I've been interested in sprites since they were first observed, and one night phoned a physicist at the BBC who was there to answer questions about the phenomenon. I put it to him that there was enough energy in the core of a "bolt" to have a collapsing field energizing the gas/vapor stem in a manner similar to lasers. He said some word that sounded like rollocks, but after some argument, went sort of thoughtful but non-committal after I protested that there was such a surfeit of energy that the lens could be very primitive; made up of rain drops or ionized gas. There has to be some answer for these jets reaching the outer limits of the atmosphere. I have often wondered what it would be like to have one hit the belly of an aircraft....just when you were feeling smug about being way above the storm.
Sorry to be alarmist, but any assurance you may get from thinking there are no amps around in lightning, is unfounded. To do work you need power, the product of volts and amps. There is a lot known about the voltage sheer across a large bolt. The core can be only 4 inches across, with zero to multi thousands of volts per inch of radius typical. Where plasma is created...well, how hot is a welding arc?
I would guess, to get real current flow and do damage, the conducting path has to be optimized, that is, take the worst possible route, say cloud - aircraft - ground. In the worst possible scenario, there is no real reason why the aircraft should not be very seriously damaged; that sort of energy is certainly available. Thank God, the conditions are hardly ever met to do more than spray out of typical hot-spots, with minor burning.
As a young Viscount F/O I got such a thrashing one night (pre-radar days ) that I almost quit flying. Horizon bar off the dial, down below MSA over the Pyrenees, and so much hail noise that it drowned I/C and R/T totally. It just seemed to go on forever...but had a funny ending. After popping out into post frontal air somewhere near Toulouse, the skipper said he was shattered and asked me to fly. He put a cigaret in his mouth and held his Zippo up to his face before lighting it. The very instant he spun the wheel, there was the most horrendous bang and the aircraft shook violently. That was in the mid sixties, and I still have this clear image of his bulging eyes, beautifully illuminated by the little flame, staring over a crumpled cigaret.
There was a four inch hole in the wing, and the odd thing was that the energy went round the fuel bags and out through the bottom surface in line with the entry point. It seems that there is a very definite path laid out by the pre-curser charge line.
It seems that several people are convinced about lightning balls. I recall an incident on a Courtline BAC 1-11 circa 1970, very similar description. There was one guy in the UK who had a stack of submarine batteries and shorted them out for a second on a huge pendulous knife switch, in an attempt to replicate a ball. It looked very unconvincing. I think that they still remain a mystery.