# High photosynthetic photon flux density (PPFD) and LED dimming (pulse width modulation)



## Simon Cole (9 Jun 2020)

With almost limitless-intensity LEDs becoming commonplace in the market. We must answer a fundamental question over the role of pulse width modulation (PWM) in mitigating photoinhibition in plants. In theory, LEDs shine at the same intensity, but this intensity is split into longer "off" and shorter "on" periods. PPFD has always been used to work out continual flux density from stable radiation sources of light like the sun or CFLs, whereas all LEDs follow a continuous pattern that is split between two modes, off and on. The human eye cannot detect these changes, but does it affect plant photoinhibition?


----------



## Nick72 (9 Jun 2020)

Sounds interesting.  I understand the basic premises, but have no idea of the real life effect.

I'll be watching this thread.


----------



## rebel (9 Jun 2020)

Simon Cole said:


> plant photoinhibition?


I don't think so. I don't think the plants would 'perceive' such fast pulses. No difference in growth has been observed AFAIK.


----------



## Simon Cole (9 Jun 2020)

What is even more interesting is that some members have used dimming to reduce leaf melt!    ... check out Ray's observations in this recent thread:


Ray said:


> My reference is I have a 25cm cube with low light - I’m running a 15w ONF flat nano on it at 25% power with no added carbon.  When I turned it up to 50%  (roughly what you have) I had major leaf melt on my Staurogyne and Crypts.  With CO2 however, that would have been fine.



Any observations more would be very welcome


----------



## zozo (9 Jun 2020)

Not in my experience... 






And this grew all under a DIY DC12 volt LED fixture dimmed with PWM, as you can see the left-hand side in the picture the TC420 PWM led timer/controller hanging to the wall.





The LED's used were the SMD 8520 dual-chip LED strip at 60 lumens per chip, 4 strips 50cm x 36 chips each, total 144 chips x 60 = theoretically 8640 lumen at 100%. Not counting the 1 strip it contained with Red and Bleu LEDs that came without lumen specs.

It's not something specifically for DIY, the Chihoros LED units that come off factory with a dimmer or the Chihiros Bluetooth controller also uses PWM...   Thus PWM controlling already is used as long since LEDs are used in the hobby.

I can not fully explain PWM away and i think the explanation as an On/Off pulse is a bit too straight forward and simplified theory. It is also used to control the speed of electrical motors. And even a simple voltmeter is kinda fooled by it. I hooked a simple digital voltmeter to the PWM controller and it shows +/- 6 volts if it is turned down to 50% output. But in theory, it should stay 12 volts at different on/off frequencies.

That was here.  The DC motor controller is a PWM unit with the voltmeter hooked to it to control the DC 12 volt pump.


----------



## jaypeecee (9 Jun 2020)

Hi @Simon Cole

The following would also be my response on this subject:


rebel said:


> I don't think the plants would 'perceive' such fast pulses.



But, if you wanted to pursue this further, perhaps Dr Bruce Bugbee at Apogee Instruments has something to say on this? If the name isn't familiar to you, Dr Bugbee is one of the foremost names in plant LED lighting. He is engaged in cutting-edge research for the likes of NASA. Check out his YouTube videos to be enlightened (pun intended!).

Or, having just seen the above post, you could talk to @zozo!

JPC


----------



## jaypeecee (9 Jun 2020)

zozo said:


> I can not fully explain PWM away and i think the explanation as an On/Off pulse is a bit too straight forward and simplified theory. It is also used to control the speed of electrical motors. And even a simple voltmeter is kinda fooled by it. I hooked a simple digital voltmeter to the PWM controller and it shows +/- 6 volts if it is turned down to 50% output. But in theory, it should stay 12 volts at different on/off frequencies.



Hi @zozo 

PWM has been around for donkey's years. I seem to recall that it was used 50 years ago when I dabbled with radio-controlled boats. And I wouldn't expect any multimeter - analogue or digital - to provide sensible measurements from PWM. Multimeters are limited to DC or 50/60 Hz sinusoidal mains waveforms. An oscilloscope would be required to do any sensible measurements.

