Illuminance is the main factor that determines the speed, reliability and ease with which our eyes can perform visual tasks (such as reading or working on a computer). Illuminance (such as luminance distribution) is very important for visual performance.

Illuminance (symbol: E) is measured in lux (lx), representing the luminous flux from the light source on a given surface.

The illuminance is one lux, and the area of one square meter is uniformly illuminated by one lumen luminous flux.

Illuminance is measured on horizontal and vertical surfaces using an illuminometer. In order to better identify vertical surfaces and three-dimensional forms in the room - especially faces - the standard used is cylindrical illuminance. This is the average vertical illuminance on the cylinder surface.

Under the same lighting conditions, a white room looks brighter than a room with a darker surface: it reflects light better. Therefore, the lower the reflectivity, the more difficult the visual task, and the higher the illuminance.

Uniform brightness distribution

The brightness is evenly distributed, which is convenient for performing visual tasks. For the working world, the standard specifies the minimum level of average illumination to be maintained, for example, 500 lux for office work, 300 lux for rough machining, and 500 lux for precision machine work.

The illuminance may naturally be higher than the value specified in the standard. Humans are programmed to live in the daytime, reaching 100000 lux in cloudless summer days and 20000 lux when the sky is overcast.