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Thread: LED spectral research

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    http://arxiv.org/ftp/arxiv/papers/1406/1406.3016.pdf

    This covered everything I have been trying to say over the last 6m so much better than I ever could.

    Should be added to every LED question thread created!

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    These are very interesting papers Butch, thanks. One thing I wonder, that you probably know, is whether "white" leds still typically rely on a blue emitter and a yellow phosphor. I have no idea whether this is still the typical way to generate white appearing light, nor whether the low red output in this figure 3 is generally applicable to all or most white leds:
    http://www.mikewoodconsulting.com/ar...ite%20LEDs.pdf

    I was turned off by the relatively low lumen/watt efficiency of blue and red leds I considered, but another grower helpfully explained that since lumens are just a measure of "apparent" brightness to humans, blue and red leds will always give off more PAR than the lumen output might lead you to believe. (Or me at any rate.) If I can come up with a $6000 led project to retrofit my operation, I could get a federal rural efficiency grant, so I have been looking into this stuff. I appreciate the links in any case. Prepackaged meter and 15 meter strips of blue and red leds are incredibly cheap on ebay, so far the blues have been reliable and worthwhile on my aquarium. If I can overcome laziness I'd like to try scaling up.

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    Av8tor1's Avatar
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    Mike,

    To be honest, I don't know if the current high CRI whites use the blue /yellow combo.... I sort of doubt it would still be that simple and get that wide of spectral response. That is just my gut instinct though. I know the first whites were bearly white, but more of a bluish white.... the high CRI models today are true white and wide spectrum.

    I think the research shows the need for white.... it is clear that the spectral needs of plants vary. It makes perfect sense that a low canopy plant might possibly benefit from wavelengths unused or reflected by higher canopy plants, etc etc.
    Personally, I don't think I would invest much coin in a blue/red only setup... or anything that didn't have some type of passive cooling.

    Yes, lumens are really a human perception based metric.... PAR and PUR are better and even those are limited to photosynthesis. I think these links also show this is only part of the story. Beyond even what the plant needs, there are wavelengths that retard the growth of botrytis, another that induces sporation of trichoderma, etc etc...

    The third link refers to the use of these units being produced by Phillips: http://www.hortamericas.com/catalog/...amp-DRWFR.html

    I have to admit, I'm tempted to give one a try... 55$ for a 14w Phillips produced unit designed specially for horticulture and it's plug and play
    I couldn't roll my own for that price
    Last edited by Av8tor1; 07-09-2014 at 08:36 PM.

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    55$ to try is not bad at all. It seems like their brochure, and the daylength extension study are focused on a slightly different question (convincing a greenhouse plant that it's still daytime) than just providing all of the light for indoor cultivated plants. It's still confusing for me, because Philips in their brochure lists the DR/W/FR photon flux as 15 "uMol/s", I'm not sure if they really mean uMol/s/ m^2. But in any case, the question for me is, how many of these are needed to adequately illuminate a 2 x 4 foot shelf of plants? If you look at this link:
    http://www.apogeeinstruments.com/conversion-ppf-to-lux/

    15 uMol/s/m^2 is supposed to be equivalent to 1100 lux of cool white fluorescent, Philips reports a nominal 3200 lumens for a single 4 foot alto t12, but it's unclear whether that is lumens/m^2 (lux) or not. If it is, that would imply 12 (!) of these would be needed to match the light output of 4 t12's, which seems hard to believe. Long story short, do you have a PAR meter? If you do, and you'll do comparative readings on one of these and a fluorescent tube, I'll buy you the philips led lamp. I tried to get my local aquarium club to group buy a PAR meter to no avail. I guess buying one and just seeing what it can grow is reasonable, I just wish it were easier to predict what you can expect (or how many you need) per shelf.

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    Moderator Cindy's Avatar
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    Oh man! Butch, thanks loads for the links! It makes me wanna give away my T5s FL and get the T8 LEDs I've been eyeing.

