Self-made LED panel general discussion

Gastanker said:

I swear those one of those pages is in mW flux -

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Those are in lumen exept for the royal blue which is stated in milliwatts.
Once we have the radiant flux in mW, it is easy to get the PAR as it is basically watts per lit square meter. And once we have the PAR it is easy to compare the micromoles of photons as it is the PAR proportional to the wavelength, as stated by jubiare. Even if it is not the only unit to take into account when designing a grow light, it is much much more satisfactory than only comparing lumens (which are only relevant when comparing lighting for human beings)

But once you have the PAR you still can't compare as plants don't use all PAR equally... Definately much more useful than lumen of course.

Gastanker said:

What do you think explains the blue LEDs emitting less lumen than the reds? Shouldn't it be the other way around? And green blows the two away while being in the middle... nvm, that's likely just the voltage difference between the colors.

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I've made a little illustration:

The blue dot represents the position of the blue LED's wavelength on the efficiency curve. The red dot is for the red LED.
The precision is not good enough to have an accurate reading but it is OK to get the idea.
You can see that the blue dot has a Y coordinate of about 0.1 whereas the red dot is roughly at 0.3
That means that the blue LED needs 3x more power output to produce the same number of lumens as the red LED. Other way around, the blue LED produces one third of the red LED lumens if the two have the same radiant output. This is why the blue LED's lumen is lower than the red's. In fact, I am pretty sure that the blue LED produces more radiant flux than the red one because blue LEDs are generally more efficient than reds; it is due to the chemical used inside the LEDs.

I'm also realizing that the colors and whites all run at different voltages so even if they are testing under the same mA they are using different amount of energy to produce the varying lumen outputs which like you say have little to do with efficiency.

yep, reds are more likely to run around 2.2 volts whereas blues and whites have a forward voltage of about 3.2 volts; this means that blue and white LEDs chew up more electrical power than reds when at the same current. This is why it is good to keep in mind the radiant efficiency (milliwatts of light emmited for each watt of electricity consumed) rather than the radiant output alone.

Someday they'll make wider spectrum colored LEDs...

Have you looked at reef forums about any of this? Many many DIY LED aquarium lights out there and they tend to be a bit more of an academic group - never once seen a lux meter over there but somehow every other person owns a really nice PAR meter. Aside from them focusing on different spectrum they use all the same gear.

Patrik what kind of "white" LEDs are you talking about? RGB or phosphorous conversion? I'm also curious to know what you know about phosphorous blends and which ones you've heard of that have excellent peaks in the blue and red spectrums that growers like. Do you prefer blue or UV based white LEDs? And what is your opinion on this: Which is better a 2 pc or 3 pc white LED? I think the yellow spectrum in the 3pc is a waste, but maybe the plants can use it. (Gastanker?)

In other words, what I'm really trying to tell you is not to get too hung up on power. You need to do a little more probing to find the right white LED than just using radial-flux and par, though I totally agree that both are very important. Many pc LEDs have a ton of green in them making them not very efficient for growing weed, but somewhat efficient for lighting a room. As far as I know no one makes a white phosphur converted LED that hits peaks in all the spectrum's a grower would covet, though there are some newer phosphors that can get close.

IMHO a white 450m blue diode pc LED can replace blue LEDs without the photo-biological damage that blue LEDs can pose. For the 450 spectrum, most blue-diode based white LEDs will do since that's the spectrum many LED makers like to use, though not all do, so you need to see the spectral output of a white LED to be sure it's what you want to use. Then I would take what your trying to deduce and see how that LED stands up. Here's a spectral output of a 7000K white Epistar. OK for blue, but that's it really. Too much green for me:


Where's the reds?

I guess what I'm also trying to say to you is LEDs are not CFLs and they shouldn't be HIDs. Good luck Patrik and if I find any good white LEDs I'll let you know.

patrikantonius said:

it is good to keep in mind the radiant efficiency (milliwatts of light emmited for each watt of electricity consumed) rather than the radiant output alone.

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That's correct, milliwatts is the best we can use

Great discussion going on in here^^^^(I'm no expert/but ill chime in anyways)..............My issue with Led market in general is that these SPD graphs/charts may not be accurate for our applications(growing)/we are not trying to light up a retail store ............The variables involved: LED Bin selection(still unreliable)/heat management(is their any light shift at high temps?)/stable current flow/driver efficiency/counterfeit leds/REAL lifespan/lumen depreciation values(not estimates)/high rh conditions/etc..........Led grow light market is still in its infancy(IMO) and due to Led's rapid progression/evolution in the general lighting industry we need standardization before we can take these manufacturers graphs and realistically apply them to our hobby. LED SPD's put out by the manfctr are under IDEAL conditions, but alas this is what we got to work with atm............I want an LED(module/diode selection) designed/built from the ground up for horticulture dammit!!!

happy growing.......

Someone mentioned spectrum of white LEDs and again, I'm no expert, but the CREEs look sexy as fuck to me.




Regarding yellow light - yes plants can use it. To what degree varies among plants. I have no idea how much of it MJ can absorb in relation to other spectrum.

