The weird thing is this first measurement they did showed double the amount of light they thought would be there. Also the darkest parts still have photons since you have other galaxies that you cant see with the naked eye in those “dark” parts.

I’m guessing that because there are always some amount of stars visible, the number would have to be above zero, but maybe as you get a certain distance away from closer stars, the darkness kind of “evens out”?