I'm trying to watch Amazon Prime Video through Chrome on my center monitor.

Video card I have is a NVIDIA GeForce GT730. Having the other 2 monitors illuminated can be annoying when a video is playing on the center monitor. Turning each monitor off is not an option.

I also do have and use displayfusion, but didn't see an option.

Have a look at this thread, it may help:

https://www.displayfusion.com/Discussions/View/request-dim-inactive-monitor/?ID=a91f95ca-1460-434f-8b1f-8c8dd371da8c
or this one.

https://www.displayfusion.com/Discussions/View/feature-dim-non-primary-monitors-all-at-once/?ID=bb39636a-589f-448c-9a6c-da69339e75a9

Is there anyway to set the "dim" darkness? It doesn't seem too dim. Also what is the difference between "fade" and "dim"