体积聚光灯

This method is inspired by elindells post on blenderartist using motion blur to fake volumetric.

Though, his method looks way more realistic it takes many, many samples to get a noise–free image.

I tried to find a similar method to reduce the amount of samples and came up with this. Well, it renders faster indeed, but it also has its flaws. The setup is pretty complex but also allows more configuration. However, both methods have a problem with animation (due to the motion blur obviously).

In general it is a rotating cone, which will fade when Motion Blur is turned on. The actual light comes from another normal Cycles spotlight.