How many watts per gallon with metal halide lighting

I would like to set up a 55 to 100 gallon planted tank (I already have a
planted 20 gal) To maintain 3 wpg florescent or even power compact seems to
be a bit difficult, 8 4ft florescent tubes for 100 gal. So I think metal
halide may be a better choice. Does the 3 wpg gallon rule apply to metal
halide? Would one pendant over the center provide even light or do I need
two? Would 2 175-watt pendants be too much over a 55, how about a 100.

I would also consider something like in place of the pendants
http://www.drsfostersmith.com/produc...=20 04+113354

The tank would have a pressurized CO2 system.

Thanks
Scott

You must take into account the efficiency of the flourescent technology.
T12, T10, T8, T5 are all increasing in efficiency. T12 is the old stuff
with lowest efficiency. The watt/gal ratings were developed a long time ago
during that period. A PowerCompact is T5 and worlds apart from an old T12
bulb watt for watt. Wattage alone does not determine how much light is
produced. You must define the effciency. You need to consider lumens per
gallon not wattage per gallon.

I have a 100G tank and use 2 - 55W 24" 6700K PowerCompacts. That's 1W/G of
T5 technology. More than enough light. I have O2 bubbles coming off my
plants. Would not want more light, unless I was trying to raise plants for
sale needing ultra fast growth.

Chris.