Is it advisable to work with physically accurate lighting ranges?

[brunoCorigliano]

Hi there! This is a question I’ve had since I started working with UE, but always thought the answer was “Yes”, until now. Let me explain: if you want to work with a physically accurate mid-day sun (a directional light with an intensity of ~100.000 lux), you need to enable “Apply pre-exposure before writing to scene colour”, else you might end up with a greatly over-exposed scene colour buffer.

However, “Apply pre-exposure before writing to scene colour” is nowhere to be found in UE5. This led me to the question in this post’s title… I want to work with physically accurate light intensities, but without pre-exposure, some lighting scenarios will over-expose the scene colour. Should I ignore this? Has pre-exposure been moved to somewhere else I’m yet to find? Or should I just stick with fake lighting intensities when working with mid-day sun scenarios?

Thanks in advance, have a nice day!

[Arkiras]

Not sure what happened to applying pre-exposure, but you can still use realistic lighting values by enabling Extend Default Luminance Range… unfortunately for whatever reason this was removed as a project setting, though it is still available via command and ini.

If you are using Lumen I would not recommend using realistic sunlight values, as it has a bunch of issues that I wasn’t able to resolve. You can read about them here:

Lumen GI and Reflections feedback thread

Bloom explodes when using realistic sunlight intensity values for directional lights in Lumen. In this example I used 75k, because that’s what the SunSky actor is set to in the plugin that is bundled with Unreal. [Bloom issue with realistic sunlight intensity] This appears to be specific to Lumen, as I tested the same scene with baked lighting via GPU/CPU Lightmass with normal results: [UE5_LumenVsBloom] In the Lumen map, all lights are moveable. Lumen final gather set to 2. In…

Lumen GI and Reflections feedback thread

Another issue I encountered with more realistic sunlight intensity: The probe grid(? voxels? idk) becomes very visible when using high values. [UE5_LumenRealisticSunlight_Squares]

Lumen GI and Reflections feedback thread

The light complexity viewmode also blows up when using high intensity directional lights, the VS/PS instructions go through the roof. But I think this is just erroneous output on the visualizers part, as this extreme increase in complexity seems to have no impact at all on the performance of the game. [UE5_LumenLightComplexityView] Won’t help in this case, as these are indirect shadows.

[brunoCorigliano]

Thank you very much Arkiras! So, I guess with Lumen we’re stuck with fake sunlight values until those bugs are fixed. Interiors can still be lit with somewhat realistic values, though. Anyways, it’d be great if we could actually use real intensities for the sun in our scenes, so I hope they dig into it.

Thanks again, and have a nice weekend!

[kurylo3d]

in 5.1 i see Extend default luminance range in Auto Exposure settings… it says in the notes when i mouse over it " Extend Default Luminance Range in Auto Exposure Settings.
Whether the default values for Auto Exposure should support an extended range of scene luminance. Also changes the exposure settings to be expressed in EV100. Having this setting disabled is deprecated and can only be done manually using r.DefaultFeature.AutoExposure.ExtendDefaultLuminanceRange."