What are the best settings for an acer led monitor

I got the new acer led montior 231hl bid 23 inch, but the default settings are too bright.How should i go about adjusting the settings.I know it has to with how comfortable it is to the user eyes.The default setting is brightness 50, contrast 50.will lowering the contrast affect image performance.Or i have a amd radeon hd7770.Should i adjust the brightness and contrast with the video card or monitor?Which would be better.