Cabin lighting at night...

[TightSlot]

My understanding is as follows:

• Permits passenger (and crew) eyes to develop some degree of night vision - useful for spotting events outside the aircraft and also as a prep in case of evac
• In an evac, some people may be reluctant to leave a brightly lit interior for a dark exterior.
• Reduces chance for dazzle if Flight Deck door comes open or is opened during take off roll
• Reduces live electical items on take-off (means of ignition)

Some of these items may be more valid than others, in the opinion of some people: These would presumably be the same people that bypass the process by switching on their reading light. BTW, the practise is route and passenger profile specific. On some routes, without fail, dimming the lights is the signal for almost all passengers to immediately reach for the reading light button: On others, those with reading lights already on will switch them off.

As with so many things in aviation, this seems such a minor imposition for a good reason, but one which is of epic inconveniece to many - C'est la vie!