Calling out to Weezard for LED advice

[Weezard]

Aloha Kyberkitsune

Excellent posts!
Kudos, Bro'!:thumbsup:

And Mahalo nui.
"you must spread..."

Weezard

[RackitMan]

Years back people were discussing the idea of pulsing LEDs. The theory was that plants need so many milliseconds to chemically process photonic energy, so a continuous light source is a waste of energy. LEDs are the only current light source with fast enough switching times to take advantage by this fact.

Some estimates were that power savings might be in the 70-90% range if done properly. Can't be very difficult technically. Any experimenters/theorists here know why this idea has not caught on?

Anyone tried it?

[RackitMan]

I vegged 4 plants in a 2' * 2' area with soley a 50w blue LED panel (0.5w 10mm 560nm? LEDS) with great results. No white, no red.

[khyberkitsune]

Years back people were discussing the idea of pulsing LEDs. The theory was that plants need so many milliseconds to chemically process photonic energy, so a continuous light source is a waste of energy. LEDs are the only current light source with fast enough switching times to take advantage by this fact.

Some estimates were that power savings might be in the 70-90% range if done properly. Can't be very difficult technically. Any experimenters/theorists here know why this idea has not caught on?

Anyone tried it?

I'm working on a pulsing unit that will take 1w Units, pump 3w through them, maintain a low thermal profile and even maintain the long life of the LED. Current tests are giving promising results (not in growing, just pulsing the diodes and watching to see how they respond,) and it looks like we might be able to offer high-powered solutions at a much cheaper cost than the competition.

[RackitMan]

What is the theoretically optimal on/off time period?

Does overdriving the 1w LEDs to 3w increase the light output roughly 3 times?

[khyberkitsune]

What is the theoretically optimal on/off time period?

Does overdriving the 1w LEDs to 3w increase the light output roughly 3 times?

Depends on the duty cycle used. We're playing with 10% duty cycle right now.

As for putting out 3 times as much light, sadly no, the best we're getting is about 2.3x. There's always a ROI wall that you hit, and it's all in the materials used for the construction of the diode.

[williston]

found this info awhile back...think it came from knna.

