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Thread: DIY COB LED info

  1. #57

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    Quote Originally Posted by nimbulan View Post
    Thank you very much naoki. It certainly is a lot of information to take in for someone as new to LED lighting as I am but this gets me one step closer to taking the plunge.
    LED stuff is a bit complicated, and it did take quite a bit to learn about it for me, too. Sorry if I don't explain things in an easy way... I'm trying to leave out too much details, but I frequently end up with difficult explanation...

    Quote Originally Posted by nimbulan View Post
    Two more quick questions:
    I've noticed that people seem to stick with <5000K lighting for LEDs, yet bulbs as high as 6500k are common with fluorescent lighting. Why is that?
    My theory is that people took "day light" spectrum of fluorescent light literally. Here is my measurement of T5HO:

    3000K 82 533 1-2mo old, Philips F54T5/830
    4100K 83 590 new F54TH/841/HO/ALTO
    5000K 80 620 1-2 mo old, F54T5/850
    5000K 85 625 new F54T5/850/HO/ALTO

    The measurement is taken at 12" from the tube in a typical fixture/reflector with Li-COR LI-190 (for PPFD) and LX1330B (fc).
    2nd column is PPFD in micromol/m^2/s
    3rd column is fc.

    There is a bigger difference in terms of foot-candle (which isn't as relevant as PPFD), and higher K seems to have higher fc. But in terms of the PPFD, the difference is pretty small. I didn't have 6500K, but the trend should be similar. I used to use whatever available between 3000-6500K for T5HO. Those purple plant bulbs do indeed have higher efficiency than white ones in my measurement (link to my measurement), but it is questionable if the extra cost is worth spending (since the output decays in 1-2 years).

    As a related note, I got some data comparing PAR efficiency of T5HO (T8 and LED, too). Here is a calculation done by some planted aquarium people from South Africa to find best T5HO bulbs. It is sorted from the most efficient to less efficient (the top is the best). Basically they digitized the emission spectra, and calculated how much plant relevant light is emitted for a given amount of electric power usage. This is the "PAR efficiency" column (micomol/J is the unit). K (kelvin) column is the calculated (not the advertised) corrected color temp. This is a bit old data, so I'm not sure if all of these are still available. To be honest, I'm not sure if the PAR efficiency of the top one is really correct. It seems to be too high for fluorescent light. Top rated ones seem to have higher K values, so there may be some reasons why people use 6500K. But this is from calculation (not measurement). Also, some of the specialty bulbs may have quite different emission spectra from the typical T5HO.



    The other factor is the emitted spectrum of fluorescent bulbs (jagged shape with a few major peaks corresponding to different phosphors) is very different from LED (smooth, 1 blue peak + yellow/red peak from phosphor). Once you start to go above 5000K with LED, the light is dominated by the blue peak, which doesn't look too good for phytochrome related response (my guess here). Many MJ people goes with 3000-4000K COB LEDs for flowering because their flowering is photoperiodic (phytochrome is relevant for this process) and requires red light.

    Note that typical spectral power distribution (SPD) curve which is in data sheet has power (watt) on y-axis. But the photosynthesis is more related to the number of photons than power, so you need to correct the y-axis. 1 blue photon has more energy than 1 red photon. So if you cover y-axis to number of photons, the blue peak becomes a bit smaller.

    Quote Originally Posted by nimbulan View Post
    What does Cree's two-step, three-step, and five-step binning mean? They have multiple "steps" for some color temperature/bin combinations but don't understand the chart at the end of the spec sheet about it.
    Those are the color accuracy. For some applications, they requires that color of one light to match with another. I forgot, but I think 2-step is more accurate than 5-step. But for plants, accurate color match isn't relevant. So I ignore that part of binning. So I go with whatever the cheaper ones with lowest CRI and highest luminous flux bin. So for example, you can look at p.3-4 of the cxb3070 datasheet. For 4000K/CRI70, you have BB or BD bins (they call it minimum flux "group", but this is the bin number which most of us are talking about). BD bin is the best, and the product number is CXB3070-0000-000N0BBD40E. This is the top bin for 4000K (the link to Cutter above is this one), and I haven't seen it available from other vendors. Now if you go to 4000K/CRI80, then the top bin is BB (which is lower than BD). There are 2-step and 4-step version, but I would go with either one (probably the cheaper one) if there is a choice. You can think that a higher CRI requires more phosphor, and more phosphor could result in a bit of light loss during the conversion of blue light to yellow/red light. Generally, if you go down in K, the top bin class becomes lower (e.g. for 3000K, AD is the top bin). So you have to look at the data sheet to decide what is the top bin of each category.
    Last edited by naoki; 02-16-2016 at 01:10 AM.

