Case 1
- Power (W)
- 8W
- Luminous efficacy (lm/W)
- 100lm/W
800lm
Open with these valuesWatts to Lumens Calculator
800lm
Result: 800 lmMultiply the watts by the lamp's efficacy in lumens per watt. An 8 W LED at 100 lm/W gives 800 lumens; a 60 W filament bulb at 15 lm/W gives 900 — barely more, for more than seven times the power. Watts alone say nothing about brightness; the efficacy is what separates the two.
The numbers at a glance
Held fixed: Power (W) 8.00 W.
| Luminous efficacy (lm/W) (lm/W) | Result (lm) |
|---|---|
| 0.0 | 0 |
| 25.0 | 200 |
| 50.0 | 400 |
| 75.0 | 600 |
| 100.0Your value | 800 |
| 125.0 | 1,000 |
| 150.0 | 1,200 |
| 175.0 | 1,400 |
| 200.0 | 1,600 |
Worked examples
Case 2
- Power (W)
- 60W
- Luminous efficacy (lm/W)
- 15lm/W
900lm
Open with these valuesCase 3
- Power (W)
- 10W
- Luminous efficacy (lm/W)
- 120lm/W
1,200lm
Open with these valuesHow it's calculated
lumens = watts × efficacy in lm/W
- StepRead the power in watts from the lamp or its packaging.
- StepEnter the efficacy of the technology — about 15 lm/W for filament, 100 for LED.
- ResultMultiply; the result is the light output in lumens.
Reference table
| Watts, efficacy | Lamp type | Lumens |
|---|---|---|
| 0.5, 80 | LED indicator lamp | 40 |
| 8, 100 | Ordinary LED bulb | 800 |
| 10, 120 | High-efficacy LED | 1200 |
| 60, 15 | 60 W filament bulb | 900 |
| 100, 15 | 100 W filament bulb | 1500 |
Questions
How do I convert watts to lumens?
Multiply the wattage by the lamp's luminous efficacy in lm/W. An 8 W LED at 100 lm/W produces 800 lumens, the same brightness as a traditional 60 W filament bulb.
What is luminous efficacy?
It measures how efficiently a light source turns electrical power into visible light, in lumens per watt. A higher value means more light for the same energy. Typical ranges are 10–17 lm/W for incandescent, 15–25 for halogen, 45–75 for compact fluorescent and 80–120 for LED.
Why are lumens a better measure of brightness than watts?
Wattage measures energy use, not light. It only worked as a proxy while every lamp had a similar efficacy. A 10 W LED now matches a 60 W filament bulb, so brightness has to be compared in lumens.
What efficacy should I enter for an LED?
Most consumer LED lamps sit between 80 and 120 lm/W, and 100 lm/W is a safe middle. High-efficiency fixtures and bare chips reach 150–200 lm/W. The exact figure is the rated lumens divided by the rated watts on the packaging.
Does the result tell me how bright the room will be?
No — lumens are what the lamp emits, not what lands on a surface. Illuminance is lumens per square metre and is measured in lux. Feed this result into the lumens to lux calculator with the room area to get that.
Sources and last check
Information, not professional advice.