The specs say this bulb works for any + or - voltage from 6V on up so I just paid $35 to be the guinea pig to see if it actually does brighten the night on my ET-equipped Triumph. The AC output of the lighting coil means a "normal" single-polarity LED bulb only would be on half the time. While the flickering of a "normal" LED would become unnoticeable above a few thousand rpm, having only half the light output would be noticeable. This new bulb should stay on through the full oscillating cycle as well as be much brighter than a stator-limited incandescent bulb, but I'll have to see it it works out that way in practice, as well as if it has an acceptable beam profile.
Just this weekend I moved the Triumph to the back of the garage so it will be a while before I test the bulb. I hope by then I don't forget I have a different headlight bulb, and I hope the bulb actually works, because getting caught out at night with no output from a bulb would be way worse than its present feeble ET headlamp.