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ALToronto
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I guess different manufacturers have different spectral profiles. My warm white LED's definitely have much greater flux density above 600 nm than the cooler white diodes. All are Bridgelux. Naoki, have you done any comparison to Cree?
When I bought my lights, I also ordered a few 1W red (660 nm) LED's. I was planning to place them among the white ones, just 2 or 4 among 14, but haven't done so yet. The driver for white LED's is at full capacity with the 70W total power, so would I need another driver to add just the 2 or 4 extra watts? The 14 LED's are wired in series pairs, seven parallel branches to match the voltage and current output of the driver.
When I bought my lights, I also ordered a few 1W red (660 nm) LED's. I was planning to place them among the white ones, just 2 or 4 among 14, but haven't done so yet. The driver for white LED's is at full capacity with the 70W total power, so would I need another driver to add just the 2 or 4 extra watts? The 14 LED's are wired in series pairs, seven parallel branches to match the voltage and current output of the driver.
naoki
Well-Known Member
Ray, you are right, that is a more accurate way. But doesn't warm white usually have a wider red peak, so if you compare the cumulative (not the peak height) amount of light in red region, warm white can have more red light? Lots of spectra plots for LEDs are relative to the peak intensity, so it's difficult to make the direct comparison. I think some people has compared theoretical PAR from the spec sheets.
But it sounded too tedious to do the calculation, so I just measured. People say that phosphor technology has been changing quite a bit. So we might not be able to say which one has more PAR in GENERAL. So it would be interesting to see if you can compare PAR of cool vs warm white of yours (I think you got the meter). My comparison of ebay COB didn't show much difference (I was expecting warm white to have less PAR for the reason you mentioned), but it is possible that my meter needs calibration (it has been shown that the spectral sensitivity of Li-Cor sensor, which I have, can shift with age). If they give similar amount of PAR, I would go with warm white. But the difference is pretty small, so either one works in practice.
Daniella, if it is exactly same amount of red, and CW has more blue, yes, I would say that CW is better (in terms of photosynthesis).
Alla, I don't have any Bridglux. Vero series (their COB) is supposed to be pretty good (slightly less efficient than Cree CXA). I don't know well about the complex wiring (and you know better about it), and I thought that most of people use only serial circuit. With the parallel circuit like yours, if a couple diodes go open, doesn't it cause overdriving the rest and fry them? Also, I've heard "matching" diodes could be tricky for the parallel circuit (i.e. some branches get more current than other branches).
But it sounded too tedious to do the calculation, so I just measured. People say that phosphor technology has been changing quite a bit. So we might not be able to say which one has more PAR in GENERAL. So it would be interesting to see if you can compare PAR of cool vs warm white of yours (I think you got the meter). My comparison of ebay COB didn't show much difference (I was expecting warm white to have less PAR for the reason you mentioned), but it is possible that my meter needs calibration (it has been shown that the spectral sensitivity of Li-Cor sensor, which I have, can shift with age). If they give similar amount of PAR, I would go with warm white. But the difference is pretty small, so either one works in practice.
Daniella, if it is exactly same amount of red, and CW has more blue, yes, I would say that CW is better (in terms of photosynthesis).
Alla, I don't have any Bridglux. Vero series (their COB) is supposed to be pretty good (slightly less efficient than Cree CXA). I don't know well about the complex wiring (and you know better about it), and I thought that most of people use only serial circuit. With the parallel circuit like yours, if a couple diodes go open, doesn't it cause overdriving the rest and fry them? Also, I've heard "matching" diodes could be tricky for the parallel circuit (i.e. some branches get more current than other branches).
naoki
Well-Known Member
Just for number geeks: here are the numbers comparing the 100W ebay Chinese COB Warm White (WW) vs Cool White (CW). I drove them with the same 50W ebay constant current driver (1.5A, YM-361500A, waterproof), and measurements were taken at 1'. No reflector was used. The setup was explained here previously.
Explanation of columns
fc1: foot-candle measured by Gossen Ultra-Pro calibrated recently.
fc2: foot-candle measured by Dr.Meter LX1330B, which is recently bought.
PPFD: micro-mole/m^2/s, Photosynthetic Photon Flux Density (more relevant for plants than fc), measured with old Li-Cor which probably needs calibration.
W: consumed Wattage by LED (includes loss due to AC-DC conversion of the driver, efficiency of this driver was 89-90%, but exclude the energy used by the CPU fan)
A couple observations:
CW is slightly more efficient than WW by 2.6% (4/3.9=1.026). But once you incorporate the fact that red light is slightly more efficient for photosynthesis than blue light, WW should be giving slightly more energy (Yield Photon Flux Density; YPFD).
But overall, the difference is minimal. But I just tested one unit of each, and the response could be different for other brands and technology.
Gossen is a slightly older, high-end meter for photography/filming. The spectral response of this meter is slightly shifted (more red sensitivity), and it seem to deviate from the CIE luminosity function. Well, most of the affordable light meters deviates quite a bit from the ideal response function. So this is just an illustration of some limitation of consumer-level light meters.
