How do you set world strength to equal a specific lumen value?

[Kolloom]

The scene has several emission materials: emission flat texture, emission window texture, cabinet lights.

Though I don’t think the difference is that significant.

Exposure centers at 0 as it can go positive and negative, akin to a real camera’s exposure control, without the physical limit of one. The gamma is likely a multiplier to the gamma curve function.

Filmic and Gamma

Gamma is a power function, filmic contrast looks are simple sigmoid functions (classic S-shaped curves you apply to increase contrast) “mapped” on filmic (18%gray as mid gray). Gamma 2.2 is already and always applied as a display transform (Display tab sRGB, Rec709…), the gamma slider is in blender just if you need an extra gamma correction and should not be used. Another thing that could make your interior render darker is clipping expecially indirect at very low values. In internet there a…

None of those modifies the scene referred data. They are just tools for quick look development.

I had in fact made several renders comparing sunlamp of different strength.

There are differences to how intensive the indirect is, but if viewed in isolation I don’t think anyone will say: “Hey your sunlamp is 10 times too weak.” The scene is also set in high contrast so the effect is greatly exaggerated. Beside the fact that darker scene has more noise I wouldn’t worry much.