Dome light vs. Environment for HDR

[ModelT]

Hey guys,

Well watching tons of 3DS max videos to learn V-ray but a lot of questions came across. I'll try to post them separately for users finding them easily.

First one is about dome vs. environment to light a scene with an HDR, what's the pros and cons?

[ingoerik]

DomeLight is easier to handle and to copy from scene to scene, the only advantage for Environment is in my eyes that you can move the sky up and down, that doesn't work with the DomeLight.

[vladimir.nedev]

The Dome light uses importance sampling, so if you have a true HDR with some very bright spots ( like a sun ), it will clear the noise much faster.
In V-Ray for Modo, there is an Environment Importance Sampling option in the V-Ray GI tab (enabled by default), which internally turns the environment into a textured dome light, so you don't have to do it manually.

You might still want to use a textured dome light, in case you need to output the dome light to a light select element, or link it for reflections/refractions to only certain objects.
You can't do these things with the EIS dome light.

Greeetings,
Vladimir Nedev

[ModelT]

Wow! Thanks Vlad, really valuable information, didn’t realize about the reflections for isolated objects. What a treasure!

[Cry0]

internally turns the environment into a textured dome light, so you don't have to do it manually.

And if I want to do it manually, how to match exactly dome light setting to the environment?

[vladimir.nedev]

In order to match the light intensity of a Dome light and an environment
you must multiply the intensity of the environment by 6.28 and enter that as the Dome light's radiance.
You must also enable dome spherical in the V-Ray Light tab.

Greetings,
Vladimir Nedev

[Cry0]

I get same pixel info readings on background, but the lighting on the object is different. Maybe I'm missing something important?

[vladimir.nedev]

Did you turn off the Environment importance sampling from the V-Ray GI tab when you added the Dome light ?
If you don't, it will be like 2 dome lights in your scene.

Greetings,
Vladimir Nedev

[Cry0]

Turning off environment importance sampling helped, thank you. But its kind of strange, because when I use black environment or set intensity to zero I get the same dark result. If Vray convert environment to a dome light I thought that it just will not contribute to the overall lighting, when using dome light with texture

[vladimir.nedev]

It's a bit confusing, I agree.
But currently there is no such logic, i.e. to turn off the environment dome light, if there is another dome light in the scene.

Could be, you are using the separate dome light for a different purpose, not as an environment replacement.
Although I am not sure if that makes sense.

Greetings,
Vladimir Nedev