PWM is of course a choice to dimming LEDs, but in general, direct dimming, meaning using a lower current level is way more efficient, at least from a energy efficiency standpoint.
Here we need to take a second, and think this question carefully.
First off, PMW refers to a way of dimming electronic devices by switching on/off very fast. The effect on the output of the circuit depends of its topology. It may produce a reduced continous current, or switching on/off LEDs aswell.
On many commercial drivers, dimming is achieved by a PWM signal, but the output to LEDs is continous, not switched.
A true PMW driver that gives the output to LEDs switched aswell, may be carefully designed to avoid transients. The highest the frecuency used, more problematic becomes the design. When using very high switching frecuencies, with individual pulses on the nanoseconds or still shorter durations (hundred of picoseconds), not all electronic components are able to handle it. Rise and fall time responses of components used must me considered.
In general the shorter PWM pulses used are in the range of microseconds. Response time of most LEDs are of a few nanoseconds. Going shorter is impossible with standard equipment.
As reference to those not used to the metric system, those prefix are diminutives:
mili: 1/1000. or 10^-3
micro: 1/1000000 or 10^-6
nano: 1/1000000000 or 10^-9
pico: 1/1000000000000 or 10^-12
Second consideretion, that refers to the nergy efficiency of the system. A LED is always less efficient as the current level goes up. So PWM is always less efficient electrically. Thus, any photosynthetic gain from the pulsed light might should compensate the lower efficiency emitting light.
The highest the peak current used, for the shorter pulses, the lower the efficiency.
Most experiments with pulsed light on plants are performed in the range of hundred of microseconds, up to a few miliseconds.
In this sense, what matter is the averaged voltage and current over a second period.
Say you are using a 50% PMW scheme: half time on, half time off. During that time you use half the current than if you were using continous. For example, 1A on continous mode equals to 2A peak current with a 50% PWM scheme (at least, it happen with relatively long pulses, as they go shorter, raise and fall time of the components may vary the average). From a current standpoint, both ways are the same. But not if you see at voltage, because voltage required to run LEDs at 2A is higher than to run them at 1A. Thus the average power burned is going to be slighty higher over a second period on the PWM scheme (how much? check datasheet for how much higher is Vf at 2A than at 1A).
Not only that, the LED not emits double light at 2A than at 1A, but way less. So the PWM scheme burns more power and emits less light. The highest the difference between the current used (thus, the higher the PWM frecuency used), the highest the efficiency loss.
Still when using relatively long pulses, a loss of 25% of energy efficiency is pretty common. Any photosynthetic gain from pulsing might be over 25% to worth doing it.
For sure. Always take in mind that voltage-current response curve of LEDs is exponential. Little increases on voltage leads to huge increments on current. What destroy LEDs is excess current. A peak current over specs result on the breakage of the very thin gold wires inside the LEDs, that act as a fuse. Often there is a wide margin for it, as many LEDs rated for 1A may support currents over 2A, and those rated to 2A often support 3A and more, but once you are over specs, you never know when its going to fail.
Notice that the study focused on the different ways of giving light to plants, for given amount of light. Its not interested on study how efficiently is that light delivered, that is an important part of the equation on actual applications.
And notice that when used 2ms pulses, photosynthesis for equal amount of light reduced to half. Why messing with pulsing then?
Aditionally, light densities used, 50 uE/m2 are very low in actual conditions. We use densities 10X of that on our grows (and same for tomato grows).
The study used a PWM scheme 150us long (148.5 off/1.5on), a 1% PWM (1%on/99%off). As a second has 1000000 us, 1000000/150=6666 cycles per second= 6666Hz= 6.67KHz was the frecuency used.
micro=μ. But for keiboard confort, u is often used instead of μ. So a microsecond is written us instead of μs, and a microEinstein, uE instead of μE (a Einstein is a mol of photons, 6.02 *10^23 photons).
pico is 1/1000 of micro.
I have linked a thread about it on my sign. But for doing it, lm emission (way better, mW emission) must be know accurately, aswell as the spectrum. With unkown bins, its impossible to know it.
Glad to find people who likes to experiement. Sure your experience is going to be usefull for all us.
:Peace: knna

[khyberkitsune]

Good info. It is important to note that the actual construction of the substrate itself, besides the gold microfilaments. Typically it is some indium-gallium alloy on a sapphire substrate (one reason LEDs are so expensive) and those do not overdrive very well, also the material design just doesn't lend itself well to higher emissions at higher current and voltage ramps, you end up with more heat loss than photon output. The key for making PWM viable in any sort is to find a diode alloy that lends itself well to overdriving (I would think a harder alloy would tolerate higher temps better - indium and gallium are very soft metals,) and without losing much to heat as you overdrive the bulb. This is probably a few years away.

Also, it is important to know which waveform you are using to overdrive - sine, square, triangle, saw, all will affect how the duty cycle performs.

[thepaan]

I checked with NASA records to check the insolation levels recorded at the edge of the atmosphere... I noticed... blue was in the lead... So
I figured a 60:40 blue:red mix for vegetation

Are you growing space-weed? What does the solar radiation at the edge ofthe atmosphere have to do with anything? I don't think the relative intensities of different wavelengths of sunlight have anything to do with it either. As green and yellow are also more dominant wavelengths than red your logic suggests you should add lots of those to your LED array. Let me know how that works out.

I'm very confused as to how you managed to infer what you just stated from my post.

Does that make it clear? I mean, you wrote it - not I. Maybe you meant something else by all that....

http://www.emc.maricopa.edu/faculty/...BK/pigment.gif - something from an educational facility. http://3.bp.blogspot.com/_pFQ0wrHWd1...pectrum_en.jpg - there's another.

