Getting More Light Over Your Tank
by Dave Millman, Silicon Valley Aquarium Society

Have you ever noticed that your tanks seem darker than they used to? If so, it’s probably the fluorescent bulb in your hood. Standard fluorescent bulbs (the straight ones with pins at either end) have a rated life of only six months before the output starts to drop. Higher end compact fluorescents (all the pins at one end) have a rated life of 12-18 months.

For example, I recently replaced four compact fluorescent bulbs in my plant tank after 23 months. Using the light meter in a professional video camera, I discovered that the difference in brightness between the new and old bulbs was more than one f-stop. This means the old bulbs were putting out about half the light the new ones were, at least in the frequencies to which the light meter was sensitive. While not a precise test, this should give you some idea how dim old fluorescent bulbs can get.

This experience caused me to take another look at my 20-gallon fry tank. I like to keep easy plants like swords and java moss with the fry, for cover and to absorb ammonia and nitrates. But lately the plants haven’t been doing too well. Sure enough, the standard fluorescent bulb was about 18 months old.

Replacing this bulb with an aquarium bulb would cost about $15, and provide only 18 watts over the 20 gallon tank. I wanted more light without spending too much money.

The answer? Replace the straight fluorescent bulb with two energy saver compact fluorescents (the kind that screw into a standard incandescent lamp socket). Two 19 watt fluorescents would put 38 watts over my 20 gallon tank, or just under 1.5 watts per gallon. This is perfect for low light plants.

A few years ago, these energy saver compact fluorescents all put out an ugly yellow light, which wouldn’t look very good over an aquarium. Today you can choose between warm white (almost indistinguishable from incandescent bulbs), cool white and daylight bulbs too. I bought the 19 watt daylight variety, which is a little cool for my taste, but has the best spectrum (or “least bad” spectrum) for plants according to online sources.

Home Depot to the Rescue
The lighting department at Home Depot has everything you need. First, buy two lamp sockets with a twist switch sticking straight out of the base. These cost me $3.50 each.

Next, buy two energy saver fluorescent bulbs. These cost me $7.50 each. You may want to bring your hood, so you can make sure the bulbs will fit. Some of the energy saver fluorescents have fat bases.

Finally, if you don’t have one left over from a dead lamp or appliance at home, buy a 6 foot lamp cord with plug. This costs about $1.29.

Easy Assembly
Assembly is simple. First remove the fluorescent bulb, sockets, and wiring from the hood. Next, screw the bulbs into the sockets, and measure where they need to be mounted on the end caps. Be sure to leave clearance above so they don’t touch the hood, and below so they don’t touch the glass (or water!).

Wire up the sockets in parallel. If you don’t know what this means, find someone who does! The lamp sockets I bought mount with one nut. I drilled one 3/8 inch hole in each end cap, pushed the switch ends through, and threaded the nuts.

Because I had removed the white reflector which contained the fluorescent sockets, I used aluminum foil to make the brown plastic hood more reflective. Double-sided carpet tape took care of this, and held the wires in place too.

In summary, for a few bucks more than the cost of one aquarium bulb, I got a whole lot more light. Assembly took me less than 30 minutes, even with “help” from a five year old. The energy saver compact fluorescents should last at least a year or two before the output drops, and then you’ll save even more when you replace them.

One word of caution: The original hood had a sticker warning never to use it over open water. The same warning goes for the modified hood-always use a glass cover! You cannot allow water to condense in the socket without disastrous consequences. And if you use aluminum foil like I did, make sure to keep it well separated from the lamp, the socket and especially the wiring!