Advanced LED Development Thread.

[DeadlyFoez]

OK, when I say a 400 watt LED system, I am saying as I would be using 400 one watt LED's. Now when you factr in PWM with a duty cycle of as low as %0.5 then then energy savings is incredible. But I will also be overdriving the LED's too.

So I've done some quick math and with a 400 watt LED system as I described (400 one watters), it would compete if not surpass the equivilant of two 1,000 watt HPS lights. But once i factor in PWM and overdriving the system would consume about 35 watts of electricity and be better than the HPS's.

The overdriving is the best factor of all because I makes the light penetrate further past the canopy so the light is effective in longer distances.

But, seriously, just about 35 watts of electricity. That would be awesome.

 

[NiteTiger]

Gotcha. So the electrical savings are based on the PWM. What I thought, just wanted to make sure :smile:

 

[knna]

Gotcha. So the electrical savings are based on the PWM. What I thought, just wanted to make sure :smile:

Not, electrical savings on using LEDs not depend of PWM. Its just another hypothetical way of obtain electric savings. As the electric savings involved are large, it worth experimenting deeper in this topic, but in fact until now nobody has been capable of prove it enhances photosynthesis efficiency.

Its all about time dinamics of photosyntetic systems. Its proved in lab that a photosynthetic antenna reflect any photon reaching it while processing a photon. But it take just some femtoseconds, too little gap to take advantage of it. The whole process of processing a H2O molecule with CO2 powered by ATP from photosyntesis take about 20 miliseconds. The question still botanics still try to determine is when in real conditions, a photosyntetic antenna can process a new photon, and although its still unquantified, its a very fast process, because one the antenna excites a electron from an intermediate molecula participating in the photosyntetic process, it seems ready to take another photon. Photosyntetic systems (PS) have a large pool of this intermediate moleculas, so experiments trying to get advantage of PWM had failed. But results depends strongly of the PWM used, from a slight enhanced photosyntesis to large losses in quantum efficiency of absorbed photons.

PWM has the potential advantage of reducing reflected photons, but this advantage is little: while HPS light is reflected in about 20-25% (depending of plant specie, but most of them are about this range), a combination of 660nm peaked LED photons (90%) and 470nm blue photons (10%) reflect just between 10-15% of photons, the potential savings of PWM are little.

The larger photosyntetic losses happen due to a imbalance between PSI and PSII and thermal problems leading to some molecules etiolation. Reducing internal leaf heat by reducing IR and a balanced spectrum allowing to a very well balanced PSI and PSII, aswell as keeping internal CO2 concentration very high (both by high ambient CO2 concentration and light stimulation to keep stomata open at optimun levels) have the potential of enhancing photosyntesis strongly, reducing respiration requeriments and increasing the RUE (radiation Use Eficiency).

As the light density increases, this three factors contribute to the disminishing returns of adicional light over the max photosynthetic point, until the level of saturation point is reached (when aditional light dont report aditional photosyntesis), and photodamage effect beyond that.

Dialing LED lighting to reduce this three factors affecting RUE potentially will lead to large electric savings. But the road to get it dialed is for sure very long.

If we refer to the ways that currently offer electrical savings by LEDs, they resume in three:

-More light avalaible.

-LED's dont need reflectors to direct the light where we want. LED's dont emit IR and dissipated little heat, allowing to put them very close to plants.

While HIDs avalaible light is far lower than light emited by the bulb:

-HID emits large quantities of radiant heat, wich apart of heating leaves, reducing quantum efficiency, and run very hot itselves, wich obligue to keep them far from plants, with large light losses.

-HID require reflectors wich reduces avalaible light by 25% in average. Best of the best reflectors block a minimum of 15% of the emited light.

-HID often require the use of cooltubes to control heat, wich blocks from 15 to 25% of the light emited (25% for colltubes for high watage HID, wich are the more efficients, so using thin glasses obligue to use low watage HID, so the light saved by using a thin glass is lost at bulb's reduced efficiency)

-HID produce a very uneven lighting. Although it depends of the reflector use, often they produced a small area with very high light density, thus reduced photosyntetic efficiency in this area, and suboptimum light levels at the edges of the grow space. The overall effect is a reduced average RUE.

Just this factors count for a strongly reduced avalaible output, up to 50% in reflectoriced cooltubes, and very often losses of 35% of the light emited by the bulb.

-Spectrum with better photosyntetic action

LEDs achieve this by two ways: the first is emiting in wavelenghts wich are best absorbed by plants, and the second is this wavelenghts are capable of producing more photosyntesis.

