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Watts to lumens calculator FullScreen

Calculate the luminous flux in lumens (lm) based on power consumption in watts (W). Ideal for understanding the light output of different light sources and comparing energy efficiency. Obtain an estimation of lumens from watts using this practical online tool.

Enter power in watts: W
Enter light source:
Or enter luminous efficacy in lumens per watt: lm/W
Luminous flux result in lumens: lm

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


What is Watts to lumens calculator

Converting watts (W) to lumens (lm) requires knowledge of the efficiency or efficacy of the light source being used.

Different types of light sources have different levels of efficiency in converting electrical power into visible light. Therefore, a direct conversion between watts and lumens is not possible without additional information.

To estimate the lumen output based on the wattage, you would need to refer to the specifications provided by the manufacturer of the specific light source. The manufacturer typically provides information about the efficacy of the light source, which is measured in lumens per watt (lm/W).

Once you have the efficacy value, you can calculate the approximate lumen output using the following formula:

Lumens (lm) = Watts (W) x Efficacy (lm/W)

For example, if a light source has an efficacy rating of 100 lm/W and consumes 10 watts of power, you can estimate the lumen output as follows:

Lumens (lm) = 10 W x 100 lm/W Lumens (lm) = 1000 lm

Please note that this is a simplified calculation and does not take into account other factors such as color temperature or any losses in the lighting system. For more accurate results, it's recommended to consult the manufacturer's specifications or seek professional advice specific to the light source you are using.

Watts to lumens calculation formula

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)


lumens = watts × (lumens per watt)


lm = W × (lm/W)


What is the luminous flux of a lamp that has power consumption of 60 watts and luminous efficacy of 15 lumens per watt?

ΦV = 60 W × 15 lm/W = 900 lm

Luminous efficacy table

Light type Typical
luminous efficacy
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).

Watts to lumens calculator Example

Converting Watts (W) to Lumens (lm) requires information about the light source's luminous efficacy, which measures its efficiency in converting electrical power into visible light. The equation for this conversion is:

Lumens (lm) = Watts (W) × 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 power consumption values in Watts (W), and you want to calculate the equivalent luminous flux in Lumens (lm) for a specific luminous efficacy. For this example, we'll use a luminous efficacy of 100 lm/W:

Power Consumption (W) Luminous Flux (lm)
10 1000
5 500
2 200
1 100

To convert the power consumption from Watts to Lumens, multiply the value in Watts by the luminous efficacy in lm/W.

For example, if the power consumption is 10 W and the luminous efficacy is 100 lm/W, the luminous flux would be 10 W × 100 lm/W = 1000 lm.

Similarly, for a power consumption of 5 W and the same luminous efficacy of 100 lm/W, the luminous flux would be 5 W × 100 lm/W = 500 lm.

Perform the same calculation for other power consumption values in the table, multiplying each value by the luminous efficacy in lm/W.

Please note that the actual luminous flux 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.