Best practice question - thousands of lights

[wizzackr]

Hi all, I have a question with regards how to best tackle this, as we have just finished a project where this was an issue:

We had to illuminate a bridge with literally thousands of little lights as you would find them on christmas decorations. Now lights were obviously neither necessary (no noticable shadow-casting) nor an option, so we opted for low-res geo as bulb stand-ins and a VRay light material shader on those. We also tried the normal vray material without any GI contribution, but that did not change anything. What did strike us in this scenario, was how rendertimes went up when there is lots of tiny very bright objects in the scene: As this was an animation and the lights would come on one after the other, rendertimes skyrocketed on full-HD frames to often well above an hour/frame as lights came on. The scene rendered super fast once the lights were off (maybe 10 min/frame max).
This is why I bring this up: Is there any better way to tackle this? We brute-forced our way out of this one, but something tells me there is a cleverer way to do this Some sampler setting that shoud be considered or something similar? Any insight would be greatly appreciated.

Finally the most important thing: All the best to all of you. Have a great time, enjoy your families & merry christmas!
J

[stezza]

I had a similar project this year for a xmas animation and with the lights I simply put a flat shader on them and created a render element. Then in comp added brightness and glow.

[dgruwier]

VRay handles massive amounts of lights very well with the Adaptive light evaluation feature, which is enabled by default. Thing is, it only works with true lights.

The VRayLightMtl is a GI effect by default, otherwise it couldn't be layered with other shaders. You can make it act like a true mesh light by ticking "Direct Illum" on the shader (Make sure it's assigned directly to the bulbs.). You can also do it by creating a VRayLightMesh and adding your bulbs to that set, same result.

[wizzackr]

Hey guys, thanks for the input.

Dgruwier, while I agree with your opinion with regards to how well vray handles lots of lights. Still, I was looking for something that is easier to compute and not add even more to any render time - as real lights would.

It seems the sampler performance drops very noticeably when there is lots of very bright spots and I was wondering if there was a way to remedy that.

[dgruwier]

So we're talking purely about rendering the actual bulbs themselves, there's no light involved at all? In that case, what Stezza suggested seems like the simplest solution. You could even just do an object matte for the light bulbs, and use than in comp. I don't think there really is a best practice for such a specific situation.

Otherwise, you could try optimizing the scene by moving the lights to a seperate render layer where everything but the bulbs are matte objects, and then either lower the brightness of the bulbs or the max subdiv samples to prevent VRay from using a lot of samples on bright edges. And using real lights may actually still yield some improvement in sampling time, even when not used for illumination.