Whatever type of marine system is kept lighting is important. With a fish only aquarium the fish need a day cycle and of course need to see where they are going. It’s also good that the aquarist can see the fish! With reef systems the lighting is also important for the same reasons as far as the fish are concerned and more important for the corals.
Before looking at LED’s (light emitting diodes) it’s necessary to see what the LED’s need to be able to do to compete with metal halides.
Metal halide lighting systems are used exclusively for reef aquariums (if used on a fish only system then electricity is being wasted). Sometimes the aquarist is able to use fluorescent T5 tubes, but this depends on the depth of the aquarium – can the light penetrate deep enough?
In this case it is assumed that metal halide bulb(s) are needed.
Metal halide is basically a bulb that uses a filament, the bulb being inside a reflector. The bulbs are rated in watts and there is a range available, the most usual ones being from 150W up to 400W. The wattage is chosen according to the depth of the aquarium. The more watts, the more expensive it will be to run because of electricity usage.
The length of aquarium that a single bulb can light with usual width aquariums is 3ft (circa 91.5cm). This is a guideline not a rule. For a 6ft aquarium two bulbs would therefore be required, doubling the running cost.
The bulbs also need to meet another demand of the corals in addition to intensity and that is spectrum. A lot of the commonly kept corals contain zooxanthellae within the flesh. Zooxanthellae are single celled algae that are essential to the well being of the coral. In order to function (photosynthesize) they need light of the correct wavelength and fortunately metal halide bulbs can achieve this light output. In fact, there is a choice of outputs within limits.
Metal halide bulbs need to be changed regularly according to the manufacturer’s recommendations or the intensity could diminish and/or the spectrum shift.
To make the reef more natural (a goal which is being achieved more and more), many if not most aquarists incorporate one or two additional fluorescent tubes which are usually in the blue spectrum. This assists the delivery of the correct light to the corals and additionally, with the use of electric timers, gives a ‘dawn and dusk’ effect. That is, the blue fluorescent tubes switch on around half an hour before the metal halide, and switch off around half an hour after the metal halide. This avoids sudden bright light or sudden darkness, both of which are undesirable.
Are there any downsides to metal halides? Yes, there are two. The first one is running cost because the bulbs are electricity hungry. Consider a bank of two 400W bulbs ‘that’s not far away from a kilowatt per hour. If the lights are on between 8 and 11 hours a day’..well, you get the idea.
The second downside concerns the aquarium livestock. Stability in any marine system is very important and should be maintained as far as possible. Metal halide bulbs run very hot, and radiate directly into the aquarium as obviously they must. This heats the seawater and it is possible for the seawater temperature to rise unacceptably. If this is the case then the aquarist needs to purchase a chiller (seawater cooler) which is not particularly cheap to purchase or cheap to run. It may be possible for the aquarist to run surface air fans for cooling and many aquarists do this. In this case ideally the seawater temperature and/or time need to be linked into the fan system or, if the seawater cools down because the metal halide has turned off, it may be overcooled and the heaters will switch on for longer periods using more electricity.
So then, what about LED’s? These type lights are used widely nowadays for decorative and commercial purposes as well as more recently being of use to marine aquarists. Aquarists could already be making use of low-powered LED lighting in the form of blue lights that switch on after all the other lights have switched off. They simulate moonlight and give a really good effect, beams of flickering weak light in the seawater. These are not a competitor to metal halides of course.
Fairly recently more powerful LED’s have appeared. They are similar to metal halides in two ways – they come in a canopy and use electricity.
The makers of some canopies have claimed that the light output (the combined output of all the LED’s in the canopy) is equal to X watts of a metal halide, this being 150W, 250W or whatever – the more LED’s the more power. I am not a lighting expert but have noted some argument over this claim. However, contributors to the argument seem to agree that the output is close and is increasing as technology advances. The important point is that there are reef systems that are thriving under LED lighting.
There is another LED system available that is not a standard canopy. These resemble to an extent a fluorescent tube in shape, and can be purchased in different lengths and, again to an extent, different spectrum outputs. So, as with fluorescent tubes, different units can be combined over the aquarium.
LED’s do not need to be changed as regularly as metal halides, in fact they could last 20000 hours. That’s a long period of aquarium lighting, just divide it by the amount of time the aquarium lights are on each day. So there isn’t a requirement to spend money on new bulbs once a year or so.
The heat from LED’s in canopies is not directed into the aquarium as the canopies usually contain a fan to channel the heat away. In warm areas this will add to the work that air conditioning needs to do. Most aquarists will not need to purchase a chiller or employ fans to cool the seawater, which should remain more stable in temperature. The LED’s that are a little reminiscent of fluorescent tubes do not have fans – to be honest I am not sure of the heat output effect but would assume that it will not be great as each ‘tube’ often has less than ten LED’s present.
There isn’t a requirement for additional fluorescent tubes, so the aquarist misses that expense and the need to change the tubes once a year or less. This is because the LED’s incorporate both white and blue LED’s and, in the canopies at least, these usually can be timed on and off according to the aquarist’s wishes. In fact, in the more expensive canopies, the effect of a cloud rolling across the sky can be timed in.
Obtaining a metal halide system costs less than an equivalent LED canopy, and obtaining a fluorescent tube costs less than an LED ‘tube’. That is the problem at the moment with LED systems, the initial cost.
However, when the ongoing cost of a metal halide is considered against the same for LED’s, the LED’s show a considerable saving. In addition, the LED’s do not heat the seawater (at least not to the same extent) and permit the aquarist to maintain temperature stability more cheaply.
Importantly, LED’s are not so electricity hungry.
LED technology continues to move forward and it seems clear that if the current LED systems can be successful then ones in the future will be and better. It is now necessary more than in earlier days to be careful with electricity costs and it is doubtful if this is going to change significantly.
My own guess is that the future for LED’s is assured and the metal halide will begin to fade away before too long. The price of LED systems does need to come down though before LED’s become the usual lighting system considered by most reef aquarists.