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Re: replacing CF bulbs

Wayne Jones made some excellent points about flourescent bulbs. 
However, to my tied old eyes, they seemed a tad pessimistic about power
compact bulb lumen output.  He said:

> There is no way to predict when an inividual lamp will have to be
> replaced. 

True, but the quality of the name brands is quite high and most bulbs
will reach the rated life span if used on cycles of no less than 3
hours.  They will last (keep burning) longer if the cycles are
typically longer,m say 10-12 hours "on."

> CF lamps vary widely in how well they maintain lumens from
> lamp type to lamp type and even within each lamp type there is a wide
> variation. Under laboratory conditions, good quality 55 watt PC is
> supposed to maintain 85% of it's lumens throughout it's operating
> life
> (usually about 12,000 hours) . The ballast, lamp coating and ambient
> temperature will have a strong effect on this however.  T8 lamps will
> generally maintain 95% of lumens for 20,000 hours while VHO T12 are
> so
> bad that they will lose 30% after 40% of their short lives.

All flouresecents lose about 10-20% of their acdtual lumen output after
their intitial burn-in period of several hundred to about a 1,000
hours.  A lot of the more dire info about VHO life spans comes from
reefers, whose critters have much higher light requirements are much
more sensitive to slight changes in lumens than many plants are.  A PC
is in fact a kind of VHO *in that* it operates at very high current in
a relatively small bulb.  You can find good VHOs (like URIs) that will
last you more than a year, no problem.

> For aquarium purposes, it is very important to look at the lumen
> maintainance characteristics of the lamps you are using. You have to
> design a system that provides more light than you need so that after
> about a certain percentage of the lamps rated life you will still
> have
> sufficient light. 

Quite true.  But if you don't want to fret about, do a lot of research,
and then run the math, just replace your bulbs every year or so and
you'll be fine, at least for all but the most exacting situations.

> Oherwise, you will be constantly replacing lamps.

Good idea, to get bigger and keep them longer.  But bigger bulbs cost
more so a little math will tell you if this is cost effiecient or not.

> You
> really want to pick the light level you want at the time you intend
> to
> replace the lamp. 

If you do this, understand that you will have *more light than you want
virutally all of the time*, and too much light can easily mean more
CO2, or algae, or both, especially at high light levels.

> This is not a consideration with most T8 lamps they
> can go until near failure but it is somewhat true with PCs and with
> VHOs

Some PC makers woulkd say that this is not true.

> and MH it is huge.
> I notice that Phillips has introduced a new 80 watt PC. I also notice
> that it only has a rated life of 10,000 hours. I bet that the really
> high wattage 96 watt PCs are even worse.

Well, let's take one of AH Supply's 96 watt bulbs as an example, rated
for 10,000 hr.s.  This bulb won't actually fail that soon, because on a
planted tank you're going to have longer "on" times, i.e., longer
cycling.  So it will last longer, but still, after 10,000 hours, it
will have about 80% of its rated lumen output. Let's suppose that about
80% is acceptable for your tank.

At 12 hours use per day, that means 2 and a quarter years of use before
it falls below the desired lumen output of about 80%.  Now supposing
that 80% of the after-burn-in output is inadequate, let's cut that in
half and use it for only half that life span -- that's still more than
a year.  At 10 hours per day "on" time, they'll last even longer.  The
55 watt bulbs are rated for an even longer life.

Check out the table on AH Supply


and then, if still concerned about useful life in terms of lumen
output, talk to Kim at AHS about useful life.

I think a lot of people have mistakenly concluded that their
flouresecent bulbs (whether VHO, NO, PC) have short life spans because
something like this happened:

they had some trouble with their tank, tried replacing a bulb to see if
that was the cause, and noticed how much brighter the new bulb was
compared to the older one.  But the initial output is very high and
drops quickly on flouresents.  You ought to get a year or two of use
out of a PC if you're burning it about 10-12 hours per day.

Rules of thumb about bulbs:
Cycling on and off is what kills most bulbs (this is not a
consideration for planted tanks since their are so few cycles each day)

All flouresents are brighter for the first few hundred to 1,000 hours
-- after this steep drop-off in brightness, the drop-off is much
slower, but steady and persistent until the bulb fails.  Most makers
rate the lumens for the output *after* the initial burn in.  Some even
rate it lower than that and then tell you the bulb keeps 90% (or
whatever high percentage) of its output all the way until failure.

Flouresecents are less efficient if they burn too cool but die sooner
if they burn too hot -- variations in design presecribe the optimum
temperature (usually around 100-120 degrees F.  This is main reason
smaller diameter bulbs are more efficient than larger ones.  (Other
factors are involved, including less restrike with smaller diameters
but also less phosphors in a samller tube, concentration of mercury
vapor, etc.)

Without a ballast to limit the amount of current that flourescent lamp
draws, it will take all the amps it can get until it the filaments (or
electrodes) flash out -- a flourescent lamp is like an Oscar, it will
eat until the eating kills it.

Ballasts that allow more current to a bulb tend to let the bulb burn
brighter and hotter but for a shorter life.

If you buy from trustworthy and knowsledgeable vendors that come highly
recommended by a wide variety of experts, you can follow their advice
and forget about all these details.  

Still looking for the end of the tunnel,
Scott H.

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