Why back light is not working in lumia 820?

[Windows Central Question]

after installing of Windows 8.1 i am facing such problem and every time i have to on the switch off button to see the screen. Very irritating feeling. Pls guide

 

[Harrie-S]

after installing of Windows 8.1 i am facing such problem and every time i have to on the switch off button to see the screen. Very irritating feeling. Pls guide

Probably during the update something went wrong.
1 Check the lock screen time out in settings and change it and see what happens. (settings > lock screen > "screen time out after"
2 Do soft reset (try it a few times) (hold Volume down + power till phone vibrates)
3 Factory reset (Settings > about > "reset your phone"