Hi welcome to the forums.
I have to be honest your the first i have heard asking to reduce the brightness below min setting.
@Pimax-Support might know if this can be done. In the meantime maybe a low tint sunglasses?
With the Render have you tried 1.3 or 1.35? (Try entering in the box) been awhile since i adjusted this setting) will take a look when home. @jonnypanic do you know off hand this one?
What is your system specs? & which game or program are you trying? You might be able to adjust quality settings in game.