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Re: Service Life of PCF Lamps?

Tom Wood said:

> . . . I started wondering about
> the
> light level. I have three 96 watt PCF lamps from AH Supply over a 90
> gallon
> that have been in service for about 11 months. I replaced the center
> lamp
> with a new one and can see a big difference between the color temp
> and
> brightness of it and the older lamp next to it. I was hoping to get
> up to 18
> months out of these lamps, replacing one every six months, but it
> looks like
> no deal. If the swords perk up, I'll know I'm looking at replacement
> of the
> other two lamps real soon. What is the realistic expected service
> life of
> these lamps?

A new flourescent lamp will look lots brighter than used ones but it's
easy to be fooled that the used bulbs are  performing worse than you
think.  Flourescents give off less light as they age, primarily due to
the inside of tha lamp becoming coated with the material that coats the
filaments as well as the filimanets themselves slowly vaporizing over
time.  But, a flourescent rapidly loses about ten percent of its output
after the first 20-50 hours, then slowly decays to about 60-70 by the
time the filaments finally blow.  So a new lamp when first installed
looks much brighter than a used lamp.  Compare them again after a few
days of use -- the difference probably won't seem so great.

That useful life is typpically based on an assumed cycle rate of about 
four hour cycles -- not atypical for most situations -- but not typical
for planted tanks.  With the 10-12 hour cycles that you have in planted
tanks, the filaments won't blow nearly so early on -- they'll usually
get pretty dark before they blow.  So you need to replace them at about
half their rated life.  

The 96 watters are rated for a useful life of 10,000 hours of burning. 
That's roughly 1 year of burn time -- but since you are only using them
for half the day, that equates to about 2 years.  By that time they
would be down to roughly half output -- probably lower than you wanted
when you designed the your tank set-up.  So the rule of thumb, to be
safe, is to replace them after half that time, or about 1 year.  All of
that is rule of thumb.  Temperature affects their lifespan and their
output too and some phospors supposedly wear out fster than others.  If
so, some wavelengths poop out before others and some of those might be
especially useful to your plants.

I use mine for more closer to a year than six months but I haven't held
a light meter under them to note the actual rate of decay.  However,
after using 96 watters for about 10 months, my amazons took finally off
like crazy -- a lot of things affected this, but they couldn't grow
like crazy without lots of light.

Good Luck,

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