Interesting light spectrums read

Discussion in 'Growing Marijuana Indoors' started by TheFxckingHero, May 3, 2006.

  1. This is all about lighting spectrums. It was taken from a thread I found on the forum for reefermanseeds by the member Cogi, who was experimenting with growing cannabis with LED lighting. It's a very interesting read. Check it out below... & for those interested in viewing the rest of his thread, here is the link:

    Traditional lights are designed primarily for human vision. Believe it or not, human eyes see green light FAR better than red or blue light. How much better? Well, the unit 'Lumen' is actually weighted to human sensitivity - one output watt of yellow-green light at 555 nanometers wavelength is 683 lumens. (555nm is where human eyes are most sensitive) Yet one watt of blue light at 470nm is only about 60 lumens, and one watt of red light at 660nm is just about 42 lumens. This has one simple consequence that's important to grasp: If you see two lights, one at 555nm and one at 660nm, and to your (presumably) human eye they appear equally bright (that means they measure the same lumens), then in actual fact the red one at 660nm is about SIXTEEN TIMES BRIGHTER that the other. Two of the attached pictures are graphs - one showing human eye sensitivity to different colors of light, and one showing the same for plants. (ROY-G-BIV RedOrangeYellowGreenBlueIndigoViolet is the visible light spectrum, which stretches from Red at about 700nm to Violet at about 400nm) The one showing the human eye response spectrum (WhatPeopleSee.jpg) tells the tale - below about 450nm, and above about 650nm, the human eye isn't very sensitive at all.

    If you examine the photosynthetic action spectrum ('Plant Response' in the PlantIrradiation pic), you quickly see that yellow/green light has VERY LITTLE effect in photosynthesis: plants 'see' almost exclusively in the red and blue ends of the visible spectrum. So we can speculate that the plant would grow just as well with little or no green light.** With traditional lighting, even High Pressure Sodium, the bulk of the output power is in the green through yellow/orange portion of the spectrum. By completely eliminating green/yellow output from the plant lighting, generating output at the 470nm blue and 660nm red photosynthetic sensitivity peaks, we can in effect greatly increase the overall efficiency: if 70% of the electricity used in an HPS creates green/yellow light that is of little use to the plant, then if we could eliminate that light from the picture without compromising the harvest, we'd save 70% of our electricity. Of course, 'eliminating green' isn't realistic with traditional lighting - if you filter it out, you've still wasted electricity and heat to generate it. But LEDs offer the ability to 'tune' the lighting spectrum to target the most efficient wavelengths for driving photosynthesis. And modern LED technology offers the ability to generate significant amounts of light, at specific frequencies, pretty efficiently. (It's important to remember that LEDs are semiconductors, like computer chips, NOT like any light bulbs or light-emitting tubes/filaments/elements with which most people are familiar)

    Oh - remember the 660nm red light that was 16x brighter than you thought? Well, to the plant, it's something like 16x brighter again, when compared to 555nm - since 555nm doesn't contribute much to photosynthesis, while 660nm is THE best wavelength for driving photosynthesis. So if the 555nm and the 660nm look the same to us, then to the plant the red is more like 256x as bright. Starting to see the picture? Ordinary bulb ratings are a numbers game based on - and targeting - human vision. I challenge anyone daring enough to filter an entire grow with their HPS light so that ONLY Red+Blue light reaches the plant. I bet it will grow just as well. Of course removing yellow/green with a filter isn't any answer, it's just an easier experiment, one to discern how much influence about 70% of the light from an HPS /REALLY/ has on flowering cannabis. (confession: that 16x figure for photosynthesis is just a guesstimate - it could be much higher, depending on ratios of various photosynthetic pigments)
  2. Im a tech guy.
    You are absolutely right.

    There is however one little issue with LED lighting.

    They are all low voltage DC power so you'll need one BAD ASS powersupply which will drive up the cost. Power leds themselves are not so cheap either and you will need at least a few hundred of maybe even a thousand.

    The one other small issue ;) is the heat production. You want to get these things close together so you can't make em in a wooden frame. If you are really interested search google for LED flashlights, especially those DIY types in which tech maniacs try to build mega power ultra bright foton cannons into a standard flashlight housing.

    The one other other small issue is the lenses they make into the LEDs own housing. This will introduce maximum light levels at a certain distances away from your LED arrays. 'Funny light patterns' to say it in simple words. This maybe an issue. I dunno.
  3. As I said, someone else wrote that up, and he was aware of the cost issues. He was simply experimenting, because he believes in about 5 years it will be a very possible choice as the prices will have gone down by then.
  4. Yes Five years is about how long before the cost comes down. My buddy is growing with LED's and his plants get a little purple and have zebra patterns on the leaves. He is still squaring out the spectrum details however. Other than that they grow nice with huge fan leaves. I am trying to get him to join this BB so maybe this weekend he will join and hook us up on his experience.
  5. Oooo weee

    I can't wait to see the results of growing under LEDs.

    I have heard the calling of the LED temptress for a long long time now:love:, but my wallet just isn't thick enough yet.

    I did however, already buy myself a completely regulatable 3-15 V DC 375W output power supply though so I'm ready for those prices to drop.

    They should start dropping quick as soon as people start installing LEDs to light up their houses en mass. You can see them more and more often in cars and such already so its coming allright.

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