Building LED lights from facts, no theories

Thank you for the reply Weezard. I've actually already read through that thread. And it is very informative. But it shares problems that almost all threads on the subject share. The information is to spread out(not huge but still problematic for beginners) and it's to complicated for beginners. For instance.

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A sense resisror is so called because it hooks to the sense input of a regulator.

Here's how the LM317 CCR circuit works;

The lm317 is designed to be a variable voltage regulator
and it "wants to see" 1.25Vdc between the output pin and the ADJ/Sense pin. before it will begin regulating anything.
We take advantage of those facts for our current regulator.
We tie a restor to the output pin and draw the current to our load through that resistor.
If we run a wire from the load side of the resistor to the adjust pin, that pin will sense the voltage drop across the resistor.
So, ohm's law.
If we want a 1 ampere current limit, we use a resistor value that will drop 1.25V at 1 amp.
Once the adjust pin senses 1.25v.it regulates voltage to keep that voltage drop, and thus the current, constant.
1 A. X 1.25 V. = 1.25 W.
While a 2 watt resistor would suffice, a 5 or 10 watt resistor will run cooler and thus regulate tighter.
I had some 10 Watt, 1 ohm power resistors laying around so I thermal glued them to the heatsink.
Overkill? Perhaps,. But overkill is a good thing in this case .
Gives me about 1.2A. which is exactly what I wanted.
Seems to be the sweet spot in photons per watt.

What is this R2 you speak of?
The current limit configuration only requires one resistor.

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And then you end with.

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It's very simple.

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Hehe. It probably is very simple in the context of building an LED Grow Light. But separated from allot of other facts and all out on it's own it's complicated to the beginner. Or at least it's complicated to me. I didn't understand most of it and what I did understand was just stand alone information. I don't know how to apply it properly.

That's why I think a full guide would be very helpful. I will reread that thread and try and digest some more information. Thank you for bringing it back up.

I will tread lightly on posting to much more about this subject in this thread unless you guys want to steer the discussion in that direction.

Thanks for the help.

But, your point is well taken.
"That's why I think a full guide would be very helpful. I will reread that thread and try and digest some more information. Thank you for bringing it back up."
Reading it over, I have to agree.
Guess we were having too much fun.;):stoned:

I was talking directly to DH by request.

He's got skills and knows electronics so we were able to shortcut a lot of the basics.
Never occured to me that we were probably confusing some folks.

OK, I'm about to construct a new light.
Soon as I have my excrement gathered, I'll try to get organized and just do a straightforward fabrication.

Plenty of pictures.
No techie talk, :( unless asked.
Insert tab A into slot B sort of thing.
That what you're looking for?

Wait a minute, who am I kiddin'?:wtf:
There's no way I'm gonna suddenly get "organized".
That thread is about as lucid as I get.:jointsmile: Sorry.

Perhaps Dreadedhermie will volunteer to translate.
Or, re-render my ramblings into a more readable style.:)

We now return this thread to it's rightful owners.
Aloha,
Weeze

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That thread is about as lucid as I get. Sorry.

Perhaps Dreadedhermie will volunteer to translate.
Or, re-render my ramblings into a more readable style.

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I'll help however I can. :thumbsup:

I can't promise to keep a straight face any better than Weezard, though. :D

Hey guys I've been researching this topic from an amateur's perspective.

I like all the info on this site it is amazing what a bunch of stoners can come up with when there's money to be made ;)

In regards to the color spectrum, specifically UVA vs UVB requirements, Click Here

I am very interested in Knna's quoted spectrum requirements. They do not appear to match the standard photosynthetic action spectrum. Any info on specific requirements for herb? Perfect led grow light thread was mentioned but I can't seem to find it...

Knna: can you tell me the exact LEDs you'd recommend currently given your spectrum suggestions? Price is not much of an object on initial purchase, but I want maximum efficiency.

Hurray! My first post!:rastasmoke:

"Hurray! My first post!:rastasmoke: "

And a darn good one too!:D

Welcome.
Weeze

Hey not to beat a dead horse, but why is the McCree spectrum different than this one? I searched for photosynthetic action spectrum. This is also the spectrum from my photosynthesis book. Kinda important when selecting LEDs...

