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Lamp Life

>Date: Thu, 19 Mar 1998 11:37:59 -0800 (PST)
>From: Jim Spencer <jimsp at yahoo_com>
>For the 40W
>T-12(F40/D865), which has a rated life of 20,000hrs, this works out to
>1.8 years if you run your lights 12hrs/day. I guess this means we
>could use these lamps at least 18 months before replacing them.

From the GE lamp catalog, fluorescent lamps:
"Rated life - The rated life (hours) is the approx. median life when
lamps are operated for three hours per start under lab. conditions using
ballasts which meet industry standards or GE Lighting specifications
where no industry standards exist.  Rated life for self-ballasted lamps
is the approximate median life when operated for three hours per start
under lab. conditions."

Looking at a chart from the Lighting Design Lab, Seattle, WA, a
fluorescent lamp with a rated life of 20,000 hours on a rapid start
ballast will have a life of about 28,000 hours when run at 12 hrs/start.
I'm not sure what the lumen depreciation will be after this many hours