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Use this calculator to estimate the lumen output that will be created from your chosen wattage of light source.
Enter the wattage, then either choose the most appropriate light source from the list or enter the lumens per watt of your light source, to get the light output in lumens.
Use calculate button if answer isn't shown automatically
The conversion of watts to lumens uses the formula:
Lumens = Watts x Efficiency (lumens per watt)
For example, an LED with an efficiency of 75 lumens per watt using 5.41 watts will create a luminous flux of 460 lumens.
460 lumens = 5.41 watts x 85 lumens per watt
As lumens measure the amount of light and watts the amount of power used to create that light, the only accurate way to calculate the luminous flux or light output in Lumens, is to know how efficient the light source is.
Efficacy is a measure of how well a light source produces visible light. It is measured in lumens per watt (lm/W) or light output per watt.
A higher efficacy means more light for the same amount of power, with different light types and even different models within a light type varying quite a bit.
For reference, here are some average lm/W efficacies for various light types: