All About Aquarium Lighting - Page 3: Characteristics of Light
All About Aquarium Lighting - Page 3: Characteristics of Light
Written by Wednesday, 09 January 2002 01:00
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| All About Aquarium Lighting |
| Page 2: Light Sources |
| Page 3: Characteristics of Light |
| Page 4: Glossary |
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Duration of light
When keeping tropical fish, the duration of the lighting period should be between 10 and 12 hours daily. This should be a continuous period and you should never split it into two separate lighting periods. Special timers will enable you to apply a regular day / night cycle, by turning the lights on at the same time every day, even when you are not at home. An irregular lighting period will have a negative effect on your plant's growth and the well being of your fish. The fish need to rest and they have an internal "clock" which needs to be set. The factor that sets this clock is light. If the fishes can't get a normal day / night cycle they are going to be under stress until they do so.
It should be noted that, for species that do not come from the tropics (such as Mediterranean marine species) the duration of the lighting period should be limited to 7-10 hours daily while a seasonal adaptation would be desired. This means that a combination of winter settings (up to18oC temperature / 7 hours lighting period) and summer (up to 26oC / 10 hour lighting period) would be welcomed by your fishes (even more so by the other animals / plants living in such a tank). Bear in mind that the temperature at the surface of the water can be higher than at a deeper level. Thus, in a tank one meter deep one may observe a difference of 4 - 6oC. It is advisable to take the measurement at the middle of the water column and definitely do not stick those "thermo - stickers" on the glass at the level of the gravel.
Light intensity
This largely depends on a) what we keep in our tanks and (consequently) b) how deep our tank is. Thus, deep water species require less light than shallow water species and the duration of the lighting period should be arranged accordingly. In the lake, the morning and afternoon sunlight does not reach the deep water which remains largely dark. Thus a 10-hour lighting period is more "natural" to them. On top of that, because of light scattering and absorption, only the blue rays reach this depth even during mid-day. Therefore the use of actinic lamps is recommended. A good combination is two actinic lamps coupled to a full spectrum white one (5500 K or thereabout).
For reef coral tanks, a very intense lighting is required. On top of that, reef tanks are usually deep (90 cm in depth or more, as opposed to freshwater tanks which usually measure 50-75 cm in depth). In this case, fluorescent tubes won't help much, unless you use too many of them. Using many of them may sound rational if you only consider the price of the fluorescent tubes. However, when you take into account the cost of the ballasts and the waterproof end caps, then other options may seem more appealing. For such tanks the much higher output required can be obtained by using metal halide lamps. Usually, a combination of metal halides with actinic fluorescent tubes is a very good choice.
For freshwater planted tanks, a bright white light is required. The fluorescent tube should be a good quality one, with a CRI (see glossary) as close to 100 (natural) as possible. Plants need both red and blue rays (green rays are also needed but to a lesser degree). For those tanks, one can use the special, high quality tri-phosphor fluorescent tubes. Sometimes you can use a combination of aquarium white tubes (5000-6500 K) with the normal plant tubes meant for terrestrial plants (the ones with an orange / red colour).
Most of us have been nourished in this hobby with the "so many watts of light / gallon or litre of water" rule of thumb. Of course this is an oversimplified rule and can easily lead to disasters. Firstly, it should read "watts of correct light". No coral will survive no matter how many household fluorescent tubes you add in your tank. Secondly, watts per litre mean different things to tanks of different depths. Thus, a lamp may serve efficiently a 20 cm deep tank while five of the same lamps will not serve a tank 1 meter deep. If we have two tanks with all the other dimensions being the same and different depths then an 1 meter tank will contain five times more water than a 20 cm one. However, the light which will reach the bottom of the deep tank (if lighted by the same light source) is only 1/25th of that reaching the shallow tank!
Increasing the light intensity
Of course we are trying to increase the light actually reaching the fish, plants and gravel in our tank since there is (usually) no way to increase the intensity emitted by the light bulb we use. To do so, we usually rely on reflectors. There are two kind of reflectors: one is in the tube itself while the other is a light reflecting construction which fits in the tank canopy while the lamp fits in it. This has the advantage (especially during winter months) to reflect some of the heat produced by the bulbs in the water. Of course, this becomes a disadvantage during hot summers. A cheap equivalent is the construction of aluminum foil stripes, which are placed over the tubes, the shinning side facing the tubes of course. This can greatly increase the light entering the tank and costs nothing. On top of that, they are easily removed during the summer months.
