# question regarding LED lights



## charlie_r (Aug 17, 2014)

Didn't know where else to post this, so if it's in the wrong place mods can move it if needed.

I'm putting together a few special purpose LED light sets, and have a question or two about why this seems to be working.

Background info:

I've got a 12V 2A switching power supply (from china), that is driving one of these: http://www.ebay.com/itm/DC-DC-3A-Bu...279?pt=LH_DefaultDomain_0&hash=item2a41fe3947

That is set for 5V, and is driving 5 of these: http://www.ebay.com/itm/5PCS-DC5V-t...575?pt=LH_DefaultDomain_0&hash=item20eaa513ff

Each of those are driving three 3W LEDs in parallel, keeping a constant 400mA. The LED sets are (subjectively) as bright as three 3W in series driven with 650 mA. 

The questions I have about this are:

Why is it even working, with the nominal Vin​ of the LEDs being 3.5V.

Each of the 5 AMS1117 units are supposed to be capable of 800mA. When I drive 1 LED, I measure about 80mA @ 3.2V output. 2 LEDs in parallel brings it to about 180mA @ 3.3V output. As shown above, 3 in parallel draw about 400mA, at 3.4V

I've tried 4 parallel, and the output only goes up to 650 mA, a bit short of the expected mA output, however, the AMS1117 starts to get rather warm. With the 3, there is very little heat generated from the chip. 

I've had this test rig running for 36 hours straight, to see if anything is going to break (let the magic smoke out).

According to conventional wisdom for LEDs as drivers, this shouldn't even be working, let alone working well.

What gives?


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## Steve K (Aug 17, 2014)

charlie_r said:


> The questions I have about this are:
> 
> Why is it even working, with the nominal Vin​ of the LEDs being 3.5V.
> 
> ...



The short answer to the first question is that LEDs, or any diode, does conduct current below Vf. It just doesn't conduct very much current. An LED with a Vf of 3.5v will still conduct at 3v.

Was there a second question? 

I do wonder why you are using 3W LEDs and are only delivering 1.5 watts to them.
I'm also wondering why you are only drawing 2A from that buck regulator that can deliver 3A. The 12v, 2A power supply can deliver 24W to the 5v buck regulator, so the 5v buck regulator should be able to supply 15 watts out (5v @ 3A).

With 5v @ 3A available to power a bunch of LEDs in parallel, I think I'd just skip the linear regulators and go with simple power resistors in series with each LED. It would be cheaper, simpler, etc.


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## charlie_r (Aug 17, 2014)

The plan is to max out the 5V buck regulator with several more sets. These will be for my workbench lighting.

By keeping the current lower than the LEDs are capable of handling, my thinking is that they should last longer. Yes, I know, 50,000 hours at rated current. These are from china. Epistar style, non binned from ebay. Out of 100 in the batch I bought, 4 were closer to warm white, and 7 couldn't even handle 300 mA.

I'm also wanting to put several sets of these over my pool, for night swimming -- if the weather ever co-operates! Those I will want to drive closer to their rated current, but I'm finding that there isn't much difference in the apparent brightness driving them at lower current.


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## DIWdiver (Aug 17, 2014)

With a voltage differential of 1.7V on the AMS1117, and an output current of 800 mA, you would have about 1.36W dissipation in the part. It looks like it's on a copper plane; if it's big and heavy (I can't really tell from the picture), that should allow you to operate there, but the part would get hot enough to burn you. Operating at it's maximum junction temperature, the case would be above 100C. But operating there for extended periods would seriously impact it's reliability.

I'm suspicious of your measurements. In particular, the fact that the voltage rises as the load increases smells very fishy. Also, the fact that each additional LED in parallel draws more then the ones before:

1 LED - 80 mA
2 LED - 80 + 100 mA
3 LED - 80 + 100 + 220 mA
4 LED - 80 + 100 + 220 + 250 mA

It can be tricky to measure current without affecting the circuit. I would recommend measuring the input current of the AMS1117 board, and with a separate meter, measure the voltages while the current meter is still in the circuit. This is the only way to get reliable measurements in this type of circuit, using standard DMMs. A clamp-on DC current probe or meter with one built in would also work, but those ain't cheap.

But as SteveK points out, the LEDs will light at 3.3V, just not at your desired brightness. The only thing the AMS1117s do is guarantee you can't get what you want. A properly selected resistor instead WILL get you what you want, without suffering any worse efficiency or waste of the 5V regulator's capability.


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## charlie_r (Aug 18, 2014)

Ok, did some checking, and you both are right. A 1/2W 4.7ohm resistor will dissipate much less power than using the AMS1117 modules. With the resistors I'll be able to power up a lot more lights without overtaxing the LM2596 module.

Thanks for the replies, and setting me on a better path. Now to order the resistors.....


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## DIWdiver (Aug 18, 2014)

charlie_r said:


> Ok, did some checking, and you both are right. A 1/2W 4.7ohm resistor will dissipate much less power than using the AMS1117 modules. With the resistors I'll be able to power up a lot more lights without overtaxing the LM2596 module.
> 
> Thanks for the replies, and setting me on a better path. Now to order the resistors.....



Right conclusion, wrong reasoning. For the same input and output voltage, the resistor and the AMS1117 will have nearly identical efficiency. With 3.5V LED and 5V supply, the efficiency is 3.5/5 = 70%. It doesn't matter what the current is, doesn't matter what the design is (as long as it isn't switching, which SHOULD increase the efficiency).

I say nearly the same because the AMS1117 modules do have a few mA of quiescent current, which does not go through the LED, causing it's efficiency to be a bit lower. But it's a moot point because the resistor is a much better option.

You never said what your target current was, but a 4.7 ohm resistor should give you around 300 mA, depending on the LED. The resistor would be dissipating 0.42W at that point. A 1/2W resistor can handle that, as long as it's used correctly. I've noticed a disturbing trend in the industry to overrate resistors. What used to be a 1W surface mount resistor is now called a 3W resistor. At that power level it will _melt the solder_ if not mounted on a circuit board that provides _substantial_ heatsinking (even at 1W they need some heatsinking). I haven't seen leaded resistors follow suit as badly, but they are headed that direction. 

I would recommend you get ones that are physically large (well, at least compared to miniaturized ones). In the olden days a 1/2W resistor was around 0.4" (10mm) long and 0.14" (3.5mm) diameter. That's a good size for 1/2W. They run hot to the touch, but not sizzling. Now you can get them as small as 0.24 x 0.09. At less than 40% of the surface area, it would run at a much higher temperature. And don't pack them in tight to each other. They need room to breathe in order to stay in spec at rated power.

In your application I'd probably use 1/2W resistors with some breathing room (with spaces something like the diameter of the body). But if I was going for high reliability (and/or surface mount), I would go the next size up to a 1W. Running near rated power for long times reduces the reliability of any part. On the other hand, modern leaded resistors are extremely reliable, and you'd have to degrade them a lot before you'd be likely to see a failure in a few parts, so maybe I'm just shooting off my mouth at this point. Hopefully at least someone finds it useful and/or interesting.


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## charlie_r (Aug 19, 2014)

Now I'll give a bit more info why I'm doing this experimentation. My wife is dissatisfied with the offerings of our local suppliers of garden plants, primarily vegetables. She wants to start them from seeds in our basement next spring, so I'll need to come up with decent grow lights.

I've been doing a lot of reading on what LEDs will give the best results. The option of HPS etc. is out of the question, due mainly to the fact that the start-up and operating costs would break the bank. Looking for good LED modules specifically designed for grow lights has revealed that pre-made quickly falls into this category as well. So I need to find good ways to cheaply drive a large number of LEDs, at low voltage.

Another aspect of this is the water. I'm not too thrilled about having near household voltages where we'll be spraying/misting the plants, so the option of ready made drivers capable of running 10 or more LEDs in series scares me. 12V and lower looks to me to be my best, least expensive option. 12V switching power supplies have come down in price to where that looks rather attractive, along with the LM2596 buck converters.

My test rigs will be utilizing white LEDs, to be placed over my small (Intex 15'x48") pool, for night swims. The plan is to make small units to be attached to each light set, and potted for weather resistance, with any heat sinks needed being the only parts open to the elements.


