Building LED lights from facts, no theories

This is something I mentioned before on another LED thread, maybe you have some thoughts about.....

I would like to see a multi color high power (10watts?) LED, (LedEngin?)
that would have instead of Red Amber Green Blue two Reds, one 660 one 627, one Blue and a forth color (cyan?) all together in one LED.

A complete grow light in one 10w LED.

I know that a lot of gains have been made with high power whites, just because that's what is marketable. Horticulture is just a small niche market, especially in comparisons to general lighting needs. Somehow we need to do better then just get trickle down technology.

Looks like there may very well be a new(er) player: induction fluorescents. The watt/lumen outperforms the best T5s and lamp life is 5 to 10 times as long. My big concern is they are very likely way too expensive for the hobbyist. Perhaps in a few years this technology will become the default and prices will drop accordingly. I requested a quote.

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OldMac,
Here are a couple of pics of what I am working currently on, whenever I can find the time. It is an anti-brick design. I have moderately high hopes for it but I am really having difficulty finding time to work on it.
The metal work is very labor intensive. My next step is to make the control panel.

Redline,

what material have you used on those heatsinks? Are they of extruded anodized aluminium? What size are they? How much watts of LED are you going to install on each?

I too think that brick design is the worst possible way of doing LED grow lamps.

Right now i ordered a batch of extruded heatsink bars (13.4cm wide, about 5 1/2") to do LED modules that may be placed either on top, using an frame like yours, or hanged between plants.

RackitMan, induction fluorescents was released at the beggining of the decade. It was a very promisory technology, but manufacturers had been unable to offer it at competitive prices. And they have a reliability problem with the induction units: while the bulb itself may last very long (60-100Kh), the inductor units often fail between 25-30Kh. So it nevers gets a decent share on sales, and prices continues high. And with 150 lm/w LED expected on 1-2 years, nobody is going to invest more on induction fluorescents development.

RackitMan,

Yeah I saw those induction tubes a few years back. I discounted thier use because they where only available in the same light range as MH, not really good for blooming. And a good producing bloom bulb is what we need to get to, we already know that in terms of dgrees Kelvin we would like a color temp of about 2,500 for MJ, that is why I was excited about finding 2,700K T5 tubes finally. ( Instead of the usual 3,000K)

Damn knna, I'm pissed at you! You have gotten me reading spec charts and science papers again, and going crazy in my head how to build a perfect LED light to meet my coming needs. Really fell back into the too much "theory" and too much thinking. But late yesterday I got some aluminum channel to build with, and started to layout my T5s when it struck me.

I need to produce LED strips of about 4', using Red only. Maybe a combo of Cree and some 660 from somewhere else. Each 4' strip could be made of aluminum extrusion, with a heatsink profile. My current design for the T5s is 4 tubes at VHO, all I really need to do is sanwhich them with 5 strips of LED, hopefully about 100watts per strip, depending on the ability to cool them.

That just made me think that I wish I had the two Ti SmartBars instead of the SmartLamp. The bars would fit the design of using 4' T5s better and would have a few more watts of LED. Oh well, let me see what I get with what I've got.

I actually have a 600 digi ballast and bulb, and was going to use it over one of my 4x4 trays and use the LED /now to be hy-bred over the other. Try to get direct comparisons. I think tho, because of some recent money set backs I'm going to have to wait a bit to build some more LED based lights.

Right now me and my partner (I'm slowly passing the baton to someone younger then I) are setting up a "quick and dirty" grow set-up in our new location in order to regroup some money losses, so that we have the money to finish off my dream grow set-up room(s). Plenty of room to work and grow, and systems that produce. He is a frustrated dirt farmer, does hydro to waste in pots of soilless mix. Setting up and 8'x9' room, with 48 sq' of grow space and 2- 1000w and 1- 600w HPS (was mine). Once he's underway, I'll set up a table to hold my 2- 4x4 aero/fog grow trays and get started with at least 1 LED/Ti SmartLamp hy-bred.

Oh, in running designs in my head, I thought about the Reflex tubes you mentioned. I think it could be good to do away with reflectors for the T5s in a LED strip design hy-bred....it could give more space to the heatsink aluminum. I googled them and can't find anything about them. Could you steer me to more info on them. Thnx knna. I'm not really pissed at you BTW, you just got me thinkin' and thinkin' about some of this stuff again.

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Originally Posted by redline

OldMac,
Here are a couple of pics of what I am working currently on, whenever I can find the time. It is an anti-brick design. I have moderately high hopes for it but I am really having difficulty finding time to work on it.
The metal work is very labor intensive. My next step is to make the control panel.

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Redline,

I reallly like that design, each brick being height adjustable and angle adjustable. Seems it could be the answer to grow taller plants with LEDs.

When I built my LED strips last year, the Red Cree's had a Vf of 2.7v and all where within a tenth of that. So a string of 10 made an easy descion to use 28v power supply. I remember you worked with some LedEngin 660nm reds, do you recall what they actually measured? and how consistent where they?
I'm thinking, just build bigger strips (48" vs 24") with more power, and a mix of reds.

I cannot remember exact number. But every single one of them was within .1 volt of the min (some were even outside of specs) I had designed for "typical" and had to end up squeezing in an extra LED.
I was a little dissapointed, since this would indicate they were a low bin unit, and will place you low on the watts/current curve.
I really haven't had a chance to do a decent comparison test on the 660nms.

hey mac thx i'm still very sick and things are looking very bad, have you seen these t5 bulbs they are the fullest spectrum i've seen
a color index 96cri !! very curious too see how well they would grow plants
BlueMaxââ??¢ Full Spectrum Fluorescent Lights

there about $11 ea or they were ,anyhow gotta go good luck

oh and 2700k hell yea!!



..

Veggi;

The T5's I used for the 2' hy-bred set-up where full spectrum blubs with a very high CRI also, don't remember exactly what it was now.

I do remember they where made by Hagen and cost 19.99 per bulb (and I needed 8!)

I'm going to replace them soon with the 2700K, and see how it effects things.

I was originally hoping to end my indoor and greenhouse grow after this year, and move everything to the new location. It's very difficult to harvest the 8x16 greenhouse because of the odor, trying to dry and cure that much material. Could not let my kids or grandkids or anyone else for that matter, near my house for a few weeks. This year I only got to harvest some top colas from some of the seed mothers, then everything got stolen from the greenhouse one night. Most of the money I live on....gone. Worst part they poisined my outside dog to get to the greenhouse. Major hurt comming to three of the town's crack-heads who did this.