Code:
fc1 fc2 PPFD W PPFD/W
WW 730 1120 180 46 3.9
CW 630 1293 180 45.4 4.0Explanation of columns
fc1: foot-candle measured by Gossen Ultra-Pro calibrated recently.
fc2: foot-candle measured by Dr.Meter LX1330B, which is recently bought.
PPFD: micro-mole/m^2/s, Photosynthetic Photon Flux Density (more relevant for plants than fc), measured with old Li-Cor which probably needs calibration.
W: consumed Wattage by LED (includes loss due to AC-DC conversion of the driver, efficiency of this driver was 89-90%, but exclude the energy used by the CPU fan)
A couple observations:
CW is slightly more efficient than WW by 2.6% (4/3.9=1.026). But once you incorporate the fact that red light is slightly more efficient for photosynthesis than blue light, WW should be giving slightly more energy (Yield Photon Flux Density; YPFD).
But overall, the difference is minimal. But I just tested one unit of each, and the response could be different for other brands and technology.
Gossen is a slightly older, high-end meter for photography/filming. The spectral response of this meter is slightly shifted (more red sensitivity), and it seem to deviate from the CIE luminosity function. Well, most of the affordable light meters deviates quite a bit from the ideal response function. So this is just an illustration of some limitation of consumer-level light meters.
D
daniella3d
Guest
Hard to get the right idea from comparing these meters though, since your older meter gives a higher value for the WW and it is the opposite with the new meter. I have the meter LX-1330B and I just received it but it's defective, does not turn OFF and the power button put the value in LUX when pressed instead of powering off or on. To turn it OFF I have to remove the battery! and I have to press the lux button many times to have it switched and staying on FC. They seem to be very very cheaply made, so is it possible that your older meter gives a more accurate reading?
naoki
Well-Known Member
Sorry that your LX-1330B had issues. Hopefully, they sent you a replacement. The sensitivity spectrum listed in the user manual seems to be pretty good, but I don't know if the response is real or not. I don't have a reference lux meter to compare them against. But fc is just for human eyes, and isn't as important as PPFD for plants. This is especially true if you are talking about artificial lighting.
Silvan
Multiflorals assassin
This is getting so complex..lol But I'm the type of person who needs to do and see for myself to fully understand.. 
Aren't you a bit afraid of short circuit when doing the wiring? Looking at some DIY
I've noticed that you even have to install the power plug. That kinda scares me
a lot...
Anyway, I'm writing 'cause I was at my hydro store last week-end and they had a super nice Led fixture using the new white lights technology. The seller told me
it was very expensive and I didn't ask how much because anyway it was 390watts
and I would need to put it at least 6feet above the foliage and I don't have that kinda height. But there was something off about it and I couldn't put my finger on what it was until I made some research on the net... it uses a passive cooling system. It doesn't have fans!
Wouldn't the diodes overheat and burn very fast ? Just wanted your opinion on that.
Here's a link of the product http://www.ledsource.com/wp-content/uploads/2013/10/LightingScienceGroup_VividGroLEDGrowLight.pdf
and you can find some additional info on the supplier website https://www.lsgc.com/products/fixtures/vgrohb/
Aren't you a bit afraid of short circuit when doing the wiring? Looking at some DIY
I've noticed that you even have to install the power plug. That kinda scares me
a lot...
Anyway, I'm writing 'cause I was at my hydro store last week-end and they had a super nice Led fixture using the new white lights technology. The seller told me
it was very expensive and I didn't ask how much because anyway it was 390watts
and I would need to put it at least 6feet above the foliage and I don't have that kinda height. But there was something off about it and I couldn't put my finger on what it was until I made some research on the net... it uses a passive cooling system. It doesn't have fans!
Wouldn't the diodes overheat and burn very fast ? Just wanted your opinion on that.
Here's a link of the product http://www.ledsource.com/wp-content/uploads/2013/10/LightingScienceGroup_VividGroLEDGrowLight.pdf
and you can find some additional info on the supplier website https://www.lsgc.com/products/fixtures/vgrohb/
NYEric
Well-Known Member
Lighting nerds! oke:
oke:
Get the warm white. I was chatting with a plant physiologist a while back and he said the plants grow best under the warm white LEDs.
With the CW and WW LEDs the blue peak doesn't shift or change in intensity. The yellow peak of the CW simply shifts towards the red.
Plant action spectrums indicate that it is red light that terrestrial plants want. You may have seen the Elodea/Anacharis action spectrum up on webpages but that spectrum is not typical of terrestrial plants.
(Just in case, if anyone has a reference for that Elodea spectrum I would love to know it... I have traced as far back as a textbook that used the image unreferenced and the publisher had no idea where the spectra came from.)
With the CW and WW LEDs the blue peak doesn't shift or change in intensity. The yellow peak of the CW simply shifts towards the red.
Plant action spectrums indicate that it is red light that terrestrial plants want. You may have seen the Elodea/Anacharis action spectrum up on webpages but that spectrum is not typical of terrestrial plants.