JPC


----------



## zozo (9 Jun 2020)

jaypeecee said:


> Hi @zozo
> 
> PWM has been around for donkey's years. I seem to recall that it was used 50 years ago when I dabbled with radio-controlled boats. And I wouldn't expect any multimeter - analogue or digital - to provide sensible measurements from PWM. Multimeters are limited to DC or 50/60 Hz sinusoidal mains waveforms. An oscilloscope would be required to do any sensible measurements.
> 
> JPC



Yes, i know it is already in use for decades as DC motor speed control.  Especially in the private radio-controlled modelling hobbies. Anything using Servo Motors... 

I guess what kinda is misconceived or incomprehensible for us hobbyists is the On/Off concept and how this reduces the output that it seems a lower voltage but it isn't. Similarly as how a computer binary code actually works simplified with Zeroes and  Ones.  0 = Off and 1 = On. Same theory, the processors switch On and Off at an amazingly high frequency to do the tasks it does and show it on your screen. Sounds so simple, but explain away?.


----------



## Simon Cole (9 Jun 2020)

I just found an interesting article showing a positive "photo-inhibition recovery" correlation in wheat:
PWM (rSP) helped the plants to photosynthesise after the light intensity got too much. 

_"We confirmed that the rapid change in Y(I) at the beginning of rSP illumination was similar between two wheat cultivars and between LL and HL growth conditions, and the decrease in Y(I) was rapidly recoverable in both LL- and HL-grown wheat cultivars *when pulse illumination intervals were prolonged* (Supplementary Figure S2)." _

Here is the figure from the article  below:




Other growth studies have shown negative correlations (e.g. lettuce), but these methods were all different.
An important consideration is that we are not measuring growth.  Instead we are looking at photo-inhibition.
I have found it very hard to find any articles on PWM vs photo-inhibition.
Perhaps it is just the way that I am looking at the data.

So yes, please continue to post your observations!


----------



## zozo (9 Jun 2020)

@Simon Cole you might want to listen to this.
http://scapefu.com/lighting-planted-aquarium-cara-wade/

Cara Wade says in the interview that she welcomes anybody willing to help and participate in experimenting to contact here via Facebook. It might be 😍 for you both... She might be able to explain a lot in detail or provide you with usefull data...


----------



## jaypeecee (9 Jun 2020)

zozo said:


> Sounds so simple, but explain away?



Hi @zozo 

Maybe one day. It's not easy to explain things like this without drawing a few graphs and throwing in some maths, as well. Or, I could simply refer you to a book by one of my University lecturers of years gone by. That's my cop-out! The book is 'Signal Processing, Modulation and Noise' by Dr J A Betts. 

JPC


----------



## dw1305 (9 Jun 2020)

Hi all, 





Simon Cole said:


> PPFD has always been used to work out continual flux density from stable radiation sources of light like the sun or CFLs


I don't know, but my guess would be that it doesn't make any difference to the plant whether the light is pulsed or continuous.

The reason would be that the photosynthetic pigments are intercepting individual photons, so that even a continuous wave light source isn't necessarily continuous at chloroplast level. It is back to the deep green _Bolbitis _or _Anubias,_ with their low light compensation points, they have a lot of chlorophyll to intercept all of the relatively rare photons.

There is also the effect of clouds to take into account. These are the solar panels on our roof, so facing SE and not shaded in any way, if this was a situation with trees as well, the differences between sun and shade would be even more pronounced, with the <"plant experiencing "flecks" of high PPFD">.





cheers Darrel


----------



## jaypeecee (9 Jun 2020)

zozo said:


> Cara Wade says in the interview that she welcomes anybody willing to help and participate in experimenting to contact here via Facebook. It might be 😍 for you both... She might be able to explain a lot in detail or provide you with usefull data...



