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Re: Leggy plants

Anthony Law suggested that Rachel's plants were leggy
becasue he PC bulbs were 18 months old and, therefore, had
lost much of their intensity:

> (Rachel was wondering why all her plants are leggy. 
> Adam & Tom asked about macro & traces dosage, etc)
> Ok I've followed this entire thread with interest but
> am surprised nobody commented on this:
> I thought regular tubes are good for 6 mths & PC for
> 12 mths.  So your 4x55W PC will have very little
> intensity left after 18 mths!
> Sounds like you're dosing a ton of nutrients & CO2 but
> giving them crappy lighting.  No?

This is a good guess but I think it's a bit off the mark.

All fluorescent and incandescent bulbs give off
progressively less light as they age, although the
mechanisms that cause this aren't all the same for each
type of bulb.

Flourescents loss a big hunk of their light output during
the first few hundred hours of use, then drop off steadily
but much more slowly until they finally fail.  This causes
some folks, when they put in new bulbs to think that their
old bulbs had really degraded -- the new ones look so much
brighter when you first plug them in.  But check them in a
few days; they won't seem or measure nearly as bright. 
Check them again in a few weeks and they'll look about the
same as the old bulbs.  

PCs, like the 96 watt bulbs that Panasonic makes and the 55
watt bulbs that Osram and Philips make will last for a very
long time.  Although they give off less light at 18 months
than when new, there's still plenty of light coming out of
them.  At 18 months they should still be at well over 80%
rated output, probably over 90%.  BTW, fluorescents,when
rated for light output, are rated for the amount of light
*after* that initial burn-in period.  The rated hours for
the bulbs is usually an estimated average longevity,
anticipating that the bulb is turned on and off every few
hours.  Aquatic gardeners generally only cycle them on/off
two times a day, so expect them to burn longer without
failing.  At half the rated life, expect to measure over
90% of rated output.  At the rated life, expect to measure
close to 90% of rated output.

If the amount of drop off was causing a problem, I think
I'd rather add a lamp (if there was room) than replace
bulbs every year, year and half, etc.

This doesn't mean that the amount of drop-off in light in
Rachel's bulbs (depending on the level to start with and
the sensitivity of her particular plants, turbidity, etc.)
might cause her plants to reach up for more light.  But
it's unlikely and bulbs are expensive so I'd walk down
other avenues first looking for casues of leggy plants. 
And in any event, don't throw away those 18 month old
bulbs! Send them to Tom Barr, whose said previously he'd be
glad to keep using them -- or to me, I would too ;-)

Scott H.

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