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Lighting Information



Of the 3 main aspects of successful reef keeping (lighting, flow, and water quality), lighting seems to be the one that many hobbyists struggle with the most.

In this article, we will attempt to provide you with the most critical and relevant information about lighting we can.

We only use LED and T5 technologies at our facility, we do not use metal halide due to the higher heat they produce and higher electrical energy they require as well as the periodic bulb replacement. From a lighting technology standpoint, this article is based on our experience and observations with LED & T5.

Spectrum

For us, the main aspects of spectrum we focus on is color temperature derived from different intensities of different frequencies (colors) of light.

We find that we get the best growth rates and best coloration from a 14K Kelvin color temperature. We, like all of you, cannot accurately measure the color temperature, so we go by the light manufacturer setting information. By whatever means you can manage approximating the color temperature of your own fixture, the range we would recommend is 12K to 16K. In addition to the color temperature, we have found 2 frequencies of light to be particularly important to corals. The first is the 420nm to 430nm wavelength. This wavelength is often called hyper violet or sometimes just violet, but in either case having a 14K color temperature with a healthy spike in this frequency makes the coral coloration deep and intense as well as helping stimulate growth. The second wavelength is 450nm to 460nm. This is often referred to as just blue or sometimes deep blue, but this is also very important for the growth and health of the corals. Wavelengths  below 420nm get decreasingly helpful, and once the frequency falls below 400nm they are into the UV range and can become harmful. Then above 460nm you start getting into the cyan, then green, then, yellow, orange and red light wavelengths. In this case, once you are above 460nm the light becomes decreasingly helpful to photosynthesis, but we have found that up to the green spectrum or 520nm, the light is still helpful for growth and research we’ve read (not done ourselves) points to those wavelengths being useful for protein synthesis.

Once you get into the yellow, and especially the orange and red, we haven’t found any benefit to spikes in these color ranges, in fact, with spikes in the red frequency (640nm to 700nm) we’ve seen negative effects on growth and color.

Intensity

Intensity is the second aspect we will discuss.

There are different ways to measure intensity of light, but the only one we use is a quantum PAR meter. If you have your spectrum right, then a PAR meter is a great way to make sure the coral is getting the right amount of that light. We spent many months of our own research and trials, as well as reading a lot of other studies on this. For us we have found some correlation between spectrum (color temperature) and intensity as measured in PAR. That is the lower the color temperature, the lower the PAR corals can tolerate, and the inverse is also true. Some examples of this we have found is that setting the lighting to as close to natural sunlight we could, 6500 Kelvin, intensities above 200 PAR had rapidly increasing negative effects on coral growth, health, and color. At the other end of the spectrum, we found that corals did quite well between 200 PAR all the way up to 600 PAR at 20K Kelvin. Since we use a 14K Kelvin color temperature, we have found that our corals do best at 300 PAR. In addition, the even spread and diffusion of that intensity is also important.

Since our systems are quite shallow as compared to the average hobbyist, we set our lights a full two feet above the water and simply drive them a little higher.

Photo Period

Lastly we’ll talk about the photo period. Our lighting cycle is 12 hours long.

We gradually ramp up for 4 hours, then we stay at peak intensity for 5 hours, then gradually decrease to moon light for 3 hours. This photo period has given us the results we want, but I can say that increasing or decreasing by 1, 2, or even 3 hours won’t make a dramatic difference. One aspect of the photo period we do observe makes a positive impact on the corals is cloud simulation. Our lighting periodically reduces by 20%-50% throughout our cycle in short 30 second to 1.5 minute bursts to simulate passing clouds. Especially during the peak intensity period, the corals seem to benefit from the little breaks in intensity.