Yes, usually (speaking more from cx845 experience). The caveat is that during the summer months, sometimes outside is not totally 100pct dark. It's like a far north summer night. During winter it is pitch black the entire way guaranteed.

I've never been bothered by light....ever....on these flights. In addition to cx811 and 845 perhaps 10x [forgot: I've also done the ex-EWR flight twice], I reckon I've flown cx873, 889, 881 and 883 (west coast midnight departures, which often also fly a very northerly route) a combined 30+ times. I wouldn't worry about the light on these flights.