Anyway, my small indoor op keeps putting out enough MJ for me and all of the patients I take care of. And a couple of fast and dirty grows and me and my partner can recoup some money and build my dream indoor set up, hopefully before I pass on.

Veggi... Sad to hear you are not doing well, hope you get better soon.

KNNA.. Each module will be about 15 watts. 12 modules total. No 660nms in the small modules, but I will be adding 2 strips 2.3 feet longstrips that will be 660nm. I will toss them in about a month before harvest.
My goal is to stay under average of 40 watt per square foot.

My primary goal is to replace a 500 watt CFL array that is used for Vegging only. If I can save 300 watts during the 6 week veg cycle, that will be a huge savings since they are running 18 hours a day.

To be honest I don't have high hopes of replacing my HPS during flowering. I am running about 50 watts per square foot for my HPS. So I will be comparing it against 40 watts per square foot LED. I think that is the best we can possibly hope for. I think the claims about 150 watt LED replacing 300 watt HPS are grossly optimistic. I have yet to see LED compete on a watt to watt basis against HPS. If I can get 40 watts LED to compete against 50 watts HPS during flowering, I will be overjoyed.

Heat sinks are extruded aluminum. I buy them from a guy on EBay who cuts larger slabs into any sizes you want. Very convenient and cheapest source I have found. I am going to try and run ducted area cooling over the top of the heat sinks, but have drilled holes to mount fans on top of each one if need be. Fans are little power hogs.

OldMac, Regarding your Red strips: Has anyone come out with a 660nm besides LED engin? Check out Luxeon K2s or the IIIs as opposed to Cree's.
They have a much wider bandwith and do a pretty fair job of delivering photon juice at 660nm. The Crees have a razor sharp bandwith around 620nm. I haven't had a chance to compare efficiencies, but imagine they are both very close.

In the past the LUXs have also been cheaper and available in better BINS. I have not worked with Crees, but from what I have read, the bare emitters are not supposed to be hand soldered. Given a choice, I will always work with an emitter instead of a star to eliminate an extra thermal barrier and save a few bucks.

I am now working on cutting the front panel to accomodate panel meters and switches. I also have to finish up two power strips with Cinch Jones plugs. The metal working is what really bogs me down, since I am working with basic tools. Lots of drilling, grinding, filing, tapping, cutting, blood,swearing etc.

Oldmac, ive been searching too for the Reflex tubes in the US and it seems Phillips dont sell them there. But there are other brands which does them, as Hagen, the same of the tubes you are using. They sell an actinic tube for marine acuariums with a 160º window. Ive seen it on acuaria webs for around 20$.

Unfortunatelly it seems that Reflex tubes are hard to find in the US.

Im sad to know what happened you and your greenhouse. I gave up growing outdoors after being robbed two years straight. All the worst karma for those sons of a bitch :mad:

Be aware, its very probably they will try to do it again next year.

Coming back to LEDs, i think is still too soon to replace large HPS bulbs. probably on about 2-3 years its going to be doable, but currently the extra cost is difficult to recover by electric savings. Spectral tunning, micro grows and suplementary lighting for lower areas seems the areas where currently LEDs may be halpul and cost effective.

Veggi, take care. All the best.

I dont see any advantage on using full spectrum bulbs. MJ likes a lot of red light, at least 60% of total. Full spectrum bulbs emits too much green, IMHO.

Redline, i was trying to calculate the thermal resistance of your heatsinks. 15w on each seems correct, although maybe some less ( about 10) would work better, specially if you are going to run your LEDs at 700mA. Are they about 10*10cm and 2 cm thick (4*4", 1")?

I try too to avoid as much as possible the use of fans. Given the large surface area we have avalaible on a grow room, i think using passive cooling is easier and more efficient, as far as heat dissipating surface is well calculated.

I have a spectrografic chart of a red Cree XL lamp running at 700mA. Peak wavelenght is at 642-643nm. Half intensity at 630 and 651nm. Not ideal, but good enough. Emiting spectrum of red leds shifts noticiably with the increasing temperature. Datasheets spectrums must be taken as orientative. Spectrum emited on operating conditions is always longer.

Although not designed for hand soldering, its possible to do it with Cree Xlamps. Ive done it several times without problems. Some leds have been soldered and desoldered some times and are still working fine. The problem is you need to do it on the top sides, where there is very little space avalaible. I solder the electric contacts directly on the side of the led, where there is no problem if there is too much tin (no shorts with the metalic ring of the center).

I use to put a piece of Kapton tape below the electric contacts, and solder the side of the led to the wire over the tape. Kapton tape do well up to 300ºC. Ive tried to put the solder tip on the tape directly for more than 10 seconds without damaging it

[attachment=o209743]

KNNA,
I am right at the 9 square inches/watt for heat sinks that Luxeon recommends for passive cooling. In practice, I have found that the figure is cutting it a little too close. I am working on ducting a concentrated flow of air across the tops of the heat sinks. Hope that does the trick.

Any reason to go with the Crees over the Luxeon IIIs or K2s?

Wit 9 sq inches per watt, you get a thermal resistance about 20 K/W. Plus the thermal resistance of the LED package itself and any aditional dielectric layer (a thin film of thermal adhesive is 0-9-1.3 K/W), it put the thermal resistance of the system near 30K/W. Although its enough to keep decent efficiencies, it may result on unaceptable LEDs duration when running LEDs hard:

At 700mA, a blue leds draws about 3.5V or more. Still at 3.5V, its 2.45W. At 30 K/W, it result on a increase on junction temps of 73.5ºC. So with ambient temps around 25ºC, the LED chip is going to work near 100ºC. Its good for many applications, but on ours, with many hours on a day, that result on shortened life. Not dramatically shortened as if Tj were 150ºC, but shortened.

Most manufacturers only "guarantee" (based on extrapolating short term measurements by stadistical analisis) a lm mantenience of 70% at 50Kh when Tj is kept at or below 80ºC. For the typical depreciation curves, its about 35Kh for 80% of initial output, which mostly is the criteria for horticultural lamps replacement (while human barely notice a drop below 30% on light intensity, for plants it means at least 30% less production, that is usually inaceptable).

For Tj over 80ºC, lm degradation is exponential with the increased temperature. So Tj about 100ºC are aceptable for many applications, where 25Kh until reaching an emission 30% lower of initial is aceptable. But for ours, if you want to recover initial higher investment by electrical bills savings, we want a lm manteinance of 80% at 30Kh minimun, and for that is a must to keep Tj closer as possible to 80ºC. It requires a thermal resistance from chip's junction to ambient temp of 22 K/W.

