Hi juaness! I'm on P3Dv4.5 so it's probably not the same brightness / lighting as P3Dv5, but I use a tweak because I think both day and night is too dark in my sim with HDR brightness set to 1.000000. However, if you think the daytime view is not to dark in your sim, then the following tweak is useless to you. I use it to make all my too-dark-views brighter, such as Virtual Cockpit and all the outside views. Let's say I want a brighter VC. Then I open cameras.cfg and find "Title = Virtual Cockpit". At the end of that section, I add this line:
LightAmplification=1.25
I guess I then get 25% brighter view both day and night. I also add the LightAmplification=1.25 line in the views section for each addon aircraft in aircraft.cfg if I think the views are too dark. This might work for you, or it might not. If you don't like it, you can try another value better suited for P3Dv5 and your screen, or revert back to the original cameras.cfg / views. Or perhaps it doesn't work at all in P3Dv5? I'm quite happy with my sim lighting now, so I don't want to change a thing. I don't know for sure if moving the HDR brightness slider to the right would produce the same result, as kmax59 suggests. If so, then the tweak is worthless, but I believe I tested this years ago and imagined the tweak to be better.