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metal halide vs. fluorescent
Shane M. Peter asked:
"And, most people say that to have a
successful planted tank you need to have at least 2 watts/gallon.
the lumens that a metal halide produces is at least 4 times the amount
any incandescent or fluorescent bulb. So, does the same 2 watts/gallon
have to be adhered to?"
I believe that the 2 W/gallon rule of thumb that you're referring to is
based on the typical 4' 40W fluorescent lamp.
To compare incandescents, MH, and fluorescents as alternatives for your
tank, you are correct in thinking about lumens. What it sounds like you
want is an equivalent amount of lumens, and the corresponding wattage
needed to produce those lumens. But don't confuse lumens per lamp with
lumens per watt. While MH systems do have a higher lumen output per
lamp, they have about the same lumen output per watt as fluorescent
systems (60 - 100 LPW). Incandescents produce only about 25 LPW or less
and are therefore not an efficient way to provide a lot of light (unless
you're also trying to electrically heat the aquarium and room).