ICOT: the Gemorra refers to creating a glowing mass of metal as “igniting”, the filament of a light bulb would be no less.
ROB: I am not familiar with a psak from Reb Moshe that considers turning off the gas “grama”, but I will look for it b”n. However in OC 1:93 towards the end he writes that there is NO difference between lowering the flame on a gas oven on YT and extinguishing it completely. The implication being that both are forbidden when not for ochel nefesh purposes and it is NOT considered grama, rather complete kibuyi. Gram kibuyi is forbidden on Shabbos but allowed on YT.