the Flashlight app in Cydia is buggy I guess. When I used it, it worked fine, then when I closed out of it, my screen brightness turned to like 0. I tried to go to Settings and do it, but it didn't work. Then I re-booted my phone, and waited for like 1hr and figured i got the Apple Logo of Death, so I went to my computer, and then it was fine. Tried it again, and it made my brightness zero again. re-booted and it was fine, uninstalled.