power nap causing bad light on screen to come on

hi all.

Power nap on the new 2017 iMac running high Sierra. Sometimes I have noticed that when the computer is asleep, sometimes when it wakes from its power nap to check email etc. The backlight of the display comes on. (see photo)

Any ideas? I have reset the SMC, no luck. I am thinking it could be a bug? Power nap I had noticed takes a while.