Vertical illumination emphasises the wall faces in terms of their physical makeup. The room is made to look bigger by brightening its walls and ceiling. Directed light makes the wall surface much more vivid. As the wall height increases the distance of the luminaire to the wall must be increased. The reduction of the mean illuminance on the wall can be compensated for by having a higher lamp power and by increasing the number of luminaires.

Lighting criteria for high walls:
- uniformity of lighting
- the choice of lamp determines the light colour and colour rendition