So when using 9 sq inches per watt instaled of heatsink dissipating surface, if you run your LEDs at 700mA you get a somewhat reduced expected useful life of the array.

Probably the use of airflow on the heatsink will help reducing further those 20 K/W of the same heatsink on open air. So probably with it, you are going to be able to expect 30Kh of useful life. But i would choose to run LED slighty below 700mA to guarantee it (about 600mA). Aditionally, it enhances LED's efficiency.

When running the LEDs at 350mA, that heatsink is more than enough, without the need of forced airflow.

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Any reason to go with the Crees over the Luxeon IIIs or K2s?

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About blues and whites, way better energy efficiency. Currently Cree is doing much better blue leds than Luxeon (as better as double light output per watt).

For red leds, benefit isnt so clear. I prefer the Crees over the Luxeons because the reduced Vf. But differnce on efficiency, although still better for the Crees, is small, and the easy avalaibility of Luxeons and price (when buying small amounts and not full reels) often does the Luxeons a good alternative.

One think you must take into account when using Luxeons and controling voltage, and not current, is their tendency to reduce Vf for same current after some hundred (or less) hours of operation. It mean that you design the system initially to run, for example, at 600mA, but after 200h, its running at 750mA.

Curently, im going to try the Seoul SemiConductor P4 red leds. If specs are correct, they are way more efficients than both Cree and Luxeons (always talking about top bins avalaible: M for K2 and S for Lux and SSC).

Appreciate the advice. I am an electronics hobbyist and don't work in the field, so I can always use some good help.
I bought a bunch of P4s, blue and cool white really cheap, so I am stuck with them. I was planning on using them with red K2s, but will probably need to buy some more reds. I might try the Crees and see if I can get a comparison.

Regarding Cree Vs Luxeon: Isn't a higher VF better? Since you will be running a higher wattage at same current.

I try to be pretty conservative on the current. Don't like to run at more then 60% of max.

I do a couple weeks of break-in during array building process.

The array I am building will have several panel current meters, so I can monitor overall current plus each string.

What are your thoughts on where to operate on current curve? What do you think is the sweet spot where you are trading off efficiency for better penetration? I am setting my rig up so I can play around different current settings and see what produces best yield/watt.

It wouldn't surprise me if we have to run these guys as close to max as possible and use aggressive cooling.

I think with LEDs we are going to have to start tailoring the grow to fit the light. We need to start thinking a little more 3D about productive growth area then we do with HPS. Maximizing available light in the Z axis is the real limiting issue with LEDs. You probably only have a couple of inches of decent penentration with LEDS. If you can somehow increase that to 4 or 5 inches you should be able to double yield in the same square footage.

I am currently playing with growing horizontal /flat plants, trying to keep the canopy depth within 6 inches.

My crude method for heat management:
I look for hotest spot on array with IR thermometer and make sure it is not more then 10 degree F above ambient temp after it has been running for a few hours. Max ambient temp is 80 degrees.

I know there are some pretty good ways of estimating junc temp with basic equipment. I just haven't got around to doing it.

I would like to set my test array up so I can continously monitor temp of each array. Any ideas?

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Originally Posted by redline

Regarding Cree Vs Luxeon: Isn't a higher VF better? Since you will be running a higher wattage at same current.

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With LED, light output is determined by current, not wattage. Any curve of light output is given vs the current level, independent of the Vf associated to that current.

So for a givent current, a given light output. As higher the Vf, higher the consumption, for the same light output: lower efficiency (more watts burned for same light output). This analysis is valid when comparing different Vf bins of same model.

When comparing different LEDs, obviously they havent the same light output at a given current level, so its necessary to compare energy efficiencies of both. But in general, for leds having similar light output at a given current, the lower the Vf, the more efficient. As manufacturers always report light output at a given current (350mA for 1W leds and 700 mA for 3W), when you compare them, the lower the Vf, the better. As higher Vf increases the wattage burned but not the light emission.

We need to forget using wattage to estimate light output of LEDs, because the wide differences between brands and models, and still between different bins of the same LED (both of flux output and Vf).

That way has worked pretty well with HID lights, because efficiencies of them are very, very similar. Saying "i have 50w of HPS per sq ft" gives a very good indication of the light used, because HPSs have near constant energy efficiencies (400-1000W).

But it dont happen with LEDs. 10w of a given LED may gives 1.5 PAR watts while others (or same with way superior bins) may give perfectly 3 PAR watts (double light for same watts burned). So watts burned dont say nothing about light emited when working with LEDs. At least, currently.

Quote:

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Originally Posted by redline

I try to be pretty conservative on the current. Don't like to run at more then 60% of max.

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I think its the right way: easier to cool. more efficients, more light points. But its more expensive (more drivers or components and heatsinks, more leds for same light).

Quote:

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Originally Posted by redline

The array I am building will have several panel current meters, so I can monitor overall current plus each string.

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I agree with that way. Its the only way to take conclusions of how the array works better.

I think current adjustable systems are almost a must. Way more versatility, specially if each color has its own control. Once you do a constant current driver, doing it supporting current limit adjusting is as simple as adding a variable resistor to the current sense circuit.

Quote:

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Originally Posted by redline

What are your thoughts on where to operate on current curve? What do you think is the sweet spot where you are trading off efficiency for better penetration? I am setting my rig up so I can play around different current settings and see what produces best yield/watt.

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For the increased efficiency, the lower the better.

From cost/performance perspective, it depends of each LED model. On most cases, below 600mA. I think 400-500mA is a good compromise on most cases. Some top LEDs support higher currents keeping decent efficiencies, but currently they are little. I believe in just 1-2 years LEDs released are going to support 700mA very well. But not yet.

Quote:

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Originally Posted by redline

It wouldn't surprise me if we have to run these guys as close to max as possible and use aggressive cooling.

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If you find that you need more light, you can only do that or add more LEDs. Anyway, id dont think we are going to use our experimental arrays for many years, so running them hard is doable.

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Originally Posted by redline

I think with LEDs we are going to have to start tailoring the grow to fit the light. We need to start thinking a little more 3D about productive growth area then we do with HPS. Maximizing available light in the Z axis is the real limiting issue with LEDs. You probably only have a couple of inches of decent penentration with LEDS. If you can somehow increase that to 4 or 5 inches you should be able to double yield in the same square footage.

I am currently playing with growing horizontal /flat plants, trying to keep the canopy depth within 6 inches.

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Fully agree. I noticed this many time ago. Thats why im insisting about the need of use side and/or intracanopy lighting. That of only grow SCROG. As i dont like SCROG at all (just personal preference), i tend to seek for ways of allowing the grow of tall plants with LEDs. And BTW, increase the light's productivity.

