iPhone is equipped with a built-in Flashlight which is easy to Turn ON and use in a dark place with insufficient or no lighting.
Turn ON iPhone Flashlight from Control Center
All that is required to switch on and use the Flashlight on iPhone is to open the Control Center and tap on the Flashlight icon.
The Control Center on iPhone can be accessed even if your device is locked, which makes it really convenient to switch on the Flashlight in an emergency.
Once you are in Control Center, tap on the Flashlight icon to Switch ON the Flashlight on your device.
Once you are done using the Flashlight, open the Control Center again (swipe up) and tap on the Flashlight icon once again to close the Flashlight.
Note: Flashlight does not turn off when you power off the iPhone, it continues to use the battery on your iPhone. Hence, make sure that you remember to switch off the Flashlight, after you are done using it.
Adjust Brightness of iPhone Flashlight
To adjust the brightness of Flashlight, open the Control Center and long-press on the Flashlight icon. If your iPhone does not support 3D touch, you will have to press and hold the Flashlight icon.
On the shortcut menu that appears, you can adjust the brightness to your preferred level by sliding your finger on the brightness slider.