The Sudden Darkness
Ubuntu, like most modern operating systems, prioritizes power saving by default. If you step away from your computer, or if you are simply reading a long document without moving the mouse or typing, the GNOME desktop environment tracks this idle time. After a relatively short period (usually 5 minutes), Ubuntu will automatically blank the screen, turning it completely black to conserve monitor power and extend laptop battery life. While useful for portability, this is incredibly annoying if you are using the computer to display a dashboard, read a recipe in the kitchen, or monitor a long-running terminal script.
Adjusting the Power Timeout
To keep your display active while you read or monitor tasks and stop Ubuntu from automatically blanking the screen during idle periods, you must increase or disable the power-saving timeout in the system settings.
Click on the system menu in the top-right corner of the Ubuntu top bar (where the network and battery icons are) and select Settings. In the left-hand navigation sidebar, scroll down and click on Power. In the main panel, look for the section labelled “Power Saving Options.” Within this section, locate the setting called Screen Blank. Next to it is a dropdown menu dictating the idle time. Click this dropdown. To simply give yourself more time before it goes black, select 15 minutes. To completely stop the screen from ever turning off automatically, select Never. Your Ubuntu display will now remain illuminated until you manually suspend the machine or physically turn off the monitor.