THE NUMORIX GUIDE
How to use the Illuminance Converter
Last reviewed September 14, 2026
What this calculator does
The engine normalizes the input to lux and divides by each configured factor.
Formula and method
The engine normalizes the input to lux and divides by each configured factor. It uses 1 lux as the base, 1 foot-candle = 10.764 lux, 1 phot = 10,000 lux, and 1 milliphot = 10 lux. The result card treats lux as the primary output and shows all four conversions.
Variables and inputs
Enter a numeric illuminance and select Lux, Foot-candle, Phot, or Milliphot. The page continuously computes the result, displays lux and each conversion to six decimal places, and does not request distance, luminous flux, area, or spectral information.
Worked example
For 500 lux, the engine gives 500 / 10.764 = about 46.4511 foot-candles, 500 / 10,000 = 0.05 phot, and 500 / 10 = 50 milliphots. These are alternative descriptions of the same incident illumination.
How to interpret the result
Illuminance is luminous flux received per unit area, measured in lux in SI. It describes light arriving at a surface, not the total lumens emitted by a lamp, the brightness of a surface, or the visual appearance of a scene.
Common mistakes to avoid
Do not confuse lux with lumens: lux includes the receiving area. Do not use this as a luminance conversion in candela per square meter, and do not infer a safe light level from a unit conversion alone. Keep foot-candle as an illuminance unit rather than a force or length unit.
Assumptions and limitations
The foot-candle factor is stored as 10.764 lux, a rounded conversion. The calculator does not model inverse-square distance, beam spread, shadows, reflections, spectral sensitivity, measurement position, or time-varying light. The input has no explicit physical-range validation.