This advantage is often very overstimated for much people working with LEDs, as the plant's PAR use is very flat (just 2x from max in the red side to min in the green side), but anyway, it offers the possibility of obtaining the same photosyntesis using less photons. HID arnt bad in this, specially HPSs, so just up to 25% less photons may be used, probably just between 15 to 20% less photons, but anyway is a very nice improvement.

-Higher energy efficiency

Here is where are the larger electric savings.

250w HPSs and most HM converts into light in PAR about 33% of imput energy. High wattage HPS reach near 40% (best of the best), but in average converts 36-38% of imput light.

LED's energy efficiency are very variable, and not any LED allow to achieve electric savings over HIDs. But LEDs perfomance is improving really fast.

Last models of GaN chips achive energy efficiencies about 40%, and mayor improvements are expected in next years. Aditionally, most of LED's growing lighting is provided by red LEDs, from 80 to 90% of photons, and red LEDs emits more photons per watt of light emited, due to its longer wl, compared to HIDs.

Adding this three advantages, its possible currently using last model LED's achieve energy savings from 40 to 60%. But of course price is still a concern, although prices are dropping, so taking into account the electric savings, not only at lighting itself, but in associated costs (ventilation, AC), LEDs will be a cost effective alternative to HIDs in few years, maybe just one of two.

Currently LEDs are now a cost effective altenative to small grows and specially, stealth grows. Due to this small grows use less efficient HIDs or CFLs (less efficients yet) and heat often beeing the mayor problem. Aditionally, HID cost isnt linear, as a 100w HPS cost just a bit less than a 400w, while 400w of leds cost 4x more than 100w, so when considering small setups, LED alternative is now worth considering it.

 

[alphacat]

This subject's totally fascinated me since hearing of it and it seems fairly obvious that while it has a ton of potential - to the point of arguably being the future of lighting - if NASA still doesn't have it dialed in 100%, and there are no large commercial outfits making these for the consumer market... this is still largely in the realm of the dedicated and hardcore solder-sniffers.

Still, I'd give my left nut (figuratively of course) for a 2' or 3' tall by 6 or 8" wide LED column already wired w/ driver and the right diodes!

 

[DeadlyFoez]

I'm working on it. I'm willing to make arrays for people if they're willing to pay. PM me if your interested

 

[sy9942]

Well, I have read one or two cached threads, to which some people have linked here (and other forums). So first of all I'd like to apologize if all (or most) my questions have already been answered.


Sorry, but for me, all this is so far hypothesis. How do you know that each receptor is able to process only one photon at a certain time? Does this receptor needs to be dis-energized (sorry, english is not my native language and it's already late) to convert photons into a chemical energy? (Or can it do so constantly, recieving steady stream of photons?)

X photons in a Y period of time ? (It's been long since I took any physics lectures and I have really bad memory so please dont laugh)




Please, show me such LED
LED's efficenty drops drastically when overdriving. It's not linear progression comparing input and output power of LED, it's more like geometrical - output power is "infinitely" (well, actually until it breaks ) closing up to a certain limit when you increase input power in linear.


Thank you for taking time, I'm looking forward for some more answers

I have somewhat overstated the efficiency of commercially available LEDs, however there are things being done in the lab to improve the efficiency of LEDs under high-current operation. Current crowding is currently one of the bigger issues involved, which can be mitigated in a variety of ways. Only really useful if you're into prototyping at a pretty hard-core level, though, and you have a lot of money to burn on what amounts to a science experiment.

Google for "flashing light photosynthesis" for more information about photosynthesis under intermittent lighting conditions. It was shown in very old experiments that plants grown under light at full intensity but a 50% duty cycle (I forget what frequency) showed identical growth (to within a few percent of leaf dry weight) to plants grown under light at full intensity at 100% duty cycle. This is a very, very old experiment however, from the middle of the last century. More-recent experiments have shown that "Tennessen et al.,(1994b), have observed that photosynthetic rates of tomato leaves were equivalent when the light was provided as a pulse of 5000 μmol.m-2.s-1 when on 1 % of the time (1.5 μs on and 148.5 μ s off) compared with a continuous photon flux of 50 μmol.m-2.s-1 (Figure 8)." (from here)

I'm pretty busy these days, I don't have much time to post to the forums or interact, although I have been keeping tabs on david zap's current efforts on uk420. I am currently finishing up a research project which will hopefully bear fruit in the form of a high-power LED grow.

