Skylight with Lumen

Development Rendering
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Hi, so how do we activate skylight GI with lumen? No matter what I try skylight doesn’t affect the GI. Current documentation doesn’t mention anything special has to be activated. It only mentions that Skylight is solved in " Lumen’s Final Gather".

I checked the console commands and the closest I found is “r.Lumen.IrradianceFieldGather” which is disabled by default. If I turn it on, lighting changes, but for worse and performance goes up, but still no GI from skylight (Indirect light intensity doesn’t do anything even with huge values).

So I have interiors still very dark, there is some GI from the directional light, but it’s insufficient, only boosting “Indirect lighting intensity” to huge values (like 50) seems to lit the interior.

Any ideas?

Thanks

Edit: Yes, I misread “rLumen.IrradianceFieldGather” as “…FinalGather” :blush:

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I also made some experiments with Global Illumination. At first I too thought that it doesn’t work. What I found out after some trial and error is that the default PostProcessing Exposure Settings seem too be bad or maybe even bugged.

I changed the Exposure in PostProcessingVolume to:
image

If I change the Metering Mode to “Auto Expose Histogram”, which is the default, the scene stays dark If the scene is very dark.

Below is the test environment i used. Skylight only.

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Edit: To clarify the “Auto Expose Histogram” Exposure only stays dark if you actually look into the dark corner.
“Auto Expose Histogram”

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image1843×1251 41.6 KB

“Auto Expose Basic”
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image1848×1258 90.4 KB

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Yeah, after further testing, it seems like the skylight is really contributing to the GI. I don’t think it’s even issue with the default auto-exposure setting. The issue seems to be that in these kind of “extreme” test scenarios, it’s contribution at least seems too low to even notice sometimes (still it could be physically correct, not sure).

What initially confused me is that with all the lights (including rectangular), the parameter “Indirect Lighting Intensity” allows you to tweak the contribution intensity to GI solution, but it does nothing on the skylight.

Also volumetric exponential fog seems to have some effect.

I hope we will be able to tweak the skylight through the “Indirect Lighting Intensity” at least for artistic if not realistic purposes.

I’m really impressed so far with Lumen. Emissive materials look really good.
Looking forward any improvements :slightly_smiling_face:

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I am also experimenting with Lumen. For new projects, it seems to be working automatically :slight_smile:

There is new article in documentation.

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From my current experience in Archiz, Lumen will be usable only after stationary baked lightmaps will be added to work with Lumen as well. Otherwise there is too much “blinking” in poorly lit interior areas (2+ light bounces).

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I found a fix for the intensity changing not working with the skylight. Just simply remove the reflection sphere and you can then change the intensity.

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“Indirect Lighting Intensity” works for you?

Because “Intensity Scale” worked before, it’s just I would love to be able to tweak the skylight contribution to GI separately from It’s general intensity like it’s possible with all the other lights.

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Looks like UE5 preview 1 introduced variaty of new Lumen setting including cache update speed and more :blush:

During my archivz rendering it also helped to have several (16-32) antialiasing subframes + warmup frames in render queue so that Lumen is properly “settled”/warmed up.

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