IPhone 4 Too Dark (Need Flashlight to See it)?

My iPhone 4 is really dim and I can only see it when I shine a flashlight. The brightness was 100%. Tell me the fix without taking it apart or sending it. Is there an easier way?

Unfortunately your backlight may have gone out. This happened to me on my macbook.you'll have to make an appt with the genius bar at apple

You can change it by phone setting
but in this technical problem you need to call your phone company or at&t technical teams to figure it out…
you might go to iphone agency to figure it out.