Modelling is the balance between diffuse and directional lighting, and is a property of light whereby an illuminated object is made to look natural, neither too flattened nor too hard or sharply illuminated. The general appearance of an interior is reinforced when its structural features, as well as people and objects in the room, are illuminated so that the shape and texture appear clear and pleasant.

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.