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[APD] let there be light!
The question "what is the best bulb" is ambiguous because the criteria
for "best" is not given. There are a number of ways to rate bulbs:
3) operating cost
4) spectral distribution
The most important consideration is not the choice of lamp but rather
the efficiency of the reflector. As Thomas has pointed out, #4 is a
matter of aesthetics and has negligible effect upon growth. There is
probably a measurable effect however for our concerns its so small as to
be unimportant. For all other effects, the efficiency of the reflector
greatly improves the cost performance. By using high efficiency
reflectors, we could use a SINGLE (!) FL lamp to light an aquarium and
achieve consistently good growth for the majority of conditions.
When the tank becomes a jungle, the leaf area ratio (LAR, a scientific
measure) is high and in order to keep the shaded areas of the tank
adequately lit, you have to do more pruning or supply a MUCH higher
Using ever higher light inputs would also increase nutrient demands
(assuming you can keep up) and this causes more over shading and
exacerbates the problems of the short plants struggling to get their
share of the light budget. Additionally a strongly lit tank consumes its
nutrients faster so there may be a shortage of nitrogen. Nitrogen
deficiency leads to low chlorophyll levels and the leaves may begin to
look red, leading to the assumption that the strong light is required
for healthy red growth. In fact, leaves are not working at peak
efficiency; but they look nice.
In terms of efficiency and cost performance, using electronic ballasts
and T8 lamps gives you a big improvement. Overdriving the lamps
increases intensity but increases operating costs disproportionately.
>From a cost performance perspective, you can use the cheapest bulbs
available with negligible effect upon growth. You can also probably
neglect changing bulbs until they are badly dimmed, provided that you
have a safety margin such as afforded by a 2-3 wpg configuration. If
you're going for a low cost 1 wpg configuration, then I think you're
going to need to replace that lamp yearly to achieve good price
performance. The replacement cost of the lamp should be more than offset
by electricity savings.
When I talk about peak efficiency using a single lamp, I'm talking about
fairly efficient wrap-around reflector with a watt per gallon rating of
less than 1 WPG! I think I can effectively light two 20 gallon tanks
with a single 4 ft 32 watt T8 lamp. Using good CO2 levels and a steady
supply of minerals especially nitrates and calcium, we should see steady
growth while minimizing problems with BGA, green water and filament
algae. Hopefully, at this lighting level, the growth rates of fast
growers should be moderated and reduce the necessity for frequent
pruning. Slow growers like Crypts, Anubias, ferns and mosses will still
have enough light to max-out their growth rates. Its the slower growers
that you need to be concerned about. The fast growers already grow too
fast; so fast that they are often short of nitrogen!
In my opinion, more work should be done to measure the efficiencies of
reflector materials and shapes. My comments about using 1 wpg are so
different from conventional wisdom that they might seem heretical. I
think its time we challenged conventional wisdom a little on this one!
[shields up! UV filters on!] ;-)
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