Lumens and Lux — Method
Luminous flux (lumens) is the total light a source emits; illuminance (lux) is how much of it lands on a surface, per square metre. They are linked by area: lux = lumens ÷ area, so to reach a design lux level you need lumens = target lux × area. This gives the raw output required; a real layout then divides by the fitting efficiency and multiplies room losses (utilisation and maintenance factors) to get the installed lumens and fitting count.
Frequently Asked Questions
Multiply the target lux by the floor area in square metres: lumens = lux x area. A 20 m2 room at 300 lux needs about 6000 lumens of installed output before utilisation and maintenance losses.
Lumens measure the total light a lamp emits; lux measures how much of that light reaches a surface per square metre. Lux = lumens / area, so the same lamp gives fewer lux in a larger room.
Typical EN 12464-1 targets: circulation/corridors ~100-150 lux, general living/office 300 lux, kitchens and desks 500 lux, detailed/precision work 750-1000 lux.
One foot-candle equals about 10.76 lux. Divide lux by 10.76 to get foot-candles, or multiply foot-candles by 10.76 to get lux.
No - it gives the raw illuminance. Real installations lose light to fitting efficiency, room reflectance (utilisation factor ~0.4-0.6) and dirt/ageing (maintenance factor ~0.8). Use the lumen-method calculator for the installed fitting count.
Lumens, Lux and Illuminance
Lighting design starts from the illuminance a task needs (lux) and works back to the light output to install (lumens). Because lux is lumens spread over area, the bigger the space, the more lumens you need for the same lux.
The relationship
lux = lumens ÷ area. Rearranged, lumens = target lux × area gives the raw output. This is the ideal with no losses.
From ideal to installed
Real rooms lose light: not all of a fitting's lumens reach the working plane (utilisation factor), and output falls as lamps age and surfaces soil (maintenance factor). The lumen-method calculator applies these to give the number of fittings.
Related: Lumen Method, LED Resistor.