 

[minimum]

1.5 μs on and 148.5 μ s off

That means at least/about 1MHz duty cycle, right? That's not so easy to accomplish for driver's side.
By the way, datasheet of luxeon claims 100ns or less switching speed (thats 0,1 μs) so you'll have limits approaching from this side as well.

Anyway, thanks for insight, I'll look forward for you research.

 

[knna]

Almost all experiments performed with duty cycles concludes that overal growth has a direct and strong correlation with total irradiance, independent of the way its given.

I believe i linked the study about PWM phostosynthetic efficiency here, but maybe i did it here.

It shows pulses between 50-100us dont report photosyntetic losses, although dont provide noticiable improvements either. High intensity pulses lengthening over 200us may produce significant losses. Notice it refers to absorbed photons, not irradiance. Pulsed light is expected to increase photons absorbance, not quantum yield per se. But with a photon absorbance of 89% for a mix 660nm peak wl leds (90% of photons) and 470nm blue leds (10%) (data from "Poster_shayela_final" (NASA, currently not avalaible, performed on wheat), the absortion improvement may be 11% max.

I agree with minimun in the difficulty of such short duty cycles on the driver side.

What can improve largelly photosynthetic efficiency is using side lighting, wich is the way NASA is working currently:

"Light-emitting diodes, LEDs, are a comparatively new
light source for plant growth and are being actively
investigated for numerous applications. Every week new
articles appear in the popular press about advances in
LED technology and the potential of this solid-state light
source for automotive and home lighting, computing,
public works light sources, etc. Red LEDs originally had
15-18% efficiency, but now are up to almost 22%,
whereas blue LEDs were only 3-4% efficient and are now
at 11%. This increase in efficiency makes LEDs
competitive with other sources for plant-growth lighting
(Tennessen and Ciolkosz, 1998; M. Bourget, 2005 Pers.
Comm.). Another important advance in LED research is
the commercial availability of “chip-on-board” LED light
engines. Unlike discrete LEDs with plastic lenses, these
light engines are small printed-circuit wafers that pack
large numbers of small LEDs of selectable emission
colors into close proximity. For example, the ORBITEC
light engine can array 132 LEDs of five colors in a 6.25
cm2 square (Massa et al., 2005a). This allows for
unprecedented color blending and very bright light levels.
LED emissions are current-controlled, and the light output
is directly proportional to input current within their
operating range, so unlike other types of dimming
systems for lighting, dimming of LEDs directly reduces
power usage. LEDs have solid-state construction, are
extremely durable, and resistant to shock. Transparent
coatings on the chips protect them against high humidity
and allow for cleaning without reducing light levels. LED
chips, like discrete LEDs, have low mass and volume.
LEDs generally emit light in a narrow region of the color
spectrum. The number of available colors is extremely
large, with one of the most efficient being red LEDs
emitting at 640 nm, where light has a relative quantum
efficiency for photosynthesis of ~96% (Sager and
McFarlane, 1997). Experimentation has demonstrated
that different species can be grown successfully under
LEDs, including spinach (Goins and Yorio, 2000), lettuce
(Goins et al., 2001; Kim et al., 2004), radish (Goins et al.,
2001), wheat (Goins et al., 1997), and micropropagated
potato plantlets (Miyashuta et al., 1995). Generally, about
15% blue light is required for normal growth, and yields
have been achieved that are comparable to growth under
white light (Yorio et al., 1998). Research has
demonstrated that green light also can have beneficial
effects for growth and plant assessment, especially within
dense foliar canopies (Kim et al., 2004; 2005)."

(This article is from August 2006, in the last quarter of 2006 was an important efficiency step forward from both red and blue leds, but specially for the blue ones: the CREE blue dies achieve 27%eff in easily avalaible products and surpass 30% on premium ones, while the Osram thin film red dies achieve from 27% (normal bins) up to 40% (premium bins). I believe this leap is what we are waiting from long time ago, allowing to do cost effective LED growing lights. Of course there will be future improvements, but the level reached now is enough to start LED growing.

