I use my iPhone's flashlight nearly every evening when walking my dog. It helps me locate -- how do I put this? -- anything she may leave behind during our lap around the block. I swipe up to open the Control Center and tap the flashlight button to turn the light on and off. There is, however, a slightly faster way to turn the light off that involves only a quick swipe and no tapping.
The fastest way to turn off the flashlight is to wake up your iPhone and then just swipe a bit to the left on the lock screen. Your iPhone will think you are attempting open the camera, which turns off the LED light. When you release your short swipe, you will return to the lock screen with your flashlight now off.
To perform this flashlight shortcut, you need to enable access to the camera from the lock screen. To do so, go to Settings > General > Restrictions and toggle on Camera in the Allow section.
If this tip sounds familiar, it's because previous versions of iOS let you swipe up halfway on the lock screen to almost activate the camera, which also turned off the flashlight.