How to use the converter
- Choose whether you start from watts or from lumens.
- Pick a bulb type to load an example efficacy, or choose “My own bulb” and enter its efficacy. For any bulb you own, divide the lumens by the watts printed on the packaging or the bulb.
- Enter the watts or lumens and press Calculate. The result also shows how many watts each example bulb type would need for the same light output.
Formula
lumens = watts × efficacy | watts = lumens ÷ efficacy
Luminous efficacy (lm/W) says how much light a bulb gives per watt of electrical power. It differs between technologies and between individual products, which is why the calculation needs it as an input.
The “roughly equal to a standard incandescent of” line interpolates linearly between the points of the U.S. Department of Energy rule of thumb below and is only shown between 450 and 1,600 lumens.
Sources: efficacy values used
| Bulb type | Example efficacy | Based on |
|---|---|---|
| LED | 88.9 lm/W | an LED bulb giving about 800 lm at about 9 W: U.S. Federal Trade Commission, Consumer Advice: “Shopping for Light Bulbs” (checked 15 October 2026) |
| Halogen (incandescent) | 17.4 lm/W | a 43 W halogen bulb rated at 750 lm: Signify (Philips) product sheet for a 43 W A19 halogen lamp: 750 lm nominal flux, “wattage equivalent 60 W” (checked 15 October 2026) |
| Standard incandescent | 13.3 lm/W | a 60 W incandescent bulb giving about 800 lm: U.S. Department of Energy, Energy Saver: “Lumens and the Lighting Facts Label” (rule of thumb for replacing incandescent bulbs) |
U.S. Department of Energy rule of thumb for replacing standard incandescent bulbs (U.S. Department of Energy, Energy Saver: “Lumens and the Lighting Facts Label” (rule of thumb for replacing incandescent bulbs)):
| Incandescent bulb | Look for about |
|---|---|
| 40 W | 450 lm |
| 60 W | 800 lm |
| 75 W | 1,100 lm |
| 100 W | 1,600 lm |
Units
Power in watts (W), light output in lumens (lm), efficacy in lumens per watt (lm/W).
Limits of this converter
- The example efficacies come from one figure each. Real LED, halogen and incandescent bulbs vary widely; the lumens on your bulb’s label are always more reliable.
- Lumens are total light output. They do not tell you the beam spread, colour temperature or colour rendering, so two bulbs with the same lumens can look different in a room.
- For LED fittings with a separate driver, check whether the rated watts include the driver.
- Car headlamp bulbs are not covered. Whether a replacement bulb is allowed in a vehicle depends on the vehicle and local rules, not on its lumens.