by Eskild Moa
Posts a sticky notification, which on dismissal (swipe) lights the camera torch/flashlight, locked phone or not. When on, posts notification for turning off, or waits 2 min before asking you if you want light for two minutes more. Prox. sensor in both cases, to help against accidental lighting. Haven't had problems, testing on Samsung S5.
After trying many flows and apps, I've stuck with this one. It occupies notification space, and is not particularly elegant, but it hopefully doesn't hog battery. After trying a plethora of funky gestures and timing/sensor logic, this one floated to the top. Hope I haven't plagiarized too horribly the very nice solutions I've seen in here.