Step 1: Enter Settings From The Home Screen
Step 2: Go To Wallpapers & Brightness
Step 3: Adjust Brightness Level
Under Brightness you will see a horizontal scroll bar that allows you to adjust the brightness of your iPad's screen.
You can lower the brightness by sliding the circle to the left or raise the brightness by sliding the circle to the right.
Adjust Brightness Through Control Center
You can also adjust brightness with Control Center, which can be accessed from any screen. To access the Control Center, swipe up from the bottom of the screen as shown in the image below. To close Control Center, swipe down, tap the top of the screen, or press the Home button.
The image below shows the control center where you can adjust settings like the brightness level.
A horizontal scroll bar will appear in the bottom right corner of the control center.
Again you can lower the brightness by sliding the circle to the left or you can raise the brightness by sliding the circle to the right.