[Theory] HDRI Power, Exposure and Noise relations

[geesve]

Hi!
As maru says in this thread, i start new topic, and i try to explain my question better and with examples. Sorry for my English and also if this is stupid question, because i'm new for Corona and rendering. I try to found answer with google and freshdesk, but still do not really understand.

In two words my question is:
Did we need to worry somehow about the power of HDRI, if we can compensate possible low lighting from it with making EV in high state?

For understanding it i make simple test scene with not big window, portal in it (properly installed) and HDRI only for lighting.

First shot was made with default 1.0 RGB Level of HDRI Output, 5 Exposure and after 10 passes i have 10.2% of Noise

Second was made with 50 RGB Level of HDRI Output, -0.6 Exposure and after 10 passes i have 10.3% of Noise

Third was made with 0.1 RGB Level of HDRI Output, 8.2 Exposure and after 10 passes i have 9.8% of Noise

I become confused with this results, because as i read in this thread, topic starter have to avoid Noise with increasing power of his HDRI. He decide to try it because previously he just make his exposure with some high value for compensate low lighting from HDRI, but i can't replicate it and as you can see from links above, looks like low power of HDRI do not really affect on the noise amount. Or maybe i need to learn something else? As i said, i no have before experience with renders and before of asking this question i try to learn anything about the noise in Corona.

Just in the case, sample scene from screenshots (scene was made in max2017 Student Version and Corona 1.5 hotfix2). I never before shared scenes from max, so let me know if i shared it somehow wrong :/

[maru]

Sorry that you did not get any answers yet. I think there is some misunderstanding here, so I'll try some explanations quickly, and will do my best to provide more info and examples later, but unfortunately I cannot do it right now.

So, the most important thing here is that when you have a light with 100% brightness and exposure set to 100%, you will get exactly the same result when rendering 200% bright light and 50% exposure, or 50% bright light and 200% exposure.

Now, it is that simple in theory, BUT there might be some factors which are changing that. One of them is MSI. See this for explanation and examples:
https://coronarenderer.freshdesk.com/support/solutions/articles/5000517899
So in short, scene exposure/appearance may change depending on if you change exposure BEFORE or AFTER rendering.

Another thing is that 2 of your example renders look the same, but one of them is slightly brighter. I think that this is enough to make the noise level slightly different. Maybe there was a mistake in your EV calculations?