  2. #58
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    That is interesting. I thought the phosphors on the white LEDs behaved more similarly to fluorescent phosphors than you are indicating. Thank you again for all the information, time to find a good price...

  3. #59
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    Well I finally took the plunge and assembled 2 COB lights. It took a lot more time than I was expecting, but they seem to be working just as well as I'd hoped. I set up one indoors to expand my tropical grow area, and the second one out in the garage so I can start collecting winter-growing sundews as well as providing more light for over-wintering outdoor plants that are not tolerant of freezes.

    For the build, I used the parts recommended to me (CXB3070 4000K 70CRI + 1400mA driver) and some old computer CPU heatsinks I had lying around. I reused some old 5V AC adapters, extending the cord with twisted pair wire out of CAT-5 network cabling for the fans, and used 16 gauge appliance wire to extend the driver cord. The 16 gauge is a bit big for the connectors on the LED holders, so I'm going to make sure I shape the wire to fit the holder BEFORE tinning it next time. I wrapped some thin copper wire around the fan mount on the heatsinks to serve as a hanger, and used some thin rubber tubing to attach that to a mounting point above.

    I'm very happy with the results, and the light seems even brighter than I expected. Comparing one of these (which should be producing somewhere around 8000 lumens) to my T5 fixture (4000 lumens) it seems to be significantly brighter, despite covering double the area. The coverage isn't as uniform as I'd like and there's still a lot of waste light to the sides so I'm planning on adding some sort of reflector and raising the lights higher though I'm still investigating the best way to go about that. I would have ordered a commercial reflector with the COBs but wasn't sure what angle would be best when I ordered. I've been thinking that those domed plastic lids they put on things like smoothie cups would be perfect when lined with foil, but I don't have any on hand.





    I am aware that my Roridula looks terrible. I found out the hard way that letting the leaves stay wet for an extended period of time is very bad and ended up cutting off the growth point due to a severe botrytis infection. It has several new growth points emerging though so it's well on the road to recovery.

  4. #60
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    Wow well done! I have a CPU fan type LED fixture too, I have just added some refectors on the sides using plastic mirror sheet.
    Looking for N. Campanulata hybrids. Also would like to grow some nepenthes from seed. Growlist/pic thread: http://www.terraforums.com/forums/sh...-Pete-s-plants

  5. #61

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    Looks good, Numbulan! If you can use recycled parts, you can get them done cheaper, and that's the way to go!

    You are probably right, if you use narrower beam angle, and hang it high, you might get a more even coverage. I've tried relatively wide DIY reflectors (from yogurt container and empty can from canned food), but I'm not using it any more. But without the reflective enclosure, you could waste some light without reflectors. In a grow tent with multiple COBs, the unevenness does get reduced quite a bit. But it is an disadvantage of this types of LED.

    pmatil, what's the plastic mirror sheet?

  6. #62

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    Nice job!

  7. #63
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    ...and I've already filled up the indoor grow area with moved plants and various pots of seeds (including some edible plants.) Oops. I would have loved to set up a few more of these but I just don't have the space right now. At least the seedlings can likely move outdoors in a couple months.

  8. #64

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    For DIY COB, drilling and tapping heatsink is probably the most intimidating part. The rest is something which can be done by anyone who can strip wires and use a screw driver.

    I noticed that Cutter is starting to offer pre-drilled heatsink + COB kit. It is not the cheapest, but for the people who doesn't want to drill, this could be an easy option. The shipping is a bit expensive for people outside of australia (especially if you are interested in only a few units). There is 10% discount for the first 2 items with the coupon code.

    passive cooling, CXB3590:
    Cutter Electronics, Supplier of lowest cost leds on the internet
    About 50W for $80 (+$35 shipping). You'll need to get your driver (about $20, including shipping) separately. I would prefer a bit beefier heatsink, but it probably works well.

    The following is similar, but it comes with 4x COB (about 200W) and a driver (i.e. a complete kit). About $430 with shipping:
    Cutter Electronics, Supplier of lowest cost leds on the internet


    Active cooling version:
    CXB3590 ($66 + $19 shipping)
    Cutter Electronics, Supplier of lowest cost leds on the internet
    CXB3070 ($56)
    Cutter Electronics, Supplier of lowest cost leds on the internet

    You'll need a driver and an AC/DC adapter 5-12V (e.g. cell phone charger).

    For the driver, you can use something like Meanwell LPC-60-1400 (data sheet).
    Here is the current price (about $16 + shipping):
    LPC-60-1400 - Octopart
    Last edited by naoki; 03-17-2016 at 03:11 PM.

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