I tried to learn how to make volume scatter in Blender Cycles. Notice also those dust particles.
Camera and all objects are inside cube with mix shader (mixing volume absorption and volume scatter).
The spot light shines up and has extremely large strength.
Then I wanted white dust particles to be visible inside rays. I made a cube particle emitter and emitted from volume, then set them to small icosahedrons with diffuse.
They looked like dark spots. Changing shader to emissive rendered also dust in shaded areas. I tried to create emissive shader that emits only when illuminated, but light path node didn't help me.
Then I made a hemisphere emitter on the light and made it's particles die on impact. When simulated, only those inside ray shafts survived. Made them emissive.
There is a slanting plane above grating gathering shadow, so everything looks less boring.