Computes the lighting due to a single light and returns the shading.
The function input allows you to change how the shading is computed, there is also an option to compute the illuminance, which is just the amount of light hitting a spot regardless of the surface normal.
This allows you to select a single light to use for shading. If set to (none), all lights will be evaluated.
There's three shading models available, however, Raw Light and Half Lambert are mostly experimental.
If this is turned on, the node will compute received shadows. Otherwise they will be ignored.
The Function input allows you to attach a function to tweak the shading.
Colour: Lambert shading for the selected light. This is the raw shading, not modified by any surface values such as the colour.