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Thread: Converting lumens to PAR/PPF

  1. #11

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    Quote Originally Posted by seymour-buds View Post
    [... lots of good stuff about LEDs ...]
    I'm pretty much with you all the way on this, Seymour. The only thing that's dissuading me at the moment is the initial cost, but I'd expect that to come down significantly as the technology matures.

    I'm not sure, however, that LEDs will ever be 'perfect'. Yes, they can be tuned to particular wavelengths, but I think we'll still have some issues with the fact that the spectra will still be 'spiky' rather than smooth.

    Given a photosynthesis aborption/response curve like this:

    then I don't see LEDs matching it exactly. It will definitely be easier to hit the peaks with LEDs than it will with other, existing techonolgies, but it will still only cover specific wavelengths, with gaps between the peaks. My anaolgy would be digital audio vs. analogue audio, I suppose.

    Well, I suppose it would be possible to hit every wavelength (at least every whole-number), but it would take an awful lot of diodes, and probably be prohibitively expensive.

    There would, as you say, be no wasted power/light with properly-tuned LED systems though, as there wouldn't be anything (or very little) in the central bands, which are the bands in which most current (non-LED) sources seem to produce the most light, which is therefore wasted.

    The full-spectrum thing you mention can, I think, be misleading. Manufacturers never really define what they mean. It could be 'matches the full spectrum of sunlight', or 'continuous with no spikes', or 'matches the photsynthesis curve', or probably other things. What I'd like is 'full photosynthesis spectrum, in the proper proportions, with no sharp spikes or gaps'. Pie in the sky?

    The plasma thing sounds interesting and might work out, but I haven't really looked into it to see how the technology achieves the claims made for it. It may be that it's more of an 'analogue' output and so might cover the bands more smoothly and completely.

    My ideal light would be one which produced light at all wavelengths, but weighted to those which are useful for photosynthesis. To continue with the audio analogy; something like white noise with tone controls, enabling boost/cut where required. If that boost/cut could produce a constant power level, such that any 'cut' frequencies had their energy moved into boosting the remaining frequencies, then it would be even better.

    I wonder... Would a plasma TV hooked up to a computer work? Use it to display a single-colour, full-screen image, adjusted so that it matches the photosynthesis spectrum? It wouldn't be truly analogue, but with 8-bit colour it would be pretty close and would offer a choice of over 16-million unique spectra (and therefore might be better than individual sources).

    Quote Originally Posted by teutonic View Post
    Is there a real temperature difference in light ?
    Kind of, but that's not quite what it means. It's "the colour of the light emitted by a black object heated to a particular temperature". As an example: heat a metal bar up and it will change colour as it goes through various temperatures. The colour at any particular temperature will be the same whatever metal is used (well, probably not, but for an 'ideal' black body it would).

    There are ways of producing those colours without the heat aspect though, by matching the wavelengths produced. This is achieved (in HID technology) by using chemicals which emit certain wavelengths when they're stimulated in ways other than by heating.
    Last edited by Anonymiss; 08-10-11 at 05:09 PM.

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  3. #12

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    Yer lights the maddest thing eh. Not even the fastest thing in the universe anymore, if the neutrinos are to be believed. I wish all the
    bulbs gave the output in nanometres (0.000,000,001 of a metre ) in their blurb, instead of the color temperature thing.

    If I follow the chart correctly:

    those peaks are the optimum wavelengths for growing the herb ?
    ☺ Click to enter my CFL percy stealth groom
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    Look Randy, I'm mowing the air Rand, mowing the air. Jim Lahey

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  5. #13

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    Quote Originally Posted by teutonic View Post
    I wish all the bulbs gave the output in nanometres (0.000,000,001 of a metre ) in their blurb, instead of the color temperature thing.
    That would be difficult, because a lamp doesn't produce a single wavelength (mostly, anyway; some discharge lights do). That's why decent manufacturers supply spectral graphs to show the actual wavelengths emitted, like this:


    If I follow the chart correctly:
    those peaks are the optimum wavelengths for growing the herb ?
    Yep. I can't vouch for that graph being cannabis-specific, but it is the absorption spectrum for chlorophyl. It shows that the most energy is abosrbed at the blue end of the spectrum, with the red end providing less.

    Looking at that curve beside the spectral graphs for most lamps shows that most lamps produce a lot of wasted light in the yellow area. There are exceptions though, such as GRO-LUX. They don't produce much in the yellow bands and are weighted more to the red and blue wavelengths, which is why they have a purple hue compared to most others.

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  7. #14

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    You swats make me feel like a dunce. lol

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    Thanks for sharing!

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  11. #16

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    Quote Originally Posted by CGIFurniture View Post
    Thanks for sharing!
    here kitty kitty, pssssssssssssssst

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  13. #17

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    Quote Originally Posted by joker_the_smoker View Post
    here kitty kitty, pssssssssssssssst
    👀👉CGIfurniture

    Sent from ⚒Thames Iron Works⚒

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  15. #18

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    Quote Originally Posted by Ironman View Post
    ����CGIfurniture

    Sent from ⚒Thames Iron Works⚒
    indeed mate, but he aint posted nothing outta line... knowing my luck he would have a crop on lol

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  19. #20

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    Quote Originally Posted by joker_the_smoker View Post
    indeed mate, but he aint posted nothing outta line... knowing my luck he would have a crop on lol
    It's the username and the linked email addy that has me sniffing around!

    I wonder if she has a table for Whiplash?

    Sent from ⚒Thames Iron Works⚒

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