"INTRACANOPY LIGHTING FOR CROP GROWTH
Intracanopy (IC) lighting aims to improve lighting
efficiency by providing light distribution throughout the
canopy of a crop. In planophile crops, where leaves
present themselves perpendicular to overhead light and
eventually close off their inner canopy to light, mutual
shading of lower leaves by those above leads to net
carbon loss via respiration, premature leaf drop, and often
flower bud and fruit abortion inside the canopy (Ohler et
al., 1996). Thus, unshaded top and side leaves end up doing all photosynthetic work for the entire crop stand. If
the light sources could instead irradiate from within the
canopy, a much greater percentage of available leaf
surface could be utilized for photosynthetic work. This
should increase biomass output per energy input
efficiency. Additionally, light intensity drops off
exponentially from a point irradiation source according to
the inverse square law, where
I = E / d 2
with I being the irradiation on a surface at a distance d
from the light source emitting radiant energy E (Bickford
and Dunn, 1972). Thus, light levels drop off rapidly with
increasing increments of distance between lamp and plant,
so that with the necessary separation of hot light sources
above a crop stand the amount of light incident upon the
leaves is highly attenuated, further requiring that the hot
source be high-emitting and high power. If a much cooler
light source can be maintained in close proximity to or
even touching leaves, more light will be available at leaf
level for lower power cost. This will lead to a greater
energy-use efficiency of the biomass-production system.
IC lighting has been previously examined, either as a
supplement to traditional overhead lighting, or as a sole
lighting source. Stasiak and colleagues tested soybean
grown under microwave lamps and supplemented with
side-mounted lighting that was piped into the canopy via
glass tubes lined with optical lighting film to levels of at
least 150 μmol m-2 s-1 PAR at 100 mm from the tube
surface. When overhead light of 400-1200 μmol m-2 s-1
PAR was supplemented with inner canopy lighting,
productivity increased 23-87% (Stasiak et el., 1998).
Also, Tibbitts and Wheeler found that using fluorescent
side lights or MH light pipes with overhead-lighted potato
crops gave increases in tuber dry weights of 12-16%
(Tibbitts et al., 1994b). Sideward lighting systems for
production of plants from cuttings was developed to
reduce the vertical PAR gradient found in overheadlighted
propagation chambers (Hayashi et al., 1992; Kozai
et al.,1992). One system used fluorescent lamps and it
was demonstrated that sideward lighting reduced the
electricity cost per potato plantlet produced from cuttings
(Hayashi et al., 1992). Fluorescent lamps, however, take
up a large volume of space, and they release heat that then
has to be removed. To counteract these issues, Kozai and
others (1992) used diffusive optical fibers as a light
source for side lighting. This allows plant containers to
be stacked, and also allows placement of containers near
the light source, thereby increasing the efficiency of light
capture and the vigor of biomass accumulation by
plantlets (Kozai et al, 1992).
If low-intensity IC lighting is used as a sole source of
PAR starting from the seedling stage, Frantz and others
demonstrated that expanding cowpea leaves adapted
physiologically to become shade leaves, with lower lightsaturation
levels and light-compensation points than
plants lit with more intense light from above (Frantz et al.,
1998). They used short, 15-watt fluorescent tubes suspended within the crop canopy by monofilament and
surrounded by transparent Mylar sleeves to prevent leaf
scorch (Frantz et al. 1998; 2000; 2001). With IC lighting
as a sole source, they found twice as much edible biomass
production per unit energy input as in overhead-lit
canopies (Frantz et al., 2000). The two lighting
architectures combined, however, did not increase overall
yield relative to input wattage, probably because the
fixed-position overhead lights were underutilized until the
plants grew to sufficient height (Frantz et al., 2000).
Frantz and colleagues demonstrated that increasing lamp
number within the canopy by 38% raised stand
productivity by 45%, and that the highest energy-use
efficiencies could be obtained by switching lights on
higher up in a canopy as the plants increased in height
(Frantz et al., 2001). When the data were normalized,
plants grown under low-intensity IC lighting produced
50% of the edible biomass of those grown under highintensity
overhead lighting but with only 10% of the total
electrical energy input (Frantz et al., 1998). Further
increases could not be accomplished, however, due to the
volume occupied by the heat-shielded lamps – if more
lamps were added to the canopy, the available planting
space decreased. Those proof-of-concept studies with
fluorescent lamps illustrated the need for a cool, smallvolume
light source that will allow switching on of lights
to keep pace with plant growth. Vertical, linear-arrayed
LEDs were found to fit those requirements."

From"PLANT-GROWTH LIGHTING FOR SPACE LIFE SUPPORT: A REVIEW", by Gioia D. Massa (and others). BTW, the ORBITEC's led array is basically what im doing now. I though i had a brilliant idea, but it seems NASA's guys are two steps forward us At least, i know my design is well though

BTW, glad to see you on the work, sy9942. Hope we can have a enrichment feedback from our high power devices

 

[sy9942]

That means at least/about 1MHz duty cycle, right? That's not so easy to accomplish for driver's side.
By the way, datasheet of luxeon claims 100ns or less switching speed (thats 0,1 μs) so you'll have limits approaching from this side as well.

