How to Change the Brightness of the Flashlight in iOS 10
Step 1. Swipe up from bottom of the screen on your iPhone to launch Control Center.
Step 2. Tap and hold on Flashlight icon appear left-bottom on the CC.
Step 3. You’ll be get a Peek with three options – High intensity, Medium intensity and low intensity.
Step 4. Choose one of them to turn on your iPhone flashlight and enjoy.