PAXboy
As has been said, the flash from these is extremely bright but is also sporadic.
Apparently you have not seen a real high speed train (you should thank Mrs T. for that
). Hopefuly, starting today, you will be able to see one without having to leave UK.
I once happened to drive at night on a french motorway (higway for our friends accross the pond) which runs for miles along the Paris-Lyon TGV line (train a grande vitesse = high speed train). As the trains were going past us (them at 270 kph = 168 mph, us at roughly half that speed - ie, the official speed limit
) huge, almost continuous showers of sparks could been seen. Quite surprising the first time you see it, especially as the train itself is not visible because of a separation fence.