Raking light

Raking light, the illumination of objects from a light source at an oblique angle or almost parallel to the surface, provides information on the surface topography and relief of the artefact thus lit.

[1] In some instances, raking light may help reveal pentimenti (changes in an artist's intention).

[2] In the case of wall paintings, raking light helps show preparatory techniques such as incisions in the plaster support.

[3] Conservators examine objects under raking light during a visual inspection and for condition recording.

[4] In the examination of wall paintings, raking light can help document surface deterioration phenomena such as the efflorescence of salts and micro-delamination, and may be used for monitoring the effects of conservation interventions.

Raking light across a wall, gives a relief like impression.
Sunlight at a narrow angle, flowers in the window cast long shadows on an inner wall.