Wow, a question directed at ME.....somebody is a bit misguided...
I am NOT the person to ask general lighting questions, but I guess I am the one for lighting these particular tanks...I guess...I certainly did enough homework...
All I can tell you is that the only attractive options I found for this tank, a Marineland 47g column, 20" x 18" x 30 frickin" tall was either:
Clamp on MH (there are at least 2 brands out there that would work, there is another member here who has our tank and uses one), and
Current USA Extreme Pro 20" 6-lamp T5.
I chose the T5.
I do not use the docking clamps; I rest the fixture directly on the tank rim. I have a narrow piece of glass under the fixture to guard against the fixture going into the tank from accidents.
I've found the light penetration sufficient to keep most anything I want from softies to SPS, given TALL rockwork for the higher light loving coral.
A huge drawback is the lack of lamp options in an 18" length (they are actually 16.5"). You only really have 12000k, 420 and 460nm options. [strike]There is a company/site beginning with "nano" that has a variety of lamps that supposedly fit this fixture (with fixture modifications), but the output rating gives me pause. I would be afraid of burning out my ballast.[/strike]
All in all, I am happy with my choice, it does the job, the lamps are inexpensive, the housing is attractive, it fits the tank perfectly. The fans are a bit noisey, but there are alternate fans that are more quiet. I may try those when I get tired of hearing the OEM fans.
Since my purchase, there has arisen the additional option to go with a variety of LED fixtures. If I had the $$$$, I would go that route myself. One of the new Ecotech units that would sync with my MP10s would be sweeeet...