    One thought though...will anyone ever come out with a list like in Table 1 in the 2nd article with just CPs? Imagine how useful that would be!!

    E.g.
    Plant
    VFT Akai Ryu

    Radiation source
    Red (660 and 635 nm) LEDs with blue (460 nm)

    Effect on plant
    Large dark red traps and compact growth

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    Av8tor1's Avatar
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    Quote Originally Posted by mikewilder View Post
    55$ to try is not bad at all. It seems like their brochure, and the daylength extension study are focused on a slightly different question (convincing a greenhouse plant that it's still daytime) than just providing all of the light for indoor cultivated plants. It's still confusing for me, because Philips in their brochure lists the DR/W/FR photon flux as 15 "uMol/s", I'm not sure if they really mean uMol/s/ m^2. But in any case, the question for me is, how many of these are needed to adequately illuminate a 2 x 4 foot shelf of plants? If you look at this link:
    http://www.apogeeinstruments.com/conversion-ppf-to-lux/

    15 uMol/s/m^2 is supposed to be equivalent to 1100 lux of cool white fluorescent, Philips reports a nominal 3200 lumens for a single 4 foot alto t12, but it's unclear whether that is lumens/m^2 (lux) or not. If it is, that would imply 12 (!) of these would be needed to match the light output of 4 t12's, which seems hard to believe. Long story short, do you have a PAR meter? If you do, and you'll do comparative readings on one of these and a fluorescent tube, I'll buy you the philips led lamp. I tried to get my local aquarium club to group buy a PAR meter to no avail. I guess buying one and just seeing what it can grow is reasonable, I just wish it were easier to predict what you can expect (or how many you need) per shelf.
    Mike,

    Yeah, the Phillips thing in the 3rd link is being marketed as a daylight extender. I have no false pretense that one 14w LED will do an entire plant rack, but after experimenting with 4w Luxeon Tristars, I suspect the Phillips unit might be worth a try on a small scale.
    Some of the newest generation of "top shelf" commercial greenhouse high bay LED's are combinations of white and red, so depending on the how far into the blue the white goes, these may be just fine. It would be nice to see a photospectral graph but Phillips doesn't seem to have one in the public domain. However, for white to be white... its got to include blue imho.

    I don't have a PAR meter, just spectrometers. Mach asked me about UV intensity measurements sometime ago. One shade tree method is to use LED's. They usually work in both directions.
    When supplied with current they produce light at a certain wavelength, but the inverse is also true. When exposed to that same wavelength they produce a tiny current that can be measured as a voltage drop across a 1 ohm 1% resistor or directly measured in mv or uv.

    We cant use Lux, it is also a Lumen based metric...

    I totally agree, its frustrating not being able to compare apples to apples...


    Quote Originally Posted by Cindy View Post
    Oh man! Butch, thanks loads for the links! It makes me wanna give away my T5s FL and get the T8 LEDs I've been eyeing.

    One thought though...will anyone ever come out with a list like in Table 1 in the 2nd article with just CPs? Imagine how useful that would be!!

    E.g.
    Plant
    VFT Akai Ryu

    Radiation source
    Red (660 and 635 nm) LEDs with blue (460 nm)

    Effect on plant
    Large dark red traps and compact growth
    l

    when you gonna start?

    Last edited by Av8tor1; 07-10-2014 at 07:22 AM.

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    > I suspect the Phillips unit might be worth a try on a small scale.

    I think it's definitely worth a try, a warranty and plug and play make it very attractive over diy. I'm really interested to see how many sq feet of plants it will illuminate. It would be awesome if 2 or 3 per shelf would do the trick; I hope that's what you find.

    >I totally agree, its frustrating not being able to compare apples to apples...

    Wait, Granny Smiths are priced in dollars per pound, but Galas are grams of silver per kilocalorie? Definitely a bummer. I appreciate that you are doing this test--

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