Question Of The Month: What Makes Grazing Light Visible?

Sidelight is light that falls from the side of a surface, more or less parallel to its surface. It can be diffuse light or a sharp beam created by artificial light or sunlight. In the grazing light, contours and unevenness of component surfaces are clearly visible through strong shading.

Differences of opinion about coated surfaces are often based on unevenness of the surface, which is highlighted by grazing light. A wall surface can only be assessed with grazing light if such a lighting situation is customary. Before and during painting work, the painter often cannot see to what extent the final lighting creates grazing light. For this reason, the light sources should be installed before the coating is carried out to reflect the actual lighting conditions.

Irregularities that are only visible for a limited period of time due to natural light from the side are generally acceptable. For most of the time of day, these irregularities are not visible. An assessment must be rejected if a lighting simulation, for example by illuminating with a headlight, is completely unusual and does not occur when actually used.

A common point of controversy when using gypsum boards as planking for walls and ceilings is noticeable marks of the filler on the board edges, which are particularly visible with grazing light. The basic performance of such substrates often only includes the standard filler Q2. This is for roughly structured wall cladding, such as B. woodchip wallpaper, suitable. In the case of silk wallpapers, metal wallpapers or glossy coatings, full-area special fillings are required, e.g. B. in quality levels Q3 or Q4, since annoying stripes should be avoided. The acceptability of any irregularities therefore depends, among other things, on whether special fillings were advertised, or whether the processor had expressed concerns about insufficient fillings prior to execution. Bumps on façades are often visible for a few minutes on sunny days when sunlight strikes the facade or a lighting fixture is switched on in the dark season. Such irregularities - or only visible from an unusual observer position - do not justify a claim for defects. Irregularities caused by grazing light can depend on many factors and must be checked individually in individual cases. Irregularities caused by grazing light can depend on many factors and must be checked individually in individual cases. Irregularities caused by grazing light can depend on many factors and must be checked individually in individual cases.