Almost all lights used to grow marijuana are inefficient. They use a lot of energy to create light that is useless and even harmful to the plant. This isn't the lights' fault; most lights are designed to emit bright, semi-natural looking light and they are generally good at this. The problem is the idea that this light is right for growing marijuana.
This is my personal summary of some pretty basic info I've collected. If you already know about this stuff just skip to my second diagram.
Marijuana uses only a few wavelengths of the wide spectrum of light and it rejects the rest; it doesn't even absorb most natural sunlight. Marijuana's specific absorption spectrum requires a specific emission spectrum and, despite our general failure to meet it efficiently, we know exactly what it is. The plant's color pigments absorb mainly high red (around 670nm) and blue (around 440) wavelengths, and very little in between. (In fact, plants appear green because they don't absorb green light for photosynthesis and it is reflected.) And light outside the visible spectrum is also useless and even potentially damaging, like ultraviolent light (< 400nm) and infrared light (> 680).
Above is a typical plant
absorption spectrum--the full range of wavelengths of light it absorbs. The perfect
emission spectrum of a grow light must be the exact same in order to fill the needs of the plant without wasting energy on unneeded wavelengths.
What lights do we use to get the best spectrum?
There are a number of lights we don't use at all, light incandescent lights and black lights, because their spectra are poor fits. Other lights, namely
fluorescent tubes,
CFLs,
metal halide and
high pressure sodium lights have better reputations for a reason. Look at their spectrums; they cover most of marijuana's spectrum but, unfortunately, they all additionally emit a lot of unneeded light. Flouresent tubes and CFLs do not emit as much useless light, so they are often termed "more efficient". Metal halide and high pressure sodium, on the other hand, are less efficient but they more fully cover the desired spectrum. This is where most growers end their search, with a choice between more efficient, cheaper lights and more powerful, less efficient ones. A tradeoff.
But LEDs are a new contender, a wildcard, since LED technology is still developing and LEDs are considerably more diverse in wavelength, watts, and lumens than traditional grow lights. LEDs are generally very efficient and they tend to emit very limited ranges of light. While LEDs are becoming increasingly popular most LED lights are poor fits for marijuana's spectrum. These lights are the "best fit" for marijuana but they are all very expensive. So we hit another roadlock.
OK, something affordable?
Yes, I think I've just found it. I've looked at the
emission spectra for most commercial lights and two of these lights offer an almost perfect fit for their range of wavelengths:
red and
blue flouresent tubes. Here I superimposed the red-blue light emission spectrum over the plant's absorption spectrum.
This is the best fit I've ever seen. There's no UV, no IR, and almost no green. These two relatively cheap, efficient lights combine to cover most of marijuana's preferred spectrum.
There must be disadvantages...
As you can see, the blue portion of the spectrum is a little weak. This isn't actually a problem because we don't need the same number of red/blue lights. Just get more blue lights than red ones.
One disadvantage with
all grow lights that I should have mentioned is that marijuana's preferred wavelength actually changes as marijuana matures. The blue range is more important for vegitating and the red range is more important for flowering, this forces some people to alternative between completely different light sources, but the red-blue method is much easier to deal with--just appropriately replace red bulbs with blue ones or vice versa.
So what do you guys think?
Is there anyone out there who has tried or is willing to try red and blue fluorescent bulbs? The stats I cited were from Philips 36W bulbs but I imagine other companies make them as well. I can see no reason why they would not work, but unfortunately I am not in a place where I can grow. I've put a good deal of thought into this and I want to hear what you guys think.
