Question: How do multiple DomeLights work?

[Art48]

Hi,

We recently started using HDRI Light Studio. Since with an HDRI workflow include/exclude becomes difficult we were wondering if we could just slap 2 domelights with different HDRIs in a scene and include/exclude the other one from certain geometry. So we tried it, and it worked. I wanna know why?

I mean basically if you have HDRI 1 with nothing excluded and HDRI 2 with some parts included, wouldnt a ray hit 2 different lighting solutions? How do you decide which HDRI to take? Does it only work when one HDRI is completely black in the area the other one is illuminating?

[tsvetan.geshev]

When you are using more, than one light, the global illumination is calculated just by adding the color of different light. You can check that, when you create 3 dome lights with red, green and blue color - the illumination will be white.
Reflection and refraction are random, so in your case it will be better to avoid illumination of one object from more, than one dome light.

[Art48]

Thank you very much for that info. That would be a suggestions I guess aswell for improving that behaviour.
You could make instead of random chosing a sample take the brighter one (or even make a setting for it and let the user decide if he wants the darker or brigther one). WOuld be useful in a HDRI workflow with multiple HDRIs

[vlado]

Why not just add the different HDRI's together with a VRayCompTex texture or something? Would be faster to render too.

Best regards,
Vlado

[Art48]

You're right Vlado. But any idea on how I would make this work with HDRI Light Studio? They support just a simple VRayHDRI in the texture slot AFAIK.

[Joelaff]

With the VRayCompTexture wouldn't it just become a single map?

I suppose you would use that combined map with one dome light for GI, but no reflection. Then put the individual maps into their own dome lights set for only reflection and excluded properly. Would that do it?