This occurs when the light comes predominantly from one direction. The shadows that are necessary for good modelling are then formed without confusion.
Lighting should not usually be excessively directional as this may give rise to sharp, harsh shadows. It should also not be too diffuse, because the objects and space are then perceived as too dull and bland, and it becomes difficult to perceive the room and its details.
In order to achieve a good result for modelling, the ratio between cylindrical and horizontal illuminance at the reference plane needs to be controlled. A value between 0.3 and 0.6 provides a rough indication of good modelling.
The values for the cylindrical and horizontal illuminance must be calculated and checked at the same measurement points.