Re: [APD] Coralife CF questions and when do CF's die

["S. Hieber" <shieber at yahoo_com>]

How long you can use your bulbs depends on what you and
your particular plants consider a significant decline in
illumination.

All electric light bulbs lose light output with use.
Incandescent, fluorescent, MH, all of of them. Even
carbon-arc lamps do but they aren't really bulbs so let's
ignore those.

The filaments vaporize and coat the inside of the bulb.
When you hold up a used bulb next to a new one, the glass
of the old one is always darker -- that's the filament
matierial coating theinside of the bulb.  the coating
blocks light. Also, with fluorescents, some of the mercury
that carries the electric current accross the bulb becomes
embedded in the glass. And with fluorescents and MH
(especially MHs) the gas in the bulb changes with use,
reducing output and shifting the spectrum). Additionally,
the phosphors in incandescents can degrade although this is
not as much of an issue today as in the past -- better
phosphpors!

Still, compact fluorescents retain a high level of output
as they age. They rapidly lose roughly 20% of their light
output in the first few hundred hours -- many manufacturers
rate their bulb output for the level *after* an such
initial burn-in period. They longer fluorescents are used,
the more slowly the output declines. That initial rapid
decline slows to a crawl when the bulbs is abut a year old.
Manufacturers usually do not count the pre-burn-in period
light lievel in the rated output. Starting from the end of
the initial rapid loss, i.e., after a couple hundred hours
use, a cf should have about 70% of it's output by the end
of its rated life. If you burn your bulbs 12 hours per day
for a year, that's only about 4,400 hours and most biaxial
(Pl-L) type cfs last an average of 2-4 times that long
before failing to light. If you were to comapre output of a
3 year old bulb to the intial pre-burn-in output, you'd
probably see drop of roughly half.

That's if run on the ballast the manufacturer intended. If
run hotter, the aging happens faster. If run cooler, it
happens slower.

A brand new bulb will always seem much brighter than older
ones, but they almost even out before too long. Whether you
change out bulbs after a year, or two years or 3 years is a
choice you make. If you and your aquarium are tolerant of
higher and lower levels of light, change the bulbs when
they fail to light, even if that means using them 12 hours
per day for 3 or more years. If you cannot tolerate much of
a decline, then change the bulbs every six months. And if
you can't tolerate any decline at all, change them every
day or so, because they're getting darker every moment.

I think Tom B uses cfs for several years, perhaps until
they fail to light. That's what I do. If you want to
compromise andyou have multiple bulbs over one aquarium,
then stagger when you replace each of the bulbs so the diff
in lighting is not all at once.

Btw, some bulbs will be advertised as not losing any of
their rated output before they fail to light. That just
means the *rated* output has been adjusted to accomodate
the normal decline in output. They all get darker as they
age -- it's as certain as taxes, death and TV reruns.

Hope that helps,
Scott H.
--- Donald <donalddavis at mac_com> wrote:

> . . .
> Also, I thought I remembered reading a reply from Tom
> Barr (several 
> years ago) about CF's and he stated that they do not lose
> "strength" 
> over time like regular FL's or MH's.  Can someone point
> me to that 
> reply?  Or at least re-iterate so I know my information
> is correct.

> 


=====
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Diana Walstad, author of _Ecology of the Planted Aquarium_ will discuss soil supplemented aquarium substrates at the 2004 AGA Convention.

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