What is the purpose of light tree in render settings?

[shaili.dewangan (Shaili)]

I see this getting computed the most when we are rendering particles which have emission on them.

For example, when I turn light tree on - it took a frame 1 min 14 seconds to render. And turning off light tree made the render time 4 seconds.

And another question for blender particles:

What does point 8 mean?

Basically, the premise of this research is how to make particle process (set up and bake) fast and render efficient. Any tips on the same would be greatly appreciated.

[goorman (Sergey)]

Hi,

I think when it says particle group or whatever, means that you would need to render exactly those objects that are appear in your camera field view. I have found something about this here:

Only render hair that are actually visible?

Hi Thomas, Not sure if I can help but maybe this will work: Make an object (object A) that is as big (or a little bit bigger) as the view of the camera, also in depth. Animatie so it moves with the camera. Use object A to dynamic paint the hair particle on the object it’s on. And put object A on a different layer so it will not render. This way, I think, the particle will only show up in the part of where object A hits the emitter. HAven’t tested it but i think it should work …

Hope it would help you anyway

As for the object group, I’m not sure, but maybe the author tried to say that you need to put your objects into a collection, but I have no clue how it could help to reduce the actual render time. But from what I know, you can use so-called Instance Collections. Means, if you have one object and you want to make a duplicate of it, let’s say, 4-5 times, you won’t have to just literally copy the original one by pressing Shift-D, because it will increase your polygons’ count at the same time. Instead of this, you can easily use Instance Collections, it works basically the same way, but here you will need to press Alt+D instead of Shift+D. The only thing about that is when you make an instance of your original object, you won’t be able to bring some different changes to that exact copied object, you be able to work only with the parent one, thus, no matter what would you do with your parent object, all instances will automatically take those changes on them, and at the same time you won’t be able to bring some changes to your instances ones. Hope I’ve explained that correctly

Hope that helps

Cheers,
Sergey

[etn249]

The light tree helps reduce the noise when a render has multiple light sources. It will help Cycles choose which lights needs to be sampled for each part of the scene instead of wasting rays on lights that are far away or hidden.

If you were to render, let’s say, a Christmas scene with hundreds of lights everywhere, the light tree would help a lot and will make the noise clear in a reasonable amount of time. However, if you render a scene with just one or 2 lights, it might be better to turn it off, because it does have a performance cost.