Lumens to Watts Calculator
Convert lumens to watts, or watts to lumens, to find out exactly how much power a bulb consumes based on its brightness. Includes accurate luminous efficacy ratings for LEDs, CFLs, and incandescent bulbs.
Introduction to Lumens and Watts
In the past, we bought light bulbs based on wattage (which simply measures power consumption). Today, thanks to highly efficient LED technology, lighting is accurately measured in lumens—the actual amount of brightness a bulb produces. Converting between lumens and watts requires knowing how efficiently the bulb converts electricity into light, which is known as luminous efficacy.
How to convert lumens to watts
To convert lumens to watts, you must divide the brightness (in lumens) by the luminous efficacy (in lumens per watt, or lm/W) of the light bulb.
You cannot directly convert lumens to watts without knowing the type of bulb because different technologies require vastly different amounts of power to produce the same brightness. For instance, creating 800 lumens takes about 60 watts for an incandescent bulb, but only about 9 watts for a modern LED bulb.
Luminous Efficacy Explained
Luminous efficacy is the measure of how well a light source produces visible light. It's the ratio of luminous flux (brightness) to power (watts). In simpler terms, it's the "miles per gallon" of light bulbs.
A higher luminous efficacy means the bulb is much more energy-efficient. As older incandescent and halogen technologies are phased out in many countries, LEDs have become the standard precisely due to their exceptionally high efficacy, often reaching 80 to 100 lm/W or more.
Reference Table: Lamp Type Conversions
The table below demonstrates the typical wattage required by different bulb technologies to achieve standard brightness levels.
| Lamp Type | Typical Efficacy | 800 lm Equivalent | 1600 lm Equivalent |
|---|---|---|---|
| LED | 80 - 100 lm/W | 8W - 10W | 16W - 20W |
| CFL | 45 - 75 lm/W | 11W - 18W | 21W - 35W |
| Halogen | 15 - 25 lm/W | 32W - 53W | 64W - 106W |
| Incandescent | 10 - 17 lm/W | ~60W | ~100W |
Methodology
This calculator determines the required power by dividing the user-provided luminous flux (in lumens) by the nominal luminous efficacy associated with the selected lamp type. The baseline values used for estimations are 90 lm/W for LEDs, 60 lm/W for CFLs, 20 lm/W for halogens, and 13 lm/W for incandescents. For the incandescent equivalent output, the tool standardizes the calculation against the 13 lm/W baseline.
Frequently Asked Questions
A standard 60W incandescent bulb produces about 800 lumens. Because modern LED bulbs have a much higher luminous efficacy (typically 80-100 lm/W), you only need an 8W to 10W LED to match the 800-lumen brightness of a 60W incandescent.
A traditional 100-watt incandescent bulb produces approximately 1,500 to 1,600 lumens. To get the same brightness today, you would look for a 15W to 18W LED bulb.
Luminous efficacy is a measure of how well a light source produces visible light, expressed in lumens per watt (lm/W). It represents the ratio of luminous flux (brightness) to the electrical power (watts) consumed. Higher efficacy means the bulb is more energy efficient.
Lumens measure brightness, while watts measure electrical power. Since different types of bulbs use power at vastly different efficiencies (e.g., an LED produces ~90 lumens per watt while an incandescent produces only ~13 lumens per watt), you must know the bulb type or its specific luminous efficacy to calculate the watts required for a certain brightness.