Light Group Improvements
There are already proposals on this but none of them mention how this would be interacted with on the user level.
With the way light groups are currently implemented, they are basically locked into a single workflow of adding light in the scene into different light groups and adding them together. Let's think of a solution to that.
Material-level light groups.
Minor extra feature, since an object can have multiple emissive materials, different materials could be able to render to different light groups. This would mean moving the light group settings from object to material settings.
Exclude light group from combined pass.
This is a big one, and actually the reason I'm writing this proposal. In the light group settings, you would be able to select individual light groups to exclude from the combined render pass AND all light passes.
You can also make the argument that this shouldn't even be an option and all light groups should be excluded from the combined pass by default, since I don't think there is a use case (without a very simple workaround) for having a light contribute to both the combined pass and a light group.
Light passes for individual light groups.
When you turn on the light passes, you should also get the individual passes for every light group. For performance reasons maybe you could set individual light groups to only deliver the combined pass?
Light group compositor node.
Addendum to above.
Light passes for every light group would create a parameter explosion on the render layers node, with each light group being able to add ~16 new outputs. Obvious solution is to remove the light groups from the render layers node and add a separate node where you can select a light group and pick its passes.
Denoise combined passes.
A simple checkbox that lets you denoise all of the combined passes of each light group. The light passes of each light group aren't denoised because the normal light passes aren't either.
2 Comments
"all light groups should be excluded from the combined pass by defaultall light groups should be excluded from the combined pass by default" Absolutelly not! It's called 'Combined' for a reason. If you want to exclude light passes from the combined why not assemble the combined pass yourself in the compositor? Just follow the formula from Blender manual: docs.blender.org/manual/en/latest/_images/render_layers_passes_combine.svg As for the material level light group that may be interesting yes, but currently you could just compose that out with cryptomattes.
When light groups are used, the combined pass becomes useless. You either have to add every light in the scene to a their own light group (which makes you lose access to all light-related render passes and GPU denoising), or render the light groups, save each as an individual file, and render the scene again with the light group lights turned off.