Hi all,
I was hoping that with UE5.3 this issue would be resolve or at least vastly improved but while 5.3 did resolve issue with multi-bounce reflection. I’m still seeing horrible artifacts caused by secondary light bounces for anything not in camera view (surface cache). I’ve attached a screencap to show what I’m seeing. Any suggestions on improvement or fixes to this? This is the one thing that prevents me from achieving near perfect archviz renders in real-time. Thanks all!
What is your lumen scene lighting detail set to in the PPV?
I’m assuming your lights are analytical light sources, in which case the direct lighting should resolve more or less smoothly. You should be seeing some artifacting, but not as much as you are in this photo.
All Lumen settings are set to max, I’ve tried turning on/off various lumen visualization layers and lights. I noticed that these artifacts are caused by the GI light mostly.
Hmm, could you turn on your editor mode so the light radius is visible?
Sure, here’s the screen snippet with the lights selected, please let me know if you need more info or a better shot of the lights. There’s 4 lights in that bathroom alone and more in the next room that might bleed over a little bit.
Just in case any of my settings are off, here’s the snapshot of my PPV settings, thanks!
Edit: previous image got some settings messed up, was messing around with the parameters, here’s the what’s actually used.
Hmm, so you’re using IES profiles? I believe there shouldn’t be any problem with their interaction with lumen, but for some reason it looks like hit lighting isn’t affecting objects the way it should.
Ah, I see. Firstoff, make sure your ray lighting mode is set to ‘hit lighting for reflections’, and your lumen scene lighting quality can be cranked up to 8 for better GI in reflections. Let me know if that makes a difference.
This is already good enough for Lumen if you’re not using support hardware ray tracing.
That’s a nice improvement, thank you! The Ray Lighting Mode is already ‘Hit Lighting for Reflection’ but tuning lighting quality up to 8 stabilized the lights in reflection (minimalized the flickering) and improved the shadow quality.
Do you know if there’s anything else I can possibly do to improve up on this? Thanks!
Here’s the new screenshot:
I do have support for hardware raytracing turned on though 
If you want to achieve the highest quality and you can, use UE4 + ray tracing reflections.
Posts like this one is because I have created this comparison chart:
Thanks for that, what’s the rendering speed for it though? My team’s project requires dynamically changing assets and render on the fly and have rather strict rendering time requirements. It basically requires us to do this in semi-realtime.
Ok, so it’s for rendering, not creating interactive expereinces, right?
Than you can’t use baked lighting, so the most advanced dynamic lighting is Lumen… but in your case, I could try to use path tracing instead, as it’s almost realtime (but it isn’t).
Why @Arkiras ? I think it was behaving similarly to what he shows, in 5.2 too.
Yea, we actually did consider path-tracing but the rendering time is slower than what we need. After a lot of deliberation, we ended up sticking with Lumen.
Lumen is not a perfect solution to ArchVis by any means. Generally speaking it’s good enough, but there are enough failure cases that it can be quite troublesome.
This is obviously a bit hacky, but you could theoretically combine GPUlightmass for large objects, lumen reflections for specular lighting, and SSGI for small dynamic objects in the scene. That’s assuming you only need relatively small objects to move, but putting that all together means you can cheap and high-quality indirect lighting, dynamic objects receive indirect lighting via the probes system, reflections are high-quality and dynamic (which means specular occlusion for the dynamic objects), and you get enough bounce lighting from the screen traces to ground the scene.
That’s assuming you only need small parts of the scene to be dynamic. If you need full-scene dynamism, lumen really is your only option. That said, you could create a material that makes the mirror look fogged up from a shower or so, or just tweak the roughness slightly, and it may do the trick.
Example:
Obvious surface cache artifacts in this mirror sphere.
Even with this slight amount of roughness, some of the worst noise becomes less obvious and distinct.
Thank you for all of that information, I’ll take a jab at the hacky solution first and see how that goes, and will talk with my team about the less ideal solution as well, better a slightly blurry mirror than a bunch of bad looking shadow/light artifacts, but that’s just my opinion.
Thanks again for your help, really appreciated it!
Hi everyone, first post I do here.
I’ve been working on developing ArchViz using lumen, and this reflection artifacts have been the big issue that keeps puching back the full use of real-time visualization.
Thought worth it to share something I just found. The artifacts are affected by the indirect lighting from the light sources. Reducing the indirect lighting, reduces the amount of artifact.
Any ideas how this is realted to the artifacts?