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## DIWdiver (Aug 19, 2014)

UL considers anything under 48V to be safe enough that they don't want to look at stuff. I'd certainly consider 24V safe for use around the pool, and up to 48V okay for indoor use. 

Even if using only 12V, if it's ultimately tied back to AC power, make sure you use properly isolated power supplies, and that your implementation doesn't compromise the isolation.


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## charlie_r (Aug 20, 2014)

Yes, it will be tied back to AC power, and I will be using an isolated power supply on a GFCI. Water and electricity scare me! The cheap Chinese switching power supplies are NOT good enough for this use, because of the lack of isolation.

It's not so much the voltage I'd be afraid of, it's the amperage. Even at 12V, in water, you can get a heck of a shock. If that goes through your heart, ...... need I say more?


Thanks for the help and concern.


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## DIWdiver (Aug 20, 2014)

Amps don't happen without enough volts. That's why it's the voltage that determines safety.

By the way, the Mythbusters determined that while possible, it's unlikely you'd be killed if you were sitting in the bathtub when an electrical appliance fell (or was tossed!) in. I'm not saying I'd try it, or that you should take unnecessary risks, just that low voltage DC is considered safe because it really is.


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## charlie_r (Aug 21, 2014)

OK, I'll take that at face value, with one exception: I've gotten nasty electrical burns (not acid) from 12V automotive batteries.

Back to the original topic, in doing a bit of looking into paralleling strings of LEDs, balancing the current between strings can become problematic. If one "string" of 3 fails, the other strings then have to take the higher current, and risk thermal runaway, right?

Looking around the web a bit today, someone has come up with a balancing scheme using small audio coupling type of transformers. Of course, to make this work, there has to be PWM added to the circuit.

OK, taking that idea, and knowing the better MIG welders have an inductor on one leg of the output, I've wound a length of 30 AWG around a #4 screw, about 40 turns in two layers. Understanding that I only have a cheap GE digital multimeter (GE2524) and it may be giving me false readings, I put this coil in series with the + side of the LEDs and noted a jump in the mA from 110 to 140. To me this doesn't make sense. I had expected a slight drop in current, due to the impedance introduced. Can anyone explain?


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## Norm (Aug 21, 2014)

charlie_r said:


> OK, I'll take that at face value, with one exception: I've gotten nasty electrical burns (not acid) from 12V automotive batteries.


Not possible, the only way you could burn yourself would be to short the battery with something that became hot a length of wire etc..

Norm


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## inetdog (Aug 21, 2014)

charlie_r said:


> OK, I'll take that at face value, with one exception: I've gotten nasty electrical burns (not acid) from 12V automotive batteries.
> 
> Back to the original topic, in doing a bit of looking into paralleling strings of LEDs, balancing the current between strings can become problematic. If one "string" of 3 fails, the other strings then have to take the higher current, and risk thermal runaway, right?
> 
> ...


The arc has a minimum voltage, which depends on the length of the air gap. But although the voltage and current pass through zero twice each cycle the arc will restrike later in the cycle because of the heated ionized gas in the area of the arc.
Take a look at the length of time the AC voltage waveform is above the threshold voltage. 
Now consider what happens with the inductor in place.
The arc will restrike at the same point, but the inductor will force the current to keep flowing longer at the other end of the window.
(SWAG, anyway.)
The coil also limits the current to a value the transformer can handle, like the ballast on a fluorescent.

So much for the welders. Since you are supplying DC to the LEDs, the fact they they have a minimum conduction voltage should not matter at all WRT the behavior with an inductor.


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## charlie_r (Aug 21, 2014)

True MIG welders are DCEP, where your flux core wire feed welders are DCEN. Every MIG I've used had full wave rectification. Rare smoothing caps, but all the good ones had the choke/inductor. Several of the tombstone AC welders had the choke, but not all.

Perhaps what I'm seeing is a combination of the cheap DMM and a small amount of ripple on the output of the LM2596 module, from what you've said about the AC welders.


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## inetdog (Aug 21, 2014)

charlie_r said:


> True MIG welders are DCEP, where your flux core wire feed welders are DCEN. Every MIG I've used had full wave rectification. Rare smoothing caps, but all the good ones had the choke/inductor. Several of the tombstone AC welders had the choke, but not all.
> 
> Perhaps what I'm seeing is a combination of the cheap DMM and a small amount of ripple on the output of the LM2596 module, from what you've said about the AC welders.


Very good point. The DC current shown could easily be the peak rather than the average of a complex waveform. Or it could be a non-RMS average.


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## charlie_r (Aug 21, 2014)

This is where no access to a scope hurts. We would know for sure why it jumped with that.


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## charlie_r (Aug 26, 2014)

Finally got somewhat of an answer from one of the sellers on ebay of the 2596 modules.

See if anyone here can make a bit of sense of some of this:

Note, this is for one of the units with 3 trim pots on it, for current adjustment.

Output ripple: 20M bandwidth (for reference only)
Input 12V output 5V 3A 60mV (MAX)
Working temperature: industrial grade (-40 ℃ to +85 ℃) (environmental temperature exceeds 40 degrees, please reduce power use, or to strengthen the heat)
Full temperature: 45 ℃
The typical no-load current: 10mA (12V 4.2V)
Load regulation: + 1%
Voltage regulation rate: 0.5%
The dynamic response speed: 5% 200uS
Output short circuit protection: A, constant current (the current setting value of the constant current)
Connection: can be directly welded wire in PCB
Scope of application: LED constant current drive, rechargeable lithium batteries (including ferroelectric), 4V, 6V, 12V, 14V, 24V battery charging, battery, NiCd and NiMH batteries (battery charger, solar panels),
Battery charging method:
1 determine the float voltage you need to charge the battery and charging current, input voltage module;
2 adjustable constant potentiometer, the output voltage is regulated to 3V.
3 multimeter 10A current block measurement output short circuit current, and adjusting the constant current charging current potentiometer output current reaches a predetermined value;
The 4 charging turn lamp current default delivery is 0.1 times of charging current (current value), such as the need to adjust adjust turn lamp current potentiometer; (generally do not adjust)
5 adjustable constant potentiometer to the output voltage to the floating charge voltage;
6 battery charging, test.
(1, 2, 3, 4, 5 steps for the module input power, output no-load not connected with the battery.)
LED constant current driving method:
1 to determine the current you need to drive LED and maximum working voltage;
2 adjustable constant potentiometer, the output voltage is regulated to 3V.
3 multimeter 10A current block measurement output short circuit current, while regulating constant current potentiometer output current up to LED working curren


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## LEDPunisher (Aug 26, 2014)

Just so you know, you can ignore pretty much every grow light out there. Just build your own using a mix of 2700K and 5600K LEDs. Works just as well as the red/blue panels, costs far less to make.


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## SemiMan (Aug 27, 2014)

LEDPunisher said:


> Just so you know, you can ignore pretty much every grow light out there. Just build your own using a mix of 2700K and 5600K LEDs. Works just as well as the red/blue panels, costs far less to make.



Not really. It works different and the efficiency is far less especially in the red.


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## charlest (Aug 27, 2014)

2700K and 5600k actually are missing the blue spectrum. Depending on usage ledpunisher is correct. The reason nobody uses these spectrums is because say in a planted aquarium "which is my area of expertise" the aquarium will look yellow and ugly. Even though those two colors would be great for growing plants.


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## LEDPunisher (Aug 27, 2014)

> 2700K and 5600k actually are missing the blue spectrum.



Most white LEDs now days start with a blue or UV LED as a base and utilize a conversion phosphor to get green and red. You can check if your LED is constructed this way by utilizing a fluorescent highlighter, they'll glow a bit under those LEDs. Plenty of blue in them. They're the lights I use in my aquariums. The primary loss of blue is caused by the water, which is fairly effective at filtering out or reflecting certain UV and blue wavelengths, and is why many aquatic LED lights come with added ~420-440nm blue added in. I recommended adding the 2700K LEDs for color balance in the red versus the overall higher blue-dominant output of the 5600-6500K LEDs. 

