The goal is to let in as little light into your eyes as possible, to see the detail you need to see. So while working at your monitor, light comes in through both ambient and monitor sources. If monitor is low, and ambient light relatively high, ambient light will burn your peripheral nerves, as eyes dilate to see the monitor. The best situation is a low ambient light and a matching low screen brightness, the dimmest that will allow you to see the details.
I can see detail on screens at a lower brightness than most twenty-somethings that have full brightness set on their screens. Maybe they have prematurely burned out their eyes, as if they had stared at the sun too long.
In practice, on most computer monitors you will just dial the brightness level to zero. They are just too bright. You can also play with the contrast to optimize image clarity and readability.