Luminous Flux Conversion
Quick answer: 1 klm = 1,000 lm, 1 lm = 1 cd·sr = 1 lx·m²; an 806 lm LED bulb replaces a classic 60 W bulb, and an isotropic 1 cd source emits 4π ≈ 12.57 lm.
Lumen, kilolumen, candela steradian and lux square metre – the luminous flux of bulbs and fixtures.
How the calculation works
Enter a luminous flux and choose the unit. The table shows the same flux in mlm, lm and klm, cd·sr, lx·m², candelas of an isotropic source and “watts of green light” (683 lm/W).
Formula and assumptions
The lumen is the SI unit of luminous flux: 1 lm = 1 cd × 1 sr. An isotropic 1 cd source radiates into the full solid angle of 4π sr, so it emits 4π lm. By the definition of the candela, 1 W of radiation at 540 THz (≈ 555 nm) = 683 lm.
More worked examples
- A 9 W LED with 806 lm = 0.806 klm.
- A 20,000 lm floodlight = 20 klm.
- An isotropic 100 cd source ≈ 1,257 lm.
- An office of 10 m² × 500 lx needs 5,000 lm (without losses).
Bulb comparison
| Incandescent | LED approx. | Flux (lm) |
|---|---|---|
| 25 W | 3–4 W | 250 |
| 40 W | 5 W | 470 |
| 60 W | 8–9 W | 806 |
| 75 W | 11 W | 1,055 |
| 100 W | 13–15 W | 1,521 |
| 150 W | 20 W | 2,452 |
Common mistakes
- Comparing bulbs by watts instead of lumens.
- Mixing lumens (flux) with lux (illuminance).
- Ignoring the beam angle – the same lumens give different illuminance.
Frequently asked questions
How many lumens are in 1 klm?
1 klm = 1,000 lm.
How many lumens does a 60 W equivalent LED give?
About 806 lm (per the EU labelling regulation).
How do I convert candelas to lumens?
For an isotropic source flux = 4π × intensity: 10 cd ≈ 125.7 lm; for a directed beam it depends on the angle.
How are lumens and lux related?
1 lx = 1 lm/m²: 1,000 lm over 2 m² gives 500 lx.
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Publisher: Art-Visum d.o.o. · Content reviewed:
Calculations use common consumption rates and manufacturers' technical data sheets; results are estimates. Methodology · Standards · About