Illuminance at the visual task area

The illuminance values standardised in European standards such as EN 12464-1 are maintained values on the respective reference values, e.g. the visual task area, which can be horizontal, vertical or tilted. Independent of age and state of the lighting installation, the average illuminance for the respective visual task must not sink below the maintained value. The values apply for normal visual conditions and account for the following factors:

• psychological and physiological aspects such as visual comfort and well-being

• visual task requirements

• visual ergonomics

• practical experience

• safety

• efficiency

The maintained illuminance can be adjusted by at least one level on the illuminance scale when visual conditions deviate from normal assumptions. Under normal lighting conditions, roughly 20 lx are required to be able to rudimentarily recognise facial features. Thus, this is the lowest value of the applicable illuminance scale for work places.

A factor of roughly 1,5 constitutes the smallest significant difference for a barely perceptible change in illuminance effective in terms of visual performance.

The recommended illuminance scale (in lx) is derived from this: 20 · 30 · 50 · 75 · 100 · 150 · 200 · 300 · 500 · 750 · 1.000 · 1.500 · 2.000 · 3.000 · 5.000.

The standardised values are minimum values representing a compromise between physiological, psychological and ergonomic necessaries and the economically justifiable. From this follows that the values should be raised by one level where complicated visual conditions are on hand. Undercuts are only admissible where the visual task features particularly large details and high contrast levels or is only performed over a short period of time.

More recent studies have shown that illuminance levels above the standard yield increased readiness to perform and well-being for people, and thus elevated productivity and added economic benefits.

The required maintained value according to EN 12464-1 should be increased, if

• the visual task is critical for the work sequence,

• a correction of faults leads to elevated costs,

• precision or elevated productivity are of high importance,

• the working person’s visual faculty is below average,

• the visual task features particularly small details or especially low contrast levels,

• the visual task has to be performed over a particularly long period of time.

The required maintained illuminance can be set lower in accordance with EN 12464-1 if

• the visual task features particularly large details or especially high contrast levels,

• the visual task is only performed over a particularly short period of time.

At permanently manned workstations inside buildings, a maintained illuminance of at least 200 lx must be provided, unless operational or physiological/optical reasons require deviations, e.g. in photographic laboratory darkrooms.

Where tasks matching those performed in indoor rooms are performed at fixed outdoor workstations, e.g. work at wood processing machines, they must be provided with the illuminance specified for the performance of these tasks in indoor rooms according to EN 12464-1.

In rooms or room zones intended for permanent human occupancy, a minimum maintained illuminance of 100 lx is required.

Figure contains a matrix for the purpose of determining maintained illuminance based on YES/NO decisions relating to the criteria for complicated or facilitated visual conditions specified in EN 12464-1.

Evaluation starts at the top with the illuminance defined for the visual task area. If visual conditions do not deviate from normal conditions, it is possible to go directly from question 1 to the next question below.

If the question of particular visual conditions is answered with YES, illuminance must be increased or reduced by one level. After deciding on questions 1 through 8, the next step is the maintained illuminance which must serve as the basis for planning with consideration of visual conditions deviating from the norm.

If, upon passing through the entire Matrix, the result is that the illuminance must be increased by more than 2 levels due to particular conditions, e.g. from 300 lx to more than 750 lx, it must be assumed that the visual task was not classified correctly with regard to visual details and work organisation according to the tables of, for example, EN 12464-1.