Hi @zozo 

Your link took me to something that says "Cara Wade, a lighting expert from Build My LED, tells you exactly what you should be looking for when thinking about lighting your planted aquarium". The company, BuildMyLED (BML) no longer exists. I have a BML LED fixture as does none other than Dennis Wong. To the best of my knowledge, BML became _Fluence (Osram)_. I will pursue this with interest even if it means looking on FB!

JPC


----------



## zozo (9 Jun 2020)

dw1305 said:


> Hi all, I don't know, but my guess would be that it doesn't make any difference to the plant whether the light is pulsed or continuous.
> 
> The reason would be that the photosynthetic pigments are intercepting individual photons, so that even a continuous wave light source isn't necessarily continuous at chloroplast level. It is back to the deep green _Bolbitis _or _Anubias,_ with their low light compensation points, they have a lot of chlorophyll to intercept all of the relatively rare photons.
> 
> ...



Good point!...  never really crossed my mind that it's something natural too... The ferns and or mosses, whatever low compensation point plants that grow on the forest floor below the canopy actually receive a kind of pulsating light intensity due to air movement through the dense canopy. (Now I'm shaded/now I'm not) So we could assume the plants are evolved not to care and to cope with this.


----------



## zozo (9 Jun 2020)

jaypeecee said:


> The company, BuildMyLED (BML) no longer exists.



Indeed they stopped manufacturing aquarium lighting and since solely put their energy (so to speak) in the horticulture industry lighting. No idea if that's still the case today, it's a rather old article from a few years back. But Cara seems to be a fanatic Aquarium enthusiast and Hobbyist. So she probably is still as active in this field as before but just not professionally anymore.


----------



## Ray (9 Jun 2020)

dw1305 said:


> The reason would be that the photosynthetic pigments are intercepting individual photons, so that even a continuous wave light source isn't necessarily continuous at chloroplast level. It is back to the deep green _Bolbitis _or _Anubias,_ with their low light compensation points, they have a lot of chlorophyll to intercept all of the relatively rare photons.



I think so too. I am pretty sure that from a plant perspective it is simply a matter of how many photons hit your chloroplasts (driving your chemical reactions) in a given time. Whether the photons arrive in pulses or a steady flow won’t make any difference at the chloroplast level.

BTW @Simon Cole there is a good CEG thread on melting here  https://www.ukaps.org/forum/threads/what-causes-leaves-to-melt-and-what-to-do-now.20421/


----------



## zozo (9 Jun 2020)

It's the power driving the light that has high-frequency puls and in this case, it can be modulated. If i remember correctly all power supplied in whatever form has a pulsating frequency but it isn't or can't be modulated as such.

So i guess all artificial light pulsates but to fast for our eyes to see it...

What else does frequency mean?


----------



## Oldguy (9 Jun 2020)

From the internet: ' Most people cannot notice the *flicker* in *fluorescent lights* that have a *flicker rate* of 120 cycles per second (or 120 Hz). *Flicker* with LED *lights* may be more noticeable due to the fact that LED *lights flicker* between less than 10% and 100%, where as *fluorescent lights* dim to about 35% and back to 100%)'

So it appears that LED's flicker whether dimmed or not if powered from AC electricity. Car LED's (12 volt DC should be flicker free.)

Incandescent filament lighting should also flicker if powered by AC but filament reaction time would be slow compared with 50Hz AC. Have heard it claimed that DC powered filaments last longer than AC powered ones due to constant power supply. No personal experience however.


----------



## rebel (12 Jun 2020)

Simon Cole said:


> I just found an interesting article showing a positive "photo-inhibition recovery" correlation in wheat:
> PWM (rSP) helped the plants to photosynthesise after the light intensity got too much.



Can someone translate this study to English? 

Do the pulses increase or decrease growth?

Thanks.


