I've purchased the ES-18004 bulbs from these guys http://harringtonlights.com/Glass/mr16_solux_lamps.htm in the past. They say about 3000 hours. I seem to get about 40K miles out of them- they are on pretty much all the time.you'll need an o-ring to get them to seat properly in the PIAA housing. Got my o=rings from McMaster-Carr online.They are not quite as bright as the PIAA bulbs... but at around 1/3 the price... well, I can live with that. I'm running HIDs as my primary lights, so these are more about conspicuity than they are vision. I do not bother carrying a spare with me, just not worth the hassle. ymmv.