Convert illuminance units — lux, foot-candle, phot, nox and more.
| Unit | Name | Value |
|---|---|---|
| fc | Foot-candle | 0.09290313 |
| ph | Phot | 0.0001 |
| nx | Nox | 1000 |
| klx | Kilolux | 0.001 |
| mlx | Millilux | 1000 |
Formula: Nox = Lux × 1000
Multiply any Lux value by 1000 to get Nox.
Reverse: Lux = Nox × 0.001
Common illuminance levels — factor: 1 lx = 1000 nx
| Lux (lx) | Nox (nx) | Context |
|---|---|---|
| 0.001 lx | 1 nx | Moonless overcast night |
| 0.01 lx | 10 nx | Dark countryside sky |
| 0.1 lx | 100 nx | Moonlit night |
| 1 lx | 1000 nx | Full moon |
| 10 lx | 1e+04 nx | Candle at 1 m |
| 50 lx | 5e+04 nx | Living room typical |
| 100 lx | 1e+05 nx | Corridor / stairway |
| 300 lx | 3e+05 nx | Classroom |
| 500 lx | 5e+05 nx | Office work / IES standard |
| 1000 lx | 1e+06 nx | Studio lighting |
| 5000 lx | 5e+06 nx | Bright overcast day |
| 1e+04 lx | 1e+07 nx | SAD therapy lamp |
| 2.5e+04 lx | 2.5e+07 nx | Overcast daylight |
| 1e+05 lx | 1e+08 nx | Bright sunlight |
| 1.3e+05 lx | 1.3e+08 nx | Tropical noon sun |
lx × 1,000 = nox (= mlx).
1 lx = 1,000 nox. 1 nox = 1 mlx = 0.001 lx.
nox ÷ 1,000 = lx.
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 lux (lx) is the SI unit of illuminance, defined as one lumen per square meter. It measures how much light falls on a surface, regardless of the surface's color or reflectivity. The lux was formally adopted by the International System of Units in 1960, superseding the older phot and metre-candle.
Lux levels define lighting requirements across all domains: emergency lighting minimum 1 lx, corridor lighting 100 lx, office work 500 lx, surgery 10,000–100,000 lx. Outdoor daylight ranges from 1,000 lx (overcast) to 130,000 lx (direct tropical sunlight).
Interesting fact: Human eyes can adapt to a remarkable range — from about 0.001 lx (moonless night) to over 130,000 lx (direct sunlight) — a factor of 100 million. Yet the lighting standards for reading (500 lx) are only 500 times brighter than a typical moonlit night (1 lx).
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.
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 lx = 1000 nx. Reverse: 1 nx = 0.001 lx.
All conversions use IEEE 754 double-precision arithmetic, accurate to at least 8 significant figures.