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That Darn Planted Tank
PART 3: Lighting

by Erik Olson
June 1997

Just as I scared away everyone last month with cabinetry details, in this installment I hope to alienate all but the most dedicated lighting gear-heads.

Factors in Choosing a Light

There are many choices for lighting a planted tank these days, ranging vastly in price (though high price is not necessarily correlated with high quality). Each form of lighting has several factors to consider, summarized below.

  1. Total light output: how bright. The unit for this is Lumens. Plants require a certain amount of lumens to grow.
  2. Efficiency: how much light can be produced for a given amount of electrical power (lumens per watt). Higher efficiency bulbs are going to cost you less to operate, and may offset the initial purchase cost after a few years.
  3. Color rendering index (CRI) and Color Temperature: How close the light approximates the sun. This can be complicated to explain, but I'll try to keep it simple. The sun's light is produced in all colors (red to violet), the combination (spectral curve) of each appears to us as white. The CRI refers to how close the spectral curve of the light approximates that of the sun, with 100 being the closest. In the crude graphs below, you can see that the sun is a nice gradually sloping curve with components from the entire spectrum, while a full-spectrum fluorescent bulb (CRI of 70-90) merely approximates this with "spikes" of different colors. A bulb with a very bad CRI, such as a "cool white" consists mostly of a big green spike.

    [Diagram of CRI]

    The Color Temperature, measured in Kelvin, refers to the color where the spectral curve is ``centered'' or ``balanced''. A higher temperature means that the curve is shifted blue, and a lower temperature means the curve is shifted red. Midday sun has a temperature of 5700 Kelvin, so most plantkeepers try to get lights of similar color temperature. The problem is that many lights are only available in lower temperatures, because people are used to incandescent bulbs of 3200 Kelvin (and before that, fire) for lighting their houses.

    [Diagram of Color Temperature]
  4. Design factor: The shape and size of the light, and how well this will fit in a given setup. A single round bulb will work quite well above a hexagonal tank, for instance. But you may need two or three of them above a long skinny tank.

Popular Lighting Choices

I'll overview some of the more popular lighting choices in terms of the above factors before detailing my own...

Incandescent lighting is the oldest form, but is rarely taken seriously now for anything other than small tanks. Its CRI is 100, being a miniature radiator like the sun, but its temperature, as noted above, is 3200K, way too low. The main problem with incandescent light is its low efficiency, 13 lumens per watt, due to high heat production.

Halogen lights, now popular as cheap 300 watt standing floor lamps and utility lights, are sometimes confused with Metal Halide lights, but are really just a better incandescent (50% more efficient). They still produce a huge amount of heat, which can cook your tank, and wastes a tremendous amount of electricity which will quickly drain the money you save in buying the light. To add to this, their color temperature is still too low. I do not recommend them!

Metal Halide lighting was originally designed for football stadiums and the like. They're often used by Reef Keepers (as well as ``Reefer Keepers'', as you'll quickly learn from reading the signs at some of the more colorful suppliers). The system consists of a 150-1000 watt ``bulb'' and ballast. Most rectangular tanks use 2-3 of them. Though initial cost is expensive (figure $200 or more per light for bulb, ballast and hardware), efficiency is 3-6 times that of incandescent bulbs, and the bulbs have a life of 2-3 years.

Standard fluorescent tubes (I'll also refer to them as T-12's) are the single most popular form of lighting. They are inexpensive and easy to install. Tubes come in a variety of sizes, temperatures, and CRI's. Efficiency is over 3.5 times that of incandescents, depending on the ballast you use.

In addition to standard fluorescents, there are other variants available: High Output and Very High Output (HO, VHO) tubes put two and three times as much light (lumens) out from the same size standard ``Normal Output'' tube. The downside is that they cost more, are harder to locate, and have 1/2 and 1/3 the lifetime, respectively, of their normal counterparts. Compact Fluorescents are small bent tubes (you can see them in modern office buildings, as well as at the hardware store in special screw-in ballasts to replace your incandescent bulbs), and can be great for cramped spaces or tiny tanks. And finally, there are high-efficiency T-8 bulbs, which is what I eventually chose for my tank.


