I finally had to change out a set of lamps in my primary rig, which uses the 4 foot long, Solacure SG-1-40. Most of the time, I run it at 32 watts, but also run it at 60w at times, and I choke the air flow, so it is a bit rough on the lamps. I rate the SG-1-40 lamps at 1600 hours at 40-50w, but I managed to get 2200 hours out of them this time. Keep in mind, I don’t cycle the lamps on and off a lot, which is what kills lamp life. Instead they run for days or weeks at a time, which is what builds up a lot of heat.
Your mileage will vary of course, but this just further demonstrates that you should get a minimum of what rate the lamps at, and how cost effective they are.