Illuminance Converter

Lux, foot-candles, and luminous flux from lux × area (or lumens ÷ area).

Lux is the base, and a lux is one lumen arriving on one square metre. The foot-candle is that same idea in imperial dress — a lumen on a square foot — so the factor between the two columns is nothing more than the 10.7639 square feet inside a square metre, which turns a typical 500 lux office desk into 46.45 foot-candles. The Area field behaves differently depending on which way you are working. Enter lux or foot-candles and the area you type has no effect whatsoever on those two rows; it feeds only the Lumens row, which multiplies up to 10,000 lumens across the default 20 m². Switch the input unit to Lumens and the relationship reverses, dividing your total flux by area to recover an illuminance, and leaving area at zero returns zero with a note explaining what is missing. The assumption underneath is worth stating plainly: this arithmetic spreads every lumen perfectly evenly across the area and lets none escape. Real fittings have beam angles, rooms have absorbing walls, and lighting designers apply utilisation and maintenance factors for exactly that reason, so a lamp's boxed lumen rating will not equal lux times floor area. Illuminance is also only half the subject. There is no luminance here — no candelas per square metre, the quantity behind screen brightness — no candela of luminous intensity, and no distance term, so nothing models the inverse-square falloff as you move away from a source.