Blue/Red, or Pure White Led's for growlights?
This article is about white and red/blue LEDs for plant growing purposes. Most led-growlights are based upon the red/blue spectrum while there are some advantages by replicating the sunlight with a white led-growlight instead. Generally all high power led's typically ranges from 1 watt to 20 watts or more. Most efficient red/blue led's are at around 1w but can be driven up to 2-3w with proper cooling.
When buying an LED, it's important to notice it's binning.
Just like computer processors, the led are manufactured at a large factory, and the quality of each LED varies. The best "crops" of leds are sorted (binned) into different categories. The best bin can deliver as much as twice the amount of light per watt compared to the worst bin. It's therefore very important to choose the best bin possible for buy LEDs for horticultural applications. I will give you some info here about red/blue vs white LEDs and then give some more info on the particular types of LEDs suitable for growlight and how to solder them in another article here on this site.
Blue/Red LEDs:
Blue and Red LED's drive the photosyntetic reactions in plants, 450nm blue light stimulates the chemical reactions needed for the plant to grow. Red light at about 660nm stimulates blooming and stretching of the plant. A high ratio of blue makes the plant short and stocky, while a high ratio of red, makes thin , frail and tall plants. A good ratio of both wavelengths , will produce healthy plants but abit shorter and stockier than normal sun light. An increase in red light will then trigger blooming, while an increase in blue might stop blooming and stimulate vegetative growt instead. It's therefore possible to control a plants blooming and growing stages by reducing or increasing these two wavelengths.
Most grow lights have the ratio of about 1 blue led for every 6 red leds. 1 to 8 is good for blooming , while 1 to 4 will give more stocky plants. The advantage of stockier plants is that they are physically shorter, and produce the same amounts of fruits/flowers while taking up less space. And also when they are shorter, the LED's can be closer to the whole ,plant and that will give a better coverage of the grow light.
LED's are extremely effective, as much as up to 60-65% efficiency with todays technology (latest osram golden dragon plus royal blue top bin, or Cree XTE). Normal white light contains only a small percentage of the 450nm and 660nm light, so we can use led's that gives the same plant growt by using very little energy. Although these two wavelengths produces alot of photosyntetic light, plants generally thrives with some other wavelengths for different chemical reactions within the plants like caroten etc, so it's generally advisable to include a few led's with a continous spectrum of white in order to give the plants a more natural spectrum and access to the other wavelenghts. Adding white light to such a lamp is also good for your eyes :)
Here's a picture of my first lamp using red/blue led's and some whites:
Plant's also generally adapt to the light given to them, or so i've read. so most of the 400-700nm light can be used to grow plants although not as effectively as the optimal wavelengths.
Pros:
-Energy efficient, 450nm and 660nm LED's hits the spot for photosynthesis. a 20 watt blue/red system have as much 450nm/660nm light as a 100watt normal system or more.
- ability to regulate plants growt pattern/height etc by using more/less blue/red.
Cons:
-Lack of more natural light makes it troublesome to see the plants and enjoy them in correct light.
-Led's like this are expensive since the suitable led's are 1 watt each and cost from $3-$6 each.
- troublesome soldering due to the high number of led's (20watt of led's = 10-20 individual leds).
White LEDs:
A white LED is actually a royal blue 450nm blue LED with a phosphoric layer that reduces the energy of the emittet photons(light particles) so that their color changes. This is why recently most effective white LEDs where blue-white. A blue LED with a very thin layer of phosphor will emit a cool white color, since alot of the photons emitted will be blue among the other green and red colours. A blue LED with a thick layer of phosphor will emit a warm white light. This will cause the effiency of the LED to drop, because a 450 nm blue photon will have about 30% more energy than a red one. But that doesn't really matter that much for plants , since the amount of photons will be quite the same. The main reason i want to build a grow light using white light however is because of the vast amounts of green light they have.
Green light in growlights:
A few months ago, i read an interesting paper about how green light affected plants.
http://pcp.oxfordjournals.org/content/50/4/684.full.pdf+html
I don't understand it all :)(i'm no expert in botanics) , but it says that in high concentrations of white light, green light seems to drive the photosyntetic reaction better than red/blue light. This is because red/blue light is absorbed at the surface of the leaves while the green light is absorbed throughout the first millimeter of the leaves thickness, while the red/blue light is only absorbed in the first few micrometers of the surface. in order for this to happen, we will need a high concentration of light to penetrate the leaf so that the green light can work the photosynthesis. While 90% of the red light is absorbed in the thin layer of the plant, only 10% of that is then used for the photosyntetic reaction, while in green light 20% is absorbed, but 80% of that is used in the reaction. So why do i then want to use white light instead of green?
The technology of green LEDs is rather poor compared to the efficiacy of blue/red led's. Blue LEDs are 6 times more efficient than a green. A phosphor converted royal blue LED with a pure white light emission, will have more green light than a green LED of the same power. By using a white LED we will then have plenty of blue and red light aswell as having lot's of green light. Other advantages of white LEDs is that they look better in the living room, and also are less expensive, because you can buy effective 10w LED that can be driven up to 40w. This makes these growlight easier to make, and easier to cool etc. I'm planning to making several smaller types of LED lamps to see which ones are most effective, and post the tests here.
Cool white leds can be used instead of blue, and warm whites can be used instead of reds to regulate flowering/blooming.
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| Cree Cxa2011 Cool white LED at 14 watt. |
Pro's:
-Cheaper leds because of the size/price.
- better for the eyes and they look better in the living room :)
- more natural light, (basically like the sun).
Con's:
- Less effective than red/blue ,not using optimal wavelenghts.
