Most airlines dim or turn off the cabin lights during night take-offs and landings so that in the event of an accident such as a fuselage separation, in which the lights would most certainly go out, the eyes of everyone on board would already be reasonably adjusted to the darkness outside.
This would speed up reaction time rather than wait a few seconds for the eyes to adjust. Remember, in situations like these, a second can make a big difference.
I too have noticed that QF
leave their cabin lights on during TO
's and landings while spotting in MEL
, have also noticed that NH
(All Nippon Airways) does the same.