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The output of fluorescent tubes is rated at 100 hours of service life. They generally produce 10 percent more light than rated during that initial period, though the manufacturer doesn't measure or guarantee this. Modern T8 tubes with electronic ballasts are expected to retain 95 percent of the 100 hour lamp output through at least 10000 operating hours. They should not drop below 90 percent during their 20000 hour service life. Most perform better than this. Lose 50% of its rated output? Replace tubes at 500-750 hours? That's terrible performance. Between the replacement cost and the maintenance cost, supermarkets and office buildings would go broke changing tubes that often. The engineer was either mis-informed or you aren't remembering correctly. Phillips and Sylvania have websites with info than any of us can read that advertise 95% lumen retention. One example is here: Link Lots of short duration cycles will degrade service life, but not by that much. A 20000 hour rated tube (based on 12 hours per start) gives around 15000 hours service life based on 2 hours per start. Modern electronic ballasts do not care if one tube is bad in a two-tube fixture. The ballasts should last essentially forever even operating into a dead short. One factor that is well known in the industry is the impact of dirt on lamp performance. Lighting design programs will de-rate tube and fixture aperformance by about 10 percent due to accumulation of dirt. And this assumes a fairly clean environment and a 6 month cleaning cycle. Dirtier environments or longer cleaning cycles are worse.
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