Lumen - what is this effect?

Development Rendering
,
1

Hello! There is a window (not nanite, if that matters) that is 10 units thick built in modeling mode, and I see a glow effect when I pan the camera around it:

Has anyone experienced this? I want to understand the reason, is it possible to somehow reduce it or is this how the lumen works. Maybe the effect is not so obvious on the video, but I have seen worse cases when a corner in a dark room starts to glow when you look at it and look up.

What I have tried:

  • change distance field resolution
  • conversion to nanite
  • disable any auto exposure
  • merging a wall and a window into one actor
  • increase GI quality
  • made sure that it does not depend on hardware or software method

But nothing helps. I also noticed a similar effect with bad geometry (not optimal for lumens), with one-sided geometry, badly aligned meshes and it is often clear what the problem is. In this case, the wall and window are closed meshes and are aligned tightly. If I lower the albedo color, set the gray color to 50%, the effect is noticeably reduced. However, I can’t refuse white, I initially had it around 0.8, which seems to be normal.

It seems to me that I am very picky, in a third-person game this will probably not be a problem, but I have an fps game. That I really miss some practical guide on how to make meshes for a lumen, yes, the documentation indicates limitations, but this does not always help.

And another small question - does anyone know if the developers plan to support one-sided geometry or should I forget about it?

2

It’s auto exposure.

You should be able to turn it off in the project settings, but that doesn’t work at the moment.

You have to do it on the actual camera you’ll be using. So, either the sequencer or player camera.

1 Like
3

The less the scene matches the lumen debug views, the more it relies on screen space. Since that short wall is missing in the debug views, screen space is doing a lot of work to compensate. Your window might need to be broken up into separate parts.

5

Thanks for the answer!

Are you saying that lumen uses screen space when it’s hard for him to illuminate some geometry? Then I should just split the objects into smaller ones until I get a good picture in lumen debugging? But in this case, the buildings will consist of a huge number of objects and textures. Yes, all this can be optimized, but I am very disappointed by the need to have such small parts. After all, they are inconvenient to work with to build a building.

By the way, I managed to slightly reduce the brightness of this effect with the r.Lumen.DiffuseIndirect.SurfaceBias command, values ​​of 1 or 2 work acceptable.
but this causes a vignette effect, if you set the value to 0 and come very close to the wall, you will see a blackout at the edges of the screen.

6

Thanks for the tip! Indeed, the character’s camera had autoexposure, now I turned it off, and when I move around the room, the exposure remains static, now I’m completely sure of it. But, unfortunately, this did not affect the effect I’m talking about. Above, I wrote about the r.Lumen.DiffuseIndirect.SurfaceBias command, which helped me a little. I will continue my research today and will write if I find something interesting.

1 Like