What this calculator does
Lumens measure light output and watts measure power drawn, and the ratio between them is efficacy. An LED at roughly 100 lumens per watt produces 800 lumens from 8 watts; an incandescent at 15 lumens per watt needs 53 watts for the same light.
That gap is the whole point of the conversion. Buying by wattage made sense when almost every bulb was incandescent and the ratio was fixed. With four technologies in the shops at efficacies from 15 to 100 lumens per watt, wattage no longer tells you how bright a bulb is, which is why packaging now leads with lumens.
The formula
Power is the target brightness divided by the luminous efficacy of the technology, in lumens per watt. The efficacy figures used here are representative rather than exact, since real bulbs vary with colour temperature, driver quality and age. LED efficacy in particular has improved steadily and good modern lamps exceed 100 lumens per watt.
| Term | Meaning |
|---|---|
| Lumen | Total light output, independent of the technology producing it. |
| Luminous efficacy | Lumens per watt: how efficiently a bulb turns power into light. |
| Colour temperature | The warmth of the light in kelvin, unrelated to brightness but often confused with it. |
| Incandescent equivalent | A marketing figure giving the old wattage that produced similar light. |
The inputs explained
| Field | What to enter |
|---|---|
| Target brightness (lm) | Target brightness in lumens. Common bulb outputs are 450, 800, 1,100 and 1,600 lm. |
| Bulb type | Bulb technology, which sets the efficacy. These are representative values; check the packaging for a specific lamp. |
When to use it
Replacing an old bulb
Matching the brightness rather than the wattage is what gets the same light, and the two are no longer related.
Estimating running cost
Power draw multiplied by hours gives energy use, and the difference between 8 W and 53 W over years of use is substantial.
Checking a fitting limit
Light fittings carry a maximum wattage, and an LED giving the same light as a 100 W incandescent draws only about 10 W, so it fits comfortably.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How much power does each technology need for 800 lumens?
The same light output from four bulb technologies.
| Bulb type | Power needed | Efficacy used | Equivalent incandescent watts |
|---|---|---|---|
| LED | 8.0 W | 100 lm/W | 53 W |
| Compact fluorescent | 13.3 W | 60 lm/W | 53 W |
| Halogen | 34.8 W | 23 lm/W | 53 W |
| Incandescent | 53.3 W | 15 lm/W | 53 W |
Questions
How many lumens replace a 60 watt bulb?
About 800 lumens, which is the figure most 60 W replacement LEDs quote. Note that this calculator uses 15 lm/W for incandescent and so reports 53 W rather than 60 for 800 lumens. Real 60 W bulbs are slightly less efficient than that, around 13 lm/W, which is where the packaging convention comes from.
Why did bulbs stop being sold by wattage?
Because wattage only indicated brightness while nearly all bulbs shared the same efficacy. Once LED, fluorescent and halogen lamps sat on the same shelf at efficacies from 15 to over 100 lumens per watt, the wattage stopped being comparable and regulators moved labelling to lumens.
Is a higher lumen figure always better?
No, it is a question of matching the room. A bedside lamp at 1,600 lumens is uncomfortable. Around 450 lm suits a small accent lamp, 800 a general room bulb and 1,600 a kitchen or work area. Colour temperature matters separately and is not a brightness measure.
Do LEDs get dimmer with age?
Gradually. LEDs are usually rated by the hours until output falls to 70% of the original, commonly 15,000 to 50,000 hours. They rarely fail outright the way a filament does, so the decline is slow enough that most people do not notice it.
For lighting running costs, see the LED savings calculator. For another household electricity figure, see the EV charging cost calculator.