----------



## Simon Cole (12 Jun 2020)

@rebel ...so with a shorter "off" gap between pulses (on-off-on-off etc.) the lights were "on" for longer. This caused photo-inhibition in wheat plants, which stopped growing. When the "off" gap was extended so that the lights were off for longer, this enabled the wheat to recover and start growing again. This showed that for wheat, using pulse width modulation (PWM) was effective at achieving the right amount of light, and without PWM the crop would have failed. This suggests that dimming switches that regulate these on and off periods, can be used effectively to manage high intensity lighting that could otherwise cause plants to stop growing. Aquarium plants could respond in very much the same way, and having an AC current with a dimmer could be advantageous when optimising light intensity... I don't know whether that helps. Most plants just stop growing and show no sign of bleaching when the intensity is too high.


----------



## Ray (12 Jun 2020)

So something like this?






Sent from my iPad using Tapatalk


----------



## oreo57 (19 Jun 2020)

zozo said:


> I can not fully explain PWM away and i think the explanation as an On/Off pulse is a bit too straight forward and simplified theory. It is also used to control the speed of electrical motors. And even a simple voltmeter is kinda fooled by it. I hooked a simple digital voltmeter to the PWM controller and it shows +/- 6 volts if it is turned down to 50% output. But in theory, it should stay 12 volts at different on/off frequencies.


Couple of points
1) Most meters will end up "averaging" so your 6V at 50% is expected..
12V 50% + 0V  50% averages to 6V 12/2 periods so to speak.
2)There is some rise/fall time but usually not important.
Sort of like this:
Blue is the signal.. yellow is the current. Just a rough example but you get the idea.



LED's do "quench" fairly instantaneous, unlike things like incandescent bulbs.
May be some phosphor lag w/ whites or other phosphor converted diodes ("lime" or like the cheap "full spectrum" diodes (magenta looking ones w/ red phosphors and a blue pump)

4) motor/fan speed PWM control usually uses much larger pulse frequencies like  2 *kHz* up to about 10 *kHz*. (rough estimate)
Most LED controllers use like 500Hz. 
Point is frequency needs to be part of the discussion.

5) Consider livestock
6) there is natural PWM such as leaves blowing, clouds though obviously not exactly KHz ranges.


----------



## oreo57 (19 Jun 2020)

https://cdn.intechopen.com/pdfs/60304.pdf


> 5. Conclusions: Pulsed light at high frequencies (2–20 kHz, 50% duty ratio, 200μmol m2s1) positively affected the growth of lettuce leaves under controlled environment. The photosynthetic performances showed differences between leaves developed under pulsed light and leaves developed under continuous light, when the CO2 uptake rates and chlorophyll fluorescence parameters were measured at lower frequencies (<2 Hz). In the pulsed light technique, it is important to determine both optimal frequency and duty ratio for plants to attain the mostefficient use of harvested light. The reason why growth was enhanced under pulsed light athigh frequencies has not been resolved by analyzing photosynthetic performances in this study.



Keep in mind some things are species/cultivar specific.


----------



## rebel (23 Jun 2020)

Would be a fascinating thing to study. pHD opportunity awaits someone. Maybe start with POT plants as people are intensely interested in them....( DUUUUDES   )


----------



## Simon Cole (23 Jun 2020)

I'm way ahead of you - I've just purchase an incredibly high wattage LED. To be honest, I cannot afford a good enough dimmer, PAR meter or the oscilloscope thingy, so any hard evince will be a while yet. I also need a deeeeeep tank.  So expect to hear more on this. It's going to be citizen science at its zenith, if I don't go broke, mad, drown, or more likely blind in the process. I'm going to do a terrestrial dry run  first. They actually call this a "pot study/trial" in science literature.


----------



## rebel (23 Jun 2020)

@Simon Cole  dude we are on your side. 

TC420 can handle a bit of PWM dimming. There are some small oscilloscopes which might be enough but they are around $200 or so.

Good luck to your wallet.


----------



## oreo57 (23 Jun 2020)

rebel said:


> @Simon Cole  dude we are on your side.
> 
> TC420 can handle a bit of PWM dimming. There are some small oscilloscopes which might be enough but they are around $200 or so.
> 
> Good luck to your wallet.


