ASR A3.4 Lighting and line of sightLighting and line of sight

Sufficient illumination is important both for the performance of work tasks and for the fatigue-free well-being of people.


As there are also workplaces where the work task requires a lower brightness level, the workplace regulation ASR A3.4 provides an overview of the workplace-specific requirements for illumination levels. A distinction is made between natural lighting and artificial lighting. 

Lighting with daylight is preferable to lighting with only artificial light, as the positive effects on people are well known. General well-being is increased and symptoms of fatigue are significantly reduced. This reduces the frequency of errors made by employees. Sufficient daylight can be assumed if the daylight factor is greater than 2%. The ASR is based on the rule of thumb that the requirement for sufficient daylight is met if the ratio of translucent window, door or wall area to the room floor area is at least 1:10.

However, employees must not be blinded by the realisation of sufficient daylight.

In order for the safety signs to be easily perceived as such, the colour rendering by artificial lighting must also be correct. Colour rendering is described by a dimensionless number between 0 and 100 (colour rendering index Ra), which describes the effect of a light source on the impression of the colour of an object by a person. The higher the colour rendering index, the better the human colour impression matches reality.

Typical illuminance levels in workspaces are specified in Annex 1 of ASR A3.4. The example of point 4 "Offices and office-like workplaces" in the table in Annex 1 shows that the minimum illuminance levels range from 200 lx (archive) to 750 lx (technical drawing by hand). For this reason, illuminance levels must be specified and implemented individually for specific workplaces.

Line of sight to the outside

Workspaces may only be operated if they have a visual connection to the outside and daylight. A line of sight to the outside enables visual contact with the environment. It supports the positive effects of daylight in the workplace and helps to maintain physical and mental health. A connection to the outside world through a view of the surroundings makes it possible to experience the course of the day and the weather and reduces the feeling of being trapped in the room. 

The line of sight to the outside must allow a view from the respective room and can be provided, for example, by windows, transparent doors or transparent wall surfaces. A line of sight to the outside through another room can fulfil the requirement for a line of sight to the outside under certain circumstances if the requirement for sufficient daylight is fulfilled at the same time and visual contact to the outside is actually provided.

The requirements for the position and area of the visual connection must be met in each room, whereby the area of the visual connection must be determined from the total floor area of all rooms served by the visual connection. Up to a room floor area of 600 m2 , the size of the areas intended as visual connections must be at least 1/10 of the room floor area. For larger rooms, the size of the line of sight must be at least 60 m2. 

The total area of the visual connection should be at least:

  • 1.25 m2 with a room depth of up to and including 5.0 m and
  • 1.50 m2 with a room depth of more than 5.0 m.

The lower edge of the surfaces intended for visual contact (Figure 1, hLE glass) should be a maximum of 0.95 m above the room floor for predominantly seated work and a maximum of 1.25 m above the room floor for predominantly standing work. The upper edge (hUE glass) should be at least 2.20 m above the floor.