Knutty,
Light requirements do depend on the volume of your system to a certain extent but they are more dependant on a: the types of plants you grow/want to grow and b: the DEPTH of the tank.
This is because:
a: different plants require and tolerate different lighting conditions. A low light plant would not thrive under very bright lights and a bright light plant would not thrive under low lighting.
b: the deeper your tank, the more wattage is required to enable the right amount of light to pentrate to the bottom of the tank. I ran some figures through one on-line calculator to get some lighting requirements (both of these work out to about 55 gallons or so):
48x16x16: 110w for low light plants, 160w for medium and 210 for high
48x14x20: 120w for low, 175 for medium and 230 for high.
I thought these seemed a bit high, so I went to another site and they had an entry for a 55 gal 48x13x20 which recommended at least 66w of fluorescent lighting....
Personally I think 66w is way too low and 230w is very high. Somewhere in between should be about right for your set-up. Either the 2x55 or 2x65 would be OK (IMO).
The 48" fittings listed look good on the site but as we don't get the same stuff over here in the UK I can't make any real recommendations. 50/50, full spectrum, daylight, plant-gro, etc. lamps would be OK, Actinic are normally for sea-water only - I don't know whether they would work on a freshwater setup.
HTH, Eddie
