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Old 10-01-2005, 04:48 PM   #2
Maculosus
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some more articles:

http://reefkeeping.com/issues/2002-08/dw/index.htm
http://reefkeeping.com/issues/2004-0...ture/index.htm

This is written by Gary Ahlers:

Reef Aquarium Lighting

There is a lot of confusion about what lighting is “right “for corals. Almost every hobbyist has his or her own opinion, often diametrically opposed. Even experts only have a varying degree of agreement and often contradict each other even in statements of supposed fact.

Improved technology has had a major impact on reef husbandry making it possible to grow and propagate even the most light demanding corals in captivity. Unfortunately the “more is better” philosophy is becoming ncreasingly popular. Watching the Internet B.B.s, I’ve seen a trend towards constantly upgrading to the next bulb wattage. It is not uncommon to see 180 gallon tanks lit with 400w or even 1000w MHs – after all, if 250s do a great job just think how good 400s will be!

Aquarists are routinely lighting their tanks with extreme overkill. This is both costly and can be detrimental to the health of the inhabitants. One guy was moaning that he put a 400w MH six inches above his 29 gal. tank and verything died. Can’t imagine why. What I will try to do here, is boil down almost three hundred hours of research and extract the most relevant conclusions as well as the reason for these recommendations.

First we need to set a few technical definitions:

Lumen – a unit of light striking a one square foot area of a sphere, 1 foot in radius with a point light source at the center. The total light from that source would then be 3.14 L. This is the standard for measuring artificial lighting.

Lux – equals one lumen striking an area of one square meter. This is standard for measuring sunlight intensity.

Kelvin Temperature – The temperature at which a body of matter will emit a given spectrum of electromagnetic radiation – light. 0 degree K equals –469 degrees Fahrenheit.

PAR (PPFD) – photosynthetic flux density. A measure of the light radiation available for use in photosynthesis

Fish only aquariums, which were the standard until the mid eighties, were easy to light. The fish lived in a spartan environment of dead rock and crushed coral. They only needed enough light to find food. With the advent of FOWLR and Reef Aquariums it was a whole new ballgame. Now you needed enough light to fuel photosynthesis based ecosystem. The questions were what kind of light, how much light, and how long. In each case we must also address the issue of too much or too little.

Light Quality

Sunlight, at the equator, at noon, has a full spectrum temperature ranging from 5,800 to 6,500 deg. K. This is not constant, but rises from about 5,000 in the morning and lowers again in the late afternoon. The light temperature (K) rises rapidly as depth increases because seawater selectively absorbs lower energy red and green light. An eighty feet the light temperature is as high as 30,000 deg.K.

Most photosynthesis by algae, plankton etc. takes place within the first several feet of the surface since green chlorophyll responds best to the red green and yellow portions of the spectrum. Agricultural grow light usually uses 4,000 – 5,500 deg K bulbs. This is a problem in an aquarium since it tends to overgrow the reef coral with algae. Higher temp light inhibits algae somewhat and stimulates coral zooxanthelle and coraline algae.

Corals are collected from about 6” under water to about 60 ft. . The majority of specimens are collected from the 20 – 40 ft. range of depth because of the greater diversity found. The light here is about 10,000 dig K. The optimum light spectrum, then, should be between 6,500 and 10,000 deg K for most coral species.

I have an ongoing experiment in this context – two 100 gal. tanks in a cascade water system. Tank 1 lighted with 6,500 deg. K - N.O. fluorescent. Tank 2 lighted with 50/50 URI - N.O about 7,100 – 7,500 deg K. fluorescent. Tank 1 is overrun with green algae and has to be cleaned every week. The coraline growth is very slow. In tank 2 there is virtually no green algae and coraline growth is luxuriant.

Duration

I have seen recommendations ranging from 8 to 14 hours, including one expert writing “ NO MORE THAN 9 HOURS”. As is often the case, most reefkeepers stay in the middle range – 10 to 12 hours. This is not the end of the story though. Sunlight changes light spectrum and intensity through out the day. Technology for varying a lightsource spectrum is not available; however, we can modify the intensity.

Quantity

According to GARF.org any coral can be raised and flourish under standard fluorescent. Another aquarist uses 2 - 1,000 watt metal halides over a 180gal tank. Of course, at the end of the text, you find that they always planned to upgrade slowly to VHO or metal Halide.

Let’s start with some measurements:

Peak sun at the equator (under clear sky) measures around 130,000 Lux, which equals 13,000 Lumen/sq.ft.
Directly under the surface this drops to 70,000 Lux or 7000 Lumen. This loss is mostly due to reflection.
At 1 meter (3.3 feet), 26,000 Lux or 2,600 Lumen.
At 30 feet, 15,000 Lux or 1,500 Lumen.
Light levels in early morning and late afternoons are 10x less than peak Lux.

It would seem that proper illumination would be 7 to 8,000 Lumen/sq. ft. for high light corals, 2,600 to 3,600 Lumen/ sq. ft. for medium light corals and 1,500 to 2,500 Lumen/ sq. ft. for low light corals. I found this to be in line with most Expert recommendations.
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