If you have these bulbs, but lights also, PIAA has a great warranty program.
My bulbs, H4, were bought last September, yes, THAT September. One recently bit the dust on its own, burned out.
Going to the PIAA site, I contacted their customer service who actually wrote back saying their bulbs are warranted for a year for defects. Just go back to the retailer and they will be replaced. Retailer wanted more info, so I sent him the email from PIAA customer service. Picked up my bulbs yesterday, brand new pair and returned the old pair, in the original packaging. Its good to hold onto that!
Retailer said his wholesaler didn't even want to be paid up front, just sent out the new bulbs and I turned in the old ones yesterday.
Incredible.
Ralf