I'm not sure exactly what the graphics options do.
It depends on your monitor settings what gamma value you should use. If you can see clearly in caves or at night, and it is not too bright outdoors in the day, then you don't need to adjust the gamma. In my case I have it set to 1.25, or so (with the darkness setting at 50 to increase the size of the light radius around the character).
Welcome to the forum.