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3.0 Lights

3.0 Lights

3.1 General Discussion

A rough "rule of thumb" is 4 Watts/gallon with successful tanks using from 1.5 - 6 Watts/gallon.1) Fluorescent is fine (some prefer) for shallow (<20") tanks. Use mix of bulbs (50-50, 03s, etc.)2) Metal Halide (MH) is required for deeper tanks.3) AVOID Mercury Vapor, Halogen, HPS, etc. - wrong spectral output.

3.2 Detail Discussion

For most aquarium lighting applications, the bottom line is getting the needed intensity and spectrum of light at the lowest cost while remaining within aesthetic limits.A lighting analysis is now presented. Everyone has their own sets of numbers they would plug in here, for now let's assume the following for comparison. Many will debate the specifics found below.  Feel free to substitute your own numbers, but the methodology is sound.Bulb cost and performance:NO lumens per lamp = 2600 (Phillips F40D daylight, initial)NO watts per lamp = 40 (ditto)NO cost per lamp = ~$20 (from memory, DLS actinic day)VHO lumens per lamp = 5940 (Phillips F48T12/D/VHO daylight, initial)VHO watts per lamp = 110 (ditto)VHO cost per lamp = ~$30 (ditto)MH lumens per lamp = 36000 (Philips MH400/U, initial)MH watts per lamp = 400 (ditto)MH cost per lamp = ~$70 (from memory, Venture 5200K)operate lamps 12 hours/dayreplace lamps once per yearelectricity cost = $.09 / KWH (your mileage may vary)Annual cost per lumen:cost = ( cost-per-lamp / lumens-per-lamp )+ ( watts-per-lamp / lumens-per-lamp ) * 12 * 365 * .09 / 1000NO cost = .0077 + .0061 = .0138 dollars per year per lumenVHO cost = .0051 + .0073 = .0124 dollars per year per lumenMH cost = .0019 + .0044 = .0063 dollars per year per lumenBasically, in fluorescents, the VHO lamps give a higher operating cost but a lower replacement cost for the same total amount of light. But it's close, and you should plug in your own numbers to see what's best for you. If you replace lamps more frequently then VHO is better, if you pay more for power, NO is better.There is a greater variety of lamps available for NO than VHO.  OTOH, it seems that NO lamps can be operated at VHO power levels, with a somewhat shortened lifetime (the higher replacement frequency is offset by lower lamp cost), so this may not be an issue.The initial installation cost (basically the ballast cost) is higher for VHO, even in terms of per-lumen, but this is a pretty small part of the total cost of the lighting system over the years.NO requires more lamps for a given total light intensity, so you may not be able to fit enough NO bulbs in your hood if you need a lot of light.MH seems to be a winner in both replacement and operating costs.  The color spectrums available in MH lights has improved substantially recently with the advent of 10K and 20K bulbs. 10K bulbs are becoming very popular as the sole light source for reef tanks. 20K bulbs are often being used in conjunction with older lighting systems to provide a more balanced light mix.On the flip side, MH bulb vendors have had some horrible quality problems, and obscene pricing practices. Recent testing has also determined that MH ballast have a manufacturing acceptable level of output variance that may result in totally unacceptable differences in individual bulb spectrum output.MH vs fluorescent also gets into the aesthetic and biological considerations. Water surface ripples causing light ripples in the aquarium and room are pronounced with MH lighting. Many people appreciate this effect. Some (e.g. Julian Sprung) feel the variation in light intensity is actually important for some photosynthetic organisms.Many people are under the impression MH runs hot, whereas fluorescent doesn't. In reality, the efficiencies are similar, with MH producing slightly LESS heat than the equivalent fluorescent. The difference is MH dumps all the heat in a small space so the local temperature rise is greater. But if you want to try to get rid of the heat it's actually easier to do it if the heat is concentrated in one spot, since its easier to get rid of a small amount of very hot air than a very large amount of warm air.A separate issue is the selection of a conventional ballast vs an electronic one. There is no doubt the electronic ones are more expensive to purchase, but the savings in electricity offset the high initial cost in a year or so. Also, if heat production is an issue, the electronic ballasts are to be favored. The Icecap VHO electronic ballast is widely advertised, however its advertised claims are also frequently questioned. Advance makes a series of NO electronic ballasts.There are yet two more issues, for which there are a lot of questions and too few answers. Specifically, the short term flicker in light intensity, and radiated electromagnetic fields.Fluorescent lamps on conventional ballasts flicker at 120 Hz, which is above the human visual response, so we don't see it (actually, the flicker is both in intensity and spectrum). But that doesn't mean other creatures can't see it, or whether they benefit or are disadvantaged by it. Electronic ballasts cause flicker at ~30 KHz; it is seriously doubtful that any creature can detect this, so it would appear constant.The flicker doesn't have to be visible to have an effect: it causes any movement to appear strobed, and this may affect the feeding efficiency of visual hunters.The fields issue is even more obscure. At least many cartilaginous fish (sharks, rays, etc) are known to be extremely sensitive to electric fields, and many crustaceans are sensitive to magnetic fields (crabs with pieces of magnetite in internal sensory organs). Fluorescent lamps, with the large area they cover, tend to radiate (using the term pretty loosely) fairly strongly, but MH, and the wiring, and the ballasts can radiate too. It's unknown how significant this could be in an aquarium (but its known sharks preferentially attack undersea cables because of the fields, so there is at least indirect evidence its an issue worth some thought).

BTW, a grounding device reduces the level of induced voltages in the tank, but this is achieved at the expense of increased induced current, so its effect (if any) may depend on the species. Also, note if you have a titanium coil chiller on the tank, it is probably   already grounded through the chiller, and an additional ground may in fact increase the electric current. This should not be an issue with epoxy or ceramic coated chiller coils.

3.3 Lighting Data
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