The answer to this question is not so simple. If your eyesight is great, you might be able to see better in a dark room. But if your eyesight is not so good, then it's better to have brightness high. It is true that our visual system can adapt to different lighting conditions and become more sensitive when it gets dark. But this process takes some time. For example, if you go from a well-lit room out into the night, at first everything will look dark and almost invisible. But after a while you'll start seeing better in the dark as your eyes adjust to less light.