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Thread: LEDs in GE grow light

  1. #1
    Flashaholic bobski's Avatar
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    Default LEDs in GE grow light

    Can anyone ID these LEDs?



    The center 4 are deep red (640-665nm using a cheapie visual spectrometer) and the rest warm white (450nm driver band). It's hard to tell through the magnifier, but I get the impression the LEDs' base plates are glass.
    It's a GE PAR38 grow light, PN 93101232. Rated 32W at the socket, hefty cast aluminum body with fins, thermal shmoo between the body and LED board, large TIR optic.

  2. #2

    Default Re: LEDs in GE grow light

    First of all, I cannot identify the LEDs, but wanted to ask how confident you were certain about the frequency of the red LEDs. 640-665nm would peak around 652.5nm, and the ideal red wavelength to encourage photosynthesis, stem, leaf, and general vegetative growth, is 660nm, which is an easy target for LED. There are at least a few manufacturers of 660nm deep or "photo red" (which gets its name for photosynthesis, not as many believe for a light that will not expose photosensitive paper in a dark room, which is incidental). However, those made by Cree are by far the most prevalent (Google "photo red LED" and nearly all the results will be Cree), and Cree makes (or made) at least three varieties, which may be generational, XLamp XP-E, XLamp XP-E2, and XLamp XP-G3. I am no expert! Just trying to help.
    Last edited by chillinn; 09-06-2020 at 06:56 PM.

  3. #3
    Flashaholic bobski's Avatar
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    Default Re: LEDs in GE grow light

    Quote Originally Posted by chillinn View Post
    wanted to ask how confident you were certain about the frequency of the red LEDs. 640-665nm would peak around 652.5nm, and the ideal red wavelength to encourage photosynthesis, stem, leaf, and general vegetative growth, is 660nm, which is an easy target for LED.
    Not particularly confident. The spectrometer I used is a black plastic box with a hole and diffraction grating at one end, and a sample light slit and nm scale at the other. You look through the diffraction grating, point the slit at your light source and get a rainbow overlaid on the scale. The red emitters have a strong band in the range I listed, but I can't quantify intensity well enough to tell where the peak is within that range. That's why I'm curious what LEDs these are - I generally trust spec sheets more than my poorly calibrated instrumentation.
    Yes, I'm aware why they use deep red LEDs in grow lights - the top image result for "chlorophyll absorption spectrum":

    So chlorophyll a soaks up that deep red spectrum, but chlorophyll b likes the more orange-y red range. The color bar under the graph is a bit off - 650 is a saturated red, not orange.

  4. #4

    Default Re: LEDs in GE grow light

    Unless you are replacing the LEDs, who makes them is really not very critical.

    They could be Cree, Lumileds, OSRAM, Samsung (LH351 series), Luminus (don't think so), lots of Asian suppliers, etc.


    There are not many vendors of deep red die though. Lumileds, OSRAM, Epistar, can't remember who else. Cree does not make their red die, it is Epistar. Cree just packages those.

  5. #5
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    Default Re: LEDs in GE grow light

    Out of curiosity I picked up a cheap LED plant-grow bulb, A19 8W 800 lumens, Noma brand. Spectrum
    shown has a fairly small sharp blue peak (454nm) relative to larger/broader spectrum peaking in orange/red
    region (612nm). CRI and CCT are not given, makes sense for this application.

    The light is definitely yellower than the average 2700-3000K bulb, but not too orangey like 2200K.

    There is a warning on the box about not being suitable for general illumination, and may require special
    safeguards. As the tint seems nice for general use, I wonder what the risk might be, any ideas? Or is
    it just some kind of CYA?


    Dave

  6. #6
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    Default Re: LEDs in GE grow light

    What strikes me about the colour of my low-cost bulb (plant growth aside, not
    my primary usage) is the resemblance to light from a good old incandescent bulb;
    white with slight orange tint.

    Seems like I got a deal, regular price of other E26 A19 bulbs like this is typically
    $15-$20 or more. Other than lower volumes and that these are "specialty" bulbs, not
    sure why so expensive, just for a slightly different mix of LED colours and spectrum.

    Meantime I picked up another low-cost A19 grow bulb, Globe which has somewhat different
    spectrum shown on package, more skewed towards red, and higher blue spike. This one
    emits pink light. Similar bulbs for the same purpose, but visibly much different.

    Unlike the OP I don't plan to open either bulb at this point, would expect to
    find a mix of whites and reds, though at 8-9W total consumption not too beefy.

    Dave

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