Fascinating!! All the Boeing twins that I've worked on (down the back) have an emergency light switch on the f/deck, and a guarded switch on one of the cabin control panels. We only ever use it during a manual safety demonstration: The system is designed to switch on automatically in a complete electrical failure. The primary switch is of course on the flight deck, from where the pilots can control the emergency light system. Us Galley Rats are told never to use the system without permission (or for safety or demo) as it has some sort of draining effect on the battery.
I've never heard (or seen) the system used after take off in the way described - but then I'm low to nil time on the strimmers!!
Waiting with interest Cpt Fowler