I don't think it's the bulb Tim, most modern timing lights use a Xenon bulb. They amplifies the battery voltage boosting it up high enough to fire the bulb. That’s why some will fire on 6v and some won’t. Some of the amplifiers are marginal so they won’t fire off a 6v.
I splurged this past summer and bought a Equus 5568 Pro-Timing Light by Innova and it’s bright enough on 6v to see the mark in the day light.
DG
