All About Aquarium Lighting - Page 2: Light Sources
All About Aquarium Lighting - Page 2: Light Sources
Written by Wednesday, 09 January 2002 01:00
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Light sources
There are many light sources available to the hobbyist today. One can easily name the sun, the incandescent lamp, the fluorescent tube (normal, HO, VHO), the metal halide lamps and even more exotic light sources.
Sunlight
The sun is of course the perfect light source. At least this should be the case - in theory. However, there are some inherited disadvantages, which make its use less than desired. The type of sunlight Northern Europe gets in the winter has nothing to do with the light falling on the Equator where our tropical fish and plants (not to mention the light sensitive corals) come from. The sunlight has an unpredictable duration (partially or totally absent in cloudy days) and of course leads to lots of algae since its intensity is much higher than what a normal tank can take. Yes, the Lake or river get the same kind of lighting but there are hundreds of thousands of gallons, hundreds of kilometres of water and great depths; all of them have nothing to do with a normal aquarium, On top of that, the sunlight increases the temperature. A tank lighted by the sun would normally experience great fluctuation of the temperature of the water, while the maximum temperature during the day may well be too high for your fish and plants. Bear in mind that, although the sunlight is white, this is only the visible part of its emission. The sun emits great amounts of infra red, ultra violet, x rays and even cosmic rays. However, the sun can be used in specially designed tanks as a complementary light source and is used as the only light source in outdoor ponds (in which case the algae growth, if kept under control, is used as a source of food).
Incandescent lamps
The incandescent lamp provides a cheap source of low quality light. However, in some cases, this is all you need. In this photo, a 100 Watt "spot" light is used with a 35 litre (10 gallon) fry raising tank with herbivore fish. The algae grows everywhere and is then eaten by the fish. During summer the duration of the lighting period is reduced to 4-5 hours daily since the heat produced would otherwise "cook" the fish.
The incandescent lamp is to be used only in emergency cases (sometimes I use them in my hospital tanks or even the fry raising tanks until I cycle a bigger tank - see Photo 1). This should be regarded as a cheap source of low quality light. The spectrum of the light produced by this type of lamps is continuous but it is biased to the red-yellow end of it. Thus, the light almost lacks the blue region, which is essential for most plants and corals. The advantages of this lamp are the low cost and the ease of installation. The disadvantages are the "yellow" cast, the tremendous amounts of heat produced and the low light intensity. This kind of lamp produces the least light per watt of electricity consumed, while most of the energy is released in the form of heat. While plants can't grow properly with this kind of light, algae can (and believe me, it will). The overall result looks too yellow but could be acceptable if there is nothing to compare against. Not really recommended. The normal bulbs produce a light with a temperature around 2700 K (red biased white) while the halogen lamps produce a light of 3000 K (a bit whiter but still red biased). The colour Rendering Index (CRI; see Glossary at the end of this article) of both types is 100. Please note that the more powerful the lamp the brighter it is. Thus, a 100-Watt lamp will be brighter (and thus more effective) than two 50-watt lamps.
Fluorescent tubes
Fluorescent tubes give out four times more light per watt consumed compared to incandescent light bulbs. There are many different types of fluorescent tubes. They differ in the physical size, composition of the phosphor and the wattage. When fluorescent tube is mentioned the standard T12 four foot (120 cm) tubes usually comes to mind. This tube has a diameter of 1.5 inches and is available in 18", 24" 36", 48", 72" and 96" lengths (lengths in inches since this is the way most lamps are sold in Europe, too). The T8 or "slim line" fluorescent has a 1" diameter tube and is available in 24", 36" and 48" lengths. T12 tubes are also available in U-shaped, that is a four foot tube is bent back on itself so it forms a large U, and is about 24" long. Circular tubes are available with several different radii, and in several different types. In the last few years, compact fluorescent tubes have become very popular mostly as replacements for incandescent bulbs. These tubes come in all sizes, from a 3" 5 watt bulb to much larger bulbs that replace 40W four foot (120 cm) tubes, yet are just one third of the size. The phosphor chemistry is what makes the difference between a cool white and a daylight tube and every tube is available with a dizzying array of choices in this area. Some of the most useful tubes for aquarists with small tanks are the 5000K compact fluorescent tubes. Fluorescent tubes are available in HO (High Output) or VHO (Very High Output) which draw more and much more current respectively, but produce more light than regular T12 tubes. As the composition of the phosphor changes so does the spectra of the visible light being emitted by the tube. For aquarium use, whether for illumination for plant growth or to simply be able to see inside the tank, only a small percentage of the dozens of available tubes are appropriate. They fall into the following broad categories: industrial, full spectrum, daylight, plant growth, actinic, tri-phosphor, special purpose and HO/VHO. Some types meant for aquarium use are shown in photo 2. In the photo below four Actinic and three "full spectrum" tubes are shown. You can see that they are marked in inches although sold in Europe.
To all appearances, the tube will put out the same amount of light until it suddenly stops dead one day, (which can take years), but for all practical purposes, because the drop off in light output is an exponential decay, the tube should optimally be replaced every six months or at the very least once a year. Writing the installation date on the tube itself with a permanent magic marker can be a big help here. Although fluorescent tubes come in many sizes, volume of scale dictates that there is really only one size - the T12 four-foot (120 cm) length. Nearly ninety percent of all fluorescent tubes made are this size, and because of this volume, this is the cheapest size.
