Travelling on the Bakerloo it seems common place at Queens Park for the terminators there to do some (deliberate!) light flicking to motivate people off the train
It is actually official. It appears in the Bakerloo line rule book supplement that reversing trains at Queens Park, Stonebridge Park and Harrow & Wealdstone are to, after having announced three times that the train would terminate, turn the saloon lights off and on twice before closing the doors.I suspect that's not very "official".
Back in winter 2012 LUL removed detrainment staff from Queens Park, Stonebridge Park and Harrow & Wealdstone for trains that were due to reverse via the sidings / depot to head back south [trains terminating to be stabled were/are still properly detrained using the porter buttons]. As part of the mitigation against the risk of this, alongside installing more enhanced inter car barriers, the aforementioned procedure of switching the saloon lights on and off was introduced. This was given the nickname "flash and dash" by the RMT, who commenced industrial action on 13th January 2013, whereby train operators would carry out a full detrainment unless station staff did so.
Following some quite significant delays, a settlement was agreed that the Train Operator would close the doors from the cab and station staff would walk alongside the train from the platform to check if anyone was still on board, but an announcement and the lights flicked off and on twice would still occur.