In recent years I've had to replace 4' T-12 fluorescent bulbs more frequently than when I first bought this house. I think this must reflect a manufacturing issue, which could be deliberate or unintended. These bulbs have gotten a lot more expensive also. I bought a yellow cfl bulb for my front porch light, paid around $8, it but it was suppose to last seven years. When it burned out in 18 months the manufacturer, Feit, sent me a new one free of charge. It burned out in three weeks, so I just said to heck with it.