Convert illuminance units — lux, foot-candle, phot, nox and more.
| Unit | Name | Value |
|---|---|---|
| lx | Lux | 0.001 |
| fc | Foot-candle | 0.00009290313 |
| ph | Phot | 1e-7 |
| klx | Kilolux | 0.000001 |
| mlx | Millilux | 1 |
Formula: Foot-candle = Nox × 9.2903e-5
Multiply any Nox value by 9.2903e-5 to get Foot-candle.
Reverse: Nox = Foot-candle × 1.076e+04
Common illuminance levels — factor: 1 nx = 9.2903e-5 fc
| Nox (nx) | Foot-candle (fc) | Context |
|---|---|---|
| 0.001 nx | 9.290e-08 fc | Moonless overcast |
| 0.01 nx | 9.290e-07 fc | Dark sky |
| 0.1 nx | 9.290e-06 fc | Moonlit night |
| 1 nx | 9.290e-05 fc | Full moon = 1 mlx |
| 10 nx | 0.000929 fc | 10 mlx |
| 100 nx | 0.00929 fc | 0.1 lx dim indoor |
| 1000 nx | 0.0929 fc | 1 lx full moon bright |
| 1e+04 nx | 0.929 fc | 10 lx |
| 1e+05 nx | 9.29 fc | 100 lx corridor |
| 1e+06 nx | 92.9 fc | 1,000 lx studio |
| 5e+06 nx | 464.5 fc | 5,000 lx |
| 1e+07 nx | 929 fc | 10,000 lx SAD lamp |
| 5e+07 nx | 4645 fc | 50,000 lx |
| 1e+08 nx | 9290 fc | 100,000 lx bright sun |
| 1.300e+11 nx | 1.208e+07 fc | Tropical noon |
1 nx = 9.2903e-5 fc.
Key references: 1 lx = 0.0929 fc. 1 fc = 10.764 lx. 1 phot = 10,000 lx.
Multiply result by 1.076e+04 to recover the original nx value.
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 nox (nx) is an obsolete unit of illuminance equal to 0.001 lux = 1 millilux, proposed for measuring very low light levels in dim conditions. It was never widely adopted and is not recognized by any current standards body.
The nox was briefly proposed in some mid-20th century photometry literature specifically for mesopic and scotopic (low-light) illuminance measurements where lux values would be very small fractions. It never entered widespread use.
Interesting fact: The nox is one of the rarest photometric units — it rarely appears even in specialty lighting engineering texts. Its value equals exactly 1 millilux, making it redundant once millilux became the preferred notation for low illuminance levels.
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 nx = 9.2903e-5 fc. Reverse: 1 fc = 1.076e+04 nx.
All conversions use IEEE 754 double-precision arithmetic, accurate to at least 8 significant figures.