What is PolylightEffect?

Can anyone explain what PolylightEffect is?

The manual and class reference description are a bit confusing.

For example what is a LightGroup?
Does this effect do something like setColorScale() internally on the node? I don’t see how multiple “PolylightNodes” could affect a single node then.

A PolylightNode basically just does a setColorScale() every frame on all of the nearby objects. It knows about other PolylightNodes, so they all work together to give a single setColorScale() to each object.

It’s cheap in the sense that it doesn’t involve OpenGL lighting and thus has no limit on the number of lights. It’s expensive in the sense that it’s performed on the CPU and can directly impact your frame rate.