Quote:

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Originally Posted by redline

My crude method for heat management:
I look for hotest spot on array with IR thermometer and make sure it is not more then 10 degree F above ambient temp after it has been running for a few hours. Max ambient temp is 80 degrees.

I know there are some pretty good ways of estimating junc temp with basic equipment. I just haven't got around to doing it.

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Measure temp at solder point or just next to the led base when heatsink temp is stabilized.

You must know the thermal resistance of the LED package you are using. Its a figure on K/W (or ºC/W, its the same) that says how many ºC junction temp raises for each watt burned by the led. Multiply it (add 1 before if there is a thermal adhesive layer) by watts drawn by the LED (If*Vf, current multiplied by voltage (A*V=W)).

Add the result to the base temp and you get a close approximation of the junction temp.

More accurate measurements implies using very short light pulses (microseconds) and compare Vf of them to Vf on continous operating condition. But this requires to know accurately how much drops Vf for each ºC more, and manufacturer's data often is not precise enough.

I would like to set my test array up so I can continously monitor temp of each array. Any ideas?

Using a thermocouple attached to each heatsink, always on the same position (preferably, the center). But if all arrays uses same LEDs, same power and same heatsink, differences shouldnt be large enough to justify measuring each one, IMHO. But doing it together with current control is going to give very valuable info. :thumbsup:

Knna, to the best of your knowledge what would be the wavelengths that would most efficiently and productively enhance marijuana growth? I was hoping you had tossed a few out.

Also Knna, here is a program that simulates LED junction temperatures, max temps, whatever. Very useful. Future Lighting Solutions | Making LED Lighting Solutions Simple

hey knna first of all thank you to share your experiences with us...i really need some facts to start in the right way my first DIY Led array.

Like you, english isn't my first language so please don't look at the form but the meaning!
I'm working with commercial 90w led arrays(R/B 8:1) like UFOs and i've already made some grow tests mixing Leds with HPS and CLFs with some good results.
I'm a "perfect led light" thread follower since physicsnole(thanks god) put the first post so after a while i decided to do my perfect led array but i already know how difficult is to make a efficient led light...and finally my techincal skills are really poor in assembly an array by myself...lukily a friend works in this field and can do it for me.
From what i've seen regular commercial arrays like procyon and ufos are good for veggi but lack in potency and spectrum in the flowering stage.
My ideal light is a "bloomer"... something to add to the 2 90w red/blue led grow lights in my room when i turn the light 12/12!

Yesterday...after a long waiting i received the Ledengin Leds and 4 35v 1050 mA drivers:

LLZ1-10R105 LEDENGIN 5W RED ON MCPCB PZ 2
LLZ1-10UA05 LEDENGIN UV ON 5W MCPCB PZ 1
LLZ1-10WW05 WARM WHITE 5W MCPCB PZ 8
LLZ1-10B205 BLUE ON 5W MCPCB PZ 3
USLEDLPC351050ALIMENTATORE LPC-35-1050 PZ 4
LLZ1-10R205 DEEP RED 5W MCPCB PZ 8

I still waiting for the 2 5w 720nm Leds that should be here in a week but i need a good projet! The glutec's antibrick idea is nice IMO but hard to move.

I've got a mover and i'd like to move this array between the 2 90w Grow Lights but now i'm thinking about at the heatsink.
I've got 20 cpu coolers with fans and i'd like to keep colors divided to play with spectrum at different blooming stages!

Any help is gold for me at this moment!

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Originally Posted by physicsnole

Knna, to the best of your knowledge what would be the wavelengths that would most efficiently and productively enhance marijuana growth? I was hoping you had tossed a few out.

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Hello, physicsnole, welcome to this thread (and welcome back to the board).

I preferred to not go that way in this thread because this issue has been well addressed on your perfect led grow light thread. I agree with conclusions there.

If any, i would like to point out two things:

-Red part of the spectrum, from 625 to 685nm must be at least 50% of all PAR watts used. And preferably close to 70%. Using 640 or 660nm leds makes little differences. Ideally, both would be used, but only one works fine. Although all the red of 660nm obliges to use higher amounts of blue and far red.

All the rest of the spectrum may share the remaining 25-50% of the PAR watts, with special weight of blue, preferably about 440-450nm, which need to be at least 10% of the PAR watts and preferably 15-20%. More than 30% of blue often harm more than help.

Green and yellow need to be at least 10% and preferably 15% (but how much of this range is optimal is what im working now, and share between green and yellow).

Out the PAR range, some far red, preferably peaked about 720-725nm, is required. Along most of the time, on small amounts. On flowering induction, it need to be higher, in order to shorten it. Ideally, far red must be independent adjustable in order to control plants morphology and phenotype expression.

Im not sold on the benefits of UVB (and im against UVA), but im thinking on carry some experiment with it right now. Obviously, i dont have any idea if it worth or at what amounts.

But we still need to learn a lot of how enhance MJ growth by far red manipulation, and the best way of doing it.

-Selection of wavelengths used are more dependent of the efficiency of the leds at each wl than to the peak wavelength:

For example, 660nm peaked leds produce about 5-10% more than 640nm peaked leds when using same amount of photons. But 640nm leds currently emits at least 50% (up to more twice) more photons per watt burned the 660nm. So currently 660nm are clearly not profitable.

This situation may change on the future, as in fact max radiometric efficiency of AlInGaP leds happen on those peaked about 654nm (almost none Al used on the chip composition). But manufacturers choose to do 633nm red leds, that still with lower radiometric efficiency, gives more lm per watt burned.

But its probable than on a near future industry need longer wl red leds for color compensation on white leds so they will be available for us. So i experiment too with 660nm leds, but only for in case they are profitable on the future. Currently, they are not, with efficiencies below 20% (21% the ledEngin ones), while there are 635nm leds with efficiencies well over 30% (50% more energy emitted as light per watt burned).

So we must differentiate between the perfect led grow light and the perfect led grow light available (or possible to build) at a given moment.

Doing this distinction was what move me to open this thread.

gioiapura, welcome to the thread, too.

I think you are right on track. I just can to cheer up on your project and ask you to share your progress.

I had to order 400Kg (about 890lb) of heatsinks of anodized aluminium. It exceed my needs, so probably ill sell it at ebay, together with the excess of current adjustable LED drivers (100-270VAC input, 50VAC output, 100-900mA current range) i had to order. Ill had them on about two months. But if i sell them ill link them here.

Im thinking on ordering a reel of the new Edixeon 740nm leds too, and for sure ill have excess of them if i finally do it.

