How Long Should a 48-Inch Fluorescent Light Bulb Last?

Average Burn Time

The same lamp, left on 24 hours a day, will last about 34,000 hours.

Economic Life

While, a 48-inch fluorescent lamp will, on average, burn for 20,000 to 34,000 hours, the quality of light output gradually decreases over time. The “economic life” of a fluorescent lamp is only about 60 percent that of its actual burn time. Once the economic life on a lamp expires, it grows dimmer and loses color, and may be considered useless, depending on its application.

Bottom Line

Though the quality of a fluorescent lamp degrades during the last half of its life, it usually does so at a slow rate. The actual burn time of a 48-inch fluorescent lamp is about 20,000 to 34,000 hours, depending on how long you typically leave it on.