How to? Enabling "add light tracing"
I've tried to create caustic using caustic caching but it crashes everytime...it seems that it eats a lot of RAM
How to? Enabling "add light tracing"
With point light in the inner part of the light fixture or at the end of?
Yes, "add light tracing", but don't enable the caustic photon cache.
Doesn't really matter, the cone should not touch the fixture anyway. And a point light is always invisible.
The ceiling spotlights contain a meshlight with disabled DLS (direct light sampling) and very low gain, just so the camera sees a white surface. Their main lighting comes from a spotlight positioned directly below the meshlight.
I usually use light points. I make lampshade from two parts. The inner a volume object with material matte (white 1,1,1) and the outer part (actually a copy of the inner but a bit larger and overlapping) with a second material, one that makes the lamp‘s appearance. Do not use single layer objects. Build the lampshade with e.g. boolean operation difference with e.g. cones or make a spin object from a mesh converted curve and then fix the normals (recalculate or flip directions, all face normals should point outwards) in edit mode.