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

The life of a 48-inch fluorescent light bulb, technically called a fluorescent "lamp," depends upon its wattage, design and application. A typical 32-watt, 48-inch fluorescent lamp will burn for about 20,000 hours, if normally left on for about three hours at a time. The same lamp, left on 24 hours a day, will last about 34,000 hours.

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The lifespan of any fluorescent lamp depends on how long it is left on.

Average Burn Time

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.


Carl Miller

Carl Miller has been writing professionally since 2007 and has freelanced for the "Western Oregon Journal." His short fiction has been featured in "Northwest Passage Literature and Arts Review." Miller is an English/writing student at Western Oregon University in Monmouth, Ore. He has worked as a cook, painter, waitperson, custodian, data analyst, retail manager and salesperson.