Illuminance

The illuminance (symbol: E) indicates how much light falls on a specific surface. It is measured in the unit lux (lx) and specifies how much luminous flux (in lumens) per square meter falls on a surface – in other words, how strongly a surface is illuminated.

Calculation of Illuminance

In practice, illuminance is measured with a lux meter, but it can also be calculated by dividing the luminous flux (Φ) by the illuminated area (A):

E = \frac{Φ}{A}

For example, if a light source generates a luminous flux of 1000 lumens and this is distributed over an area of 10 square meters, the illuminance on this area is 100 lux.

Good to know: According to the inverse square law, illuminance decreases the farther you move away from the light source. Specifically, if the distance to the light source is doubled, the brightness is reduced to a quarter.

Standards and Regulations

Standards and regulations for illuminance are important guidelines that determine how bright different work and living areas should be lit to ensure safety, health, and comfort. In Germany, for example, DIN EN 12464-1 for indoor spaces and DIN EN 12464-2 for outdoor areas set minimum requirements for illuminance. These standards regulate how much light is needed in various environments, such as offices, workshops, or streets. The requirements depend on the type of activity: Fine work, for example, requires higher illuminance than rough work. Additionally, factors such as glare, shadow formation, and light color are taken into account to ensure optimal visual conditions. Such regulations help prevent accidents, improve productivity, and enhance people's well-being.

10 Examples of Minimum Illuminance Requirements for Activities, Workplaces, Workrooms, and Areas:

Activities, Workplaces, Workrooms, and Areas	Minimum Illuminance E
Open-pit mining: Orientation lighting	3 lx
Storage: Storage rooms for uniform or large goods	50 lx
Traffic routes: Stairs, escalators, moving walkways, elevators	100 lx
General: Canteens, tea kitchens, self-service restaurants	200 lx
Office: Filing, copying	300 lx
Office: Writing, reading, data processing	500 lx
Office: Technical drawing (hand drawing)	750 lx
Electrical industry: Very fine assembly work	1000 lx
Jewelry making: Gemstone processing	1500 lx
Printing: Steel and copper engraving	2000 lx

Source: BAuA ASR A3.4 [PDF], Technical Rules for Workplaces, Lighting and Visual Connection | Section 6.2 & Annex 3

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