My aquarium does not look yellow and ugly with a mixed set of lighting. My 55g runs everything from 2700K to 7500K.












I hate the auto-white balance on my Z981. Too sensitive to green lighting which is why it looks about ten shades greener than the human eye is seeing it. Especially given I did a 50% water change/vacuum/substrate re-set last night, the tank is pretty much pristine.



> Not really. It works different and the efficiency is far less especially in the red.



Thankfully, lower red efficiency isn't much of a concern for growing, as green light ultimately is more efficient than red for photosynthesis over time. Green ends up with a higher quantum yield (this is why HPS lighting works so well despite being predominantly green light and has a horrible spectral coverage.)

http://pcp.oxfordjournals.org/content/50/4/684.full 

But this is the current science, and later experiments might demonstrate that paper to be not entirely accurate, or accurate but for the wrong reasoning. Only time and controlled reproduction of the experiments will tell. Of course, I don't expect LED panel makers to pay attention to the real science, so we'll continue to see red/blue only grow lighting for a long time, yet.


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## charlest (Aug 27, 2014)

Here is what I meant by clean white light. Compared to your tank. Nice setups btw.


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## LEDPunisher (Aug 27, 2014)

I like your setup, so much more plant life versus mine! 

I'm not entirely sure but I think the picture difference could be due to the cameras and their exposure/shutter settings. I changed my shutter speed and ISO and got different results, with a lot more blue and still the oversaturation of the greens, but this is a lot closer to what my eyes are actually seeing.


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## LEDPunisher (Aug 27, 2014)

Oh! I just thought of something! How thick is your glass? Mine's pretty thick (8mm,) that also might explain a bit of the extra green oversaturation in my photos.


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## charlest (Aug 27, 2014)

Ohhh I like that color dude. Maybe we should talk about your spectrum in another thread. I feel like we are hijacking this one hah. But yea my phone camera doesn't pick up reds it's probably why.

I actually just tore everything out of this tank and redid it. Because I swapped to r/o water and everything I was growing I was trimming twice a week so I changed it all out to difficult sp.


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## LEDPunisher (Aug 27, 2014)

I've noticed that some cameras just aren't great at getting red. Looks like you're pumping in the 8000K+ range with your lights!


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## charlie_r (Aug 28, 2014)

While that paper LEDPunisher linked is a bit more technical that I'm able to fully understand, I did pick up the general sense that he's mostly correct. Most of the info I had obtained thus far has been from cannabis grower type websites, which may be slightly erroneous due to the possible sampling of the end product by the writers.

I'm very willing to try the warm white/neutral white route as it appears quite a bit less complicated that trying to get just the right mix of several reds and blues.

I've got a few months to experiment with both methods before going into production of the required number of fixtures for our vegetable starts.

Thanks for all the help so far!


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## charlest (Aug 28, 2014)

Charlie for vegetable starts I would'nt worry as much on specific lighting. Aquarium lightning is more tailored towards algea prevention and marijuana growers are more tailored towards color and buds none of them are going to help you. And honestly your seedlings are going to go out in the sun anyways I wouldn't scratch your head to much over spectrum. I'm an avid gardener and I generally sow my seeds straight into the soil. But I live in salt lake city and they always have a late start so I have put a lot of thought into seed starting as well. There is a few articles on my website for indoor hydroponics non cannabis if your interested in the read, pm.

The light over my aquarium is 2x39w 6500k 2x39w wavepoint ultra grow which is a purple blue very high in red spectrum. The first photo I had giesmanns floragrow instead of the wavepoint.


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## LEDPunisher (Aug 29, 2014)

charlie_r said:


> While that paper LEDPunisher linked is a bit more technical that I'm able to fully understand, I did pick up the general sense that he's mostly correct. Most of the info I had obtained thus far has been from cannabis grower type websites, which may be slightly erroneous due to the possible sampling of the end product by the writers.
> 
> I'm very willing to try the warm white/neutral white route as it appears quite a bit less complicated that trying to get just the right mix of several reds and blues.
> 
> ...



Simply put, emulate the sun as best as you can. Cree is about to start dropping LEDs pushing 300+ lumens per watt at room temp, 350mA drive, and 5150K, which might, might likely mean that the ~85C temp still results in equal or greater lux than an HPS light (~150 lux/w @ 2700K @ 600W) but since the color temp is higher, more blue and red, which ultimately means more photon flux density. If you could keep those LEDs even around 50C you'd be blowing every single light source out of the water in terms of efficiency across the entire visible range.


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## LEDPunisher (Aug 29, 2014)

charlest said:


> The light over my aquarium is 2x39w 6500k 2x39w wavepoint ultra grow which is a purple blue very high in red spectrum. The first photo I had giesmanns floragrow instead of the wavepoint.



That explains the look of a very very high color temp. I fixed my camera lighting issue (dropped a ND -red filter on it to let more red light through,) and also reorganized it some.






That's almost exactly what it looks like to me (remove the 'l' at the end of the filename before .jpg to get a full resolution pic.)


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## SemiMan (Aug 29, 2014)

LEDPunisher said:


> Most white LEDs now days start with a blue or UV LED as a base and utilize a conversion phosphor to get green and red. You can check if your LED is constructed this way by utilizing a fluorescent highlighter, they'll glow a bit under those LEDs. Plenty of blue in them. They're the lights I use in my aquariums. The primary loss of blue is caused by the water, which is fairly effective at filtering out or reflecting certain UV and blue wavelengths, and is why many aquatic LED lights come with added ~420-440nm blue added in. I recommended adding the 2700K LEDs for color balance in the red versus the overall higher blue-dominant output of the 5600-6500K LEDs.
> 
> My aquarium does not look yellow and ugly with a mixed set of lighting. My 55g runs everything from 2700K to 7500K.
> 
> ...



I have to read the paper in greater detail to understand the conclusions but the point of using blue/red for grow lights as opposed to white LEDs is not just about spectrum but radiometric efficiency. 2700k LEDs have poor radiometric efficiency especially in the red due to large stokes losses. Even in green you have significant stokes losses.

Blue LEDs on the other hand are > 60% radiometric efficiency and deeper red around 40%. Lumens mean nothing to plants, photons do.

That is not to say that blue/red is optimum. You could end up with big plants and blooms but nutrient deficiency depending on what you are trying to accomplish. A mix of highly radiometric blue and red with white may be the best overall without getting too complex.


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## LEDPunisher (Aug 29, 2014)

> Lumens mean nothing to plants, photons do.



Generally speaking, yes. However, assuming a fairly-balanced ~5150K CCT light, one can do a simple conversion from lumens to PPFD with the magic number 8 (this has been tested to be fairly accurate with everything from my LiCor to FieldScout quantum meter, to within a +/-4% tolerance.)

But, ultimately, when you get down to it, (let's use cannabis as an example, despite being a poor example) green light does win out ultimately versus red or blue in how much is absorbed and utilized. I've had a pair of 15W MK-R at ~5300K beat out a red/blue only 50w panel in flowering mature cannabis clones, sharing the same nutrient reservoir, room (light-separated for variable control,) method of growing (NFT) light cycle (12.5/11.5) same nutrient flow rate, same oxygen/CO2 levels at root/leaves (respectively) and airflow in CFM over the channels at 5cm.

The real issue with red/blue only LED grow panels is that while they might have some insane photon flux output, red and blue only go so far through a canopy (blue gets attuned/absorbed by water in the plant, red is absorbed more efficiently on the surfaces of leaves.)


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## LEDPunisher (Aug 29, 2014)

Let me give a quick picture example - pure red/blue LED lighting. Notice how my lettuce bolted while the dill is semi-lush but still thin.






The shelf life of this stuff is horrible. Freshly-harvested dill didn't last two days in my fridge even with a good supplementary solution. The lettuce lasted about a week before the interior meristems began to turn to mush. What we determined was the red/blue only light caused thin walled parenchyma cells in the interior of the root mass, which caused this shelf-life failure, as the plant would take nutrients from the leaves to keep the root mass alive.

The morphological characteristics of red/blue only light is horrible on most vegetative food crops. Two Australian clients helped me with testing this. The crops exposed to red/blue versus crops exposed to white light, the white light ones had higher nutrient density and also had higher shelf life.


