Illuminance converter
Convert illuminance between lux, foot-candles and phots.
Fill in the fields and the result will appear here automatically.
Converts illuminance between lux, kilolux, millilux, foot-candles, phots and nox. Lux appears in workplace lighting standards, foot-candles in US lighting documentation.
How it works
Formula and logic
The units convert through lux using their factors: these cover prefixes, area ratios and the chosen historical nox factor.
Example
Example of converting an entered value: 500 lx ≈ 46.45 foot-candles. This is a numerical example, not a workplace lighting requirement.
Fields and units
- Illuminance — in the selected source unit
- From unit — list option
- To unit — list option
How to use
- — Enter the value.
- — Pick the source unit.
- — Pick the target unit.
Method and limitations
- Calculation method
- Formula and logic
- Data or methodology source
- BIPM: SI Brochure, version 4.01 (2026) NIST: conversion-factor tables, Appendix B.9 Luxenberg (1965): Table I, historical nox factor Luxenberg (1965): DOI of the article “Photometric Units”
- Limitation
- The result is a rounded unit conversion. Check the entered value and selected units. Nox is an obsolete unit: Table I in Luxenberg (1965) gives 1 nox = 0.001 lx. This converter uses that historical factor. It does not establish current SI or lighting-standard acceptance of nox; the BIPM and NIST links support the other units.
FAQ
How does illuminance differ from luminous flux?
Luminous flux is measured in lumens and describes the whole lamp; illuminance is the flux falling on a square metre of surface.
What is a foot-candle?
One lumen per square foot. Since the foot is exactly defined, a foot-candle is 10.7639 lux.
Where is the phot used?
In the CGS system: one lumen per square centimetre, that is ten thousand lux.
Can lux be converted to watts?
No — they are different quantities, and the relation depends on the spectrum of the source.