Illuminance Conversion
Quick answer: 1 lx = 1 lm/m² ≈ 0.0929 fc, 1 fc (foot-candle) = 10.7639 lx, 1 phot (ph) = 10,000 lx; offices need about 500 lx ≈ 46.5 fc.
Lux, kilolux, lumens per m², phot and foot-candles – illuminance for workplaces, rooms and streets.
How the calculation works
Enter an illuminance and choose the unit (for example lx or fc). The table shows the same illuminance in lux, kilolux, lm/m² and lm/cm², phots, nox, foot-candles and lm/in².
Formula and assumptions
Illuminance is luminous flux per area: 1 lx = 1 lm/m². The foot-candle is 1 lm/ft² = 1 / 0.09290304 lx = 10.7639 lx. The phot (ph) = 1 lm/cm² = 10⁴ lx.
More worked examples
- An office at 500 lx ≈ 46.5 fc.
- A corridor at 100 lx ≈ 9.3 fc.
- A workshop at 50 fc ≈ 538 lx.
- A sunny day at 100 klx = 100,000 lx.
Typical illuminance
| Space | lx | fc |
|---|---|---|
| street at night | 10–20 | 0.9–1.9 |
| corridor | 100 | 9.3 |
| office, classroom | 500 | 46.5 |
| precision work | 1,000 | 92.9 |
| overcast day | 10,000 | 929 |
| sunlight | 100,000 | 9,290 |
Common mistakes
- Mixing illuminance (lx) with luminous flux (lm).
- Confusing the foot-candle with the foot-lambert (luminance).
- Converting fc to lx with 10 instead of 10.764.
Frequently asked questions
How many lux is 1 foot-candle?
1 fc = 10.764 lx; 1 lx ≈ 0.0929 fc.
Is lux the same as lm/m²?
Yes, 1 lx = 1 lumen per square metre.
How many lux does an office need?
EN 12464-1 recommends about 500 lx for writing and computer work.
How do I get lux from lumens?
Divide the luminous flux by the area: 4,000 lm over 10 m² ≈ 400 lx (without losses).
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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