Illuminance on calculation areas.
The areas to be lit are task areas, immediate surrounds and background areas. The illuminance and its distribution have a great impact on how quickly, safely and comfortably a person carries out the visual task.
To give a perceptual difference the recommended steps of illuminance in lux:
20 - 30 - 50 - 75 - 100 - 150 - 200 - 300 - 500 - 750 - 1000 - 1500 - 2000 - 3000 - 5000
Illuminance on task and activity area
The values given in Tables (6.3) are maintained illuminances over the task or activity area on a surface which can be horizontal, vertical or inclined. The average illuminance for each task shall not fall below the chosen value, regardless of the age of the installation.
The value of the illuminance may be adjusted by at least one step in the scale of illuminances, if the visual conditions differ from the normal assumptions.
The required maintained illuminance should be increased when:
Visual work is critical
Errors are costly to rectify
Accuracy, higher productivity or increased concentration is of great importance
Task details are unusually small size or low contrast
The task is undertaken for an unusually long time
The task or activity area has a low daylight provision
The visual capacity of the worker is below normal
For work stations where the task or activity area are unknown:
The whole area should be treated as task area
The whole area is uniformly lit to an illuminance level specified by the designer.
If the type of the task is not known, the designer has to make assumptions about the likely tasks. This also applies to the activity areas.
Illuminance on the immediate surrounding area
The immediate surrounding area should be a band with a width of at least of 0.5m around the task area. Large spatial variations in illuminance around the task area can lead to visual stress and discomfort.
The illuminance of the surrounding area shall be related to the illuminance of the task and shall provide a well balanced luminance distribution in the visual field. The illuminance may be lower than the illuminance on the task area but shall not be less than the values in the table below.
Illuminance of the background area
In indoor workplaces, a large area outside the immediate surrounding area needs to be illuminated. This is very important in spaces with a lack of daylight.
The area known as the background area should be a band around the immediate surrounding area within the limits of the space. It should be illuminated with a maintained illuminance of ⅓ of the value of the immediate surrounding area.
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