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## SemiMan (Aug 29, 2014)

LEDPunisher said:


> Generally speaking, yes. However, assuming a fairly-balanced ~5150K CCT light, one can do a simple conversion from lumens to PPFD with the magic number 8 (this has been tested to be fairly accurate with everything from my LiCor to FieldScout quantum meter, to within a +/-4% tolerance.)
> 
> But, ultimately, when you get down to it, (let's use cannabis as an example, despite being a poor example) green light does win out ultimately versus red or blue in how much is absorbed and utilized. I've had a pair of 15W MK-R at ~5300K beat out a red/blue only 50w panel in flowering mature cannabis clones, sharing the same nutrient reservoir, room (light-separated for variable control,) method of growing (NFT) light cycle (12.5/11.5) same nutrient flow rate, same oxygen/CO2 levels at root/leaves (respectively) and airflow in CFM over the channels at 5cm.
> 
> The real issue with red/blue only LED grow panels is that while they might have some insane photon flux output, red and blue only go so far through a canopy (blue gets attuned/absorbed by water in the plant, red is absorbed more efficiently on the surfaces of leaves.)



Unfortunately, without having full details on the 50W red/blue panel you were using, it is difficult to make any comments on its effectiveness. Many of them are absolutely atrocious whereas the MKR is generally speaking a pretty good LED. Odds are good that the blue was of average efficiency and most grow panels I have seen unfortunately use 630nm LEDs which will generally start with a lower efficiency, i.e. 20%, and then take easy 25% as they heat up. Deep red will hit 35%+ and have little thermal droop. I am not saying it is the ideal color, but for the same power will get you 2x the photons.

Agreed on getting into the canopy, but even a single leaf can attenuate green by 80+%. There is quite a bit of research on LED grow lights w.r.t. their form factor. One thing that is certain is that a panel light is not the best ... at least not a single on top. Newer implementations include top and side panels, as all as cylindrical lights that emit 360 degrees and drop into the canopy.

You do realize that pure H2O (water) attenuates blue a lot less than red right? That said, for all intents and purposes, for the total water thickness of a canopy, water is near perfectly clear. The blue (and red) attenuation is due to organic material, possibly in suspension, but not from H2O on its own.


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## SemiMan (Aug 29, 2014)

LEDPunisher said:


> Let me give a quick picture example - pure red/blue LED lighting. Notice how my lettuce bolted while the dill is semi-lush but still thin.
> 
> 
> 
> ...




Many people are working off 20 year old data and only looking at chlorophyll a/b (and I would admit to falling into that trap initially), and not looking at other photosynthetic processes that are stimulated by different wavelengths. That said, even the improper use of blue/red will result in nice looking but failed plants. How did you adjust the ratios of blue/red over the growing season for the plant?

semiman


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## SemiMan (Aug 29, 2014)

LEDPunisher said:


> Let me give a quick picture example - pure red/blue LED lighting. Notice how my lettuce bolted while the dill is semi-lush but still thin.
> 
> 
> 
> ...




I am a little surprised you don't have the lights higher and use a mirrored enclosure to get more light deeper into the canopy without much losses. Look again at your results, given how bad the results are, if you used the same red/blue throughout the growth, likely the excessive blue was an issue at the end of the growth cycle.

Semiman


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## LEDPunisher (Aug 29, 2014)

> Unfortunately, without having full details on the 50W red/blue panel you were using, it is difficult to make any comments on its effectiveness.



At 350mA, 20 blue LEDs at 460 and 420 nm (equal split) with 30 red LEDs (60/40 split 660/630nm respectively.) 1W diodes.



> Many of them are absolutely atrocious whereas the MKR is generally speaking a pretty good LED.



The MK-R has a balance close to sunlight, which is why it works so well.



> Agreed on getting into the canopy, but even a single leaf can attenuate green by 80+%.



Depends on the wavelength, but yes you are right there.



> There is quite a bit of research on LED grow lights w.r.t. their form factor. One thing that is certain is that a panel light is not the best ... at least not a single on top. Newer implementations include top and side panels, as all as cylindrical lights that emit 360 degrees and drop into the canopy.



360 degrees with a focused directional element is useless IMHO. Why irradiate the area around with no leaves? Focus that light onto the plants!



> You do realize that pure H2O (water) attenuates blue a lot less than red right?



Rayleigh scattering would say differently, so does physics.



> That said, for all intents and purposes, for the total water thickness of a canopy, water is near perfectly clear.



But you ignore quantum efficiency in that situation.



> The blue (and red) attenuation is due to organic material, possibly in suspension, but not from H2O on its own.



This is wrong. The attenuation in blue is due to water being partially opaque to blue wavelengths of light, specifically in the 420nm and down range, with a few low peaks allowed for roughly 380nm and 280nm though the atmosphere as shown with my graph above.


----------



## LEDPunisher (Aug 29, 2014)

> You should have quit while you were ahead.



I was ahead of you before you were double my young age of 32 years, proven in Kirby High School Memphis TN greenhouse class, as I was head master of the class after my junior year. Anthony Baldwin was the teacher, for reference, and he can't forget me after I blew yields away by 400% versus any other class he had.



> Are you defining photon energy as another term for wavelength?



Nope, but it appears you're ignoring real biology (photon flux) versus luminous and radiometric output. Plants don't care about that, they care how much energy each photon imparts to the system. In that respect, green wins, period. This is why HPS lights work so well despite a poor balance of light. Proven over the time period of a decade, now. Are you purposely ignoring science? Google gives these results in the top results (with number of people citing these journals.) Until you're citing these journals with me, you've got zero professional credential to argue (and yes I realize that's an argument to authority fallacy. Guess how science works along with any judicial system?)



> Blue light causes your pupils to close due to a recently discovered (rediscovered) retinal ganglion cells that has response from 450-520nm. That is not the exclusive pupilar mechanism, but it is responsible for a good majority of the pupil response. From dark though, even bright red light causes your pupils to close .. as will any visible wavelength of enough intensity.



Nothing new to my half-blind self. Next poor explanation that fails to take into account my half-depleted cones and rods. Oh, you don't hold an optrician certification or doctorate, so I shouldn't trust your words, given your assumption of authority.

Do you even hold a medical license? If not, I would highly recommend not talking about medical issues. I possess a first responder cert, plus JEDEC eye damage certs for concentrated light (which the panels I used to sell reflected the hazard.) What do you have, sir, besides your posts on this forum?



> Dark adaption comes from several mechanisms though, how wide the pupil is (largest macro response), neuron gain (mid response but also fastest response), and chemical receptor saturation.



All of those bound to a single system with a balance. It's like you ignored the reproduction of the human eye for photography, and the infinite possibilities of variation due to analog biological systems. An actual biology degree would help you understand where you're wrong.

I can't address the rest of your coment until you actually possess the knowledge. I don't fight unarmed opponents that have ZERO journalistic contribution to the community with proof or living evidence.




> You also talk about sophisticated setups for comparing plant growth, but show a few cheap blue/red lights poorly mounted over some plants with no improvements for canopy lighting in a what looks like a cluttered basement.



Okay, let me shut you up.



Now deal with my 'cluttered basement' in a fully scientific-controlled environment in the UK provided by Oxford University.

Oh, you can't. 

Walk away while you've still got a chance. The next two sentences I can speak will ruin your reputation. 

Oh, that's a video from a company, not an acceptable source?

http://tinypic.com/player.php?v=14ujcqc&s=5

Okay, how about a direct tour of the place from my camera, as shown in the link above this sentence?

You're about 30 years behind me in this field, sir. Please do try and keep up if you've got the resources to do so. I've been doing this for a good long time, now, to where I can sit at home for the rest of my life. I've proven my tech, right over to NASA (and I have an NOP contract with them) which nets me two million dollars over ten years. I'm on par with Japan's space-based farming research, alone, versus fifty+ people working the same thing in another country. I have that resource they don't have - space.

Apologies if I put this in the wrong thread. My browser is being stupid.


----------



## SemiMan (Aug 29, 2014)

Again, you may know plants, but you do not know science which is obvious in your replies.

