Therefore, it is not possible to directly convert lux to watts without additional information about the specific light source being used.

To estimate the power consumption in watts based on illuminance, you would need to consider the efficiency or efficacy of the light source. This information is typically provided by the manufacturer and can be found in the specifications or datasheet of the light source.

It's important to note that the conversion from lux to watts is an estimation and may vary depending on factors such as the type of light source, its efficiency, and other environmental conditions.

To get a more accurate estimation, it is recommended to consult the manufacturer's specifications or seek professional advice specific to the light source you are using.

## Lux to watts calculation formula

### Lux to watts calculation with area in square feet

The luminous flux ΦV in lumens (lm) is equal to 0.09290304 times the illuminance Ev in lux (lx) times the surface area A in square feet (ft2):

ΦV(lm) = 0.09290304 × Ev(lx) × A(ft2)

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

P(W) = ΦV(lm) / η(lm/W)

So the power P in watts (W) is equal to the 0.09290304 times the illuminance Ev in lux (lx) times the surface area A in square feet (ft2), divided by the luminous efficacy η in lumens per watt (lm/W):

P(W) = 0.09290304 × Ev(lx) × A(ft2) / η(lm/W)

So

watts = 0.09290304 × lux × (square feet) / (lumens per watt)

or

W = 0.09290304 × lx × ft2 / (lm/W)

### Example

What is the power consumption with illuminance of 50 lux, luminous efficacy of 15 lumens per watt and surface area of 200 square feet?

P = 0.09290304 × 50 lx × 200 ft2 / 15 lm/W = 61.94 W

### Lux to watts calculation with area in square meters

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

ΦV(lm) = Ev(lx) × A(m2)

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

P(W) = ΦV(lm) / η(lm/W)

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

P(W) = Ev(lx) × A(m2) / η(lm/W)

So

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

or

W = lx × m2 / (lm/W)

### Example

What is the power consumption with illuminance of 50 lux, luminous efficacy of 15 lumens per watt and surface area of 18 square meters?

P = 50 lx × 18 m2 / 15 lm/W = 60W

## 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

## Lux to watts calculator example

Converting Lux (lx) to Watts (W) requires additional information about the light source's luminous efficacy, which measures how efficiently it converts electrical power into visible light. The equation for this conversion is:

Watts (W) = Lux (lx) × Area (in square meters) × Luminous Efficacy (lm/W)

Here's an example that demonstrates the calculation using a calculator:

Let's assume you have a light source with different illuminance values in Lux (lx) and you want to calculate the equivalent power consumption in Watts (W) for a specific area. For this example, we'll use an area of 4 square meters and a luminous efficacy of 100 lm/W.

Illuminance (lx) Power Consumption (W)
1000 400
500 200
200 80
100 40

To calculate the power consumption from Lux to Watts, multiply the value in Lux by the area in square meters, and then divide by the luminous efficacy.

For example, if the illuminance is 1000 lx, the area is 4 square meters, and the luminous efficacy is 100 lm/W, the power consumption would be (1000 lx × 4 square meters) / 100 lm/W = 40 W.

Similarly, for an illuminance of 500 lx, the same area of 4 square meters, and the luminous efficacy of 100 lm/W, the power consumption would be (500 lx × 4 square meters) / 100 lm/W = 20 W.

You can perform the same calculation for other illuminance values in the table, multiplying each value by the area in square meters and dividing by the luminous efficacy.

Please note that the actual power consumption may vary depending on the specific characteristics and efficiency of the light source. The luminous efficacy value used in the calculation should be based on the manufacturer's specifications or industry standard values for a similar type of light source.