Anyway, thanks for insight, I'll look forward for you research.

The duty cycle is only 1% (1.5μs is 1% of 150μs). The frequency would only be 6.66666...(continuing) kilohertz (1 second / 150 microseconds = 6666.666...).

Depending upon the accuracy required, this short of a pulse may not be a huge design issue. For example, see this somewhat outdated page which contains a prototype design for an avalanche-mode LED pulser. By tweaking some of the component values it will be possible to achieve the desired pulse length, I believe, without complicating matters with microcontrollers or otherwise.

The system would consist of a simple and relatively stable waveform generator that would cause a one-shot high-current pulse driver to switch on for 1.5μs for every 150μs cycle.

A reasonably fast microcontroller could get us the sub-microsecond accuracy required to control pulse duration directly with software which would enable all sorts of tweaking to be done, but I am left wondering how many people want to program a microcontroller.

With regard to my high-power LED investigations, I'm pondering the idea that a HPS lamp has little output at 660nm, and yet we see incredible growth from them. Further, they lack any considerable output at 730nm as well, although they do possess some and the sensitivity of phytochrome may be enough for this small amount to matter. I'm curious if perhaps we're barking up the wrong tree by looking purely at the absorption spectrum of chlorophyll A and B instead of trying to mimic the radiometric qualities of existing lamps that we know to work very well.

Here's a typical HPS output spectrum:

See what I mean? I think we might be going in the wrong direction by targeting the absorption peaks for chlorophyll dissolved in a solvent and centrifuged in a test tube. I don't think that the absorption data, isolated, is giving us a full idea of what's going on. I think we might be limiting ourselves unnecessarily. Here's another picture for you to enjoy:



Oh, I forgot to mention, this data comes from a study more than 10 years old: http://ncr101.montana.edu/Light1994Conf/1_5_Bugbee/Bugbee text.htm

The study mentions, "Not all species are sensitive to spectral quality, however. Low-pressure sodium lamps did not decrease the growth and yield of wheat compared to HPS and MH lamps (Table 3), a finding we recently confirmed. The plants under the low pressure sodium lamps of course did not look green, but the apparent difference in green color disappeared when the plants were removed and placed together in full spectrum light. Studies with wheat grown under red LED's also indicate that chlorophyll synthesis, photosynthesis, growth, and yield of wheat (Triticum aestivum) are insensitive to spectral quality." also interesting is "Soybean leaves grown under HPS lamps are visually chlorotic and have reduced chlorophyll concentrations compared with plants grown under MH lamps. However, most plant leaves have excess chlorophyll, and small reductions do not necessarily decrease photosynthetic rates." -- another hint that looking solely at chlorophyll absorption might not be the way to go. I suppose that something worth keeping in mind is that efficiency isn't necessarily about having the most of something (like happy little chlorophylls) but rather having the most effective balance of things. Perhaps stimulating chlorophyll too much and causing too many chlorophylls to be created isn't a good idea? This just speculation, but I think it's healthy speculation.

Another thing that interests me is the analsysis of biomass and grain produced by wheat grown under LPS, HPS and MH lamps. The LPS produced the most biomass at 171 grams, then MH at 162 grams and HPS at 159 grams. In terms of grain, MH produced the most at 62.4 grams, then LPS at 61.7 grams, then HPS at 58.8 grams. Now, while this next statistic isn't computed in the study and isn't necessarily going to help us at all, I still find it interesting: in terms of the amount of grain produced per unit of total biomass, 38.5% of the biomass produced under MH was grain, 37% under HPS was grain and 36% under LPS was grain. Although the LPS produced the most biomass, it didn't produce the most usable grain with respect to unit of biomass in comparison to the wheat grown under the other lights sources. Just something to think about.

Anyhow, I think this is worth discussion because at this point, it is possible (and easy) to acquire LEDs in a spectrum replicating the output of a HPS lamp, the output of which appears to be concentrated in the region of 560nm to 610nm. The most common LED wavelength in this range is 590nm although you can find 540nm and 625nm LEDs as well. I think that trying to replicate the HPS spectrum and then work forward from there would be a good use of time and effort and is the direction I'll be going in, in the future. I will of course supplement with a small amount (2-5%) of far-red @ 730nm and a slightly larger amount (10-15%) of blue near 465nm. Right now I'm looking at something like 10% 465nm, 5% 730nm, and 85% 590nm. I will let you know how things are going when I get started, I need to work on some other things before I can start pouring money into these new ideas.

