The Planted Tank Forum - View Single Post - Blue leds for vegetative growth?
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post #13 of (permalink) Old 01-07-2013, 05:21 AM
Planted Member
Join Date: Mar 2006
Location: Dallas,TX
Posts: 298
Besides some experiments with the blue part of the spectrum we also need some more understanding of how the light intensity works versus the spectrum. I say that because recently I stumbled on a bit of a strange situation:

I'm running a 30W 10,000K LED together with one 24W 6000K Giesemann Midday T5HO bulb. This combination caused the plants to pearl within minutes after setting up both lights for the very first time. This is the LED:

Now check this out:

- LED+T5HO are on: Pearling = 100%
- Only T5HO: Pearling = 0
- Only LED: Pearling = 75%

Why isn't the pearling staying at 25% with the T5HO only? Looks like there is a beneficial interaction between the "strong arm" light and the "good spectrum" light. Or maybe the blue-er light is indeed better for the photosynthesis. Unfortunatelly I do not know the wavelengths of the 30W LED and I am comparing a single element LED with a 24" long fluoresent bulb. Of course the LED will hit the plants with more light in one spot. Anyway - the LED has got to have a lot of blue because without the 6000K bulb the colors in the tank are very washed and the backs of the neon tetras glow very strong blue.

Today I added a third light to the above combo - a 14W red and blue light (has 272 leds: 204 Red (615-655nm) + 68 Blue (455-485nm)):

I wanted to see if that weird (mainly red) color grow light will do something interesting to the aquatic plants. I can say for sure that it did speed up the photosynthesis - I turned the grow light on and off and counted the release rate of a single Oxygen bubble that came out of one of the plants. With the grow light the bubble came out every 3 seconds. As soon as I turned the light off it slowed down to 5 and eventually 7 seconds. I repeated that a few times and there was a definite connection. Very scientific, I know, but it did show that the grow light with its mostly red LEDs sped up the photosynthesis. And from what I see now the range 615-655 nm that my grow light provides may not be the best (some graphs show Chlorophyl A absorbing best at about 680 nm):

Also, another observation - after 4 hours of exposure to that light I saw a 1/2 inch flower stem with buds forming showing up on the sword that was right under the light. I don't know if the grow light had something to do with that but the stem was not there when I installed the grow light.

I should have experimented with the grow light only by turning off the other 2 lights. I will do that tomorrow. That's a light that gets pretty close to both areas of interest for the photosynthesis. I'm interested to see if there will be pearling despite the low intensity. There shouldn't be any - 14 Watts going through 18 inches of water should not work. But read the weird observation about the LED + T5HO pearling above. I experiment again tomorrow.

Last edited by niko; 01-07-2013 at 05:34 AM. Reason: added a picture
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