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Originally Posted by knna

...I had to order 400Kg (about 890lb) of heatsinks of anodized aluminium. It exceed my needs, so probably ill sell it at ebay, together with the excess of current adjustable LED drivers (100-270VAC input, 50VAC output, 100-900mA current range) i had to order. Ill had them on about two months. But if i sell them ill link them here.

Im thinking on ordering a reel of the new Edixeon 740nm leds too, and for sure ill have excess of them if i finally do it.

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That's a lot of good intel, Knna!
Mahalo!:thumbsup:

Hmmm, "50VAC output":confused::D
If you meant DC, I could sure use a few if the price is right.:cool:
Please give us a "heads-up" when you e-bay them.

Sorry to be so scarce lately. Been re-searching this Martian method.
(Also reading up on Dogz "Martin" method.:rolleyes:)
Thanks for the rep, Dog.
I'd also kill for an uncle like that.:thumbsup:


You guys are all way over my head, but some of it is slowly sinking in.
I'll just keep quietly readin' and :weedpoke: for a while.

No worry, if/when I have any new info to offer, I'll come back out of lurker mode with fingers blazing.:)

Aloha nui.

Weezard

Right on Weeez. This tread is great.... Thanks Knna for your time..:clap:

knna.....i wll start my own thread to avoid pollute yours...thanks for the big help!

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Hmmm, "50VAC output"
If you meant DC, I could sure use a few if the price is right.
Please give us a "heads-up" when you e-bay them.

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You are right, Weezard, it was a typo. Its 50VDC output actually.

So they work directly from mains AC and power up an array up to 50VDC. 82% efficiency slightly below half load, close to 90% when near full load. Ive done more efficient drivers myself, but those are very versatile, due the wide range of operation both on voltage (6-50VDC) and on current (100-900mA). They are CE certified. Current adjustment is done with a screwdriver.

I dont know the price yet, but they are way cheaper than any similar driver ive ever found. When i pay duties and taxes ill know accurately how much they cost, but i believe i will be able to sell them below 30$ each.

The reason to order 400Kg is its the minimum order requeriment Ive been able to find for extruded aluminum. But as its been hard to find LED heatsinks large enough to build illumination arrays, i think i wont have problems selling the excess. Ill get them on 6m bars, so ill cut them at any desired length (they are 13.4cm wide and 2cm deep with 15 dissipating fins).

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Originally Posted by knna

You are right, Weezard, it was a typo. Its 50VDC output actually.

So they work directly from mains AC and power up an array up to 50VDC. 82% efficiency slightly below half load, close to 90% when near full load. Ive done more efficient drivers myself, but those are very versatile, due the wide range of operation both on voltage (6-50VDC) and on current (100-900mA). They are CE certified. Current adjustment is done with a screwdriver.

I dont know the price yet, but they are way cheaper than any similar driver ive ever found. When i pay duties and taxes ill know accurately how much they cost, but i believe i will be able to sell them below 30$ each.

The reason to order 400Kg is its the minimum order requeriment Ive been able to find for extruded aluminum. But as its been hard to find LED heatsinks large enough to build illumination arrays, i think i wont have problems selling the excess. Ill get them on 6m bars, so ill cut them at any desired length (they are 13.4cm wide and 2cm deep with 15 dissipating fins).

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Aloha Knna.

So, you have heatsink to burn, variable CCs that go to 50V at 1+amps, and deep understanding of PAR.:cool:

Hmmm, an enviable position!:)

I gotta wonder what's stopping you from fabricating a few 100+ Watt gro-lights and flogging them on e-bay instead of, or along with, the parts?
There are thousands of folks out here that can't construct a paper pinwheel without needing stitches:D.
Or, that have the skills to build, but not the knowledge.
Or, are just too darn busy/lazy.
Heck, I'm so lazy, I'd buy a few from ya.:rastasmoke:
Food for thought?

Mahalo
Weeze

Very good suggestion, Weezard. Ill think on that. I thought of only selling the exceeding components, but why not selling finished modules as well?

Anyway, it would be just some ones. Im waiting to have built and tested some arrays, and know accurately how they works and to how many watts of HID equal. 6 months, i believe.

But my idea is to order them when they are cost effective against HID and produce them at large quantities (so unitary costs keep low), not building them myself. With current labor costs, its cheaper to order them.

But next Tuesday i have a date on a mounting electronics company which is near bankrupt, and ill see if i can get some industrial equipment for cheap. With a reflow owen and a pick and place machine, i should be able to do many modules a day myself. I let my job to work in this project, so indeed im plenty of free time.

Yep, you gave me food for thought :thumbsup:

I'll leave it to you experts to make a tutorial :)

KNNA, Thanks for the info. I was able to comprehend about 80% of it.
This will give me an opportunity to educate myself trying to understand the other 20%.

Another question: I bought some LED drivers, 24 volt, 180 watt, voltage regulated.
Why are the larger wattage LED drivers all voltage regulated? instead of current regulated like the small drivers?
Is the voltage regulation tight enough that you don't have to worry about excessive current swings. Or is it expected that you use secondary current regulation, like a resistor or a reg chip in each string?

I am currently using a resistor in each string since it is cheap and simple. I could make some small reg circuits if need be, but am lazy. I burn them in for a couple hundred hours, then I customize the resistance on each string to get desired current.

[quote=redline]
Another question: I bought some LED drivers, 24 volt, 180 watt, voltage regulated.
Why are the larger wattage LED drivers all voltage regulated? instead of current regulated like the small drivers?

There are some CC high wattage drivers out there, but they are very, very expensive. Ive seen up to 400w ones. They are similar to HID electronic ballast. Often they comes together with a DMX unit, as mostly this equipment is used on discos and such, using RGB leds.

I dont know exactly the reason of almost nobody doing these type of devices. Although as the voltage increases the driver design becomes more complex and the components used are more expensive, any manufacturer should be able to do it without mayor problems. At least, if they dont seek for very high efficiencies.

I believe that manufacturers thinks that any that want to do arrays of high wattage have the knowledge to do a dedicated driver for the application with higher efficiency than any generic one, thus demand for high wattage generic CC drivers is not enough for mass production.

Along the last year, most manufacturers of power ICs have been releasing components designed specifically for high power LED arrays. They have integrated the current sense circuit and the FET with comparators, so often only needs an external capacitor, inductance and a resistance to complete the basic CC circuit. So a basic CC circuit is now easy to do yourself. Tuning it to take care of the LEDs (avoid transient spikes) and work with the higher efficiencies is more complicated, thought.

