The RAT is deployed automatically if both AC transfer busses lose power in flight. The RAT can be manually deployed by pushing the RAM AIR TURBINE switch on the overhead panel.
Actually, the 777 RAT has a 3rd way of deploying. It also deploys for low hydraulic pressure (the logic too extensive to list here). Since the RAT on a 777 provides both elec power and hydraulic power, it makes sense to have two sets of logic.
RAT deployment logic includes airspeed or groundspeed, air-ground, engine below idle, time delays. etc. Loss of power to the Left and Right Transfer (Electrical) Busses also autostarts the Auxilliary Power Unit.
The RAT deploys in 2 seconds after the logic has been satisfied, but will obviously take a few seconds to get up to full operating speed.
The 777 is most definitely Fly-By-Wire. Don't be fooled by the traditional-looking control wheels.
Re the flickering of lights.. If AC power changes sources in the air, there is a "break power transfer", so the lights might flicker. There may also be automatical loadshedding disturbing the electrical system.
Regards.
NSEU
P.S. I think a Malaysian Airlines 777 had an uncommanded thrust reduction (but I thought the manufacturer fixed that problem with new software).