Real World lux values (sun, etc) vs Not

Posting a question… (UE5 GI/Lumen)

What are your thoughts on using real world lux values on lights (vs not) - I am working with a TD that really wants to match sun to 120k lumen intensity… as the ‘only way’ to achieve true light energy for GI, etc… thoughts on that? would really love to hear people’s thoughts/findings, etc…

I’ve read mixed results/opinions for it and against it… and folks struggling to get good results with exposure, etc… The ‘Valley of the Ancients’ demo, for UE5, had a sun intensity of 2.9 - and that was presented as a ‘best practices’ type of level/map… and I read that the ‘Meerkat Demo’ that Weta created in 4.26 had a sun intensity of 170k (FYI)


I always struggle with finding the correct lighting strength values myself,
mostly because the visual end result is not only based on a lighting strength setting, but also on the entire shader system, post processing, camera settings and artistic preference. It could be very interesting to explore this and create a standard for photorealism though, if one UE standard actually fits any environment.

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I doubt that the lumen gi contribution is calibrated exactly to real world lighting values. Listening to the Inside Unreal talks it seemed like the team was very much tuning gi and texture brightness by eye. But I agree it is unclear what values are defaults for lights/exposure/textures to get correct bounces.

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This makes logical sense, but from my testing it doesn’t seem to significantly improvement in bounce lighting for Lumen. The difference was very pronounced with Lightmass.

I’m not really sure why the effect is so subtle, perhaps the surface cache has a bounce limit? No idea…

Here’s the difference in Lightmass for comparison:

Currently, using realistic lighting values also has some other drawbacks. But I’m guessing those issues will be fixed.

I think right now the biggest issue with using low sunlight values is that it makes all your other lights unrealistically bright relative to the sun. Which is something you can’t easily fix when using low sunlight values. Think of a cars headlights during the day, people routinely forget to turn their headlights off because in direct sunlight you can barely even tell they’re on. But if you reduce the intensity of the sun then they become relatively brighter.

That is not the impression I got from it. It seemed more like an exploration of the toolset by their artists, trying to showcase what’s possible. They emphasized that they were looking forward to learning from the community as we get our hands on the tools, so I wouldn’t interpret it as if it were a guide.


Good info Arkiras - thanks for sharing!