I am not ignoring photon flux but photon flux is on a relative basis (wavelength)/radiometric. I.e. at the same relative power, there must be more red photons than blue photons.

And since we are talking about REAL science, we need to talk about quantum efficiency. Total energy efficiency is mainly comes into play w.r.t. heat transfer. We are talking photo stimulated chemical processes what are not about total energy but about total photons that stimulate chemical reactions, hence why quantum efficiency is often used when talking about any photonic generated reaction whether photo biological, or solar cells for that matter. 

Most medical doctors, ophthalmologists included are not experts in the deep photo biological workings of the eye. They don't have to be as that is really not that they are experts in. That expertise generally falls to specific researchers. The fact you even bring this up shows you are clutching at straws.

Of course, as opposed to clutching at straws, please feel free to refute what I wrote about night vision. Please don't site the U.S. Army Research manual I think from the 60's or 70's ... I have that one too (overall it's a good read, but out of date).

Actually mainly you clutch at straws, and come up with an excuse to avoid the argument (I am not prepared .... give me a break). It is quite obvious from what you wrote about blue and night vision that you really do not understand this topic, but keep writing, as you are not helping yourself.

HERE IS AN IDEA: If you think I am wrong about night vision and misleading people, why don't you do everyone a service and refute what I wrote about night vision. That is the whole point of a public forum. When someone posts something that is wrong, other people should jump in. I certainly encourage it.

It's actually funny how you say I ignore the balance and concentrated on one thing. You will notice that I pointed out the three processes involved in night vision while you concentrated on only one. I believe that is the pot calling the kettle black. 


In terms of water absorption its really not up for debate. Pure water is virtually clear, and it is clearer in blue. Let me emphasize, pure water. You are probably used to seeing water absorption charts that are based on environmental water which passes more green ... almost completely due to dissolved organic matter.

Rayleigh scattering concerns the scattering of light with small particles <10x the wavelength of light (approximately). That does not apply to pure water. Since you like links, here is a nice summary on water absorption .... no point recreating the wheel:

http://www1.lsbu.ac.uk/water/vibrat.html (notice how attenuation is lowest in the blue)

which comes from this: http://www1.lsbu.ac.uk/water/vibrat.html


----------



## SemiMan (Aug 29, 2014)

p.s. I can't believe you referenced a high school accomplishment.

Can you please tell me something though .....

In the second H2OFARM video, it clearly shows RED and BLUE LEDs being used, and yet you in other posts shoot down using RED and BLUE LEDs for plant growth. Keep in mind that video was from 2013, so you can't claim it was really old.

Actually from the H2OFARM website I found this picture:

 http://www.h2ofarm.co.uk/img/news/HF50.jpg 

There is quite a purple cast to those pictures suggesting again RED/BLUE LEDs.

Now I know you said vegetative plants, but you have been implying that white is far better in general so I am wondering what the right answer is?

Now that picture is from July 2013 and it specifically relates to the H2OFARMS own FUTURELED which at least in 2011 was most definitely blue and red, and those colors were picked to grow, what's that you say, lettuce?

I am not making this up, it's there for everyone to see, at least in 2011, http://www.stockbridgeonline.co.uk/wp-content/uploads/downloads/2011/09/STCH20.pdf 

So again, please let me know which is best, blue/red, white? .... cause what you are saying and at least what you are writing seem to be out of alignment.

I am disappointed in the purely overhead canopy light as this has been proven to be not as effective. I don't think you understood my 360 light comment, but my fault for not showing pictures:

https://encrypted-tbn0.gstatic.com/...jLJyI9vJ_yIeKpB1dOvDC2ILnbTwvH-tHb9WVdFBM_IEZ is an example of more advanced lighting methods to get light into the canopy.

I can't quickly find the cylindrical hanging light I was talking about, I though that was Philips, but now I am thinking GE. It was the result of a research grant. The basic hanging one like I showed above would do the same thing. Philips has lots in this area:  http://www.lighting.philips.com/pw...t-philips-led-lighting-in-horticulture-EU.pdf

What I don't understand is why you have an off the shelf UV LED in your basement when you have developed somewhat commercial products? I can't fault your $90 ebay lights as I believe they have multiple LEDs colours in them, though I do not get the impression you can run a recipe on them? Can you? The UV is not that deep, 390, and the IR (850) does not seem to be anywhere of value. Near IR (750) I know has been shown to stimulate flowering in some plants, but had not heard of 850 doing anything, but then again, thats about all you can cheaply get in the LED world in the near IR.


----------



## SemiMan (Aug 29, 2014)

LEDPunisher said:


> Thankfully, lower red efficiency isn't much of a concern for growing, as green light ultimately is more efficient than red for photosynthesis over time. Green ends up with a higher quantum yield (this is why HPS lighting works so well despite being predominantly green light and has a horrible spectral coverage.)
> 
> http://pcp.oxfordjournals.org/content/50/4/684.full
> 
> But this is the current science, and later experiments might demonstrate that paper to be not entirely accurate, or accurate but for the wrong reasoning. Only time and controlled reproduction of the experiments will tell. Of course, I don't expect LED panel makers to pay attention to the real science, so we'll continue to see red/blue only grow lighting for a long time, yet.




Thank you for the link. It is a good read, but can we consider 2009 current science 

Also, the conclusion of this paper is not that green is better, it is that additional green is better in the presence of strong white light. I am not saying that green may not be better, simply that this paper has not reached that conclusion.

What the paper indicates is that under strong white light conditions, the amount of blue/red coupled with their relatively shallow absorption results in a saturation of the limits of photosynthesis in those portions of the leaf where blue/red is effective. As green is not absorbed so readily, it can penetrate deeper into the leaf and generate more photosynthesis in areas not saturated by blue/red.


This differs from indoor farming where properly implemented, blue/red should not be at a level beyond saturation, but one has to expect over the whole canopy at least some of it will be. Using monochromatic red/blue would still be effective from an energy standpoint, but supplementing with with green (via phosphor less currently), would allow you to increase the total amount of photosynthesis possible in the plant.

I have to expect that by generating photosynthesis deeper into the leaves, that nutrient transfer would be superior as well?


----------



## DIWdiver (Aug 29, 2014)

LEDPunisher said:


> Apologies if I put this in the wrong thread. My browser is being stupid.



Yes, you quite clearly posted this in the wrong thread. I hope you'll take the opportunity to edit it and remove some of the content. Taken out of context it makes you sound dogmatic and spiteful. We wouldn't want people here getting the wrong idea. So far your conversation with SemiMan here has been both civil and interesting.


----------



## DIWdiver (Aug 29, 2014)

SemiMan said:


> In the second H2OFARM video, it clearly shows RED and BLUE LEDs being used, and yet you in other posts shoot down using RED and BLUE LEDs for plant growth. Keep in mind that video was from 2013, so you can't claim it was really old.
> 
> Actually from the H2OFARM website I found this picture:
> 
> ...



In the video, those look blue to you? I'd swear they were red and GREEN.

There's clearly something wrong with that picture. In the video all the colors (especially fleshtones, which are notoriously hard to get right) look fine, and the whole place has a very white appearance, no purplish tint. Plus, if you listen to the audio, the owner says they grow everything in the dark. The lighting is for the benefit of the people, not the plants.



SemiMan said:


> I am disappointed in the purely overhead canopy light as this has been proven to be not as effective. I don't think you understood my 360 light comment, but my fault for not showing pictures:
> 
> https://encrypted-tbn0.gstatic.com/...jLJyI9vJ_yIeKpB1dOvDC2ILnbTwvH-tHb9WVdFBM_IEZ is an example of more advanced lighting methods to get light into the canopy.



Growing plants a few inches high, there's no point trying to penetrate the canopy, as there is no canopy. The picture you linked is a very different situation. With plants several feet high, there can easily be a canopy which blocks most light from leaves below. By adding illumination below the canopy, you can prevent the lower leaves from becoming dead weight, and keep them contributing to the productivity of the plant. Again, _two completely different situation_s.


----------



## SemiMan (Aug 29, 2014)

Are we looking at the same picture? On my macbook, my big monitor and my phone they all have a very distinctive purple cast. The LEDs definitely don't look green they look blue and red. 

