When the scene is lighted with “Spot” or “Point” light sources, the rays from such lamps do not propagate in parallel. This makes noticeable distortion, for example when lighting with textures.
The parallel ray’s propagation (orthogonally to its plane) we can get from the “Sun” lamp, but such light source does not support lightning with textures.
We can get parallel propagation of rays from the “Spot” and “Point” light source, to exclude visible distortions, with nodes.
A common node tree for lighting with texture looks like the following:
Texture distortion is clearly visible at the edges of the lighting cone.
To remove them, we can use the combination of the following nodes:
by embedding them in the node tree between the “Texture Coordinate” and “Mapping” nodes.
In this case, the rays from the light source will be casting parallel to its Z-axis (normal) and texture distortions will be removed: