Nice article on T-5 lighting from Calfo

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Things You Thought You Knew about T5 Lighting - Part 1[/style]
By Anthony Calfo ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 
Reefkeeping is such a beautiful hobby for many reasons. It has an appeal to most any sensibility, from the creative arts to medical or earth sciences, physics and chemistry... even electrical engineering and carpentry! At the heart of it all though is animal husbandry and the joy of caring for magical reef creatures.
 
The biological equation of a living coral reef is founded on energy as sunlight. Sunlight drives the food chain starting at the surface of the ocean with plankton, on through to the cnidarian animals that we cherish so dearly, and beyond. In turn, the most crucial component of a coral reef aquarium is light. Indeed, it is the most significant investment in any reef system, and it is generally the most researched issue by aquarists. Without reef quality lighting, a captive reef cannot survive, let alone thrive.
 
Despite the abundance of information at large about reef aquarium lighting, a seemingly like-weighted measure of mythinformation abounds. Too many reef aquarists spend considerable time and money on lighting yet still end up with inferior, if not dangerous, systems. I regret to say that my position is not a statement of superlative exaggeration for the purpose of emphasis, but rather poignant testimony to a sad reality in the marine lighting industry. It is an unfortunate fact that many aquarium hobby products at large get designed and released with little to no R&D. The reality is even more sobering for lighting products - domestic and imports alike. But, as the saying goes, the numbers never lie. The following is a short survey of what I'm calling "things you thought you knew" about T5 lighting. You can verify most of these statements on your own with little effort or expense.
 
COOLING
Having the proper operating temperature of T5 lamps is probably the most neglected and underrated element of lighting systems. A startling number of commercial fixtures run way too hot, and DIY systems run an even wilder gamut of cool to (mostly) too hot. You need to understand that adequate cooling is crucial to maintaining lamp life and quality. Without it, the lamps will ignite and look bright or at least fairly so initially, but the amount of useful light (PAR) can be wrecked in mere hours to days of lamps running too hot (decaying significantly due to overheating).
 
Some manufacturers skimp on cooling because of the added expense of fans, although this initial savings is soon negated in premature replacements. Others do it because of the nuisance (a common consumer complaint) of too many wires on lighting systems such as those with additional fans. Another reason is to save money and make their units appear cheaper than others. Others skimp on active cooling to maintain a slimmer product profile. Others still rely on helpful but still inadequate passive ventilation or heat sinks. At the end of the day, it doesn't matter how the lamps maintain optimal temps just so long as the job gets done. Some sort of active cooling (fans) is likely necessary in most cases.
Buy or borrow a good (quantum) PAR meter and see the amazing differences between bright hot systems and bright cool systems; the difference can be staggering. DIYers need to heed this warning especially. Suspending a homemade kit and hoping for the best (passive cooling) is almost certainly not going to give you good light or long lamp life. As an example, I recall consulting a commercial anemone farmer recently that bought top shelf quality T5 lamps, reflectors and ballasts. It was a small fortune of an investment. After several months though he complained that the growth in his anemones and corals was remarkably slow... taking 4 to 6 times longer than other farmers. I tried diagnosing the problem by email but quickly resorted to simply visiting him on a trip to lecture at the local hobby club. When I first walked into the door of this farmer's facility my heart sank; a field of magnificent T5s were suspended in the right number and proper heights from the culture tanks... but without any appreciable heat dissipation whatsoever! Instead of getting PAR readings at the surface of 500-600, he was getting about 100. And PAR readings on the floor of the tank where the anemones were that should have been 200-300 were reading only 19! Thousands of dollars in new T5 lamps were ruined and as bright as these fixtures seemed, the useful light being issued from the hot lamps was dismal.
 
REFLECTORS
Perhaps nearly as neglected an issue as cooling, reflectors are a crucial component of optimal lighting efforts. You maybe surprised to learn a few things here too. For starters, contrary to popular beliefs, lamps with internal reflectors do not produce more light than non-reflector lamps that employ a good external reflector! With a range of lamps, IceCap has tested the difference to be on average 40% favoring standard lamps with external reflectors. And not all external reflectors are alike or similar enough. Materials and designs make this category spread over a wide range of efficiency. IceCap T5 reflectors lead the industry with heat dissipating clip-on aluminum units that are 95% reflective. Be sure to buy the best reflectors you can afford to maximize the value of your investment (the fixed lamps and your ongoing electricity expense).
 
OVERDRIVING
On a slightly more advanced topic, aquarists often debate the merits of overdriving T5 lamps. As the name suggests, overdriving is a matter of running more electricity through a given lamp than it is labeled for. The advantage is more light produced and less lamps needed (a considerable savings over time on additional lamp operation and replacements). The disadvantage is that overdriving shortens the life of the lamp. Where the critic's argument really falls apart though is when it comes to the useful life of a lamp. Properly cooled T5 lamps will not expire from overdriving before their useful life has run to term. That is to say... while a normally operated T5 lamp might last for years before it blinks off, its useful life (producing adequate PAR illumination) is only about a year. Overdriven lamps can last the full useful term of their lifespan and as such are an advantage in my opinion. There are also some brands of T5 lamps that utilize a heavy-duty filament inside the lamp that is designed to handle more current and be overdriven. Keep your coral reef running smoothly by also keeping your lamps clean - free of dust and debris - and replace lamps regularly to reduce the risk of severe light deprivation or shock to corals. T5s should be replaced annually or sooner and preferably in a staggered sequence for multi-lamp systems.
 
Look for coverage on understanding and choosing the best lamp color combinations in our next installment on Things You Thought You Knew About T5 Lighting.