Question of the Day Does light spectrum matter to aquatic plants?


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  • Oct 29, 2022
    Miami, FL
    We've talked a lot about intensity (PAR) and photoperiod. They certainly are important, but more and more people are thinking about optimizing light spectrum for our plants.

    This is especially important when we are looking at technology like LEDs where you can design a combination of LEDs to come up with different spectrums. Same thing applies to T5s.

    What's your understanding of this? Does it matter or will any light grow plants?

    Have a wonderful week everyone!
    I'd love to see some scientific data / discussion about it, but for me, what looks good to my eyes is what I roll with.

    I used to subscribe to the "6500K - 10,000K" theory, but not anymore. None of my T5's fall within that range, and my LED's probably don't either.
    So I appreciate your comments. Thanks and I do agree to some extent.

    To me, my light system has to do two things well:
    1. Provide the right amount of energy for my plants (optimized photosynthesis); and
    2. Look great to my eyes (and those of my wife, more importantly ;)).
    What I do know is that photosynthesis requires a certain light spectrum. This is why grow lights for commercial settings all look red to us. Specifically, the best wavelengths of visible light for photosynthesis fall within the blue range (425–450 nm) and red range (600–700 nm). Therefore, an optimized light source should have peaks in these two ranges. However, as the linked article suggests, more and more research is showing that green light is important in practice unlike what was previously thought.

    Our friend, Dennis Wong, has a good description of it on his site where he discusses light spectrum. His lighting 101 page has a good summary of the three things that light for aquariums needs to achieve.

    The K component is, to me, more for how the light makes the aquarium look to me. Again, Dennis talks about this in his 6500K v 2700K article. I'm also reminded of the old Aqua Design Amano T5 bulbs that I started with. They were all 7000K giving the tanks a very crisp, slight blue light that made the colors really pop.

    I too want to see more science here. While I do believe that any light can grow plants, I don't believe any light can grow plants well. I would really like manufacturers that design plants for planted aquariums to be more transparent with the science being used and why their light is designed for aquarium plant growth.

    As aquarists, we should be asking for this. We need some help with all the variables involved: PAR, Spread, Spectrum, Color Rendering, Kelvin, etc.