 

[DeadlyFoez]

730 nm is bad. I'll have to find the post the thguyman made on davids uk420 LED grow, but it comes to be that displaying 730nm at any time other than night hinders the plants growth. 730 nm is known to help put the plant to sleep, which kinda help explains why sunset is so red, because there is more 730 at that moment.

This also explains why hps seems better for flowering then like CF's, because even aftr the power to the hps goes out, for a few moment there is still considerable amount of heat emmitted, and some of what is emmitted is that 730 so it helps put the plant to sleep faster. But where as when the power is cut from CF's there is nothing much more that is emmitted after that, and because of that the plant takes longer for it to goto sleep, about an hour or 2, so during a 12/12 cycle the plant is effectively awake for 13-14 hours in total.

I did a test with my buddy who was growing under CF's, I hade him change his light cycle to a 13/11 and there was considerable more flowering growth aafter that where his yeailds were comparable to hps at that point, well as far as how the plant would have grown under a comparable amount of HPS.

There is a lot more to it, but I'll look for the supportive info for this.

 

[sy9942]

730 nm is bad. I'll have to find the post the thguyman made on davids uk420 LED grow, but it comes to be that displaying 730nm at any time other than night hinders the plants growth. 730 nm is known to help put the plant to sleep, which kinda help explains why sunset is so red, because there is more 730 at that moment.

This also explains why hps seems better for flowering then like CF's, because even aftr the power to the hps goes out, for a few moment there is still considerable amount of heat emmitted, and some of what is emmitted is that 730 so it helps put the plant to sleep faster. But where as when the power is cut from CF's there is nothing much more that is emmitted after that, and because of that the plant takes longer for it to goto sleep, about an hour or 2, so during a 12/12 cycle the plant is effectively awake for 13-14 hours in total.

I did a test with my buddy who was growing under CF's, I hade him change his light cycle to a 13/11 and there was considerable more flowering growth aafter that where his yeailds were comparable to hps at that point, well as far as how the plant would have grown under a comparable amount of HPS.

There is a lot more to it, but I'll look for the supportive info for this.

I don't know how reliably you can trust this information. While this may be true about 730nm for some plants, it isn't necessarily true for all plants. For example, there is a ratio of 1 parts red light (660nm range) to 0.88 parts far-red (730nm range) light in natural sunlight at noon on a sunny day. This should give an idea of how much far red there is in actual sunlight, the light source that just about all plants are geared to grow under.

The most-recent published plant-growing LED experiment that I know of is this one: http://www.hortiled.ff.vu.lt/apzvalgos/high power leds.pdf
They highlight the need for 730nm light for photomorphological requirements. In one of their experiments (EXP1) with radishes and lettuce, they used photon flux distributions from their various LEDs as follows, in μmol per square meter per second: 9 @ 455nm (6.4%), 120 @ 640nm (85%), 9.4 @ 660nm (6.6%), 2.9 @ 730nm (2%). The net productivity in terms of grams per square centimeter per day was highest with this mixture for radish at about 2.4 and lettuce at about 4.2. However, the photon distribution in EXP3 was such that 640nm was reduced to only 80 umol/m2/sec, and this produced the most growth at 3 weeks' time, about 25% more growth than the mix in EXP1. EXP4 was identical to EXP1 except there was no daytime 735nm light, only nighttime for one hour between 2 and 3 AM, and this produced the most growth for radishes after a 3-week period. For radishes, the spectral distributions in EXP1 and EXP3 produced nearly identical results at 3 weeks, although EXP1 was ahead for the first two weeks. A quote from their conclusion, "The LED-based illumination with a proper proportion of light components enhances photosynthetic productivity and ensures better plant morphology in comparison with illumination using high pressure sodium lamps." (emphasis mine)

 

[DeadlyFoez]

Ok, yes, not EVERY plant is like that to sleep from 730 nm, mainly plants that dont require a specified light cycle to produce whatever it produces, BUT EVERY plant on earth, pretty much, recieves that same exact ratio.

All that the 730 nm does is tell the plant on whether its in the shade or not and also to help put the plant to sleep. So for certain plants, like trees that fight for sunlight in a forest, it does matter, but in plants of our liking we dont want the plant to think that it is constantly shaded because then you get stem enlongation, which is wasted plant energy and causes the flowers to not be as dense.

