light spectrum

[Doodaa]

Is there any specific light spectrum that is best for certain types of corals? I've read a lot about PAR values and actinics, 6500-20K lights. Most of what I've found is geared towards the person's point of view as to what looks pretty to them, brings out the corals colors, and comparing bulb manufacturers. Also lots talking about MH, T5, VHO, even actual sunlight piped in through fiber optics, but nothing about what the corals actually need.

I want to know what is best for the corals as in what wavelength etc. for certain types of coral...deep water, sps, lps, softies...regardless of what it looks like to me. Is there a good resource for that or am I just being to specific and it doesn't matter that much?

[Ninong]

The answer to your question can be found in detail, charts and all, in various texts on photosynthesis in corals but you can get a general idea from a few hobby articles.

Dr. Sanjay Joshi touches on this topic very briefly in this article.

Andrew Trevor-Jones (ATJ) has written a nice article on The Properties of Light and another one on Underwater Lighting Conditions.

This topic is treated in depth in Yuri Sorokin's Coral Reef Ecology but unfortunately it is no longer in print. I'm sure it's covered in a lot of other texts, too.

It is difficult to apply this knowledge directly to the selection of lamps (metal halide or fluorescent) because you have no way of knowing the true spectral distribution of a lamp unless it has been independently tested by someone qualified to conduct such tests using the best equipment available. The problem is that the various manufacturers are not always helpful in the naming of a lamp's alleged Kelvin rating. Frequently the advertised number has little relationship to reality. Manufacturers have been known to drastically change this number without having made any changes to the lamp. You might attribute that to 'marketing strategy.'



P.S. -- Aquarium professionals -- meaning people who operate public aquaria for a living -- almost always use a combination of 20,000K and 'daylight' metal halides, supplemented with natural sunlight whenever possible. An excellent 'daylight' metal halide is the 400w Iwasaki 6500K lamp. That lamp in combination with a good 20,000K lamp and lots of actinic fluorescents (preferably VHO or T5's) would make an ideal lighting setup for a large aquarium.

Unfortunately, most hobbyists (myself included) find the coloration of the Iwasaki 6500K lamp a little too 'yellowish' in appearance. That's mainly because human eyes are sensitive to the green-yellow part of the visible spectrum. It really contains a lot of blue but since it also contains a considerable amount of yellow, our eyes perceive it as mostly yellow.

I like the appearance of a decent 10,000K metal halide supplemented with actinic fluorescents. You can achieve a similar appearance with the right combination of T5's. Any of these combinations can be made to cover the full photosynthetically usable range (PUR) required by corals. An aquarium that is lit exclusively with 20,000K lamps covers only the blue end of the spectrum (which is the most important part) but it ignores the yellow-red end, which is also important.

You can cover the full spectrum using a decent 'daylight' lamp supplemented with actinic fluorescents or you can cover it even better using 'daylight' lamps in combination with 20,000K lamps plus actinics.

You can operate an aquarium with just 20,000K or just 6500K or just 10,000K but that wasn't your question. Your question was what's best for the corals. I have to throw this in here to cut off people from posting, "I have just 20,000K and my corals are doing just fine," or, "I have just 6500K and my corals look great."

[CharlotteSteve]

I ran into this same issue trying to choose what LED combination to use for my DIY hood. I know in the specifications for Philips LED's they give the color temp or wave length and also some test information (color charts and what not). Also you may be familiar with "binning". Which is basically how a manuf. can produce something that isn't up to specs. For example I will use Philips LEDs since I am familiar with the product line. The parts all described as "Cool White" @ 1000mA with model numbers beginning in LXK2-PW14-. The kicker is the last three char. Suffix's are T00, U00 or V00. The T00 is ~4100-4500k, the U00 is 4500-5000k and the V00 is 5000-6000k. As you can see there is a very big difference in the same model just by manufacturing tolerences if you will. The other b**** is that the higher bin is usually for commercial sale or very $$$. I think an issue with trusting the color temperature on any other light bulb is that they loose/change spectrum after a short period of time and cont. fall off unlike LED's. Esp. the cheaper the bulb, the more you can expect fall-off.

Another thing to consider is the origin of your species. The deeper the coral is in the water column the more blue the light needs to be to replicate a natural environment. The same goes for the latitude of the coral, the closer to the equator, the more intense the light will be naturally. My THEORY is to try and replicate the natural environment because that is where the coral "chooses" to live, not to say that they will not be prosperous in other situations.

[Doodaa]

Thanks guys.

My main motivation was to assess my current lamp fixture which is 2 150 watt 10K PowerPaQ HQI bulbs, 2 420nm actinic T5 Sunpaqs, and 2 460nm actinic T5 sunpaqs. I know, not the best bulbs out there, but was convenient in one nice package that fit perfectly (Current USA outer orbit 48" model 1042).

I cut back the MH time from 10 hours to 4 hours because my softies started hiding (mushrooms and leathers), I have been slowly increasing (over 2 months now) and now am at 5 hours for the MH's with the 4 actinics on for 11 hours. My thoughts were the MH's were too bright or intense or maybe the wrong color for the mushrooms. Since I cut back, they have opened up more and seemed to quit moving to the shade.

Also, if you remember, I had a low calcium count (240ppm) for a while and maybe that was part of the problem, but I was looking at everything that I could think of and couldn't find info on specific color for specific corals.

My conclusion is that what I have is sufficient in my standard 75 gallon tank with 5" of sand.