Not sure, but we had shop lights in our stripping room (a place where we took leaves off tobacco stalks, not a den of inequity!) and they lasted for years. I have some used ones I use for seedlings and though some of the bulbs are 15 years old, they still work fine.

Mike

It's probably a ballast issue. I would buy a new fixture from HD or Lowes for less than $10. If that doesn't solve the problem then you have some electrical issues.

LOL @ Mike, (den of inequity)

You may be encountering a wattage mismatch. Over a decade ago, T12 shoplights began appearing on the market which are 25 watts instead of 40 watts. The lamps for those shoplights are not always clear that they are actually 25 watts. They will light up, but will not last long. There is a bit of discussion on that topic in these links:
http://tiny.cc/w2wiy
http://www.electronicspoint.com/re-currently-manufactured-34wt12-lamps-t190087.html

I have seen some very good technical explanations on this subject, but I do not recall where.

Zink

I primarily use GE bulbs from Home Deopt that are explicitly labeled 40 watts. They used to last a lot longer than they do now.

I assume it might be a ballast issue, but I can't really tell unless I decide to buy a new fixture and see if the lifespan any better.

Maybe the constant turning on and off of the fixture (about 4-6 times a day) is wearing the bulb out? Again, with a different fixture in the past this did not seem to make the bulbs burn out monthly (more like every 3 to 4 months).

Buy a new fixture. make sure it has a GOOD electronic ballast. Why so specific? Because cheap shoplights often have lousy magnetic ballasts that last 2 or 3 months and then blow out. Cheap electronic ballasts generate so much RF noise that they bleed in on your phone line or cause your computer to fail to link to a wireless network.

Fluorescent bulbs are rated for number of hours of use. If you are getting significantly less hours from the bulbs, then either the bulbs you are buying are bad, the ballast is bad in the fixture, or you are getting electrical spikes on your incoming service.

Most bulbs will be rated for 8000 hours or above, caveat that some specialty bulbs will be much less. If you are using bulbs rated at 15,000 hours and are getting roughly 500 hours from them, then it is time to fix the problem.

I had a problem a couple of years ago with erratic electricity. The lights were flickering and appliances such as the microwave would spike up and down both audibly and visually. I went out and looked at my power service wires. We had a severe electrical storm a few days before. Lightning had hit the lines and arced from my service loop to a nearby tree limb. The ground lead had burned out a section about a foot long. I'm not saying you have a problem this serious, but if you are having significant light flickering or erratic operation of appliances like a microwave, then you should definitely call the power company.

DarJones