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: Lux = Phot × 1e+04
Multiply any Phot value by 1e+04 to get Lux.
Reverse: Phot = Lux × 0.0001
Common illuminance levels — factor: 1 ph = 1e+04 lx
| Phot (ph) | Lux (lx) | Context |
|---|---|---|
| 1.000e-06 ph | 0.01 lx | Dark night |
| 1.000e-05 ph | 0.1 lx | Moonlit night |
| 0.0001 ph | 1 lx | Full moon |
| 0.001 ph | 10 lx | Indoor dim |
| 0.01 ph | 100 lx | Indoor bright |
| 0.05 ph | 500 lx | Office work |
| 0.1 ph | 1000 lx | Studio lighting |
| 0.5 ph | 5000 lx | Bright overcast |
| 1 ph | 1e+04 lx | Operating room / bright overcast |
| 2.5 ph | 2.5e+04 lx | Overcast daylight |
| 5 ph | 5e+04 lx | Hazy sun |
| 10 ph | 1e+05 lx | Bright sunlight |
| 13 ph | 1.3e+05 lx | Tropical noon |
| 100 ph | 1e+06 lx | Extreme |
| 1000 ph | 1e+07 lx | Maximum |
phots × 10,000 = lx.
1 phot = 10,000 lx. 0.05 phots = 500 lx (office).
lx ÷ 10,000 = 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 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).
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 = 1e+04 lx. Reverse: 1 lx = 0.0001 ph.
All conversions use IEEE 754 double-precision arithmetic, accurate to at least 8 significant figures.