Brightness problems oO

I’m programming a 2D RPG and it works fine.
My test map is a dark dungeon.

Today I started the same project on another PC and:
I could nearly see nothing. It was too dark. The monitor was simply to dark.

Now I guess I have to program something like a brightness correction (in a setup menu where users can select their brightness).

But I don’t know how to program something like that.
Should I simply set a transparent white plane over everything oO"
I guess that it would look very bad…

Please help me ^^

This is usually done with the SetGammaRamp function from the windowing system. The user can probably adjust the gamma already so its not really needed. You can help him by displaying some image.