I'm not sure you know what you are looking at. The first image is the relative absorption by wavelength of different pigments in solution (that means in a test tube in a laboratory). It really doesn't show how well a living plant uses each wavelength. Why did you pick one that includes pigments found only in algae? Lets try not to present irrelevant information - people might be mislead. The pigments of note there are chlorophyll a and b. They absorb blue light but it doesn't drive photosynthesis efficiently because they have to down-shift (for lack of a better descriptive word) the energy level in order to transfer it to the P680 and P700 dimers (remember, a lower wavelength has higher energy) which are the cores of photosystem II and I, respectively. On top of that, virtually every other pigment (reference here QUANTITATIVE ABSORPTION SPECTRA OF THE COMMON CAROTENOIDS -- Miller 9 (3): 693 -- PLANT PHYSIOLOGY and here THE PREPARATION AND ABSORPTION SPECTRA OF FIVE PURE CAROTENOID PIGMENTS -- Zscheile et al. 17 (3): 331 -- PLANT PHYSIOLOGY) in a plant also absorbs in the blue range and their energy is not always transferred to the dimers or suffers from the same requirement for down-shifting the energy. Furthermore, there is some loss involved when transferring energy from one pigment to another which accounts for even more inefficiency. The second image is a crappy representation of PAR, it is just wrong in so many ways.

Counterpoint: I present this document. I realize it isn't an actual study but I can't find a copy of the one they cite as the source of the data. http://envsupport.licor.com/docs/TechNote126.pdf Figure 1a shows leaf absorption spectra. Compare to your second absorption image and to the absorption spectra on page 4 of this study The Photosynthetic Action Spectrum of the Bean Plant -- Balegh and Biddulph 46 (1): 1 -- PLANT PHYSIOLOGY and notice how 6 different species of plants represented on page 6 (labeled page 375) in this study Absorption Spectra of Leaves. I. The Visible Spectrum -- Moss and Loomis 27 (2): 370 -- PLANT PHYSIOLOGY. Furthermore, in that last study, notice how on page 10 and beyond they show that as you destroy the leaf the absorption characteristics change to show the absorption of the base components - such that the absorption begins to look more and more like your first image the more desiccated the leaves become. I cannot make this clear enough; absorption is not a measure of response.

Figure 1b shows action relative to incident energy. Remember, different wavelengths of light have different energy? When you weight the amount of photosynthesis that occurs (measured from the amount of oxygen produced) by the energy of each wavelength you get something that shows how low-energy waves (670-680 nm) elicit a greater response than the high energy waves of 450 nm. Compare to page 3 of this study Photosynthetic Action Spectra of Trees: I. Comparative Photosynthetic Action Spectra of One Deciduous and Four Coniferous Tree Species as Related to Photorespiration and Pigment Complements -- Clark and Lister 55 (2): 401 -- PLANT PHYSIOLOGY showing the relative rate of photosynthesis of 5 different trees. Notice how all 5 of them produce oxygen at a high rate in the red but somewhere between a lowered rate and a negative rate in the blue. That's correct: a negative rate. The Blue Spruce actually stops photosynthesizing and begins photorespiration under exclusive blue light instead of photosynthesis.

Figure 1c shows action relative to quantum absorbed. "Quantum" in this case is the number of light particles absorbed (light is both a particle and a wave). Higher-energy wavelengths need fewer particles to have the same intensity. The higher-energy 450 nm light gets an advantage in this one and yet, it is still only 70-80% as efficient as 640 nm light. Compare again to the action spectra on page 4 of this study The Photosynthetic Action Spectrum of the Bean Plant -- Balegh and Biddulph 46 (1): 1 -- PLANT PHYSIOLOGY.

What we gather from all this is first, all plants have a similar response to all wavelengths. Second, this response is maximal in the red - specifically red peaks which correspond to chlorophyll a and b. When measuring by energy, which is what the output of LEDs is given in, (as opposed to quanta) of light, blue is only half as efficient as red. From this we can deduce that the most efficient way to cause a plant to produce oxygen, which is the measure of the rate of photosynthesis or the rate of response, is by exposure to red light corresponding to the red peaks of chlorophyll.

Depends on the plant being studied - not every plant responds the same - every species has vastly different requirements. For example Tradescantia pallida actually thrives under yellow and green light, which is why it does so well on the forest floor and in well-shaded areas. If you have the materials to conduct a colorimetric analysis, you will see that against a blackbody emitter, a tube filled with chlorophyll actually allows more red light to pass through than blue light. Actually, you can do this with a light bulb and a test tube full of centrifuged chlorophyll - put the light next to your head, hold tube in front of your face - the tube appears to be filled with green fluid. Put the tube between your face and the light, you see mostly red.