This time around I'm using commercial T-8 F32 bulbs instead of traditional T-12 F40's. The terms ``T-8'' and ``T-12'' refer literally to the diameter of the tube (in eighths of an inch); T-8's are 2/3 the diameter of T-12's. More tubes can be packed in together, or in my case, there is more room between them for light to reflect off the fixture and back into the tank. This alone, I think, makes the light output appear 50% brighter than T-12's.

There are some other advantages of T-8's. First, they're relatively inexpensive. Each tube (Color Temp 5000K, CRI of 75) cost me about $6, and ballasts for two or four tubes cost $20-25. I nearly made up the cost of the ballasts just in money I saved by not buying Vitalites (or their locally-available clone, Spectralites). Second, T-8's use electronic ballasts, which cuts down immensely on my electric bill. The six tubes draw about 200 watts, which is less than my previous 4-tube shop light arrangement (once the energy wasted as heat by the shoplight ballast is taken into account). In fact, at 96 lumens/watt (7.4 times that of incandescents), T-8's are currently the most efficient lighting method available today; they're even better than Metal Halide.

The only problem with T-8's is that they're mostly used in places like office buildings, not the home, so they're not widely available at hardware stores. Home Depot, the only place I've seen stock T-8's, has ballasts, but only 3500K tubes (the closest color balance to incandescent lights). I needed to find a commercial lighting supplier! Luckily, this is easy. I just went down the yellow pages under ``Light Bulbs and Tubes'' until I found a place that would sell me the right bulbs and ballasts in small quantities. (As a side note, of the places that didn't work, one of them didn't stock 5000K bulbs, and the other flat out refused to deal with me when I mentioned aquariums; apparently they have some sort of exclusive deal with fish stores. Now I like our fish retailer brethren; it was a fish store that first turned me on to 13 watt compact fluorescent tubes, for instance, and I happily paid them $30 for my first bulb, socket and ballast. But when I'm going to be buying a lot of them, I sure as heck don't want to pay 2-3 times what they cost from the lighting supplier. So kids, if dealing with a supplier that features ``Aquarium Bulbs'' in their ad, I recommend you LIE. Tell them anything else, tell them you need it for growing pot if you have to, just don't say it's for a fish tank. Happily, I eventually found a place which doesn't care about this nonsense.)

[Ballast Wiring Diagram]

I should say a few words about ballasts, since they have confused many, including myself. You can find two types of electronic ballasts, ``Rapid Start'' or ``Instant Start''. Rapid Start ballasts run current through the filaments on each end of the tube (between the two pins) in order to get the gas hot enough to ignite, while Instant Start ballasts merely pulse a very large voltage across the tube itself. In practical terms, Rapid Start ballasts have over twice as many wires and use a slightly higher amount of electricity, while Instant Start ballasts may shorten the tube life if you turn the lights on and off several times a day. I like and recommend the Instant Start ballasts, mostly because running 8 wires to my hood is far nicer than 24, and I only turn on the light once a day anyway.

I decided to use six tubes in my hood. Going by the old adage ``2-4 watts per gallon of standard fluorescent tubes'', this puts the light at 3.2 watts per gallon. Doesn't matter. I found 4 standard bulbs worked quite well over my previous 45-gallon tank, and this one has 50% more footprint, so... tada... 6 tubes. I nail-stapled the wiring to the inside of the hood and ran all the cabling out the back to the ballasts via 6 feet of normal lamp cord. The ballasts themselves were kept, along with a power strip and the heating transformer, inside a black box I bought at an electronic surplus store for a couple bucks.

Wiring a hood is often a matter of serendipity. I was looking around at a hardware store and happened on some nice double-bulb clips that mount on the two ends of a fixture rather than the top. This was cool! All I needed to do was make the fixture exactly the right length (48'' inside, to be precise) for the bulbs to sit in the clips, and I could mount the clips anywhere on the two trapezoidal endcaps.

Next: the last of the ``hardware'' sections, plumbing and filtration.
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This page was last updated 29 October 1998