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Originally Posted by redline

Is the voltage regulation tight enough that you don't have to worry about excessive current swings. Or is it expected that you use secondary current regulation, like a resistor or a reg chip in each string?

I am currently using a resistor in each string since it is cheap and simple. I could make some small reg circuits if need be, but am lazy. I burn them in for a couple hundred hours, then I customize the resistance on each string to get desired current.

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If you use a voltage regulation, you always need a secondary current regulation. But a resistance on each array is enough.

This secondary control is needed because the negative coefficient of electric resistance vs temperature of LEDs: Vf associated to a given If drops when chip temperature increases. Thus, if you drive the array controlling just the voltage, as the chips heat, for the same Vf, there is more If (current) flowing. As the relationship between Vf and If is exponential, little changes on Vf lead to huge changes of If.

As the resistor drops more voltage as higher is the current, it filter this effect and strongly minimize the current swing: as chips heats, for same Vf, If increases. But when If increases, the resistor drops more voltage, thus there is less voltage available for the leds, thus If increase is controlled.

So although not ideal (the ideal is to limit the current, not the voltage), a tight voltage supply with a resistor on each string works fine enough. And its by far the easiest way, and currently, the cheaper way, of driving high wattage arrays.

The problem of this way of driving leds is its inefficiency: the resistor burns power and rest efficiency to the circuit. Additionally, as LED's chips heats, their efficiency drops. By this effect is partially compensated by the fact of the reduced Vf at a given current (because power burned is Vf*If and light emitted only depends of If). When using resistors, you lose the efficiency gain by the dropping Vf, because what you do is burn those volts at the resistor: all the theoretical gain is wasted.

So as higher the resistance of the resistor used, higher filtering effect (lower If swing) but more power losses.

And when you add the loses of the PS converting AC to DC to the losses on the resistors, you may get perfectly an overall efficiency of the driver design at 70%, meaning that each watt used by the LEDs needs 1.4W. Way larger than any HID or floro ballast, which are about 10% (1.1W for 1W of bulbs consumption) and still less. And that way is difficult to get true electric savings.

So for experimenting arrays, constant voltage PS and resistor are easy and cheap, but expensive on the long run.

The better the thermal path of you arrays, the smaller resistances you may use and you will have lower power losses. When using a good thermal setup and using not high currents (Tj raises very fast with the increased current), it allow you to use resistances with way lower power losses (because less ohms). But obviously this will require the sum of the LEDs Vf is very close to the voltage supplied to the array, and that is not always possible.

In this scenario, if the sum of Vf is just a bit over the supplied voltage, maybe you could use the array without resistances at all. You wont have any control over current, but you can do a try an measure the current after temps are stabilized and if it falls on a good range, run it that way (the disadvantage of no using any resistor, or still small ones is in case one led fail and open: the increased current on the array may fry all it)

A way of eliminating the need of resistors is using a linear voltage regulator on each string, on CC mode (with a sensing circuit with a small resistance).

Linear regulators are problematic when they must reduce many volts. But when they only need to reduce voltage on some tenths of a volt, they work pretty well. And they are cheap. And that way you are controlling directly current of the array. Way better than the resistors way (although still worse than a switching CC driver, way easier to do)

I got a bunch of LM317s kicking around, but wasn't planning on using them.
I figured resistors would do the job as long as I will willing to do a 200 hour array break-in and readjust resistance if needed. I am also going to have a couple of panel current meters monitoring 6 arrays each. I am also going to have a couple more meters where I can spot check current to individual arrays.

Does an electronic regulator have about the same power loss as a resistor?

Also, I figured using 24 volt power supply is better then using a lower voltage since any power supply voltage variation is distributed across a larger number of LEDs.

I was trying to find info on how large arrays are set up in the sign industry, but could find very little on the web.

I don't know how to calculate thermal efficiency (yet), so I have another question. I figured mounting bare emitters directly to the heat sink is preferable to stars, since you eliminate an extra thermal barrier. But you need to use an adhesive instead of a grease which cuts down a bit on thermal efficiency. Any thoughts on best way to go...stars or emitters?



I am getting ready to start constructing the individual modules. I will run the design specs by you for criticism before I start inhaling solder fumes.

I am going with 10 to 12 watt arrays. so will be running around .5 amp. I am going to try and keep the resistor around the .5v to 1.5v drop range. Do you think this will provide adequate secondary regulation? I hate to see it eating up more then 10% of the power.

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Originally Posted by redline

I got a bunch of LM317s kicking around, but wasn't planning on using them.
I figured resistors would do the job as long as I will willing to do a 200 hour array break-in and readjust resistance if needed. I am also going to have a couple of panel current meters monitoring 6 arrays each. I am also going to have a couple more meters where I can spot check current to individual arrays.

Does an electronic regulator have about the same power loss as a resistor?

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No, it has lower losses. But it depends of how much voltage it need to adjust. If its little, the power loss is kept small. The closer the voltage of the array to 24V (supplied by th PS), the less volts drop.

You will notice it for how much hot get the LM317 (if i remember well LM317 have a max current rating of 0.5A, so you could use them).

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Originally Posted by redline

Also, I figured using 24 volt power supply is better then using a lower voltage since any power supply voltage variation is distributed across a larger number of LEDs.

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Yep, but the issue here is not variation on the PS, but different current flowing for same voltage with the changing chips temperature. So the larger the array power, the larger the variation:

say Tj is about 80ºC, for example. The K2 drops between 2 a 4 mV for each ºC over 25ºC. So 80-25=55ºC of increase on Tj lead to 165mV less (at 350mA, average of -3mV/K). The more LEDs in the array, the higher voltage drop along the array, so you need an higher resistance resistor to compensate for it, but lower than the sum of two resistors if you split the string in two series, each one with its own resistor (so better a 24V PS than a 12V one)

In this example, with 165mV less the associated increase in current is about 250mA. If you dont compensate that with the resistor, the array will work at 750mA (in the practice, still higher, because at 750mA and only 0.165V less, the power being burn is over 20% (near 25%) higher than initially, and that lead to the chips getting still hotter, and so on.

So you need a resistor that when all leds on the array drops 165mV, as current increases it increases the voltage dissipation as closer to that figure as possible. For example, if the string is 8 leds long, 8*165mV=1.32V. At 500mA, it implies 2.64 ohms. Power dissipated by the resistor would be 0.5A*1.32V=0.66W.


But obviously, you will determine the value of the resistor according to how much difference of voltage are between that supplied and the string requirements at the target current. In this case, its going to be similar, as you say its going to be about 1 and 1.5V, so its going to be very similar of that calculated before (about 2.5 Ohm, which drops 1.25V at 0.5A).

