Light Importance

[Leandro Oliveira]

Hi. This attribute is quite abstract to me. I have been watched some tutorials, which the author uses values like 5, 20, 50... I´ve understood that importance determines what light needs more computation power. But, in a scene with 3 lights sources, wouldn´t be easier to setup values like 1, 2 and 3? How can I know the correct value for each light source in a scene, and what exactly these numbers mean?

Thanks,

[Sharlybg]

You can setup light easily if you do it one by one :

Let say i'm rendering a particular interior project with HDRi/mesh light for the ceiling/ floor lamp. So here i have 3 light sources.Each light don't contribute to the final image at the same level. Also a particular light could introduce a lot of noise. So my setup start this way :

Turn ON each light individually to see wich one bring more light and wich one introduce more noise.Let say the HDRi is fine and bring enough light and the noise is easy to clean for the engine. But the floor lamp don't contribute that much to the lighting but give a lot of unresolved noise. In this case i just reduce the importance value of the Floor lamp compared to the HDRi and spot light.

More contribution to the lighting == Higher importance (more computation to this light)
Low contribution high noise == Lower importance ( less computation power for the light)
More contribution high noise == Higher importance (more computation to this light)

[CodeHD]

But, in a scene with 3 lights sources, wouldn´t be easier to setup values like 1, 2 and 3?

The light importance is not just a discrete sorting as with volume priorities. It basically tells you how often the respective light source is picked in the step where light sources are sampled. So if you set values of 1, 1 and 999999999, you effectively remove the first two light sources

[Leandro Oliveira]

Thank you Sharly and CodeHD!

Sharly, great explanation! It opened my eyes! Thanks a lot!