To obtain the efficacy (lumens per watt) of compact fluorescent lamps (CFL), refer to
http://www.eere.energy.gov/buildings/info/documents/pdfs/lmc_vol1_final.pdf. Table A-1 (page 74) shows that pin-based compact fluorescent lights generate 42-77 lumens per watt.
To obtain the efficacy of T5 and T5 HO lamps, I use the following reference:
http://www.lrc.rpi.edu/programs/nlpip/lightingAnswers/lat5/pc1a.asp.
To figure out how much light is needed for a tank, I look at pictures of similar tanks where someone has used a light meter to measure the amount of light (PAR) reaching a certain spots in the tank. This picture of a 40-gallon breeder tank with a Tek T5 fixture and PAR figures belongs to “hahnmeisterâ€Â:
Photosynthetic Active Radiation (PAR) is the light spectrum used for photosynthesis. It is measured in µmol•m²•sec.
To vary the light for different depths of the tank, I use a two-level lighting scheme also known as a “dawn-to-dusk†scheme. Half of my lamps are on all day and the other half is on only during mid-day. For example, my fluorescents are on for 12 hours from 7am to 7pm. My MH is on for 6 hours from 10am to 4pm.
The full lighting is important for the depths of the tank (PAR<100). If the full lighting is too bright (PAR>260) at the top of the tank, coral photosynthesis may stop (dynamic photoinhibition). Many corals, such as small polyp stony (SPS) corals, can tolerate dynamic photoinhibition and resume photosynthesis when the mid-day lighting turns off. This is why SPS corals are popular at the top of a tank. My PAR figures are from Dana Riddle’s article (
http://www.advancedaquarist.com/issues/july2004/feature.htm).
I frankly believe that most reef aquarium lighting is too bright. The flexibility provided by most T5 fixtures include removing lamps, using lower intensity lamps (blues are dimmer), and using two timers to vary the light levels. If your tank is flat-bottomed with no live rock or shading, then your lighting needs are much less.