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: Kilolux = Phot × 10
Multiply any Phot value by 10 to get Kilolux.
Reverse: Phot = Kilolux × 0.1
Common illuminance levels — factor: 1 ph = 10 klx
| Phot (ph) | Kilolux (klx) | Context |
|---|---|---|
| 1.000e-06 ph | 1.000e-05 klx | Dark night |
| 1.000e-05 ph | 0.0001 klx | Moonlit night |
| 0.0001 ph | 0.001 klx | Full moon |
| 0.001 ph | 0.01 klx | Indoor dim |
| 0.01 ph | 0.1 klx | Indoor bright |
| 0.05 ph | 0.5 klx | Office work |
| 0.1 ph | 1 klx | Studio lighting |
| 0.5 ph | 5 klx | Bright overcast |
| 1 ph | 10 klx | Operating room / bright overcast |
| 2.5 ph | 25 klx | Overcast daylight |
| 5 ph | 50 klx | Hazy sun |
| 10 ph | 100 klx | Bright sunlight |
| 13 ph | 130 klx | Tropical noon |
| 100 ph | 1000 klx | Extreme |
| 1000 ph | 1e+04 klx | Maximum |
1 ph = 10 klx.
Key references: 1 lx = 0.0929 fc. 1 fc = 10.764 lx. 1 phot = 10,000 lx.
Multiply result by 0.1 to recover the original ph 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 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.
Kilolux (klx) equals 1,000 lux and is used for high-illuminance environments including daylight simulation, horticulture, and phototherapy. Direct sunlight registers 80–130 klx; overcast daylight 1–25 klx.
Seasonal affective disorder (SAD) treatment lamps provide 10 klx at close range for 30-minute daily sessions. Horticulture lighting for fruiting plants targets 20–60 klx. Industrial quality control inspection stations may require 5–10 klx.
Interesting fact: The human circadian rhythm is most strongly reset by 10 klx blue-enriched light in the morning. Even 2.5 klx has measurable circadian effects — explaining why indoor living (typically 200–500 lx) can disrupt sleep cycles.
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 = 10 klx. Reverse: 1 klx = 0.1 ph.
All conversions use IEEE 754 double-precision arithmetic, accurate to at least 8 significant figures.