Full spectrum tubes imitate, as closely as possible, natural sunlight by emitting light in every spectral range. All the different colours of visible light and a very small amount of ultraviolet is emitted. All these tubes have an output spectrum that is similar to sunlight - about as close as modern chemistry can bring us. These tubes try to imitate equatorial sunlight at noon, which has a colour temperature of around 5000K. Noonday sunlight from northern climes has a larger amount of blue in the spectrum, as has a colour temperature of 7500 Kelvin. Among them, we should note the tri-phosphor tubes which emit in the three basic bands blue, green and yellow. Since the phosphor producing the red colour is the most expensive one, usually there is less red emitted from those lamps (see photos 3 and 4).
A tri-phosphor fluorescent tube emits a full spectrum. Note the reduced amount of red. The complementary use of an incandescent bulb would make the ideal combination. This lamp gives the end user enough information as to what kind of light should be expected.
Another "full spectrum" tri-phosphor tube (photo above). Note the differences in the spectrum (far less yellow in this one) and the colour temperature (9500 K as opposed to 18000 K of the other one).
Next come the Actinic (or Actinic blue) tubes. These tubes emit light only from the blue end of the spectrum and are used in marine set-ups to supply the blue that is missing from normal aquarium lighting but is required by marine algae, anemones and corals (see photo below).
Other exotic fluorescent lamps
In addition to the white lamps, other interesting types of lamps include all sorts of real colours (red, green, blue, yellow), blacklight lamps (which create a moonlight effect), germicidal lamps in which there is no phosphor coating at all and a quartz tube to transmit short-wave UV light (e.g., EPROM erasers and PCB photoresist activation), sunlamps, plant lights and special purpose specific wavelength lamps such as reprography and copier lamps.
HO, VHO
There are also High Output and Very High Output types of lamps that have a discharge current of 0.8 A and 1.5 A instead of the standard 0.3 A. HO and VHO lamps are used when high light output is desired but are being outmoded by HID lamps like metal halide. The advantage of such a set up is less wires and less space occupied by tubes in your tank canopy. If we reverse that, they allow you to have much more light in your tank by utilizing the same (often limited) space in your tank canopy. The main disadvantage of these lamps is the cost, coupled to a considerably reduced lifespan. If space is not really a problem and an unusually high light level is not required then you should really go for the normal fluorescent tubes and spend the extra money on some reflectors or high frequency ballasts.
HID LAMPS
HID or High Intensity Discharge are the big bright lamps you see in grocery stores, street lighting and industrial lighting. They can be very large and draw a lot of power. Indeed 2000 watt and 6000 watt lamps exist, however small ones, down to 70 watts are available. These lamps produce a lot of light output quite efficiently, however they can be quite expensive to install initially and may require a fan for cooling in the housing/reflector as they can produce phenomenal amounts of heat. These lamps are used by aquarists who need lots of light, such as marine reef tanks, of large (and deep) freshwater plant tanks.
HID lamps require a ballast, and almost every bulb requires it's own type of ballast. The ballasts are expensive and bulky and are not something you trot on down to the corner hardware store to pick up, although larger hardware stores may have some; they are usually reasonably priced. You'll have to go to a lighting supplier for most of them however.
There are three basic types of HID lamps: mercury vapour, sodium vapour and metal halide:
Mercury vapor: When you see a bright light illuminating some industrial building and it has a characteristic bluish cast - that's mercury vapor. Mercury vapor lamps have an output spectra that is almost entirely blue-white, with very little red. Worse, the spectra is not continuous, there are spectral peaks at certain wavelengths. These lamps, although not useless - there is no doubt very good results can be obtained with them - are equivalent to cool white fluorescents. Yes they work, but why bother going to this expense and trouble when other bulbs will yield much greater success?
One interesting variation on this theme is the self-ballasted bulb. These bulbs (around 250 watts) require no ballast; they just screw into a standard medium base (i.e. incandescent) fixture and they simply work. The downside is that these bulbs are not as efficient as regular mercury vapour lamps because they use the resistive properties of the large filaments as a ballast, and worse of all these bulbs are very expensive. Of course with mercury vapour lamps having a 10,000 hour lifespan the high cost of the bulb must be considered in view of the lack of expense for a ballast.
Sodium vapour lamps: These lamps come in two varieties, high pressure sodium and low pressure sodium, although this is rather a moot point, as the light they output is monochromatic (pure) yellow, and is all but useless in terms of aquaria. It's rather a shame, as they are a full ten times more efficient then incandescent bulbs, in fact these are the most efficient bulbs made, and have a 24,000+ hour lifespan. These are one of the cheapest HID bulbs to Recent advances in high pressure sodium bulbs have improved output spectra, and are quite popular for terrestrial plants, although they haven't as yet gained great acceptance with aquatic gardeners.
Metal Halide: Like sodium vapour, these lamps come in two versions, regular and colour corrected (HQI) versions. The HQI versions have a uniform, sunlight like output spectra, whereas the standard halide bulb has a lot of yellow, some blue and not much red. Unlike sodium vapour, these lamps are very useful to the aquarist needing a lot of light. They can be found nominally in 250, 400, and 1000 watt sizes, from most manufacturers, while some of them also make a 70 watt and a 150 watt size.
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