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Re: T-8 lamp and ballast questions (fwd)

Bill Wichers <billw at waveform_net> wrote:

>>2.  From somewhere in the archive, paraphrase...  T-8s
>>don't degrade as quickly as T-12s.  It isn't necessary
>>to do a T-8 bulb replacement on a 6-12 month 
>>schedule.  Is this true?
>Somewhat. In my expierience they do last longer, but not significantly so.
>You don't start seeing the really big jumps in lifetimes until you get into
>CF and especially MH lighting (where one lamp can last a few years). I'm a
>big MH fan though so I'll try to hold back and not get too far off topic
>here :-)
>I don't think a T8 will go much past a year without a noticeable amount of
>light dropoff. I've never tried running one into the ground though.

Your experience let me puzzled. How do you relate your observations with
the manufacturer's data ? I have a lumen maintenance curve that compares 
T-5, T-8 and T-12 tubes (from a Philips publication). The T-8 curve shows
a drop from 100% to 90% at 5,000 hours. From then on the lumen level falls
off just a little, to 88% at 20,000 hours, their average life. That's
about 4.5 years @ 12h/day. T-12s on the othe hand will fall to about 75% 
initial lumens @ 2,000 hours, and continue falling steadily to below 50%.
They have an average life of 7,500 hours typically, or about 1.5 years.

Based on manufacturer's data, I would say that one should replace T-8s
only when they fail, and that will be after a few years of use tipically. 

On the other hand you seem to imply that CFs have a longer average life
than T-8s. Again according to the Philips and Osram/Sylvania data sheets,
CFs have a typical average life of 10,000 - 12,000 hours, not much better
than T-12. They are high-output types after all. But they do keep a lumen
level close to 95% of initial for their entire lifetime, so they also 
should be replaced only when they fail.

MHs have a large range of avergae lifetimes, but most of the interesting
types fall in the range 10,000 - 15,000 hours. HPS and MV are the only
ones that beat T-8s, with average lifetimes of 24,000 hours. There are a
few T-8s rated at 22,000 hours though.

That's what I can gleam from the manufacturer's data. What could be causing
your light setups to blow off so quickly ?

- Ivo Busko
  Baltimore, MD