You can actually use the DAC in your computers soundcard .. 


> For external sources care has to be taken, not to exceed the voltage range of the inputs. The range is usually only ±0.7V !! If higher voltage need to be analyzed, a voltage divider has to be used. Additional protection diodes are recommended in order to avoid any damage to the sound card and to the computer.


.
https://www.zeitnitz.eu/scope_en
I briefly tried some software (Zelscope???) ..
Aduino based  "Typhon"  (a DIY project turned commercial in the US, now StevesLED "hurricane" controller (upgraded version) ) controller 5v pwm output.



I am not responsible for people burning out soundcards or any computer issues.. JUST a suggestion..
I'm sure it has a bunch of limitations..
I do not remember if I  limited the voltage in any manner. Do not believe I did though and the card survived the "5V".
Only played with it briefly.


----------



## Simon Cole (23 Jun 2020)

I think I'm on 0-10V dimming. The chips will be regulated but the unit is 240V. Good idea though @rebel . I'd probably run comparisons against a series of quartiles, at points in height when we know light intensity should result in photosynthesis inhibition. Obviously light through water at depth does funny things. But if the problem could be solved - boy what fun. We could have a light on a moving boom that goes over shallow plants at a wide PWM, into deep water carpets at zero PWM - all with one high intensity light at one set height, just with a single programmable dimming switch, and a moving boom. We could have planted carpets at 3 metres depth in indoor swimming pools and still grow stem plants around the margins. It would be like ADA mark II.


----------



## rebel (23 Jun 2020)

Simon Cole said:


> the unit is 240V.


There are 12V/24V DC units.


----------



## rebel (23 Jun 2020)

oreo57 said:


> I am not responsible for people burning out soundcards or any computer issues.. JUST a suggestion..


Dude I didn't know my computa had a sound card???? I used to use sound blaster cards on my PC but these days seem to be built in....


----------



## oreo57 (23 Jun 2020)

rebel said:


> Dude I didn't know my computa had a sound card???? I used to use sound blaster cards on my PC but these days seem to be built in....


Showing my age.. Sound card..sound chip..


----------



## rebel (24 Jun 2020)

Sound chip eh.... It must be part of the mother board in that case! What an interesting idea to use it to monitor wave forms!


----------



## oreo57 (24 Jun 2020)

rebel said:


> Sound chip eh.... It must be part of the mother board in that case! What an interesting idea to use it to monitor wave forms!


It has limitations...
*



			Bandwidth
		
Click to expand...

*


> , or how wide a frequency range they can measure effectively. The lab-grade scope in this case has a 200MHz bandwidth, meaning it can measure from 0 to 200MHz very well. The bandwidth of the sound card is much lower: about 20 – 15kHz. Anywhere out of this range and measurements get sloppy.
> 
> *Sample Rate* The lab model here has a sample rate of 2GS/s! The sound card in your computer is only around 44kS/s. So, you see why faster waveforms may not be captured as well. In essence, the sample rate is how often the system measures the voltage. So, a lab model can measure up to 2 billion times per second while the sound card model does it 44 thousand times. You may think this really negates the use of this DIY tool. Not so! In many hobbyist circuits 14kS/s is more than fast enough to measure your pulse widths and frequencies.


https://makezine.com/projects/sound-card-oscilloscope/


----------



## Simon Cole (24 Jun 2020)

Hopefully I can borrow a certified instrument. I want to be certain the results are reliable.


----------



## jaypeecee (24 Jun 2020)

Hi Guys,

Just thought I should mention the following:

https://www.picotech.com/data-logger/drdaq/overview

You will see that it can be used as a 100kHz bandwidth 'scope. Generally-speaking, _pico Technology_ produces some good stuff. I have many times considered getting one of these little boards and it may still happen. My hands-on electronics knowledge is now pretty rusty. But, I once built an oscilloscope with CRT and that was 50 years ago! Everything was discrete in those days. ICs were just beginning to appear on the market!

JPC


----------

