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Re: Aquatic Plants Digest V3 #272
>>> Specifically I wonder how things differ between using T12s and T8s. The
>>> T8s have a lower wattage, but can possibly produce more lumens. Do I
just
>>> fudge and say any 4' fluorescent bulb is 40W/bulb
>>
>>That's what I've done in the past. THe uncertainty is enough, though,
>>that it doesn't matter...
>>
>> - Erik
There seems to be a lot of confusion when talking about the difference
between T8s
and T12s because the ballast can make a large difference in the light output
of T8 tubes.
Consequently, the wattage marked on the tube is actually not necessarily the
wattage consumed
by the tube.
An electronic normal light output ballast has a ballast factor of about
.88 and when used
in a T12 system will produce about the same ammount of light as with a
regular tar ballast but
with a 36% increase in efficiency over cheap ballasts.
An electronic normal light output ballast in a T8 lighting system will
actually produce 7% less
light but at a 50% increase in efficiency over standard flourescent tubes
with tar ballasts.
There is however, an electronic ballast available for T8 lighting that
has a 1.28 ballast factor
and will produce 35% more light than standard (actually obselete) tar
ballasts and flourescent
tubes. Efficiency is also 45% greater.
An increase in efficiency of this degree is bound to have an effect on
any watts/gallon or
watts/area rule. If 3 watts/gallon is sufficient with tar ballasts then just
over 2 watts/gallon would
give the same ammount of light if one were using T8s with a high light
output electronic ballasts.
168 watts are required to run a 4 tube 48" system using T8s and high light
output ballasts. In a 90
gallon tank that would be 1.85 watts/gallon.
The only fly in the ointment is that AFAIK these ballasts cannot drive more
than 2 48" tubes
and that for a four tube system you must purchase 2 ballasts.