Author Topic: grow led diy  (Read 1635 times)

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Offline honeybadger

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Re: grow led diy
« Reply #25 on: March 16, 2019, 03:12:17 pm »
Using red and blue is not more efficient because there are no efficient red and blue LEDs. There are white LEDs with 210lm/W because that is what market wants. Yes there is a luminofor loss but overall white is an efficient winner.

Plants are not made entirely from chlorophyll. Plants only reflect small amount of green light. Yes from all colors they reflect, green is dominant, that is why they look green, but  they still absorb more than 80% of green light.

Try to live in the same room with red-blue grow light - it is not possible (at least for me).
 

Offline james_s

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Re: grow led diy
« Reply #26 on: March 16, 2019, 05:08:52 pm »
There are lots of efficient blue LEDs, white LEDs are just a blue LED with a white phosphor. The efficiencies of red LEDs are not bad either, but you can't use lumens to measure the efficiency of non-white LEDs.
 

Offline Zero999

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Re: grow led diy
« Reply #27 on: March 16, 2019, 06:50:29 pm »
Using red and blue is not more efficient because there are no efficient red and blue LEDs. There are white LEDs with 210lm/W because that is what market wants. Yes there is a luminofor loss but overall white is an efficient winner.
Nonsense, red and blue LEDs are more efficient than white ones and Lumens per Watt is meaningless in this context.

Quote
Plants are not made entirely from chlorophyll. Plants only reflect small amount of green light. Yes from all colors they reflect, green is dominant, that is why they look green, but  they still absorb more than 80% of green light.
Even if that's true. it doesn't change the fact they mostly use red and blue for growth

Quote
Try to live in the same room with red-blue grow light - it is not possible (at least for me).
Not everyone lives in the same room as their plants.
 

Offline honeybadger

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Re: grow led diy
« Reply #28 on: March 16, 2019, 08:38:56 pm »
Most efficient grow lights with most PPFD/PAR output are full spectrum based around CREE CXB-3590 or Samsung LM301B or some Luminus white COB LEDs. I don't believe there is any blue-red grow light with comparable efficiency, no matter how expensive. But of course it is OK if you don't agree.
 

Offline Zero999

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Re: grow led diy
« Reply #29 on: March 16, 2019, 09:41:10 pm »
Most efficient grow lights with most PPFD/PAR output are full spectrum based around CREE CXB-3590 or Samsung LM301B or some Luminus white COB LEDs. I don't believe there is any blue-red grow light with comparable efficiency, no matter how expensive. But of course it is OK if you don't agree.
I accept you may not want your room light with hot pink light and respect your preference in that regard, but as far as efficiency is concerned, there's no opinion involved. I'm talking about fact.

What's important here is, radiometric efficiency in the parts of the spectrum most important for photosynthesis. Radiometric efficiency is a measure of electrical power in vs optical power out in a certain bandwidth. A UV light might have a luminous efficacy of near zero Lumens per Watt, as most of the light is invisible, yet a radiometric efficiency of 30%.

Lumens is a measure of intensity scaled to the response of the human eye and is therefore irrelevant to this discussion. A green LED will be brighter than a blue or red one, given the same optical power output, purely because the eye has greater sensitivity in that region of the spectrum. Radiometrically speaking, green LEDs have appalling efficiency, compared to blue or red ones, they just look brighter. Perhaps one day better green LEDs will be developed.

As mentioned above, white LEDs are just blue ones with a phosphor to convert some of the blue to longer parts of the visible spectrum. They are radiometrically less efficient, than the equivalent blue LED because a lot of energy is lost in the phosphor: again, look up Stoke's shift. A white LED will appear brighter, than a blue one of the same power level, but that's only because the inefficiency is more than compensated for by the fact that the human eyes are more responsive to the phosphor emission, than the blue light. The white LEDs you've mentioned above are very good, but they have inferior radiometric efficiency, compared to equivalent red and blue ones.