So if you use a 2.5Ohms resistor to regulate the current at 0.5A, then as chips heats, current across the circuit raises. But each 0.05A of increased current does the resistor drops 0.05A*2.5 Ohm=0.125V more. At a increase of 250mA, it would drops 625mV more. In the first example, we calculated a drop in each led of 165mV, so the resistor would compensate fully a string 5 leds long.

In order to calculate it accurately, you need to estimate the raise of Tj. Thermal resistance of your setup is about 20 K/W, eyeballing. Maybe 25 K/W. At 0.5A, blue K2 draws 3.51V (average, you should measure it for your batch), that may drop to 3.35 after 200h. Its 3.51V*0.5 A=1.575W, for 25K/W, increase of Tj= 39K. So at -3mV/K, you may expect a max drop of voltage at each led of 117mV. In 24V, you may fit 6 blue leds (at 3.51V each), up to 7 (at 3.35V). So you get a max drop in a blue string of 117*7=819mV.

Ive done this calculations so may may know how to do it.

But the right way to do them is by first calculating the number of LEDs on each string. To do it accurately, you should measure the voltage drop of your leds at you current target. Ill use the average Vf from the K2's datasheet: 3.51V for blues and 3.22V for reds (at 0.5A).

The PS gives 24V. So in each string fits 6 blues or 7 reds, and rest 2.94V (blues) and 1.46V (red) to dissipate with the resistor. At 0.5A, then you need to use a resistor of 2.94V/0.5A=5.88 Ohms (remember, R=V/I) for blues and 1.46/0.5=2.92 Ohms for red strings.

In order to compensate for the voltage drop due to the increased temperature, always choose the closer value of resistance over the calculated figure. That way, you set the current in cold below the current target, so as leds gets hotter, the final value is close with your actual target.

For the average figures of Vf of the K2, it would be a 6 ohm resistor for blue strings and a 3 Ohm for the red strings.

Would this minimize the current swing? Lets go to calculate it, although with the calc done in the example, i know the answer is yes.

At 25 K/W (estimated thermal resistance junction to ambient temp), blues may increase Tj up to 39K, as seen before. At -3mV/K, its 117mV less. For 6 leds in the string, its 702mV. How much the resistor will let increase the current before compensate it? As I=V/R, I=0.7V/6 ohms=0.117A, about 100mA.

As the setting for cold LEDs were regulated below 0.5A, final current on operating conditions is going to be lower than 600mA. Likely, about 550mA.

The problem of this design is that a 6 ohm resistor is going to dissipate about 550mA and 3.3V, or 1.8W wasted for each string.

Notice that the excess voltage on operating conditions for that Vf figure is pretty close to the Vf of another blue led. If the Vf of your leds is exactly that, then you could use a string of 7 blue leds connected directly at the 24VDC PS without any resistor and get a current very close to 500mA. As far as the PS is solid giving the 24V, it should work perfectly. But in order to do it you need the Vf of your leds were exactly that (and likely, it wont :(, but who knows?).

Measure accurately the Vf of your leds is a must if you are going to control them by voltage.

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Originally Posted by redline

I was trying to find info on how large arrays are set up in the sign industry, but could find very little on the web.

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They mostly use strings of 3 leds with a resistor on a 12V PS, and prefer to forget about reliability of the system. Mainly because they rarely use LEDs over 200mW, in which thermal effect is way less important than when using high power leds.

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Originally Posted by redline

I don't know how to calculate thermal efficiency (yet), so I have another question. I figured mounting bare emitters directly to the heat sink is preferable to stars, since you eliminate an extra thermal barrier. But you need to use an adhesive instead of a grease which cuts down a bit on thermal efficiency. Any thoughts on best way to go...stars or emitters?

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If you keep the thermal adhesive layer thin enough (by applying some pressure during the curing process), the thermal resistance added is kept below 1.5 K/W, and very often, below 1K/W. Of course, a good thermal adhesive makes a difference. The Arctic Silver is common and very good.

If possible, better the emitters. Mounting is more complicated, but it worth the thermal enhancement.

The problem of many stars is they are of poor quality. Thick layers of dielectric, poor soldering jobs, bad adhesives. Very often they penalize thermal path. With good ones, there is little difference with the emitter glued on the heatsink directly.

But if you know to mount directly the emitters, its cheaper and better.

Knna,
I have an idea that I have also been working on in order to get more growth in Z-plane. This would also help if you are wanting to grow taller plants.

I have a design for a vertical plug-in module that drops down below the top of the canopy. The problem is with cooling. Heat sinks block too much light, plus they are dissipating heat onto the plants.
My design low profile water cooled module, where I am mounting emitters right onto a piece of U bent copper tubing about 6 inch long. I have only built one and it seems to do okay. I don't know how ganging up mulitple units will work.

Another issue is that you would have to reduce top lighting in order to keep within your watts/sq. ft. parameter. So the question that needs to be answered is "where will a watt of LED power need to be positioned to get the best results?" On the top?, On the side? or a combo?
I hate to introduce more complexity into the array if it is not beneficial

Aloha Knna,

Beeg mahalo fo' all dem fish.:)

Just a quick FYI.
The LM317 maxes at 1.5 Amps.
And they need about a 2.5V drop.
Not all that bad for 24 -36V strings.
So, 2.5W wasted as heat. and only half of it is regulator heat.
(1.25V X 1 amp in sense resistor)
Got some running @ 50 C. :cool: @ 1 amp with a 2" sq 1/2" high finned 'sink, no fan.
That help, R. L.?

ciao
Weeze

A basic high-power led circuit???

Say i have a 24V DC @ 1 amp power supply
6.84V @ 700ma 5W high-power LED (3 led's in total)
high-power constant-current source input 6v-24v @ 700ma

If i connected the three LED's in series with the constant-current source and connect it to the power source, would this work?

Ignoring the thermal issues, just need to know if my understand of LED array is correct using high-power LEDs

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Originally Posted by AfricanAlien

A basic high-power led circuit???

Say i have a 24V DC @ 1 amp power supply
6.84V @ 700ma 5W high-power LED (3 led's in total)
high-power constant-current source input 6v-24v @ 700ma

If i connected the three LED's in series with the constant-current source and connect it to the power source, would this work?

Ignoring the thermal issues, just need to know if my understand of LED array is correct using high-power LEDs

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Yes.:cool:

Weezard

Weez,
So you are saying that I will most likely loose more energy in a LM317 then I would with a sense resistor?
I haven't had the time to really study linear regs, so I am very weak on this subject.
But it just seems to me if you are dropping 2.5 to 4 volts (LM317 instead of 1.5 volts (resistor) at equal currents you are going to dissipate more power.
Of course the trade off is you are giving up better current regulation.