It should be noted that more light will pass through clear water than through water with debris or other particulates. This is because the light will be scattered and reflected when it falls on those particles thus following random directions instead of reaching the bottom (or your plants). You should note that the presence of floating material (even air bubbles) will scatter the light unevenly thus shifting the colour balance - unpredictably. This is easily observed in tanks illuminated by actinic lamps only. The presence of tiny air bubbles or food particles, create the impression of "milky" water. In short, water, as a medium (and especially salt water) has a much higher refractive index than air. Thus, while air has a refractive index of almost 1, water has 1.33 (even higher in turbid water). Simply put, the higher the refractive index the more light is lost while travelling through that medium.
Ideally, the three sides of the tank and the cover should be covered with mirrors or reflectors, so no light would escape from the tank but this would induce too much stress to the fish. However, painting the tank sides with a pale light colour will increase the light that stays in the tank.
Special electronic ballasts can reduce the flickering of the fluorescent tubes and are highly recommended since they prolong the useful lifespan of the bulbs and consume less electricity (which is also an issue!).
Special tricks in Lighting an Aquarium
The correct lighting of the aquarium has two parameters, which the hobbyist must take care of. First, make sure the correct lighting setup for this aquarium is installed and working properly. The second is that this set up is not visible, light is not escaping from the canopy joints or covers and the wiring is neatly arranged (this has always been my weak point). After experimenting a lot with the lighting conditions in my tanks I have ended up with hundreds of meters of wires running along the tank, tens of starters and ballasts, a tremendous amount of heat when all the lights are turned on, and a terrible mess under my tank. This is because when I started my tanks I thought 4 tubes would be enough, so I made provisions for 4 sets of wires. Then came another four to increase the light reaching the sand bottom. Then came the four actinic tubes (while the first four lamps were never used again but stayed in place). Then came two black light bulbs for the "moonlight" effect and then, I decided to add some 9500 K tubes... In short, 24 tubes have found their way to my tank while I can't find my way to any of those tubes when I need to change it. So, plan first, execute later! If you plan to use many lamps, it could be a wise move to identify them. Thus, you can make a mark on the tube itself with a permanent marker and then make the same mark on the ballast and starter. This will make your life easier if you have to change or check a particular tube. If your tank design allows for that, put the starters and ballasts in a well aerated place and definitely not close to the intake of your air pumps. Blowing hot air in the tank is a plus in winter but becomes a minus in summer.
A specific colour of your fish or plants will be emphasized by adding one or more bulbs biased for this colour among the full spectrum white ones. Actinic blue lamps give a more natural appearance in many tank set ups, especially those with fish from deep waters.
Lighting your tank at an angle may reveal colours that are not visible (or so prominent) when the light comes from directly over them. This is especially true for most Malawi Haps which have much more intense colours when lighted at an angle of 60 degrees (light falling through the front glass on them). Those lights can be turned on while you are watching your tank and need not stay on during the whole lighting period.
You can create the effect of a sunrise / sunset easily with the use of timers. Ideally, you should use actinic tubes for a start, then the first set of white bulbs come on and after an hour or so the rest of the white lamps. For the sunset you simply reverse the order. There are sophisticated dimmers / starters available which will not allow the tube to reach it maximum lighting capacity immediately but allow for a gradual increase in light. A bit more expensive than the normal timer approach but it is really impressive and reduces the fish stress a lot.
Maintenance
After a six-month period of use, a fluorescent tube will emit approximately 60% of the initial light intensity. Switching on and off is the factor which is mostly responsible for this decrease. The same effect is also observed for Metal Halide lamps. Reducing the number of switching on and off the lights increases the life span of the lamps. You can achieve that by using a timer that will switch on and off the light on a regular basis. Using an alternative light source when working in the tank after the lights are off, or before lights are on, you avoid the fast "ageing" of them. More problems with switching on and off are associated with Metal Halide lamps. Never try to switch on a lamp of this type, if the lamp is not completely cooled, after eight or ten hours of function.
It is recommended to change the tubes or bulbs every six months, to maintain the same amount of light year round, especially if you have keep plants and/or invertebrates.
Some of the sodium and mercury vapour lights are unsuitable for lighting reef aquaria. Also avoid the HQL and HQI - NDL lights as their spectra and colour temperature (4300° K) are not suitable. Nevertheless, if one manages to block the ultraviolet emission they can help invertebrates to grow as this type of light source gives a lot of bright light. The quartz halogen lamps, although they cost a little, are also unsuitable for aquariums mainly because of the tremendous heat and low colour temperature.
A good quality reflector may increase the quantity of light in the tank by up to 50%.
It is also recommended to clean the light bulbs/tubes from time to time. This is more requisite when the lights are placed near the water level, so water splashing fills them with salts and other depositions, which reduce the quantity of light emitted. Before cleaning turn off the lights and let them cool enough for handling. A piece of cloth moistened with distilled water is perfect for this job.
Metal Halide lights should not be placed closer than 30 cm to the water surface, or they will overheat the tank.
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