Lighting of VDU workstations
Working in front of a screen demands particular requirements of the eyes. Professional lighting is a condition for good visual functioning and optimized visibility.
Flawless and fatigue-proof vision is dependent on the lighting level, which is measured through the illuminance (Lux (lx)). The challenge now is: The more difficult the visual task, the higher should be the illuminance.
Equal illuminance within a room is generally described as disturbing and it increases the energy consumption. Therefore these three types of lighting are usually used in offices:
- Room related lighting
It creates equal visual conditions in all areas of a room and is independent of the arrangement of workstations.
> Minimum illuminance: 300 lx
- Work area related lighting
Refers to the work area itself (desks, meeting desks, functional surfaces) including the individual movement area.
> Minimum illuminance: 500 lx
- Subarea related lighting
A subarea of the workplace of at least 600 x 600 mm should have a higher illuminance to improve the readability of printed documents.
> Recommended illuminance: 750 lx
The measurement is always at a height of 0.75 meters above the floor. Attention should be paid to the illumination level, which is decreasing because of aging and pollution of light sources. Therefore it might be necessary to install higher illuminance levels. Higher illumination levels are also useful when the working task sets high standards to the vision at a workplace.
At workstations and within the working environment you should allow for a well-balanced luminance intensity of all areas.
The following contrast ratio is suggested:
- For the direct field of vision a ratio of 3:1.
- For the extended field of vision (working environment) a ratio of 10:1 should not be exceeded.
Glare affects the vision and optimal visibility, which leads to higher error rates and to early fatigue. Among others the VDU work regulation dictates the prevention of glare as it can lead to an impairment of health, too.
One has to distinguish between two types of glare:
- Direct glare
Direct glare occurs from excessive luminance contrasts and can reach the face area through window areas or non-protected light sources.
- Reflected glare
Reflected glare occurs by the reflection of light on glossy surfaces (screen, keyboard, desktop, walls etc.).
Appropriate measures to avoid glare:
- Arrangement of work stations so that the vision is parallel to the main windows of the office.
- If there is a strong incidence of light from the outside, an adjustable light protection should be installed.
- Parallel arrangement of linear fluorescent luminaries to windows.
- Lateral positioning of luminaries for direct lighting to the workplace.
- Incidence of light diagonally from above.
- Usage of fluorescent lamp.
- Compliance with the suggested levels of reflection for desktops, furnitures and equipment.
The VBG recommends the following levels of reflection:
- Sealing: 0.7 to 0.9 %
- Walls: 0.5 to 0.8 %
- Floor: 0.2 to 0.4 %
Regarding desktops, furnitures and equipment a reflection level of 0,15 to 0,75 % at a gloss level of mat to silk-mat is acceptable.
Optimal workplace lighting
Case studies show that a lighting concept, which combines ceiling lights with individually adjustable workplace lighting leads to better wellbeing and less fatigue of the user. Reasons for this are manifold:
- Humans have different lighting requirements.
- Visual tasks vary.
- Many visual objects are glossy.
- Some visual tasks require a special direction of light incidence.
- Humans have different sizes and adopt different postures.
Therefore the so called 3-components-lighting is ideal. It supplements to a mainly indirect illumination from workplace lightings. The “mainly indirect illumination” can be achieved through hanging ceiling lights, which bring 30 per cent of the luminous flux with low luminance to the lower workplace and 70 per cent to walls and ceilings. Corresponding results can also be achieved with standard lamps, which do offer more flexibility.