ShowFlag.VisualizeHDR 1


With that command L shows the average luminance of the surface it’s pointed to. What unit L is in?

cd/m^2 ?

It is just floating point values. Anything over 1.0 is considered to be in the range considered for bloom based on default settings etc.

ie, you should be able to make an unlit emissive material with constant 1.0 emissive, and sampling that pixel should read back the exact same value.