Just found this in Coral magazine and thought I would share with you guys. It's an interesting read.
The hobby began in the early 1970s, and in those days fluorescent lamps were the lighting method of choice— usually the thick, 1½-inch (38-mm) tubes (T12) that are practically never seen in the trade any more. Before long, however, these were superseded by the slimmer T8 tubes with a diameter of 1 inch (26 mm), and people experimented with different light colors. In the final analysis, it is not only light for viewing that is important in coral-reef tanks, but above all the right type of light, with a suitable color spectrum, to permit corals to photosynthesize and grow. A combination of daylight tubes and blue tubes was the recipe for success in the 1980s.
In the 1990s, halogen metal vapor lamps gradually became more popular than fluorescent lamps. The stronger light permitted better growth in the light-hungry stony corals that, from around 1992 on, were increasingly found in our aquaria; previously, these had been the occasional exception rather than the rule. In the beginning there was the “Berlin model,” which enthusiastic marine aquarists had encouraged a large lighting manufacturer in that city to produce. Over the following years halogen metal vapor lamps were increasingly developed by the aquarium industry, and before long there were also special lamps that provided light with a particular Kelvin rating. By the mid 1990s 10,000 K was possible, and by the end of the decade the available spectrum included practically the entire range—from daylight types to exclusively blue-light lamps.
Back in 2001, in KORALLE in Germany, Manuela Kruppas and Robert Baur-Kruppas discussed a type of fluorescent tube that was little known to aquarists in those days: the “T5,” just 5/8 inch (16 mm) in diameter. Nowadays these tubes are firmly established in the reef aquarium hobby and represent the alternative to HQI lamps; the T8 tube has been largely superseded. T5 tubes, which are also available in special spectral mixes designed for the coral reef aquarium, are excellent for the maintenance of stony corals, even light-hungry species.
But now the latest innovation has appeared: the light emitting diode (LED), an electronic semiconductor element that has numerous advantages over all other types of lighting. Whether it will also prove as effective as previous lighting solutions in the aquarium hobby is something that only time will tell and marine aquarists
must discover in practice. There is no more guarantee of this than there was in the past with other types of lighting. But it is precisely that uncertainty that awakens the pioneering spirit—anyone who takes an interest in LED lighting in the marine aquarium hobby will have gotten in right at the start.
I saw the first LED lights that could be used in the aquarium hobby in 2003, at the Marine Aquarium Conference of North America (MACNA) in Louisville, Kentucky. They immediately demonstrated the direction in which things were heading, but back then they were very expensive, handmade units, and although they were already available for purchase, they were more suitable for preliminary experimentation than for general usage in the aquarium hobby.
For a long time LEDs were known only as indicator lights, but in the past decade lighting engineers have been able to continually increase the effectiveness of these elements, and they soon came to be regarded as having genuine potential as sources of illumination. A few years ago the majority of LEDs had a light output of 30-80 lm/W. In mid-December 2006, a prototype producing 150 lm/W was revealed. This LED from Nichia has been on the market since May 2009, but in February 2010 the engineers announced their latest prototypes, which produced 208 lm/W, and in September of the same year another appeared with a fabulous 250 lm/W. The experts currently estimate that the maximum output that can be achieved with LEDs is 350 lm/W. For comparison: fluorescent lamps achieve a light output of 45-100 lm/W, and for the majority of halogen metal vapor lamps the figure is around 100-110 lm/W.
At present, work is being done on the development of transparent materials to avoid shading by structural components. These include transparent carrier materials and semiconductors as well as transparent electrical leads. This promises a further increase in efficiency, and it is exciting to consider what LED innovations will be introduced by the lighting industry in the coming years, as there is already a general view that this lighting technology will become firmly established in the reefaquarium hobby.
A little bit on LED's
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