Ok, I'm sure you know this, but also infor for everyone else, when light travels to the plants leaf, the plant notices how much of a ratio of red to infared there is, if it sees more red then the plant knows its not shaded (1:0.88 ratio), but since the plant will absorb more red than infared, more infared passes on below that first leaf, so the then plant sees the there is more infared and less red and then the plant knows it's shaded. So also because of this, if an area is shaded, the plant will start to stretch, and also will start to not work as hard to make growth in that area as area that are recieving more red.

Ok, so knowing that info will tell you why infared is bad....in our case.

 

[sy9942]

Ok, yes, not EVERY plant is like that to sleep from 730 nm, mainly plants that dont require a specified light cycle to produce whatever it produces, BUT EVERY plant on earth, pretty much, recieves that same exact ratio.

All that the 730 nm does is tell the plant on whether its in the shade or not and also to help put the plant to sleep. So for certain plants, like trees that fight for sunlight in a forest, it does matter, but in plants of our liking we dont want the plant to think that it is constantly shaded because then you get stem enlongation, which is wasted plant energy and causes the flowers to not be as dense.

Ok, I'm sure you know this, but also infor for everyone else, when light travels to the plants leaf, the plant notices how much of a ratio of red to infared there is, if it sees more red then the plant knows its not shaded (1:0.88 ratio), but since the plant will absorb more red than infared, more infared passes on below that first leaf, so the then plant sees the there is more infared and less red and then the plant knows it's shaded. So also because of this, if an area is shaded, the plant will start to stretch, and also will start to not work as hard to make growth in that area as area that are recieving more red.

Ok, so knowing that info will tell you why infared is bad....in our case.

You've said initially that all 730nm does is tell the plant whether or not parts of it are in the shade, but then you say that it's the ratio of red to far red that actually does this. These are slightly contradictory statements. I agree with the second point, which is why I think that 730nm should be a small component (as long as it's small in comparison to red light in the spectrum, it won't trigger the elongation response) but I don't think it should be omitted all together because I think that 730nm light is used in flowering.

If I have enough space to run trials of spectra both with and without 730nm, I will make an attempt to lay this issue to rest. As it stands though, I would like to put 4 plants under each spectrum and I don't know if I will have enough space to experiment too diversely. We'll see. My estimated time for project initiation is about 2 months from now, after I have sexed some plants and confirmed some females and I have enough clones at the same stage of growth to permit a valid comparison.

 

[DeadlyFoez]

You've said initially that all 730nm does is tell the plant whether or not parts of it are in the shade, but then you say that it's the ratio of red to far red that actually does this. These are slightly contradictory statements.

Yes to both. its because of the ratio of red to 730 nm, Sorry, I meant NEAR infared. If the whole plant gets exposed to higher amounts of 730 nm then thats when it starts to goto sleep. So in the day, those parts that are shaded start to goto sleep in a way, but since the shaded parts dont go dark until the end of the light cycle they start to stretch.

Another thing that I can say that will kinda help a little in a different way is that you can sex a plant with doign the paper bag trick on one branch of a plant. That just kinda shows about that not just because the majority of the plant recieves something, that doesn't mean that you can't make one little part act differently.

I say that too kinda show how one portion of a plant seeing just a majority of 730 nm that that part of the plant would be caused to stretch while the rest doesn't.

I dont know how to fully explain it because I've been up for about 22 hours now and just got done having drinks with friends.

 

[LED_experiments]

sy
we had a disgussion at uk420 and OG about 735.
the way i see those things goes like this:
if using 735 during the whole light period, it causes plant to stretch. we don't need that in our projects, because leds are good for sog and scrog, not for growing monster plants. maybe run a test sy and try to grow one plant only with 735. i'm quite sure that you will get 15cm of steam and 2 small leaves at the top.
if not using 735 at all, you will have small bushy plant with small internode spacing, but you will have big problems when it comes to flowering (unless you use lowryder). in my case it took more than 2 weeks from switching to 12/12 before the plant started showing first signs of flowering. in my next grow i used shorter day periode 11.5/12.5 and i got smaller delay time.
if you don't use 735, you have a very high Pr ratio at the end of the day. it tooks a long time before that ratio drops and the plant feels dark (emerson effect). i think you are one of those, who posted quite a lot of posts about emerson at og, so i guess you know what i'm talking about. the point is that you have to convert as much Pr to Pfr at the end of the day as possible. at uk420 we came to the conclusion that you can do that with seperate use of those lights:
first you grow without 735 for let's say 11.5 - 12 hrs so that your plants don't stretch too much. after the end of that light cycle you use 735 for 15-30 minutes to convert Pr to Pfr (to lower the Pr ratio and slam your plant to sleep). maybe it would be better to use 11 hours without 735, then run all the leds (with 735 included) for another 0.5 h and at the end 0.5 h only 735.
the problem is that nobody is sure how much 735 we need and how long should we use that 735 to convert as much Pr to Pfr as possible. on the other hand we don't want to use too much 735 or too long duration of that cycle to prevent unwanted stretching.