See above. It is true that not all plants respond the same but all plants respond similarly. This includes your tradescantia pallida which Floridata: Tradescantia pallida. It does well on a forest floor because it tolerates that type of light (not to be confused with requiring it). The color, which is from the excessive anthocyanin (another accessory pigment and the giveaway that I was recently burning my Jalapenos) allows it to thrive better in (again, does not require) the shade - absorbing wavelengths that most plants don't block (reference here for absorption and compare to transmission of a leaf on page 2 of this study Far-Red Light Reflection from Green Leaves and Effects on Phytochrome-Mediated Assimilate Partitioning under Field Conditions -- Kasperbauer 85 (2): 350 -- PLANT PHYSIOLOGY). While the pigment does absorb strongly in the yellow region, just like any other accessory pigment, it suffers from a requirement to down-shift the energy in order to pass it to a photosystem dimer and move electrons. This makes it still less efficient than stimulating chlorophyll directly, which all plants contain. As for your colorimetric analysis - we are back to confusing absorption for response.

Red is required for photomorphogenesis, root development, and for vegetative growth. Blue is for control of certain day-night reactions, seasonal identification, and most importantly, for actual plant growth and bulk. This is why CMH and MH are the recommended primary HID light source by large commercial-scale horticultural operations, and not HPS.

Physiological and morphological responses = control of certain day-night reactions and seasonal identification so at least we agree on something. However, you are dead wrong on plant growth. Plant bulk is directly related to how much photosynthesis takes place and, as I showed it to be true above, that rate is much higher for a given amount of red light. Show me some evidence and I'll consider changing my stance. Metal Halide lamps are recommended for the amount of light they give off. The spectral content is leveraged only as a marketing ploy to discredit High Pressure Sodium lamps. And, it may be true that MH is better than HPS but at that point we are talking about blue light compared to orange light.

Those NASA-conducted studies are old, and they recanted half of them, their new panel design has 33% blue, 67% red.

The only lighting panel designed for NASA growing chambers that I have ever seen is here WCSAR - Advanced Astroculture and has blue LEDs delivering maximum light just under 20% of the red maximum intensity. If you have something newer, then it better be newer than 2006.

That again depends on the species of plant - The phytochrome can also respond to the ratio of red versus blue and the intensity of both wavelengths in order to determine seasonal changes.No, it will not eventually flower without regard to light color or duration unless you're growing a Ruderalis. How do you think we keep mother plants for decades?

Phytochrome definately can not detect ratio of red to blue. If it can, then where is this third form of it which you have discovered? Are you going to call it Pb (phytochrome blue) to keep with the nomenclature for Pr (phytochrome red) and Pfr (phytochrome far red)? It is true that flowering is not limited to the phytochrome response and phytochrome responses are not limited to flowering. But then, I never said that it was. Let us keep in mind here that we are only talking about one species.

It appears cannabis is either a short day obligate, short day facultative, or day-neutral. So, you may be correct in some cases but the point is flowering related to light exposure is caused by the length of the dark period and not the ratio of blue to red. In the case of non-obligate strains it will eventually flower on its own regardless of light quality.

Chapter 1, page 3 : here Marijuana Botany: Propagation and ... - Google Books "Cannabis flowers when exposed to a critical day length which varies with the strain. Most strains have an absolute requirement and less than this will result in the formation of unformed flowers only." (obligate) published in 1981.

Cannabis sativa is a SDP facultative http://www.lhup.edu/smarvel/biol206/...phogenesis.doc

Wikipedia lists cannabis as short-day facultative but take that with a grain of salt....

More on plant flowering: floinduc

I think you have the misconception. I do this across the globe and don't get paid to be wrong. If I was wrong and selling a bad product, I'd have been sued already.

There are many ways to make money with a mediocre or even bad product. That you say you are successful is more of a tribute to your ability to make a sale and less of a sign of a quality product. Haven't you ever heard of magic beans?

I knew I should have saved that picture or site link

How convenient.

[McLuvin]

Sorry I know this is off topic but "DreadedHermie" I love your avatar man!

I do know about LED's and work with the technology but your question is a little too deep for me to try and answer.