Convert illuminance units — lux, foot-candle, phot, nox and more.
| Unit | Name | Value |
|---|---|---|
| lx | Lux | 10000 |
| fc | Foot-candle | 929.0313 |
| nx | Nox | 10000000 |
| klx | Kilolux | 10 |
| mlx | Millilux | 10000000 |
Formula: Foot-candle = Phot × 929
Multiply any Phot value by 929 to get Foot-candle.
Reverse: Phot = Foot-candle × 0.001076
Common illuminance levels — factor: 1 ph = 929 fc
| Phot (ph) | Foot-candle (fc) | Context |
|---|---|---|
| 1.000e-06 ph | 0.000929 fc | Dark night |
| 1.000e-05 ph | 0.00929 fc | Moonlit night |
| 0.0001 ph | 0.0929 fc | Full moon |
| 0.001 ph | 0.929 fc | Indoor dim |
| 0.01 ph | 9.29 fc | Indoor bright |
| 0.05 ph | 46.45 fc | Office work |
| 0.1 ph | 92.9 fc | Studio lighting |
| 0.5 ph | 464.5 fc | Bright overcast |
| 1 ph | 929 fc | Operating room / bright overcast |
| 2.5 ph | 2323 fc | Overcast daylight |
| 5 ph | 4645 fc | Hazy sun |
| 10 ph | 9290 fc | Bright sunlight |
| 13 ph | 1.208e+04 fc | Tropical noon |
| 100 ph | 9.29e+04 fc | Extreme |
| 1000 ph | 9.29e+05 fc | Maximum |
phots × 929.03 = fc.
1 phot = 929 fc. 0.054 phots ≈ 50 fc (office).
fc ÷ 929 = phots.
Specifies illuminance levels in lux (metric) or foot-candles (US) for architectural, retail, and workplace lighting per IES and EN 12464 standards.
Measures scene illuminance in lux with a light meter to set correct exposure for available-light photography.
Verifies that workplace lighting meets minimum requirements (typically 500 lx for offices, 300 lx for corridors) per local regulations.
Monitors grow-light illuminance in klx to optimize plant growth — fruiting plants typically need 20–60 klx.
Prescribes and measures light therapy intensity in lux for SAD treatment (10,000 lx standard) and circadian rhythm research.
Measures ambient light in lux to set appropriate display backlight levels for consistent image quality.
The phot (ph) is the CGS unit of illuminance, equal to 10,000 lux = 1 lumen per square centimeter. It was the standard photometric unit before the adoption of SI units, defined in the CGS system in 1900.
Phots are found in pre-1960s scientific literature on optics, photography, and photometry. 1 phot = 10,000 lux = 929.03 foot-candles. Bright sunlight at ~100,000 lux = 10 phots. A well-lit operating room at 10,000 lux = 1 phot.
Interesting fact: The phot's name comes from the Greek phos (light), the same root as photograph and photon. Though obsolete in modern use, the phot appears in classic photometry texts and some specialized optical engineering references.
The foot-candle (fc) is the US customary unit of illuminance, defined as one lumen per square foot. One foot-candle = 10.7639 lux. It has been used in North American lighting specifications since the early 20th century and remains standard in US architectural and theatrical lighting.
US lighting standards use foot-candles: Illuminating Engineering Society (IES) specifies office work at 30–50 fc (300–500 lx), surgery at 200–400 fc, and roadway lighting at 0.5–2 fc. Stage lighting designers in North America universally work in foot-candles.
Interesting fact: The foot-candle's name reflects its origin — the illuminance on a surface one foot from a standard candle. The international candle standard was defined in 1909, and American lighting engineers adopted the foot-candle as their practical working unit from that era.
Illuminance measures light falling on a surface. The SI unit is lux (lm/m²); the US standard is foot-candles (lm/ft²). Key reference levels: moonless night ~0.001 lx, full moon ~1 lx, office work 500 lx, SAD therapy 10,000 lx, bright sunlight 100,000 lx.
Exact factor: 1 ph = 929 fc. Reverse: 1 fc = 0.001076 ph.
All conversions use IEEE 754 double-precision arithmetic, accurate to at least 8 significant figures.