 

[knna]

See what I mean? I think we might be going in the wrong direction by targeting the absorption peaks for chlorophyll dissolved in a solvent and centrifuged in a test tube. I don't think that the absorption data, isolated, is giving us a full idea of what's going on. I think we might be limiting ourselves unnecessarily. Here's another picture for you to enjoy:

Im saying the same long ago. Whole plant's photosynthesis is far more complex than chlorophills. And we have avalaible excelent photosyntesis action curves for whole plants. Some time ago, i realized that we are largelly overstating the importance of spectrum. Its important, but plant's use of PAR for photosynthesis is very flat (just 2x tha max in red than the min in green).

A good spectrum have other advantages than the differential pohotosynthesis of absorbed photons: while a 33% of HPS light is reflected, just 11% is reflected for a LED lighting (90% red photons from 660nm peaked leds and 10% blue photons from 470nm peaked LEDs) (data from NASA, performed on wheat)( anyway, there is accurate analysis of cannabis absorbance at each wavelenght).

Aditionally, the longer the wl, more photons per watt emited.

But taking into account both concepts, photosyntetic efficiency of 1watt of 645nm photons are just 94% of 1 watt of 660nm.

Most of the recent research and development in LEDs is toward blue/white light, and in the red side, in shorter wavelenghts than 660nm (due to the higher photometric effficiency). Its relatively easy find 640-645nm peaked LEDs, while it a lot more difficult finding it in 660nm peak, and very often, with lower radiometric efficiency.

If we are seeking for the max light's efficiency, then makes a lot of sense using more efficients 645nm leds than 660nm leds, due to the enhaced photosynthesis action of the 660nm (6%) is too little. Aditionally, Pr/Pfr is less descompensate using 645nm, wich minimize far red light requeriments.

About far red light, i fully agree what LED_Experiments said. I believe that adding a bit of far red light during flowering, and probably just during flower induction and rippening is enough. Anyway, im going to carry some experiments about to check the best quantity and timinig of adding far red.

Ok, yes, not EVERY plant is like that to sleep from 730 nm, mainly plants that dont require a specified light cycle to produce whatever it produces, BUT EVERY plant on earth, pretty much, recieves that same exact ratio.

This isnt correct at all. Most plant species in Earth (in number) live in the tropical forest, in a environment far higher in far red. The ratios of R/Fr are very different along the same plant, depending on the node you measure.

Anyway, what we need are experiments to check what are the Cannabis' far red requeriments ,if any, and if this is the case, check if adding far red can improve photosynthesis or grow duration.

 

[Tripco]

There's 2 plant pigments that absorbes light at 730nm: Phyitochrome and Plastocyanine. First one works in a range of (aprox.) 580-760nm, and the second one in 445-770nm. But amount of light absorbed by these 2 pigments is very small, less than 2% combined.
About one half of total amount of sunlight goes to infrared end of spectrum. Plant leaves uses about 25% of infrared light in the range of 760-2500nm, but mostly to about 850nm or so. This light is not absorbed by pigments (if we don't count Plastocyanine in range 760-770nm, absorbed in promiles), but by the molecules of water. Energy from this light is used mostly for traspiration and for some photochemical reactions that ensures photosynthesis.

 

[Mickey696]

Check out these links... very interesting!!!

http://www.metaefficient.com/archives/hydroponics/red-leds-to-grow-lettuce.html#more

http://www.metaefficient.com/archives/leds/led-lights-efficient-indoor-growing.html

Price just seems a bit prohibitive , but it probably pays for itself in electricity usage. That in itself should be a huge win because there will no longer be the problem of the sky high electricity bill!!

 

[Guest]

Man you guys are really into this LED stuff for growing,I guess its the wave of the future.Do you think you can really flower plants better with led's than with hid's though?

 

[Mickey696]

Maybe not with current levels of technology and research. But in future it will be a force to be reckoned with. They have so many benefits.... Check out those links!