Knna/Weez- If I go with resistors and 24v VR driver, do I need to be concerned about start up transients damaging LEDs?

I mount directly and use Artic Alumina. Is the silver a better way to go?

I didn't use pressure since I was worried about shorting out the pad. I did try to minimize layer thickness.
Now it seems I would be better off using pressure and if it shorts, just tear it up and mount another one. I will custom make some kind of fixture that applies weight to the LED

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Originally Posted by redline

Weez,
So you are saying that I will most likely lose more energy in a LM317 than I would with a sense resistor?

Little bit.

I haven't had the time to really study linear regs, so I am very weak on this subject.

Not that much to know really. Take you about 15 minutes to learn all you need for practical application.

But it just seems to me if you are dropping 2.5 to 4 volts (LM317 instead of 1.5 volts (resistor) at equal currents you are going to dissipate more power.

That is correct.
Don't matter how you do it. V x A = W

Of course the trade off is you are giving up better current regulation.

Exactly!
I don't stress over a Watt or 3.
And a dropping resistor will happily pass-on a voltage spike!:)
The LEDs may not be quite so happy to receive it.:(

Knna/Weez- If I go with resistors and 24v VR driver, do I need to be concerned about start up transients damaging LEDs?

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In a word? Yes.
Not to mention shut-down spikes, lightening strikes and plain old everyday "gotcha" spikes.
Of course that does depend on the VR supply used, how heavily you load it, and what you feed it.
I'd just rather Pay the piper daily when considering the cost, time and effort of LED replacement.

With voltage controlled devices, I use VR.
With current driven devices ,CC is the best way to go for full control, consistency, and longevity. IMO.

I'd really like to see your multi-source lighting scheme in operation.
It sounds like a good idea.

Aloha,
Weeze

Much time since i worked with LM317. But for what i remember, although specs usually advice to let 3V for the possible drop in the regulator, when you measure it often is around 1.5V. You know, there is wide tolerances and manufacturers obviously give safe margins of operation.

Anyway, i think the better current regulation worth using the LM317. Resistors arnt adequate to drive high power leds. Doable, but seeing the maths on my last post, is easy to understand why current control is advisable. 10%, and still 20% of variation on the current target is not a problem. But with resistors the variation may go way far from that.

I dont think transients are a practical problem. Although any manufacturers recommend to avoid them, there are many systems working without compensating them and work fine. So its preferable, and life test are done avoiding them, so its difficult to know if not compensating them shorten leds life. But on large strings i dont think its a mayor problem. But i dont know for sure, i use smooth regulators.

The Alumina and the Silver works pretty similar. In the practice, no difference. Any of them have low heat transmission compared to a metal. The key with them is to keep layer thin if you want it dont penalize heat transfer too much. I like the Crees because the electrically isolated bottom slug, as it allows to forget concerns about derivations if the adhesive layer not cover fully the slug.

I like to apply the adhesive directly to the slug, ensuring all is covered and then place it and apply some pressure with the hand (i use a nut to avoid pressing the dome). I let the adhesive cure enough to keep LED in place and then i put a book over the module (a nut over each led) for all the night. Using anodized aluminum is a secondary way of avoiding electrical derivations (the aluminum oxide layer is not electrically conductive).

You can try too to add kapton tape to the conductive slug. It works very well isolating. But then the problem is to glue the led itself to the board. But i think it would be possible to add adhesive (and not requiring to use thermal conductive one) on the perimeter of the base.

I think the main reason of many people to use stars is ensuring that there is no problems with conductive bottom slugs (and beware with that, ive found stars which indeed have the bottom electrically connected)

AfricanAlien, it will work perfectly as far as the constant current device is able to give 3*6.84V=20.5V @700mA. From 24V input, it should, still if its a linear regulator. But be ensure about that.

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I have an idea that I have also been working on in order to get more growth in Z-plane. This would also help if you are wanting to grow taller plants.

I have a design for a vertical plug-in module that drops down below the top of the canopy. The problem is with cooling. Heat sinks block too much light, plus they are dissipating heat onto the plants.
My design low profile water cooled module, where I am mounting emitters right onto a piece of U bent copper tubing about 6 inch long. I have only built one and it seems to do okay. I don't know how ganging up mulitple units will work.

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Heat from a heatsink shouldnt be any problem for plants. All thermal issues of LED arrays are about themselves perfomance and duration, not about plants. If you design well the system, the heatsink shouldnt be over 40ºC. A max, you should feel it slightly warm at the touch. That temp wont be any problem for plants (its similar to T12 fluorescents walls temperature).

Heatsinks on side walls shouldnt block any large amount of light either. But intracanopy, light losses may be noticeable, i agree with that.

I think there are two ways to fighting it. By using low power densities arrays intracanopy, able to be mounted on flat heatsinks, flat white painted (i use a highly reflective DIY mix, by adding barite to latex paint).

Or by mounting the leds on tubes (preferably, at least with some flat area, or directly squared) and aircooling them.

NASA intracanopy modules used this last option: each module has its own driver on a edge with a fan sucking thought a tube where LEDs are mounted.

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Another issue is that you would have to reduce top lighting in order to keep within your watts/sq. ft. parameter. So the question that needs to be answered is "where will a watt of LED power need to be positioned to get the best results?" On the top?, On the side? or a combo?

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Yep, this question is very important. I believe nobody along the Mj forums has studied this topic. And not only about LED lighting, but for any type of side lighting.

On the group buy im doing on a local forum, most people is going to use side and/or intracanopy lighting (mostly, side because cabs are small, mostly microgrow areas).

The initial rule of thumb we are using to size LED modules is to use 300uE/m2 from top and 180uE/m2 for lower areas. We think that each module should cover one cubic feet.

So we put 27uE for each upper cubic feet, so the distance covered for each LED module is about 1ft. And 16 uE on each bottom cubic feet.

But as the system is modular, at any moment each grower may change the configuration and put more or less power to up or sides.

We expect that we may learn the best power distributions from this experience, as there are 20 growers participating.

The initial rule of thumb has been extracted from the light distribution of a 400W HPS in 1 sq meter (about 11 sqft) for plants 75cm tall (2 1/2 ft). But translating some more light to bottom areas than the HPS does, and less directly on top (about 25%), so keeping light density way more even, and just about 60% higher on the top of the plants than on the bottom.

I hope that the experience of 20 growers using different styles of growing allows us to learn fast the best way of distributing light along the 3 dimensions of a grow.