Are you talking about 787-8 or 787-9? If it's the latter, windows can go completely blind that absolutely no light can go through, so it shouldn't make any difference, as long as everyone turn off their windows. The windows don't go fully blind on 787-8, so perhaps row 5 is slightly darker?

but generally speaking, the brightest light source in the cabin are those large IFE screens. I also find that the brightness in the cabin has much to do with the direction and the time of the travel. For example, flying YYZ-YVR, the north side of the cabin is darker than the south side.