There are a lot of aquarium lights on the market these days that allow us to change the spectrum and give us full control over each LED color. But what are the best settings for plant growth? We're going to cover that in this post.
An article published by Michigan State University titled "Green light: Is it important for plant growth?", found that "Greenlight is considered the least efficient wavelength in the visible spectrum for photosynthesis, but it is still useful in photosynthesis and regulates plant architecture." So that leads me to think, out of all the LED colors, which colored LEDs are best for plant growth? What should be turning up and down on our lights to maximize plant growth. Well, the short answer is red LEDs and super red LEDs... but let's talk about wavelengths real quick.
There was a hypothesis that plants don't use green light to photosynthesize, they reflect it
back at us, hence why plants look green. But plants will use any color with the 300-800nm wavelength as shown in this graph. The nice thing about being able to control a light is we can change the curve in this spectrum to give our plants the optimum curve for growth. Here is what they found out in their tests.
What did they find?
"Plants grown with 50 percent green and 50 percent red light were approximately 25 percent shorter than those grown under only red light, but approximately 50 percent taller than all plants grown under more than 25 percent blue light (Photo 2). Therefore, blue light suppressed extension growth more than green light in an enclosed environment. Twenty-five percent green light could substitute for the same percentage of blue light without affecting fresh weight. However, the electrical efficiency of the green LEDs was much lower than that of blue LEDs
They go on to comment that "One potential advantage of including green in a light spectrum is to reduce eye strain of employees. Under monochromatic, or sometimes two colors of light such as blue and red, plants may not appear their typical color, which could make noticing nutritional, disease or insect pest issues difficult. Another potential advantage of green light is that it can penetrate a canopy better than other wavebands of light. It’s possible that with better canopy penetration, lower leaves will continue to photosynthesize, leading to less loss of the lower leaves."
So how should we set up our programmable aquarium lights?
Well first of all, if you have NOT purchased an aquarium light yet, find a light with as many different LED colors as possible that we can program. For a medium, 80 PAR light, we really like the Finnex Planted+ 24-7 ALC model. If you want a high PAR light, like around 110 PAR, Fluval's Fresh and Planted 3.0 light is great. The only downside to the Fluval 3.0 is that there are no green LEDs, just red, blue and white... but the white lights will toss out some green within their spectrum, so we're ok with overlooking this for now.
So now that you have a light you can program, kick the reds, super reds, warm whites, and/or whites up to the highest PAR value your tank can handle... more on this "your tank can handle" stuff later. If you have green LEDs, bring those up to around half of where your reds and white are at. Now your aquarium is going to look really redish, or warm, and if you want to balance that out or make it look less warm and more neutral, slowly introduce blue LEDs back in until you are satisfied with the color of the light being produced. Most of the time we've found that around 15% brightness of where your reds and whites are at, is where the tank starts to look less warm, and more of a neutral white! Blue LEDs are known to cause algae issues in excess and even will make plants grow more compact, so we want to limit the amount of light blue LEDs throw to simply balance the warm color of the red and white LEDs. And wha-la! Your aquarium light is all dialed in.
Now we can't just go around hitting all of our tanks with 110PAR, as some tanks are designed to be low-energy tanks. Like, those that are not running CO2, or have all slow-growing plants like Anubis, Java ferns, buce, etc. So for balancing purposes, if you have the Fluval 3.0, and you're tank should only be at around 60PAR, because you have slow-growing plants, only raise your red LEDs, and/or whites a little more than halfway, because a little more than half of a 110 PAR light would put us around 60PAR. Remember, an excess of light can lead to algae, so we want a little less, than a little too much. Then bring in greens if you have them to 50% of half, which is 25%, and then blue can sit around 15% of that, which would only be around 7% brightness. Make sense? Reds and white all the way up to the desired PAR, green halfway to where red and whites are at, and blue around 10-15% of that.
Here is what these curves would look like. Now if you don't have individual control over RGB leds, do the best you can with what you have. If all you have is white and blues, crank up the whites and turn down the blues. If all you have is white, reds and blues, do the same thing... crank up the white and reds, turning down the blues. Again, do the best you can with what you have! Or, think about upgrading your light to something that gives you more control.
Final thoughts.
Don't use the ramp up and down setting on the lights. If you don't want to scare your fish by having the lights abruptly come on, dim the lights up and down as fast as the light will allow, without exceeding a 30-minute ramp. Plants don't need a sunrise and sunset each day. This is just a gimmick that we as humans have romanticized. We've actually see it cause more harm than good as it extends the light cycles keeping the lights on for longer than they should be, creating excess light and algae. We recommend having the lights turn right on, to the desired PAR, for an 8-hour photoperiod, then turning them off. With all the nutrients and CO2 that we recommend providing to your plants, they are going to be super happy and eager to growing right when the lights turn on.
Source:
Green light: Is it important for plant growth? - Michigan State University
Toward an optimal spectral quality for plant growth and development: The importance of radiation capture - Utah State University
https://digitalcommons.usu.edu/psc_facpub/763/