The Lightning Mode uses the internal light sensor to detect lightning events. It has 2 parameters:
Sensitivity: This value determines the sensitivity level of your device for lightning. The higher the value you set, the more sensitive it will be. You can move the threshold bar by holding and moving circle with arrows or use "+" and "-" buttons.
You can see the light level of environment without starting the mode so you can adjust the sensitivity threshold according to light level bars. When a light event detected which exceeding the threshold value, it will be shown as "Orange" bar in this screen.
Prefocus: Pre-focus pre-trigger also known as pre-trigger or half press, is holding down on the shutter release half way to focus or meter for the scene. With pre-focus option enabled, your camera will response faster.
The lock icon at the bottom is there to prevent accidental transactions. If you click as one tap, you unlock it. After, you can push the stop button that be active.