MacBook Pro Screen Flashes

The screen on my 2017 MacBook Pro "flashes" every 20 minutes or so. Not a real problem, no lost data, not even long enough to lose my place when I'm reading.

At first I worried this was some sort of virus or spywear, using the camera to - - - I don't know what.

But now, I wonder if it is somehow connected to notifications, or hardware testing.

Even more, I wonder if there might not be a simple answer, if I just take the trouble to post this question.

Thank you for any useful, or amusing, counsel.

Bill Emmons