You may want to check your monitor settings and/or screen angle. Something is not right and I know I don't have color issues.


----------



## SemiMan (Aug 29, 2014)

Ledcrusher posted a good link about green with bright white . it had some good data on green absorption. Even with plants that are not tall, the top foliage blocks the bottom. Likely with a wide area light on top you are okay. Often just narrow growing tunnels and mirrored sides works well.


----------



## charlie_r (Aug 30, 2014)

From what you guys have been bantering back and forth about, it seems like the ongoing research into this has a few problems.

With that in mind, perhaps I should use a mixture of reds, greens whites and blues. I'm not sure it will matter that much how close to optimum I get, as this project is for vegetable plant starts, not hydroponics.

I do appreciate the input.

I haven't looked at all the links you have provided, but those I have glanced at look very interesting. Thank you.


----------



## DIWdiver (Aug 30, 2014)

SemiMan said:


> Are we looking at the same picture? On my macbook, my big monitor and my phone they all have a very distinctive purple cast. The LEDs definitely don't look green they look blue and red.
> 
> You may want to check your monitor settings and/or screen angle. Something is not right and I know I don't have color issues.



That picture looks purple to me too. But in the first video link LEDPunisher posted, which is of the same equipment, everything is clearly white with no purple cast. That's why I say something's wrong with the picture, not our displays.

In the latter part of the second video, which is of a different area of the farm, everything does have a purple tint, clearly from the LED lighting. Yet in the views where you can see the LEDs directly, they look red and green to me. I've sometimes wondered if maybe I'm partly colorblind. I've had situations before where I call something green that others say is blue. Perhaps this is just another of those times.


----------



## SemiMan (Aug 30, 2014)

charlie_r said:


> From what you guys have been bantering back and forth about, it seems like the ongoing research into this has a few problems.
> 
> With that in mind, perhaps I should use a mixture of reds, greens whites and blues. I'm not sure it will matter that much how close to optimum I get, as this project is for vegetable plant starts, not hydroponics.
> 
> ...



The white is likely to provide more green than the green. Green LEDs are not very efficient.


----------



## charlie_r (Aug 30, 2014)

I've almost got my driver arrangement for the pool lights finalized, and will be installing them sometime in the next couple of weeks. I'll post a few pics of my hillbilly setup then.

For the grow lights, I'm probably going to go with higher voltage than for the pool, just because it won't be close to standing water. Probably 24 or 36V powering longer strings. I'll start with a mix of whites in one area, and red/blue/white in another just to see if there is much of a difference.

I do have another related question. Once I start the plants, should I leave the lights on 24/7 until they are ready for hardening to outdoors?

Maybe this will help convince SWMBO that I should work on converting all our household lighting to well placed LED sets.


----------



## slebans (Aug 31, 2014)

LEDPunisher said:


> Generally speaking, yes. However, assuming a fairly-balanced ~5150K CCT light, one can do a simple conversion from lumens to PPFD with the magic number 8 (this has been tested to be fairly accurate with everything from my LiCor to FieldScout quantum meter, to within a +/-4% tolerance.)



OK - I'll play.
I always approximate a conversion from lumens to PPFD via the following logic:
Estimate LER value from CCT. For example, most 5000K lamps I have looked at have a LER value range from 300 - 320 lumens per watt. 
Divide the lamp's efficacy by the LER value to derive a wall plug efficiency value(WPE).
Multiply the WPE by the lamp's stated wattage to calculate a PAR value.
Multiply the PAR value by a umoles/m2/s value for this CCT. For 5000K I generally use 4.5.

I will freely admit that dividing the lamp's efficacy by 8 is a much easier method to estimate a PPFD value then to follow the logic I outlined. But I do not like approximations when real world data is available.

First, find an LM-79 report for a 5000K bulb:
https://www.lsgc.com/downloads/dl/file/id/220/fg_01448_ls_br30_65we_cw_120_cb_bx.pdf

Next, derive a PPFD value from an integration of the output at each wavelength. For this first run through, I will use the entire wavelength range of the SPD so that I can show how the numbers add up with the stated values. I will restrict the wavelength range to the accepted PAR range in the next iteration.

IE will does not play nice with the formatting capabilities of this site. It's not going to respect the table spacing I pasted from a spreadsheet - sorry about that but it is only the totals that matter for this example.