The spectrum action curve you have posted, and that you may find on most botanic books, is just a sum of the absortion of the different pigments present in the higher green plants.

But it notably differ from what is observed actually on live plants, that uses green way better than that, along with other differences.

There is some things that explain that difference:

-Pigments arnt distributed homogeneously along leaves, but stratified.

-They arnt present of the same relation, and almost never at the 1:1:1 (Chl a: Chl b: carotenoids) that is used to obtain the action curve. It varies with the tipe of light, for plant specie, light intensity that they receive on the long term...

-And the most important: absortion of lab's extracted pigment on solution is very different to absortion of those same pigment in vivo. The process is still very unkown, but the fact is same pigment molecule may absorb the better light of a given wavelenght depending of its orientation (into the leave) and depending to the protein its binded. For example, the central Chlorofill a molecules on the Photosynthetic Reaction Center have a max of 680nm (Photosystem II) and 700nm (Photosystem I), while its the same molecule. Max absorbance from 650 to 720nm of the same molecule has been reported.

So the action spectrum curve you posted is a virtual creation, from unrealistic lab's extractions, while McCree and Inada curves were obtained measuring the photosynthetic response of in vivo plants.

Ok, so I've been researching action spectra and quantum yields of in vivo photosynthesis. I can't seem to find exactly what I'm searching for:

Is there a spectrum which indicates the maximum amount of each wavelength which can be absorbed in vivo?? Also I need to know the relative lumens/einsteins/intensity or whatever per meter squared so I have a rough idea not only of the appropriate spectrum to construct, but the irradiance necessary for each bit of plant...

I'm also capable of searching for academic papers if you've got any citations.

After this, I will find the most efficient LEDs in the proper amounts and wavelengths. Any choice picks?:angelsmiley:

Good luck in the search, Im on it since 4 years ago.

There are many studies about it, but with limitations. The most known are those written by McCree and Inada, along the 70 and 80's of past century. You can fin the same curves for individual specias and strains of commercial crops in agronomic studies. Differences with the averaged curves are small, anyway.

But these studies all have three main limitations:

-They are measurements of usually sun growth plants performed under not saturating photosynthesis irradiances. Efficacy of each wavelenght has proven to be dependent of the irradiance level, specially on the long term, after plant's acclimatation.

-Plants adapt their photosynthetic systems to both the intensity (irradiance) and light's quality they receive, in order to do the best with it.

-All studies concentrate on the effect of isolated wavelenghts. But its different when plants receive all wavelenght at a time. There are sinergies between wavebands that modulate the response. The most known is the Emerson Effect, that is universal (related to the electron flow between photosystems), but there are many unkown ones that are specie especific. Each plant specie have somewhat different liking in their light's quality preferences.

Photosynthetic response is something that is not fixed at all. If there is something remarkable about plants is their adaptation ability in the way to use resources. And light is their main resource.

:thumbsup:Thanks for all the help Knna, you really know what you're talking about!

I've downloaded all the McCree and Inada journal articles I could find. Here's what I learned:

Enhancement (Wavelength modulations such as the Emerson Effect) seems to only be about 7% different from the action spectrum.

McCree has some great data in the 1971 paper, "Action Spectrum, Absorptance and Quantum Yield of Photosynthesis in Crop Plants". On Page 206 species #13 is a tomato plant. From this you can see the quantum yield of 16 key wavelengths in vivo.

Also, according to McCree's article in Plant Physiology vol. 49(5) pg 704, the difference in photosynthesis between the action spectra taken from the sum of each individual wavelength and that of the white light combination was within +/- 7%.
I find this close enough, especially if the emmerson effect is accounted for. I believe this will be my starting point.

Now, the question of photosynthesis saturation must be explored. What are the maximums? I understand that this is a sliding scale, because of the variables of temperature, humidity, nutrients, soil moisture, and CO2 content in the air. What conditions are ideal here? Temp? CO2? Humidity? Given these ideal parameters, I can begin running experiments.:cool: