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Lumens to watts calculator FullScreen

Determine the approximate power consumption (watts) based on the luminous flux (lumens) of a light source. Ideal for energy efficiency assessments, lighting comparisons, and electrical planning. Obtain an estimation of wattage from lumens using this practical online tool.

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

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


what is Lumens to watts calculator

Converting lumens (lm) to watts (W) is not a direct conversion because lumens measure the brightness or luminous flux of a light source, while watts measure power consumption or the amount of energy used by a light source.

The relationship between lumens and watts depends on the efficiency or efficacy of the light source. Different light sources have different levels of efficiency in converting electrical power into visible light.

In general, for traditional incandescent bulbs, you can use the following rough approximation:

Lumens ≈ Watts x 10

This means that for incandescent bulbs, you can estimate the lumens by multiplying the wattage by 10. However, please note that this approximation may not be accurate for other types of light sources such as LED or fluorescent lights, as they are more energy-efficient.

To get a more accurate conversion, it is advisable to refer to the specifications provided by the manufacturer or consult a specific conversion chart for the particular type of light source you are using.

Keep in mind that the relationship between lumens and watts does not directly indicate the brightness but rather the power consumption of the light source.

Lumens to watts calculation formula

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)


watts = lumens / (lumens per watt)


W = lm / (lm/W)


What is the power consumption of a lamp that has luminous flux of 900 lumens and luminous efficacy of 15 lumens per watt (lm/W)?

P = 900 lm / 15 lm/W = 60 W

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).

Lumens to watts table

Lumens Incandescent
light bulb
 / LED
375 lm 25 W 6.23 W
600 lm 40 W 10 W
900 lm 60 W 15 W
1125 lm 75 W 18.75 W
1500 lm 100 W 25 W
2250 lm 150 W 37.5 W
3000 lm 200 W 50 W

Lumens to watts calculator Example

Converting Lumens (lm) to Watts (W) involves considering the efficacy or efficiency of the light source. The efficacy represents the amount of visible light emitted per unit of electrical power consumed.

Here's an example that demonstrates the conversion of Lumens to Watts using a table:

Assuming you have a light source with different luminous flux values in Lumens (lm) and you want to estimate the equivalent power consumption in Watts (W), you can use the following table:

Luminous Flux (lm) Efficacy (lm/W) Power Consumption (W)
1000 100 10
500 80 6.25
200 70 2.86
100 60 1.67

To estimate the power consumption, divide the luminous flux by the efficacy for each value.

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

Similarly, for a luminous flux of 500 lm and an efficacy of 80 lm/W, the power consumption would be (500 lm) / (80 lm/W) = 6.25 W.

You can follow the same calculation for other values in the table.

Please note that the efficacy values used in the table are hypothetical and may vary depending on the type of light source, such as incandescent bulbs, fluorescent lamps, or LED lights. The actual power consumption may differ based on the specific characteristics and efficiency of the light source being used.