Quote - > Quote - > Quote - so the mathematical pure sphere is in the code?

and the code tells Lux if the sphere is bigger or smaller? 

Yes in the LuxRender engine. Hit-testing a ray against a sphere (a point and a radius) is mathematically the 2nd simplest thing to execute in ray tracing. The simplest is hit-testing against an infinite plane.

Even one triangle is more complicated than a sphere. A low-poly spherical mesh is about 100 times more expensive than a sphere.

Thanks! This is an important information. Does this mean all Lux "build-in" shapes () are mathematical solutions? If yes. wouldn't it make sens to replace spotlights with a disk-shape to make the lightsource visible in the scene if checked in the GUI?

Not a disk - that still throws light in all directions.

My render of the boxed point light earlier "points" the way. You want to have some kind of shell around an area light that contains the light - just like real life.

So - what I'm thinking to do is provide the ability to use any arbitrary prop as a shell around a light. Then I will provide two ways to set it.

1) For each spotlight, individually, you can pick a shell and it will be emitted as an area light inside the shell instead of a Lux spotlight. The shell will rotate and scale with the Poser spot light, so you can easily point it just as you do in Pose.
2) For all spotlights that don't have an individual shell assigned, define a default shell. This will have a separate toggle switch so you can leave the spotlights as they are.

This is very easy to do. And it gives me ideas for little products - a collection of spotlight shells that you can use in LuxPose.

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