That should not be an issue given that objects can be part of any number of collections.
One of the issues with light/shadow linking from my limited test in my personal opinion is the user experience. Itâs kind of annoying to manage collections for light linking in certain circumstances.
An update to the UI could help, such as the proposed changes by Pablo Vazquez: Blender Chat
The most noticeable change is the addition of + and - buttons.
Specifically this proposed idea could be useful:
Ideally I think [the + button] could:
- If there are selected objects, add them to the list
- If there are no selected objects, pop up the search dialog to type an objectâs name and add it quickly
Maybe an eye dropper (object selector) could be useful too?
It also helps if people learn about all the different ways lights can be linked to objects, as some are easier to manage than others. They are documented on the release notes page, but not all people have read them. Here are some videos showing the different ways.
Using an existing collection (Less than ideal for some situations):
Using the linking menu to link objects to lights (can be opened with Ctrl + L):
Drag and drop into Light Linking Collection (You can drag collections as well):
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While we do want to give the maximum control to technical artists throughout the studio pipeline via collections, we are also aware that there are cases where simple list and couple of operators will bring the desired goal of a scene quicker. And we do want to make the latter use-case easier and more clear.
The interface changes youâre describing makes sense. There are some technical details in the code why it is taking longer that it seems it should, but it is definitely something weâd be working on next for the light linking project.
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I also noticed that when using the âexisting collectionâ method, if you decide to remove an object from the light linking panel (using the little x), it deletes the object from your scene. Is that the intended outcome?
If a user decides to use the âexisting collectionâ method, It might be better to have Blender duplicate and rename the âexisting collectionâ to a linked collection so if someone decides to remove it, the object wonât be deleted because it still exists in the original âexisting collectionâ.
Itâs not deleting the object, itâs unlinking it from the selected scene collection. And if thatâs the only collection itâs in, then it gets removed from the scene, and looks like itâs been deleted.
I think this behavior is just inherited from how light linking is kind of designed to be used. If instead of using a scene collection and you press the âNewâ button in the light linking panel. Then every object you add there will be in your scene and linked to the light linking collection. When you press the X button, the objects will be unlinked from the light linking collection, but leaving your link in your original scene/collection.
I understand why this is a desirable thing, but I personally donât like this approach. Assuming there were no other changes made to Blender, this leads to an issue. You canât manage which objects are inside the light linked collection through the outliner without adjusting the outliner view settings (most people wonât do that). And most people will use the âexisting collectionâ approach because they can manage objects in the collection through the outliner.
Modifications could be made to Blender to keep the two collections in sync with the exception of the objects that have been Xed to get around that issue. But Iâm not sure how easy this is or if itâs desirable.
Another issue comes to mind. Letâs just say you have a collection called Box and in it an object called Cube. If you link that collection to a light, it will create a duplicate collection called Box - Light Linking. Now lets say I press the X button on âCubeâ. Itâs gone from Box - Light Linking but still in Box. If I wanted to add Cube back to the light linking collection, how would I do it? I could use the link menu Ctrl + L or the drag and drop method in the UI. But then at that point itâs no different from Pressing the New button in the UI instead of using an existing collection.
Maybe a better solution exists?
- Maybe Light Linking Collections are put in the active scene and viewlayer? And when you use an existing scene collection, it creates a duplicate of the collection with all the objects linked together? (Very similar to what you proposed, but now everything is in the current scene and viewlayer allowing for easy management of the collection from within the outliner)
- This does have the issue that multiple lights canât share a scene collection. And if all light linking collections are a âscene collectionâ, then lights canât share collections at all.
- Donât use collections at all?
- This will remove some of the flexibility of managing light linking collections in the outliner. And I believe there is a preference to using collections due to it being similar to how USD(?) handles light linking.
- Maybe hide the X button when a collection is a scene collection?
- Maybe if an object is linked to only one collection in the current scene and viewlayer, and you press the X button, a pop up appears âAre you sure you want to unlink this object from the scene?â
- Maybe this sort of pop up will appear no matter how many collections the object is in, as long as one of them is the current scene and viewlayer.
Maybe someone else has a better idea.
Is there a convenient way to assign a linking collection to multiple lights? Copy to Selected (and Alt shortcut for that) is not enabled for the collection assignment.
Setting a collection as light emitter collection might be useful. (And maybe the same for light group too?)
As it is now we still get the bounce from the light onto the unlinked object, will this get fixed? 
And the behavior of the light on and off buttons are quite strange to say the least. Canât really say that I understand whatâs it doing.
Also when having both objects enabled the light will only shine on them (except for hat bounce that is), and then disabling one of them will do what you expect to not shine on that one, but then if you manage to disable both (this might take a while because of the funky behavior) the light will all of a sudden shine on everything else. I guess we can learn to live with that, but I still find it a bit odd.
And tbh, have a look how Maya does light linking, itâs much more intuitive than this
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For various use cases, this is the desired effect (E.G. You use light linking to selectively light a character, and you want them to look consistent in mirrors, or through glass, or when theyâre close to a diffuse surface, all bounce lighting effects). Maybe settings could be exposed to allow turning this off. But this decision will have to be made by the Blender/Cycles developers.
Note: You can reduce the max bounces of a light to 0 to get this effect now. Itâs in the light settings section (the same place you change the light colour and strength)
Once again, this may be the desired effect. Turning off all light links results in the light linking to everything else.
This means that if you have a light and you want it to shine onto all objects except a few, then you can do that my selecting the objects you donât want to shine onto, add them to the light group, then disable them, as opposed to adding every objects to the light group then disabling the ones you donât want to shine on.
Obviously. Arguments can be made in both directions for both of these behaviours, and these arguments are valid. So weâll probably have to see how the Blender/Cycles developers feel about this.
Yeah for some use cases this might be desirable, but thatâs probably more of an edge case than general use. So a toggle for bounce or no bounce would be nice, but it really should be defaulted to no bounce.
Reducing the max bounces to 0 of the lights is a workaround that I personally wouldnât use since you probably want the light to behave normally for the stuff the stuff thatâs not light linked away.
It might be what they intended yes, but it still feels a bit odd.
I suspect weâre talking about different things. You can select a single light and set itâs light bounces to 0 while leaving the rest at their default. Iâve attached an image showing where it is. And since youâre changing the bounces to 0 only for the light thatâs light linked, it will have no effect on the lights that arenât light linked to other things.
Yeah I was talking about that one (accidentally wrote an S after the first âlightâ). It will affect how that light behaves with the other stuff in the scene which is probably not desirable.
Yeah sorry, I forgot about the case for when you want bounces between objects inside a light linked collection, but no bounces outside the light linked collection.