If you notice the backlight on your monitor or TV has become darker over time, this is what is referred to as a dimmed screen. 

How To Fix a Dimmed Monitor?

This can be caused by the backlight degrading or reaching the end of its life span and usually requires a repair to fix, however there can be other reasons why your display may be appearing dimmer than usual. One of the first places to check is the brightness setting on your monitor, brightness can be checked by pressing the corresponding menu buttons on your monitor to ensure it has not been turned down. If your laptop or monitor has an adaptive brightness or power saving setting built-in, both of these settings can automatically dim the screen depending on the lighting of your environment. This can be turned off in your monitor's settings or by doing the following:

• For windows: Navigate to Start > Settings > Display > Brightness & Color, here you will be able to uncheck adaptive brightness and any brightness-related power saving settings.
• For masOS: Navigate to System Settings > Display and uncheck Automatically adjust brightness.

Assuming none of these solutions fix the dimmed screen, here are some steps to troubleshoot this further:

• Try reconnecting and restarting the monitor.
• Fully restart your laptop.
• Update any outdated graphics drivers. 
• Try a different connection cable or power supply if possible.

If all else fails, please contact the manufacturer of your laptop or monitor for further assistance.