Hello, I am a bit confused on what settings to use for lighting in Lumen. I noticed the Meerkat Demo uses real world settings, the sun is around 170,000 lux vs Valley of the Ancient the sun is aprox 2.9 lux. I was just wondering if this is to work better with Lumen or just a choice on how to work?
If anybody has some documentation to share or can point me on why the difference in settings I would really appreciate it.
Thank you.
I’m not a pro at all, just studying. I used to work with real light settings and found that 100k lux works well with the sun (12-13 EV for day setting).
0 or even -1 EV looks strange for me.
But it’s very interesting what the pros have to say.
I believe in the lumen livestream the developers mentioned that UE5 lumen (at least in EA) wasn’t fully compatible with real-world lighting values. That could very much be changed in 5.1, but I wouldn’t actually know what changes were made.
That being said, the developers did hand-tweak the albedos of the rocks from the megascans defaults. What’s an art direction vs. physical accuracy choice I could not tell you.
Lumen clamps ray intensity which means it doesn’t work correctly with high intensity directional lights, generating unrealistic bounce light and over-shadowing. This is apparently done to prevent fireflies.
For reasons I don’t really understand, light leaking is also much worse with a high intensity directional light. Requiring much thicker walls to avoid leaking in dark areas.
Yes, I remember them mentioning that now. I believe they said they doubled the maximum ray energy in 5.1 because they had improved sampling and denoising tech and could get away with it.
Is it particularly with a directional light?
I just noticed that the default starting scene from Architecture profile (with water one) uses the sun with 75000lux. The leaking is here though too…
Seems to affect all lights. Mostly an issue with the directional light though, seems Lumen was tuned so that local lightsources don’t seem to have issues at their typical intensities. If you push local lightsources too far you’ll get similarly bad results as a bright directional light though.
For reference, the ray intensity can be raised via cvar:
r.LumenScene.Radiosity.MaxRayIntensity
r.Lumen.ScreenProbeGather.MaxRayIntensity
r.Lumen.TranslucencyVolume.MaxRayIntensity
r.Lumen.Reflections.MaxRayIntensity
Though I really wouldn’t recommend it outside of testing.
So I guess its safer to stay on lower values. This is such a shame if you want to stick with real world values for checking and validation 