Photosynthetic Efficiencies of LEDs: Results of Short Term Exposure to LED Lights

[jahmic]

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Dana Riddle studies zooxanthallae exposed to varying intensities and colors of LEDs between 365nm (UV-A) and 657nm (red). The collected data sheds light on how different spectra affect photosynthesis and the Xanthophyll Cycle, helping us to better understand how corals use and respond to light.

Abstract
Zooxanthellae within stony corals (Porites sp.) were exposed to LED-generated light of differing spectral qualities and photosynthetic efficiencies were determined. Red light (631nm and 657nm) was most efficient, followed by Violet (peaking at 400nm and marketed as 'UV'), Blue (420nm), and White (433nm and phosphors). Blue/White light (453 & 467nm with phosphors) was least efficient. Protective xanthophylls (absorbing blue and blue/green light at ~440-490nm thereby competing with photopigments chlorophyll a, chlorophyll c² and peridinin) seem to be responsible for the different rates of photosynthesis. Black light (365nm) was found to promote photosynthesis. Reports for coral growth at very low PAR values (25 µmolm²sec) were also investigated.The Xanthophyll Cycle (a 'pressure relief valve' for excessive photosynthesis that might result in coral bleaching) was found to begin at different light intensities of LEDs of various colors. Protection did not occur in Red light (631nm and 657nm; Up to an intensity of 170 µmolm²sec, possibly explaining the damaging effects of red light at very high intensity) but did so in Blue/White and Blue light (90 and 100 µmolm²sec, respectively) and 'White' and 'UV' (400nm) at 40 and 50 µmolm²sec, respectively. Long-term experiments are in the planning stages.

 

[sethsolomon]

Interesting article! only understood about 1/3 of it but sounds like its better to stick with blues, cyans, violets, UV's, and reds. for the LED world. so maybe a 4 or 6 to 1, colors to white ratio, might provide better results.

 

[Balz3352]

So green is bad am I reading this correctly?

 

[jda123]

Remember that most Porites is a shallow water coral that can be exposed to the air at low tide. This matters and should be a distinction in the research.

Yellow and red can also be bad when there is too much. There will surely be more and more studies, but just do your own research about how light gets diffused in the ocean and the depth at which the corals that we keep come from. You can get a feel for this that will get you most of the way there... and then the studies can confirm what you already knew. Some corals can be very shallow to very deep - Birdsnest, for example - that can do quite well under LED with lots of white. A SPS like Pearlberry is a deeper water acro that won't do so well with lots of yellow, green and red. The same goes for Zoas... some that are notorious melters under some LED (Space Monsters, Darth Mauls, etc.) come from deeper water and can do quite well under other light sources.

It does not seem that too much blue is an issue, but I am sure that there is a point where it can be.