Aquarium LED Lighting –A Major Advance Or Is Metal Halide Still The Light Of Choice?

I’ve already written about LED’s (Light Emitting Diodes) of low output (see ‘LED Lighting On The Marine Reef Aquarium‘. Those low output LED’s create excellent moonlight effects. This time the subject is still LED’s but ones of high output.
The aquarist has had the choice of two major forms[ of lighting for the reef aquarium, first, fluorescent tubes, and second metal halides. Many very beautiful captive reefs have been lit using one or the other, or a combination of both. Fluorescent tubes have been used to great effect on soft coral reefs where light doesn’t need to be so powerful. Hard coral reef aquarists, however, have usaquaed metal halide bulbs because of the more intense illumination they provide. Many aquarists have supplemented this lighting with actinic fluorescent tubes for two reasons – to supply the blue light which satisfies the light needs of symbiotic algae, and to provide a light step-down system (dawn and dusk) by using timers, for the benefit of fish.
The light to be considered here in comparison to high output LED’s is metal halide. As said, metal halide is usually the light of choice for hard coral reef enthusiasts because of the high light output, and it is sometimes used on soft coral reefs. In addition to this, there are now available bulbs of 10000K, 14000K, and 20000K etc. (K = Kelvin = colour temperature.) The higher the Kelvin rating the more blue light and the cooler the colour appears.
So what’s this ‘major advance’? Metal halide is the light of choice, isn’t it?. For power output and Kelvin selectivity there isn’t a rival. That last sentence has been correct for a good while. However, there is now a rival and it looks good.

The new entrant is high power LED lighting. What is meant by high power? As I understand it, there are four LED arrays available at the moment. Two of these are rated at 120 watts LED auqarium light and 300 watts LED aquarium light, probably the most popular wattages for reef aquariums. So what? Well, there are some definite advantages to LED’s that metal halide cannot match.
To start, the LED array is contained in a rectangular box that hangs above the aquarium in the same way a metal halide would, though it could be hung considerably closer to the water surface if required. There are 25 LED’s in the array for every 12″ (the length of arrays vary from 14″ to 72″), 12 white and 13 blue (therefore the lighting colour is arranged in a similar way that fluorescent tubes would be).
The Kelvin rating of the LED’s is stated to be 20000. So it is just as suitable for corals. That is point one, LED’s equal metal halides in colour output.. So it is one all.
Metal halide bulbs need to be changed at two years (or less), to avoid light intensity reduction and spectrum shift. The LED lights can run for up to 50000 hours. Generally the ‘lights on’ period for a reef aquarium is 12 hours. This means the LED’s can run for 11 years! It is reported that there is a reduction of light intensity of 30% after that period. However, 70% light output after 11 years! If the metal halide bulb was changed every two years, five bulbs would need to be purchased – plus any supporting fluorescent tubes would need to be changed every year, so they would be changed 11 times. Two to one for LED’s.
A big problem with metal halides is the heat output. The radiated heat can and does warm up aquarium seawater. It can perhaps be reasonably argued that in cooler areas the heat from the metal halide bulb(s) cuts down on heater use. True – but what about summer, or reef aquariums in warm areas. The water heats up beyond the design temperature. If this temperature increase is regular enough and/or great enough then a chiller (cooler) is often employed. The LED unit, however, has been shown to direct heat away from the aquarium seawater. This is done by means of internal fans. The seawater is not heated up. I feel this lack of heat impact is important to the needed stability of the reef aquarium. So three to one for LED’s.
Metal halide bulbs emit UV radiation and need a UV shield to protect the corals (the corals may bleach with excessive UV). Hardly any UV radiation comes from LED’s. Four to one for LED’s.
The glitter lines produced by a metal halide bulb are very attractive and assist in making the captive reef appear more natural. LED’s also produce glitter lines. So that’s one each, five to two for LED’s.
The LED array has controls that will allow the light output to be adjusted for full sunlight, cloudy days, daylight, sunset or moonlight.. The LED bulbs can be dimmed from maximum output to zero output. Score, six to two.
Metal halides as said are able to light a beautiful reef. However, there is a cost. Electricity. Running one, two, three, or even more 150, 250, or 400 watt bulbs is expensive. The aquarist sees this when the postal service drops the bill! Included in this bill is the cost of running a chiller to control excessive heat rise in the seawater, applicable particularly in warm areas. In warm areas air conditioning may be in use, and the heat production of metal halide bulbs will not help the cost of running the conditioning. Any cost saving will be very welcome. The LED system may not be more efficient in energy usage than metal halides as far as light production is concerned. However, it has already been mentioned that heat is not transferred to the seawater, meaning a chiller unit will not be required (unless the areas normal temperature has a detrimental effect on the seawater anyway). The purchase cost saving on a chiller is worthwhile. The electrical running cost of a chiller is also saved. Assuming that the chiller would have been in use year on year, it is significant. If air conditioning is in use, then the conditioning has to deal with the heat put into the air by the fans on the LED system. The heat production of the LED system is stated to be ½ of metal halide, therefore the air conditioning will have less work. Score, seven to two.
The cost of a decent metal halide system is reasonable, not beyond the means of most aquarists. However, (yes, here it comes) the cost of an equivalent LED system is expensive. A ‘middle’ size LED system currently can cost circa $1800. Not cheap. However, the score might reasonably be considered as one all, as long term cost (potential electricity usage reduction, and bulb changing as opposed to no bulb changing) needs to be taken into account. So, eight to three.
To my knowledge, this is the biggest step forward in reef aquarium lighting systems for a long while, and a very exciting one. The aquarist with one of these LED units not only has a very adequate reef lighting system with a number of advantages over metal halide, but one that can be adjusted to simulate the light conditions that a wild reef encounters. In addition, in these times of environmental concern and ‘carbon footprints’, the aquarist would not only be successfully growing corals but might well be reducing the cost to the environment by using less electricity at the same time.


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