Lux

Lux (lx) is the unit of illuminance, describing how strongly a surface is lit. While lumens describe the total light leaving a source, lux describes how densely that light arrives on a given surface. The definition is simple: if one lumen falls evenly on one square metre, that surface has an illuminance of one lux. (In Turkish the unit is written as luks.)

Why lux matters

What you actually feel in a room is the light on the desk, the counter or the floor. The same fitting delivers more light to a surface under a low ceiling and less under a high one, and its beam angle changes the result as well. That is why lighting calculations and standards define required light levels on specific surfaces in lux, according to how a space is used. Targets for an office desk, a corridor, an operating theatre or a warehouse are very different, and they are set in the relevant standards and project specifications.

How it is measured and calculated

In an existing space, illuminance is measured with a lux meter. At design stage, lighting calculation software uses the photometric data of fittings, such as IES files, to calculate the lux distribution across surfaces and display it as color maps. These analyses look not only at the average but at how evenly light is spread.

Lux is a numerical target, but good lighting does not end there. How bright walls and ceilings feel, glare and the color of light all shape comfort. The same principle holds in rendering: when lights are set up in physical units, the brightness of a space can be judged realistically together with exposure.