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Re: replacing CF bulbs

Wayne Jones quoted me and commented:

" Scott wrote:
> A lux meter, if it is weighted for PAR rather then human sensitivies,
> will certainly tell you just how much useful light is coming from a
> bulb.  If you know just what your tankful of plants need you can tell
> just when a bulb is ready for use and when to replace it to maintain
> precisely x amount of light for your plants.  You'll need a very
> special lux meter for you the bulbs in your UV lamp ;-).  But if you
> use a PC for a year, you won't have much of a problem.
> I reply:
> You do not require a PAR meter to test lamps. The amount of lumens
> that
> lamp emits is proportional to the amount of PAR for a given lamp
> spectrum. So as long as the spectrum of the lamp does not shift then
> a
> LUX meter will do the job. If you want to compare lamps of different
> spectra you just have to use a lumen/PAR conversion factor like the
> ones
> found  in Ivo Busko's article.

I agree that lux meter isn't necessary, but for a different reason. If
you really are concerned this much about the light level, then you
probalby know that some phosphors "die off" faster than others.  So
there will be color shifts, but rarely ones that can be seen.  I jsut
think a light meter is more finicky than most aquarists and rules of
thumb will give great results.  For a PC a good rule of thumb is "you
can use them for a couple of years, at least, without a problem.
> Scott wrote:
> Most folks going for a Boothian or Barroque high-light tank will have
> to base total wattage on how many bulbs they can fit on their tank.
> PCs give a few more options in many cases.  People using the slow and
> Walstady method might have even more options.
> I reply:
> AFAIK George Booth never used any more light than he had to. A
> concept
> that I really agree with. I wonder if he is wondering when he should
> replace his lamps? Not sure what Tom's light levels are but I am
> pretty
> sure it not simply the maximum possible.

Folks trying for 4 watts per gallon are often hard pressed to get that
many watts on top of their tank unless they they go to VHO or PC and
then, the choice can be either considerably over or under the target
level.  That was my only point.  My puns were meant only to distinguish
basics styles or methods -- not to imply that these folks did something
a certain way al  the time.  Tom has has said more than once that he
keeps high tech and low tech tanks (my words, not his).  If you're
aiming for less watts/gal., then you have more choices.  It's not
possible to have the maximum ( and just the maximum light possible all
he time, not unless you change bulbs every few weeks or so.  ;-)  Same
goes for any light level.  It changes over time so you aim for a
configuration and replacment schedule that you can have success with. 
Some people measure a lot of things and some measure fewer.  I would
put a lux meter very low on the list of things to get before the money
runs out.  But even if I used one, I would still burn my PCs for
several years and that duration would be the least of my problems.

I'm not saying my choice is right and Wayne's is wrong.  I'm offering a
different point of view -- one that doesn't require the purchase of a
lux meter or frequent replacment of PC bulbs.

Your choices may vary,
Scott H.

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