The immediate surrounding area is adjacent to the visual task area. It consists of areas in the field of vision surrounding the visual task area – according to EN 12464-1 – which are at least 0,5 m wide. The next area is the background, for which EN 12464-1 also contains photometric specifications (see section 22.214.171.124 "Background lighting").
The luminance distribution in the entire field of vision which consists of the visual task area and its immediate surrounding as well as the near and distant vicinity determines the state of adaptation and, correspondingly, visual performance. The width of the immediate surrounding area according to EN 12464-1 of at least 0,5 m is sufficient for small visual task areas, e.g. a horologist workstation, however insufficient for extended visual task areas, e.g. a lathe workstation, where it can measure up to 3,0 m. Particularly for workstations in industrial or handcraft applications, the surrounding area must be determined contingent on the dimensions of the visual task area.
Assuming that the visual task area with the depth a (see also figure) is similar to the ergonomically corresponding handling area, the immediate surrounding area should be larger than the visual task area by a measure a of at least for visual reasons. In order to be able to apply rectangular coordinates to calculate illuminance and uniformity, it is helpful to replace both areas with tangent rectangles (figure).