Finally found this - doesn't include the secondary pigments but here's the Chlorophyll spectral absorption for spinach in ether and alcohol solutions.




http://www.jbc.org/content/140/2/315.short

R/B leds miss what makes hps so good- the mid band


The following is copied from The Lurker (TL)

This is a Eye Hortilux HPS vs. Photosynthetic Absorption Spectra Curve.






I'm glad we've finally gotten some good studies on green light over the past several years, as has been mentioned previously (link) by a few of us.

While 'every lumen (or rather, PPFD) is sacred', I'm of the camp that would prefer a higher level of (adjustable) full-intensity, multi-spectrum (i.e. 'white') light incorporated into the main fixture, for that very reason.

And with the recent increases in the efficiency of neutral whites, there's no reason why you can't get perfectly good results with just a two-channel, adjustable led fixture (neutral white, and red), supplementing with the aforementioned only as needed.





(note: neutral white I called 'normal white' here for some reason. Wonder what I was smokin' at the time...<whistles>)

As one can see, the CREE Neutral White (I call it 'Goldilocks', because it's almost 'just right' ) has a RSPD that still allows nearly ~25% of its total power in the blue range (and plants only really 'need' ~8-10%), and more that 1/3 of which (i.e. the area under the curve) is over ~580nm or so (which has a Photosynthetic RS of over 90%!) - which is much better than even your typical 'Enhanced HPS'.


So like Gastanker, I too thing these whites are very SEXY

Damn I wish TL would lurk a little less and chime in more..........SO who's gonna be the first to run(build) a cree xpe neutral white/630/660 only panel???love to see that, sounds very promising on paper.........YES very sexy indeed

Wish Hilo would update his white/red panel grow..........happy growing fellas

edit: hey Pet where did you get that info that cannabis only needs "8-10%" 400+nm during veg?????

Thank you for contributing
One remark though, you can clearly see it isn't exact science as the two photosynthetic curves (from the first picture and from the second one) are not the same at all. And for which plants are they anyway ? as I remarked on the other topic, for instance, tomatoes and lettuce don't respond the same way at all to different light spectrums. So far, I've never seen anything scientifically supporting the fact that MJ can really benefit from light in the middle of the spectrum. Results with high quality red & blue LEDs are already very satisfying and quite superior to HPS.

It seems to be very difficult to find objective information on this subject as most discussions are flooded by either ignorant individuals or people with a commercial interest in the debate. I'm glad to have a rich discussion here

I think IR is an important ingrediant that isn't being used enough in most panels. I supplement with extra IR spotlights and have found them to be of value. Makes for bigger/denser flowers and supposed to help promote germination in seedlings but I haven't tested that part yet.

PSUAGRO. said:

Damn I wish TL would lurk a little less and chime in more..........SO who's gonna be the first to run(build) a cree xpe neutral white/630/660 only panel???love to see that, sounds very promising on paper.........YES very sexy indeed

Wish Hilo would update his white/red panel grow..........happy growing fellas

edit: hey Pet where did you get that info that cannabis only needs "8-10%" 400+nm during veg?????

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from da man, TL Where else?

RapidLED kits are based around Cree Whites. Great for small closet growers/vegging/cloning, or anyone with $$$

jubiare said:

yes but, cree warm whites are important too; I mean if you are keen on IR, without using IR you get real good IR from warm whites ! Plants can grow without IR, that's proven, but it seems to add on roots structure and flowering time (it shortens that)

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Yes, light in the 740nm range seems to be very beneficial, but, as we can see from the radiant curve of the Cree XP-E warm white, only less than 4% of the total light is emitted above 700 nanometers. This means that putting independent far red LEDs seems to be more efficient to cover that part of the spectrum.

puffenuff said:

I think IR is an important ingrediant that isn't being used enough in most panels. I supplement with extra IR spotlights and have found them to be of value. Makes for bigger/denser flowers and supposed to help promote germination in seedlings but I haven't tested that part yet.

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Yes, but what I learned from TL is that you only need it for a short period immediately after lights out, so it would need to be separate fixture and on a separate timer. Problem is finding small wattage IR bulbs. Reptile lights has one with a remote ballast. Now all that's needed is a cheap light mover. Alas, this won't work with my 8 bulb Quantum BB. Next time I would get 2 @ 4 bulb, unless I bite on some RapidLEDs

patrikantonius said:

Thank you for contributing
One remark though, you can clearly see it isn't exact science as the two photosynthetic curves (from the first picture and from the second one) are not the same at all. And for which plants are they anyway ? as I remarked on the other topic, for instance, tomatoes and lettuce don't respond the same way at all to different light spectrums. So far, I've never seen anything scientifically supporting the fact that MJ can really benefit from light in the middle of the spectrum. Results with high quality red & blue LEDs are already very satisfying and quite superior to HPS.

It seems to be very difficult to find objective information on this subject as most discussions are flooded by either ignorant individuals or people with a commercial interest in the debate. I'm glad to have a rich discussion here

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Objectively, a good hps/ballast is proven to grow excellent fat buds. Also proven: they generate a lot of heat. LEDs are sol on less heat, so why not simulate the SDG of hps using leds?

Earlier you were talking about efficiency. Well that's relative. Blue/Red diodes are totally inefficient at producing any other spectrums, and yet those other spectrums are very important. Whites are very efficient at producing a total PAR range, and pretty muich all the 450-650 mj growers need.