With a growing number of companies utilizing green and red leds, I felt it important to point out the benefit, or should I say lack, of benefit of their use. While the green and red region of light play a major role in photosynthesis. It is crucial not to confuse science with hype.
I good place to start would be with a basic overview of photosynthetic radiation (Par). In short there are multiple key wave length of light in the blue, green, and red region of the visible spectrum that most effectively promote photosynthesis in corals and invertebrates. While the same is true for plants and other terrestrial organisms that utilize light for their survival. Their needs obliviously differ from marine based organisms.
PAR is the measure of all photosynthetic radiation in the blue, green, and red region. Regardless of whether you are taking measurements for your reef aquarium, or your garden. While there is activity in the far red, or infer red region (700-800nm). Since we are discussing green and red leds, we will be focusing on light in the visible spectrum. When dealing with corals and invertebrates most of the key wavelength that promotes light absorption is in the blue region. Yet there are key wavelengths in the green and red region that are equally important.
Ironically most of the green and red leds offered to hobbyist either DO NOT target these key wavelengths. Or they do so ineffectively making their use questionable. Some companies install multi color leds or offer RGB led systems in hopes of targeting some of the key wavelengths with little or no proof of their effectiveness. When attempting to promote photosynthesis in your aquarium. It is important to keep in mind that corals and invertebrates are not the only opportunist when it comes to light absorbtion. Unwanted nuisance algae love the misinformed.
As with any of my posts I encourage hobbyist not to take my word for it. The next time you come across a RGB or multi color led system being promoted for reef aquarium use. Ask them what basis they used in the selection of leds. Most likely the response you will get is they are high power leds (wattage) and they produce high par reading. Since wattage is irrelevant when determining the output of a light source in terms of photosynthetic radiation. I won’t waste my time discussing power or wattage in this post. For more information on wattage be sure to read my post “Radiometric Vs Photometric output.”
Now when discussing PAR it is often over looked that there is a big difference between a wavelength of light (or color led) that produces PAR and a coral or invertebrates ability or efficiency in absorbing light at that particular wavelength. Various wavelength of light can and will allow photosynthesis depending on intensity. But as we have been discussing there are key wavelengths in the blue, green, and red regions that enable maximum light absorption and therefore are most efficient in promoting photosynthesis.
Here is a simple example. If we selected 2 wavelengths of light. We will call them wave length A and wave length B. Wavelength A produces a Par reading of 200 but is not at a wavelength that is absorbed effectively by corals. Now wavelength B only produces a Par reading of 100. But wavelength B is at the peak of one of the absorption curves. Even though wavelength A produces twice as much Par. Wavelength B will promote more photosynthetic activity.
This is one of the main reasons why par alone is not an effective way to determine the suitability of the led or other light source for reef aquarium use. As we have just demonstrated. Par meters will measure all photosynthetic radiation and not just specific wavelength that are beneficial to corals. This is not opinion, it is fact.
A lot of hobbyist and professionals do not realize that par meters are primarily used for horticulture. At the time they were first introduced in our hobby many years ago they were a welcome improvement over the watt per gallon method. I myself have always preferred spectral composition and intensity. When designing an led or bulb, spectral composition and intensity not only allows me to target specific wavelengths known to be beneficial to corals, it also allows me to monitor the amount of spectral energy produced at any given wavelength.
After all, even when designing a led or bulb. Too much of a good thing can be bad for your corals. Just as an incorrect wavelength will not efficiently promote photosynthesis, too much photosynthetic energy can damage cells or photo receptors causing physical harm or worst to your corals. It is known as photo inhibition and can not only harm corals and other photosynthetic organisms, but shut down photosynthesis entirely. At some point I will write a post on the dangers of over exciting photosynthesis and fluorescence in your reef aquarium.
In closing, I would like to state that there is nothing wrong with using par meters as long as you understand their limitations. I would also like hobbyist to keep in mind that when evaluating color leds, or any light source, that while they may produce par (regardless of how much), it does not mean that corals and invertebrates will be efficient at absorbing the wavelengths of light or par being produced.
Until next time, happy reefing.