Milliwatts	Umoles	Mw
nm	per nm	per watt	PPFD
350	0.118	2.927	0.345
351	0.126	2.935	0.370
352	0.139	2.944	0.409
353	0.136	2.952	0.401
354	0.135	2.960	0.400
355	0.132	2.969	0.392
356	0.133	2.977	0.396
357	0.137	2.985	0.409
358	0.134	2.994	0.401
359	0.131	3.002	0.393
360	0.133	3.010	0.400
361	0.140	3.019	0.423
362	0.137	3.027	0.415
363	0.135	3.036	0.410
364	0.137	3.044	0.417
365	0.141	3.052	0.430
366	0.141	3.061	0.432
367	0.139	3.069	0.427
368	0.145	3.077	0.446
369	0.141	3.086	0.435
370	0.141	3.094	0.436
371	0.143	3.102	0.444
372	0.140	3.111	0.436
373	0.143	3.119	0.446
374	0.144	3.128	0.450
375	0.147	3.136	0.461
376	0.146	3.144	0.459
377	0.151	3.153	0.476
378	0.154	3.161	0.487
379	0.156	3.169	0.494
380	0.164	3.178	0.521
381	0.164	3.186	0.523
382	0.165	3.194	0.527
383	0.165	3.203	0.528
384	0.171	3.211	0.549
385	0.176	3.220	0.567
386	0.182	3.228	0.587
387	0.186	3.236	0.602
388	0.190	3.245	0.616
389	0.196	3.253	0.638
390	0.199	3.261	0.649
391	0.208	3.270	0.680
392	0.212	3.278	0.695
393	0.219	3.286	0.720
394	0.224	3.295	0.738
395	0.234	3.303	0.773
396	0.243	3.312	0.805
397	0.252	3.320	0.837
398	0.262	3.328	0.872
399	0.273	3.337	0.911
400	0.283	3.345	0.947
401	0.295	3.353	0.989
402	0.309	3.362	1.039
403	0.326	3.370	1.099
404	0.348	3.378	1.176
405	0.370	3.387	1.253
406	0.394	3.395	1.338
407	0.423	3.404	1.440
408	0.455	3.412	1.552
409	0.494	3.420	1.690
410	0.536	3.429	1.838
411	0.594	3.437	2.042
412	0.652	3.445	2.246
413	0.728	3.454	2.514
414	0.809	3.462	2.801
415	0.903	3.470	3.134
416	1.010	3.479	3.514
417	1.140	3.487	3.975
418	1.270	3.495	4.439
419	1.440	3.504	5.046
420	1.600	3.512	5.620
421	1.790	3.521	6.302
422	2.010	3.529	7.093
423	2.230	3.537	7.888
424	2.490	3.546	8.829
425	2.780	3.554	9.880
426	3.090	3.562	11.008
427	3.390	3.571	12.105
428	3.760	3.579	13.457
429	4.160	3.587	14.924
430	4.560	3.596	16.397
431	5.000	3.604	18.021
432	5.450	3.613	19.688
433	5.920	3.621	21.436
434	6.450	3.629	23.409
435	6.980	3.638	25.391
436	7.560	3.646	27.564
437	8.110	3.654	29.637
438	8.770	3.663	32.122
439	9.420	3.671	34.582
440	10.200	3.679	37.530
441	11.000	3.688	40.566
442	11.800	3.696	43.615
443	12.700	3.705	47.048
444	13.700	3.713	50.867
445	14.600	3.721	54.331
446	15.500	3.730	57.809
447	16.400	3.738	61.303
448	17.100	3.746	64.063
449	17.700	3.755	66.459
450	18.100	3.763	68.112
451	18.300	3.771	69.017
452	18.200	3.780	68.793
453	17.900	3.788	67.808
454	17.300	3.797	65.680
455	16.600	3.805	63.161
456	15.700	3.813	59.868
457	14.700	3.822	56.178
458	13.800	3.830	52.854
459	12.900	3.838	49.515
460	12.100	3.847	46.545
461	11.400	3.855	43.948
462	10.700	3.863	41.339
463	10.100	3.872	39.105
464	9.670	3.880	37.521
465	9.240	3.889	35.930
466	8.820	3.897	34.371
467	8.450	3.905	32.999
468	8.050	3.914	31.505
469	7.750	3.922	30.395
470	7.380	3.930	29.006
471	7.060	3.939	27.807
472	6.720	3.947	26.524
473	6.430	3.955	25.433
474	6.230	3.964	24.694
475	6.000	3.972	23.833
476	5.810	3.981	23.127
477	5.660	3.989	22.577
478	5.540	3.997	22.145
479	5.470	4.006	21.911
480	5.450	4.014	21.876
481	5.440	4.022	21.881
482	5.430	4.031	21.887
483	5.460	4.039	22.053
484	5.540	4.047	22.423
485	5.580	4.056	22.631
486	5.640	4.064	22.922
487	5.700	4.072	23.213
488	5.820	4.081	23.751
489	5.900	4.089	24.126
490	6.000	4.098	24.585
491	6.150	4.106	25.252
492	6.260	4.114	25.756
493	6.360	4.123	26.220
494	6.480	4.131	26.769
495	6.660	4.139	27.568
496	6.790	4.148	28.163
497	6.920	4.156	28.760
498	7.050	4.164	29.360
499	7.220	4.173	30.128
500	7.360	4.181	30.774
501	7.480	4.190	31.338
502	7.660	4.198	32.156
503	7.780	4.206	32.725
504	7.900	4.215	33.296
505	8.050	4.223	33.995
506	8.170	4.231	34.570
507	8.320	4.240	35.275
508	8.420	4.248	35.769
509	8.510	4.256	36.223
510	8.650	4.265	36.891
511	8.750	4.273	37.390
512	8.820	4.282	37.763
513	8.950	4.290	38.395
514	9.010	4.298	38.727
515	9.100	4.307	39.190
516	9.220	4.315	39.784
517	9.290	4.323	40.164
518	9.390	4.332	40.675
519	9.460	4.340	41.057
520	9.500	4.348	41.310
521	9.620	4.357	41.913
522	9.700	4.365	42.342
523	9.790	4.374	42.817
524	9.850	4.382	43.162
525	9.910	4.390	43.508
526	9.990	4.399	43.942
527	10.100	4.407	44.511
528	10.100	4.415	44.595
529	10.200	4.424	45.122
530	10.300	4.432	45.650
531	10.300	4.440	45.737
532	10.400	4.449	46.268
533	10.500	4.457	46.800
534	10.500	4.466	46.888
535	10.500	4.474	46.976
536	10.600	4.482	47.512
537	10.700	4.491	48.050
538	10.800	4.499	48.589
539	10.800	4.507	48.679
540	10.900	4.516	49.221
541	10.900	4.524	49.312
542	11.000	4.532	49.857
543	11.000	4.541	49.949
544	11.000	4.549	50.041
545	11.100	4.558	50.588
546	11.100	4.566	50.681
547	11.200	4.574	51.231
548	11.200	4.583	51.325
549	11.300	4.591	51.878
550	11.300	4.599	51.972
551	11.300	4.608	52.067
552	11.400	4.616	52.623
553	11.500	4.624	53.181
554	11.500	4.633	53.277
555	11.500	4.641	53.373
556	11.600	4.649	53.934
557	11.600	4.658	54.031
558	11.600	4.666	54.128
559	11.700	4.675	54.693
560	11.700	4.683	54.790
561	11.700	4.691	54.888
562	11.700	4.700	54.986
563	11.800	4.708	55.555
564	11.800	4.716	55.654
565	11.700	4.725	55.280
566	11.800	4.733	55.851
567	11.800	4.741	55.950
568	11.800	4.750	56.048
569	11.800	4.758	56.147
570	11.800	4.767	56.246
571	11.800	4.775	56.344
572	11.800	4.783	56.443
573	11.800	4.792	56.542
574	11.800	4.800	56.640
575	11.800	4.808	56.739
576	11.800	4.817	56.838
577	11.800	4.825	56.936
578	11.800	4.833	57.035
579	11.800	4.842	57.134
580	11.800	4.850	57.232
581	11.800	4.859	57.331
582	11.700	4.867	56.943
583	11.800	4.875	57.528
584	11.800	4.884	57.627
585	11.800	4.892	57.726
586	11.800	4.900	57.824
587	11.700	4.909	57.432
588	11.700	4.917	57.530
589	11.700	4.925	57.628
590	11.700	4.934	57.726
591	11.700	4.942	57.824
592	11.700	4.951	57.921
593	11.600	4.959	57.523
594	11.600	4.967	57.620
595	11.500	4.976	57.220
596	11.500	4.984	57.316
597	11.500	4.992	57.412
598	11.400	5.001	57.008
599	11.400	5.009	57.104
600	11.300	5.017	56.697
601	11.300	5.026	56.792
602	11.200	5.034	56.383
603	11.200	5.043	56.476
604	11.100	5.051	56.065
605	11.100	5.059	56.158
606	11.000	5.068	55.744
607	11.000	5.076	55.836
608	10.900	5.084	55.419
609	10.800	5.093	55.001
610	10.700	5.101	54.581
611	10.700	5.109	54.671
612	10.600	5.118	54.249
613	10.500	5.126	53.825
614	10.500	5.135	53.912
615	10.400	5.143	53.486
616	10.300	5.151	53.058
617	10.200	5.160	52.628
618	10.100	5.168	52.196
619	10.000	5.176	51.763
620	9.930	5.185	51.484
621	9.850	5.193	51.152
622	9.720	5.201	50.558
623	9.640	5.210	50.222
624	9.520	5.218	49.677
625	9.410	5.227	49.181
626	9.310	5.235	48.737
627	9.200	5.243	48.238
628	9.080	5.252	47.684
629	8.990	5.260	47.287
630	8.870	5.268	46.730
631	8.740	5.277	46.118
632	8.620	5.285	45.557
633	8.520	5.293	45.100
634	8.390	5.302	44.482
635	8.270	5.310	43.915
636	8.150	5.318	43.346
637	8.050	5.327	42.881
638	7.920	5.335	42.255
639	7.800	5.344	41.680
640	7.700	5.352	41.210
641	7.570	5.360	40.577
642	7.440	5.369	39.943
643	7.340	5.377	39.467
644	7.220	5.385	38.883
645	7.120	5.394	38.404
646	6.990	5.402	37.761
647	6.870	5.410	37.170
648	6.760	5.419	36.631
649	6.630	5.427	35.982
650	6.530	5.436	35.494
651	6.410	5.444	34.896
652	6.290	5.452	34.295
653	6.160	5.461	33.638
654	6.040	5.469	33.033
655	5.950	5.477	32.590
656	5.830	5.486	31.982
657	5.710	5.494	31.371
658	5.600	5.502	30.814
659	5.480	5.511	30.199
660	5.380	5.519	29.693
661	5.270	5.528	29.130
662	5.160	5.536	28.565
663	5.040	5.544	27.943
664	4.930	5.553	27.375
665	4.830	5.561	26.860
666	4.720	5.569	26.287
667	4.630	5.578	25.825
668	4.530	5.586	25.305
669	4.420	5.594	24.727
670	4.320	5.603	24.204
671	4.220	5.611	23.679
672	4.130	5.620	23.209
673	4.040	5.628	22.737
674	3.950	5.636	22.263
675	3.850	5.645	21.732
676	3.770	5.653	21.312
677	3.670	5.661	20.777
678	3.590	5.670	20.354
679	3.500	5.678	19.873
680	3.430	5.686 19.504
681	3.340	5.695	19.021
682	3.260	5.703	18.592
683	3.170	5.712	18.106
684	3.100	5.720	17.732
685	3.030	5.728	17.357
686	2.950	5.737	16.923
687	2.880	5.745	16.546
688	2.820	5.753	16.224
689	2.740	5.762	15.787
690	2.670	5.770	15.406
691	2.600	5.778	15.024
692	2.540	5.787	14.698
693	2.470	5.795	14.314
694	2.400	5.804	13.928
695	2.340	5.812	13.600
696	2.280	5.820	13.270
697	2.220	5.829	12.939
698	2.160	5.837	12.608
699	2.100	5.845	12.275
700	2.040	5.854	11.942
701	1.990	5.862	11.665
702	1.940	5.870	11.389
703	1.880	5.879	11.052
704	1.830	5.887	10.773
705	1.780	5.895	10.494
706	1.730	5.904	10.214
707	1.680	5.912	9.933
708	1.630	5.921	9.651
709	1.590	5.929	9.427
710	1.550	5.937	9.203
711	1.510	5.946	8.978
712	1.470	5.954	8.752
713	1.430	5.962	8.526
714	1.390	5.971	8.299
715	1.360	5.979	8.132
716	1.320	5.987	7.903
717	1.280	5.996	7.675
718	1.250	6.004	7.505
719	1.220	6.013	7.335
720	1.180	6.021	7.105
721	1.150	6.029	6.934
722	1.120	6.038	6.762
723	1.090	6.046	6.590
724	1.060	6.054	6.418
725	1.030	6.063	6.245
726	0.998	6.071	6.059
727	0.969	6.079	5.891
728	0.942	6.088	5.735
729	0.915	6.096	5.578
730	0.889	6.105	5.427
731	0.864	6.113	5.282
732	0.838	6.121	5.130
733	0.814	6.130	4.990
734	0.789	6.138	4.843
735	0.768	6.146	4.720
736	0.747	6.155	4.598
737	0.726	6.163	4.474
738	0.705	6.171	4.351
739	0.682	6.180	4.215
740	0.663	6.188	4.103
741	0.644	6.197	3.991
742	0.626	6.205	3.884
743	0.608	6.213	3.778
744	0.591	6.222	3.677
745	0.576	6.230	3.588
746	0.560	6.238	3.493
747	0.543	6.247	3.392
748	0.528	6.255	3.303
749	0.513	6.263	3.213
750	0.498	6.272	3.123
751	0.486	6.280	3.052
752	0.472	6.289	2.968
753	0.459	6.297	2.890
754	0.445	6.305	2.806
755	0.432	6.314	2.727
756	0.420	6.322	2.655
757	0.408	6.330	2.583
758	0.397	6.339	2.516
759	0.388	6.347	2.463
760	0.376	6.355	2.390
761	0.364	6.364	2.316
762	0.355	6.372	2.262
763	0.344	6.381	2.195
764	0.335	6.389	2.140
765	0.325	6.397	2.079
766	0.316	6.406	2.024
767	0.306	6.414	1.963
768	0.298	6.422	1.914
769	0.290	6.431	1.865
770	0.282	6.439	1.816
771	0.274	6.447	1.767
772	0.266	6.456	1.717
773	0.258	6.464	1.668
774	0.251	6.473	1.625
775	0.243	6.481	1.575
776	0.237	6.489	1.538
777	0.231	6.498	1.501
778	0.224	6.506	1.457
779	0.219	6.514	1.427
780	0.211	6.523	1.376
781	0.206	6.531	1.345
782	0.200	6.539	1.308
783	0.194	6.548	1.270
784	0.189	6.556	1.239
785	0.184	6.564	1.208
786	0.179	6.573	1.177
787	0.175	6.581	1.152
788	0.170	6.590	1.120
789	0.164	6.598	1.082
790	0.159	6.606	1.050
791	0.156	6.615	1.032
792	0.151	6.623	1.000
793	0.147	6.631	0.975
794	0.144	6.640	0.956
795	0.140	6.648	0.931
796	0.136	6.656	0.905
797	0.132	6.665	0.880
798	0.128	6.673	0.854
799	0.124	6.682	0.829
800	0.122	6.690	0.816
801	0.118	6.698	0.790
802	0.114	6.707	0.765
803	0.112	6.715	0.752
804	0.109	6.723	0.733
805	0.106	6.732	0.714
806	0.103	6.740	0.694
807	0.101	6.748	0.682
808	0.097	6.757	0.655
809	0.095	6.765	0.643
810	0.093	6.774	0.627
811	0.090	6.782	0.608
812	0.089	6.790	0.601
813	0.086	6.799	0.587
814	0.084	6.807	0.573
815	0.082	6.815	0.560
816	0.079	6.824	0.538
817	0.077	6.832	0.523
818	0.075	6.840	0.512
819	0.073	6.849	0.500
820	0.072	6.857	0.492
821	0.070	6.866	0.483
822	0.069	6.874	0.471
823	0.067	6.882	0.459
824	0.065	6.891	0.451
825	0.063	6.899	0.432
826	0.061	6.907	0.423
827	0.060	6.916	0.413
828	0.058	6.924	0.402
829	0.057	6.932	0.397
830	0.057	6.941	0.396
831	0.054	6.949	0.377
832	0.054	6.958	0.374
833	0.052	6.966	0.363
834	0.051	6.974	0.354
835	0.049	6.983	0.345
836	0.048	6.991	0.338
837	0.047	6.999	0.330
838	0.046	7.008	0.323
839	0.045	7.016	0.313
840	0.044	7.024	0.310
841	0.043	7.033	0.305
842	0.042	7.041	0.294
843	0.040	7.050	0.284
844	0.040	7.058	0.279
845	0.039	7.066	0.276
846	0.038	7.075	0.272
847	0.037	7.083	0.264
848	0.037	7.091	0.265
849	0.035	7.100	0.248
850	0.035	7.108	0.248