I like the Luminus devices products because they specify both radiometric power output as well as luminous flux. Refer to the data sheet linked below. Note how the green LED is 2000lm, yet it only has a power output of 4.1W and the blue LED is only 400lm, yet it has a much higher power output of 7.2W! Do the calculations and you'll find the green LED is poorest in terms of power in vs power out, even though it's the brightest.
http://www.mouser.com/ds/2/245/Luminus_CBT120_Datasheet-472561.pdf

In summary: a white LED is pretty inefficient, as a grow light. Not only is lots of light lost in the phosphor, but most of the light is emitted in the middle of the visible spectrum which isn't used by plants.
 

Offline honeybadger

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Re: grow led diy
« Reply #30 on: March 16, 2019, 10:19:08 pm »
So what is the best red-blue combo and what PPFD/watt it gives? Currently for full spectrum about 2.1 PPFD/watt is the limit.


https://gn.uk/guides/par-ppf-ppfd-and-dli

So why is there such a difference between the absorption spectrum and the action spectrum if chlorophyll is responsible for photosynthesis? The answer is simple: Chlorophylls are not the only photoreceptors that are responsible for photosynthesis. There are other types of antenna photoreceptors (mainly carotenoids) which also promote photosynthesis, and by utilizing narrow band red/blue LEDs in sole-source lighting conditions these pigments are not able to optimize their light harvesting capabilities. Also, it should be noted that green light does in fact promote photosynthesis in chlorophylls, quite efficiently in fact. Recent work has shown that green light is able to penetrate deeper into leaf surfaces to drive photosynthesis in chloroplast located towards the bottom surface of the leaf, in fact, more efficiently than red light at high PPFD.

« Last Edit: March 16, 2019, 10:30:02 pm by honeybadger »
 

Offline Zero999

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Re: grow led diy
« Reply #31 on: March 16, 2019, 11:44:21 pm »
I honestly don't know the answer to that question. I agree that other wavelengths as well as red and blue are used by plants and haven't disputed this. I've just noted the majority of photosynthesis seems to occur in the red and blue regions. I believe the optimum spectrum depends on the plant, the stage of development and is something which is the subject of ongoing research.

If you look at the spectrum of a typical white LED, you'll find it looks nothing like that of any grow lamp, hence why I believe it's not optimum, although I can understand why you might prefer it for practical reasons.
https://www.cree.com/led-components/media/documents/ds-CXB3590.pdf

It also depends on whether you're growing solely under artificial light or supplementing ambient light. If it's the latter then I imagine it's not too critical.

In any case the efficiency of converting electrical energy into different optical wavelengths needs to be taken into account, as well as photosynthesis.
 

Offline metrologist

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Re: grow led diy
« Reply #32 on: March 17, 2019, 11:49:43 am »
Solar powered grow lights   ;D
 

Offline Zero999

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Re: grow led diy
« Reply #33 on: March 17, 2019, 01:46:30 pm »
Sorry for the late response.

Thanks for your feedback so far.
I found these LED's on ebay, but im not sure if they have enough power for my little grow box.
Link
https://www.ebay.com/itm/10-x-High-Power-LED-OSRAM-OSLON-SSL-660nm-hyper-red-Platine-3W-Pflanzenwachstum-/172846213449

All in all its for some garden plants like Physalis, paprika and chili.
The box size is 90 x 60 x 60 cm. Im not quite sure if i get enough light out of my LED' stripes. They running with 5050 smd LED's.

Link:
https://www.ebay.com/itm/5pcs-SMD-5050-LED-Grow-Light-Strip-Lamp-for-Indoor-Veg-Flower-Plants-Hydroponic/264077183863?hash=item3d7c3a0b77:g:Mn4AAOSw3fxcCiz-&frcectupt=true
Why not stick with branded produces from reputable distributors? I don't think this is the sort of thing you should be trying to save every penny on.

I'd probably go for the LEDs on little aluminium PCBs mounted to a large heat sink.

Either something like this:
https://www.digikey.com/product-detail/en/thomas-research-products/132541/1121-1640-ND/7693230

Or separate red and blue modules: four red and one blue in the middle.
https://www.digikey.com/product-detail/en/led-engin-inc/LZ4-40R208-0000/1537-1042-ND/4976732
https://www.digikey.com/product-detail/en/led-engin-inc/LZ4-40B208-0000/1537-1037-ND/4976727

With a suitable LED driver module.
 


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