(Just in case, if anyone has a reference for that Elodea spectrum I would love to know it... I have traced as far back as a textbook that used the image unreferenced and the publisher had no idea where the spectra came from.)
naoki
Well-Known Member
This is getting so complex..lol But I'm the type of person who needs to do and see for myself to fully understand..
Aren't you a bit afraid of short circuit when doing the wiring? Looking at some DIY
I've noticed that you even have to install the power plug. That kinda scares me
a lot...
Silvan, I don't think short circuit is an issue. When wiring, you shouldn't have anything plugged-in!
oke:I use solder, then liquid tape and rubber self-sealing tape. The rubber style tape is much better than the vinyl electrical tape. I used something similar for repairing wiring harness in the engine compartment (of an old car) about 20 years ago, and it hasn't failed.
If you are worried about the LED terminal is exposed (the place where you attach + and - wires to the LED), you can paint it with the liquid tape. Then nothing is exposed to cause short circuit.
The LSG LED fixture you saw is one of the most efficient models according to this test. The test confirmed that the claimed output is true. You get 1.64 micromoles/J (larger number means more photosynthetically relevant light produced for a given amount of electrical energy consumption), the efficiency of fluorescent light is 0.84 micormoles/J, and the top HPS is around 1.7 micromoles/J. The article says the price is around $1200.
But you are right, it might be a bit too much for our purpose. It is better to have more fixtures with less power (so you can get more even light, and more illumination to the lower leaves).
Passive cooling is nice because it doesn't make noise. But it is much more expensive since you need huge heatsinks and you need to use lower current (meaning you need lots of LEDs). I think if it is well designed, it shouldn't burn out.
One disadvantage of active cooling is that, fans can break down, and LEDs can overheat. Some of them may have overheating protection, but mine doesn't. The other issue with active cooling is that it may be more difficult to get water proof certificate (i.e. in a large commercial greenhouse, they may require these certificate).
Some people use CXA3070 with passive cooling. But it is too expensive for me.
Tyrone, if you are looking for the action spectra of photosynthesis for land plants (I don't know where Elodea figure is from), you can check
Inada, K. 1976. Action spectra for photosynthesis in higher plants. Plant & Cell Physiology 17: 355-365
McCree, K. J. 1971/1972. The action spectrum, absorptance and quantum yield of photosynthesis in crop plants. Agricultural Meteorology, 9:191-216
I think you are in an academic institution, so you can get them there. But if you can't get them, you can email me.
Some basic textbooks seem to have a bit sketchy figure about the action spectra (or confused it with absorption spectra).
D
daniella3d
Guest
Would it not be better to mix both? Like 3 WW for one CW? to get some blue as well. I have read that without the blue the red will make the plant elongated?
Hello,
See below:
from http://www.digikey.com/en/articles/...ining-the-color-characteristics-of-white-leds
This is pretty typical. As you move from CW to WW the red peak shifts and grows. There is some expense of the blue light but this isn't very consequential. Plants need some 430 nm light to stimulate growth but this effect isn't cumulative. You only need to add enough and the plant will grow. A friend bought some cheap CW LEDs that didn't have a peak close to 430 nm at all... The plants stayed green but never grew. We took a look at plant growing lamps and figured on a 1:9 ratio of blue to red being the minimum so he fitted enough 430 nm LEDs to meet this criteria and all of a sudden the plants started to grow.
You only need a little violet/blue light and the WW seem to provide it.
My only concern is the we grow shade plants and they may be adapted to more blue light than full-sun plants. Blue transmit well through the forest canopy compared to red... I refer you to this thread: http://www.slippertalk.com/forum/showthread.php?t=32896&highlight=Fluora
The spectrum of the Fluora is interesting as it has a lot of Blue and Red light.
Here is a daylight:
Cool white:
Warm white:
All have the 430-440 nm peak and then varying amount of red. The violet light is needed to stimulate the opening of stomata.
Sadly, I was hoping someone would know where the Elodea action spectrum came from... Oh well.
See below:
This is pretty typical. As you move from CW to WW the red peak shifts and grows. There is some expense of the blue light but this isn't very consequential. Plants need some 430 nm light to stimulate growth but this effect isn't cumulative. You only need to add enough and the plant will grow. A friend bought some cheap CW LEDs that didn't have a peak close to 430 nm at all... The plants stayed green but never grew. We took a look at plant growing lamps and figured on a 1:9 ratio of blue to red being the minimum so he fitted enough 430 nm LEDs to meet this criteria and all of a sudden the plants started to grow.
You only need a little violet/blue light and the WW seem to provide it.
My only concern is the we grow shade plants and they may be adapted to more blue light than full-sun plants. Blue transmit well through the forest canopy compared to red... I refer you to this thread: http://www.slippertalk.com/forum/showthread.php?t=32896&highlight=Fluora
The spectrum of the Fluora is interesting as it has a lot of Blue and Red light.
Here is a daylight:
Cool white:
Warm white:
All have the 430-440 nm peak and then varying amount of red. The violet light is needed to stimulate the opening of stomata.
Sadly, I was hoping someone would know where the Elodea action spectrum came from... Oh well.
