screen dims whenever I open LibreOffice

Whenever I open LibreOffice my laptop screen dims which I find most frustrating. I have only just started using LibreOffice after MS Windows and have never had this problem before. I would be grateful of any advice.

started using LibreOffice after MS Windows

What does this mean? Should it read:"…started using LibreOffice on MS Windows" or “…started using LibreOffice after MS Office” ?

Sounds like an operating system power setting or possibly a OS screen setting to match ambient light or to reduce light levels and/ or colour temperature before bedtime

Try Screen keeps dimming on its own or maybe Screen is dim