Fluorescent lighting

Fluorescent light. Besides warning you about letting real sunlight pollute your tank with algae, numerous sites will offer you some daunting technical information about the precise spectrum emitted by various fluorescent tubes, the pros and cons of metal halide, and lots of DIY tips on building your own reflectors. I'm just marginally competent enough to understand dimly  that with the increased efficiency of modern lighting, especially the new light-emitting diode (LED) lighting, the old "watts-per-gallon" rule of thumb is history; instead lumens or  photosynthetically active radiation (PAR) per watt provides the better scale. Lumens measure the strength of light perceived by our eye; PAR measures the strength of light emission in the narrow peaks that plants use for photosynthesis. The human eye is most sensitive in ranges of yellow and green light, which are not the same wavelengths used in photosynthesis. In fact plants look green precisely because their surfaces reflect those wavelengths rather than absorb and use them.
 
Up-market fluorescent bulbs promise to deliver specific spectra, with peaks at the wavelengths plants use for photosynthesis, especially while they are brand new. Sometimes it seems that the more bulbs cost, the sooner you're meant to renew them. I have noticed a graphic design more than passingly suggestive of a spectrum graph printed right on the packaging of an expensive line of fluorescent tubes marketed for the aquarium trade, and I've been momentarily impressed, I admit it. But my habitual skepticism recovered rapidly and reminded me that there was no identifying text connected with the graphic of a photospectrum to justify its use, and that package designers commonly work with the marketing department rather than with the engineering section. ...hmm.
 
As skepticism reasserted itself, I'd been going with the general-duty "full-spectrum" or tri-phosphor "daylight" or "cool white" tubes that I got at the hardware store and on-line. These are not to be confused with the "warm white" tubes, which merely look brighter to the human eye, by the way. 
 
Kelvin rating. When you're bulb-shopping, look for a K rating of about 6700. The K rating (K for Kelvin) describes the color of light that would be emitted by a hypothetical object burning at such-and-so many degrees centigrade. Very high K ratings, near 10,000, may be useful to reefkeepers with demanding invertebrates that have photosynthesizing symbionts. You don't need such a high K rating. If you want to use special plant-friendly "Gro-Lux" bulbs, for gosh sakes combine them with a daylight bulb to kill that weird purple glow. But be warned that an informed minority of planted-tank specialists connect "Grow-Lux" lights with algae encouragement.
 
Compact fluorescents. I've dropped mention of the old fluorescent tube lights, both the fat T12s and slimmer T8s or the even more efficient and slender T5s, because I switched about 2006 to much more efficient compact fluorescents, which with their long slim u-shaped bulbs give three times the light per watt, making the old rule-of-thumb of wattage-per-gallon obsolete. My largely undemanding plants thrive.
 
The bulb packaging may not give you the Kelvin rating that you're looking for. Lightbulbs Direct provides a table of compact fluorescent bulbs that gives the K values for each, Generic, Philips, GE, Osram/Sylvania..
 
The clear plastic plate screwed into the housing isn't enough to protect the bulbs and wiring  from aquarium evaporation: you need  a glass lid over your tank. I get half-inch plates, since a cheaper, thinner plate snapped once under the heat of the Coralife lamp, plunging the lit lamp into the aquarium. When I fished it out by its cord, I was reminded how easily one could reach in with one's hands and get a life-threatening shock. We all know better than that, but instincts move faster than training, unless you've prepared yourself.
 
Early plastic housings by Coralife deformed and cracked with the heat that built up under the hood when placed on glass plates;  I've not had this problem with their redesigned reflector, which is also less obtrusive.