Radiant Flux	2510.075 Mw PPFD	11617.972
Mw/Watt 1000.000 Mw/Watt	1000.000
Watts 2.510 PPFD 11.618


Using the data in the LM-79 report we can verify the SPD data and the PPFD calculation in the table above.

Watts In	8.802
Radiant Flux Out 2.510
WPE	0.285
L/W	86.600
LER	303.687
Est Umole/watt	4.500
Est PPFD	11.295
Actual PPFD	11.618
Actual Umole/watt	4.629


As I mentioned earlier, we will now perform a second iteration and restrict the radiant flux to the PAR wavelength range of 400 - 700 nm.

Watts In	8.802
Radiant Flux Out 2.431
WPE	0.276 
L/W	86.600*
LER	303.687*
Est Umole/watt	4.500
Est PPFD	11.295
Actual PPFD	11.157
Actual Umole/watt	4.590

LEDPun Est 86.6/8	10.825
Diff %	0.031(3.1%)

*
The L/W and LER values are not accurate because I would have to subtract the lumens from the original wavelength range - I don't feel like performing that integration right now as it is not critical to this specific explanation. 

In summary, we can see that dividing the lamp's efficacy by 8 does produce an viable approximation of PPFD.

To relate the previous info to a real world example we must consider a few more factors.

1) PPFD readings taken outdoors under direct sunlight are generally accurate for the entire square meter that PPFD reading refers to. In other words, you are taking a spot reading and can apply the results to the entire square meter area. That logic does NOT hold true when taking a PPFD reading indoors under 100% artificial light. 
In fact, it is one of my pet peeves when I see a very high PPFD specification for a LED grow lamp. The majority of these fixtures use lenses/diffusers of some type - and take a spot PPFD reading directly under the focus of said lens. This produces a hyper-inflated value that is nowhere near accurate.

2) Inverse square law. LED grow light specification PPFD values generally do not specify the distance of the sensor from the fixture during the spot reading. A PPFD value - without knowledge of the distance of the sensor from the fixture - is basically useless.

Let's build a practical example based on the LED bulb profiled earlier. I generally work directly with the PAR radiant Flux values but for purposes of clarity we will stick with PPFD values.

We desire a PPFD reading of 600.
We will assume that 100% of the bulb's output falls within our 1 square meter area.
Each 8.802 watt bulb yields a PPFD of 11.157
600/11.157 = 53.777

We would require 53.777 bulbs over our 1 square meter area to yield a PPFD value of 600. 
But we are still lacking accuracy because the above logic assumes the plant's leaves are all touching the fixture(inverse square law) and that the bulb's output is homogenous in nature. 

Just my $.02 on a Sunday afternoon.


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