T8 vs MH vs VHO...

> From: Tom Roberts <troberts at getnet_com>
> I am in the process of setting up 125 gallon plant tank.  It is 72 inches
> long, 18 inches wide, & 20 inches tall.   I was thinking of using 8
> standard
> T8 bulbs staggared which would give me a little over 2 Watts per gallon.
> Would it be more cost effective in the long run to use a 250W metal
> halide
> setup?  Would one MH bulb provide enough light to cover the entire length
> of
> the tank.  What kind of lighting configuration do most people use with
> this
> size tank?  I am open to any and all suggestions.  

First off, you must consider the adage that "watts aint watts", especially
in cross-bulb comparisons.  From the Krib (yes, it's still down, I'm
pulling from the master on my workstation):

  fluorescent T8, GE rare earth, electronic ballast (!), 2650 lumens, 27
watts, 98 lumens/watt
  MH, E28 universal burning horizontally, 7100 lumens, 175 watts,
    41 lumens/watt
  MH, E28 universal burning VBU, 8300 lumens, 175 watts,
    47 lumens/watt
  MH, E28 horizontal [EP39 base], 11300 lumens, 175 watts,
    65 lumens/watt
Which means that MH's are only 1/2 to 2/3 as efficient as T-8's.  Adjust
your bulb count accordingly.  8 T-8's are 250 watts.  Since the "2 watts
per gallon" rule was invented before MH's and T8's, you could consider
less T-8's (NO WAY!  I use six of them in my 75, and the plants love it!),
or the inevitable two 175 or 250W MH's.

Now let's look at price.

MH's, the last time I was in the maket, ran $200 (one bulb setup) - $400
(two bulb setup), although you could drop that down if you looked
carefully & did a lot yourself.  Replacement bulbs were on the order of
$25-50 ($50-100 for two) every 2 years.

T-8's, I beleive, are better.  You can get 500K bulbs somewheres around
$5-7 each, and 4-tube ballasts are available (here) for $25.  Initial
investment becomes $90-115.  The info I've heard on this group suggests
you can keep T-8's for longer than the normal tubes, up to two years.  If
this is true, then bulb replacement is still less than MH.  If you have to
replace them yearly, it'll break even with MH.

The only reason I might think otherwise is the dimensions of your tank
(which, actually, works out to be only 106 gallons). I was able to cram in
6 T-8's just fine in my 75 (which, I beleive, is 18" front-to-back depth)
with space between every pair of tubes for a reflector/reinforcement bar.
An alternative you may which to consider is using 6 four foot T-8's and
four or so 2-foot or 18" T-8's to fill in the extra space.

I think having space for external reflection is key, by the way.  Based on
some tests George did a few years ago, a normal "shoplite" white paint
reflector can increase the illumination up to 50% over no reflector at
all, depending how far you are from the source.  This does get difficult
when you pack in the tubes extremely close. 

> Reply From: mlt at juno_com (Michael L Taylor)
> Tom,
> You had inquired about lighting a 125 gallon plant tank. I would say that
> you would be better served to cut down on the number of bulbs and go with
> either that MH setup @ 250 watt you suggested, or consider purchasing a
> VHO ballast and running them. 
> I think you would find that using standard bulbs
> in the quantity you mentioned would still only be marginal and very
> cumbersome. 

First, note that T-8's are by no means the same as "standard" bulbs.
Unfortunately, I don't have a VHO entry in the same chart I quoted from,
but I do have another piece of data that shows VHO's to be (at most) 2/3
as efficient as T-8's.  In effect, maybe only twice as luminous as the
equivalent T-8, for about three times the power.  VHO's also expire three
times as fast as NO bulbs.  (If we believe the story about replacing NO
bulbs every 6 months, then hmm...)  You'll still have to stagger 4 VHO
bulbs, and either buy an expensive electronic ballast, or a bulky tar
ballast.  Cost should be similar to (or slightly more expensive than) the
other two.

    - Erik
    (in surprisingly dreary Summery Seattle)

Erik D.. Olson					         amazingly, at home
eriko at wrq_com