Illuminance Conversion
Lux (lx) and foot-candles (fc) both measure illuminance—luminous flux per area. 1 fc = 10.76 lx (1 lm/ft² vs 1 lm/m²). Phot = 10,000 lx; nox = 0.001 lx for very low light.
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1 foot-candle ≈ 10.76 lux (exact: 1/0.0929). Office: 300–500 lux (30–50 fc); retail: 500–1000 lux. Sunlight: ~100,000 lux; moonlight: ~0.1 lux. Phot (ph) = 10⁴ lx; nox = 10⁻³ lx for night vision.
Ready to run the numbers?
Why: Illuminance units vary by region: SI uses lux; US often uses foot-candles. Lighting standards (IES, OSHA) specify required levels in both.
How: 1 fc = 10.76 lx from 1 ft² = 0.0929 m². Phot and nox extend range for very bright or dim applications. Candela and distance give illuminance via inverse-square law.
Run the calculator when you are ready.
Conversion Parameters
Conversion Results
Lux
500.0000 lx
SI unit (lm/m²)
Foot-candles
46.4515 fc
Imperial unit (lm/ft²)
Phot
0.0500 ph
CGS unit (lm/cm²)
Nox (Millilux)
5.00e+5 nox
Low-light unit
Kilolux
0.5000 klx
Millilux
5.00e+5 mlx
% of Sunlight
0.5000%
× Moonlight
2,000×
× Candle@1m
46.4684×
Total Lumens
5,000
Standards Assessment
Excellent - meets office/retail standards
Step-by-Step Calculation
Visualizations
Lux and foot-candles are units of illuminance—the amount of light falling on a surface. Lux is the SI unit while foot-candles are commonly used in the United States.
Lux (lx)
1 lux = 1 lumen per square meter (lm/m²). Used internationally in lighting standards and specifications.
Foot-candle (fc)
1 fc = 1 lumen per square foot (lm/ft²). 1 fc ≈ 10.76 lux. Common in US construction and photography.
Illuminance Reference Values
| Condition | Lux | Foot-candles |
|---|---|---|
| Direct sunlight | 100,000 | 9,290 |
| Overcast day | 1,000 | 93 |
| Office lighting | 500 | 46 |
| Twilight | 10 | 0.93 |
| Full moon | 0.25 | 0.023 |
| Starlight | 0.0001 | 0.00001 |
Industry Lighting Standards
| Application | Minimum (lux) | Recommended (lux) | Standard |
|---|---|---|---|
| General office | 300 | 500 | ISO 8995 |
| Detailed office work | 500 | 750 | IESNA |
| Retail (general) | 300 | 500 | CIBSE |
| Surgery | 10,000 | 50,000 | IEC 60601 |
| Emergency exit | 1 | 5 | EN 1838 |
| Warehouse | 100 | 150 | OSHA |
| Classroom | 300 | 500 | EN 12464 |
Practical Lighting Tips
💡 Energy Efficiency
LED lighting provides 80-100+ lumens per watt, compared to 10-15 lm/W for incandescent. This means you can achieve the same lux level with much less power.
📐 Distance Matters
Illuminance follows the inverse square law. Doubling the distance from a light source reduces illuminance to one-quarter of its original value.
🎨 Color Rendering
Higher lux doesn't always mean better lighting. Consider CRI (Color Rendering Index) for tasks requiring color accuracy like art or medical work.
🌙 Circadian Health
Bright light (1000+ lux) in the morning helps regulate circadian rhythms. Lower, warmer light in the evening promotes better sleep.
History of Illuminance Units
The lux was adopted as the SI unit of illuminance in 1954, derived from the Latin word "lux" meaning light. The foot-candle predates the metric system and was originally defined as the illumination cast by a standard candle at a distance of one foot.
The phot, used in the CGS system, represents one lumen per square centimeter and is 10,000 times larger than the lux. The nox (from Latin "nox" meaning night) was introduced for measuring very low light levels, particularly useful in astronomy and night vision research.
Today, lux is the internationally recognized standard, while foot-candles remain common in the United States construction and lighting industries due to continued use of imperial units.
1 lux defined as
1 lumen per square meter
1 foot-candle defined as
1 lumen per square foot
Related Calculators
For educational and informational purposes only. Verify with a qualified professional.
🔬 Physics Facts
1 lux = 1 lumen per square meter; SI unit for illuminance.
— SI brochure
Foot-candle is non-SI but common in US lighting codes.
— IESNA
Full daylight: 10,000–25,000 lux; overcast: 1,000 lux.
— Lighting handbooks
Starlight: ~0.001 lux; used in astronomy and night vision.
— Photometry
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