It is Winter and that means the temperature is low, you rarely see the sun and I am
sitting all alone in my greenhouse in which there are no more crop plants to be found.
“But It doesn't have to be that way”: thought my trusty electronics partner
Würth Elektronik and promptly sent me a care package consisting of 4 types of different LEDs.
Those LED can of course not increase the outdoor temperature or let the sun shine
more often. But they can be used to build a sort of like indoor greenhouse which supposedly
can improve the quality parameters of plants and therefore most importantly let them grow faster.
At first sight that obviously sounds amazing but is this claim of a quicker growth really true?
Is it worth it to use such an illumination and how difficult is it to pull off?
I will answer all these questions and much more in this video. So let's get started!
This video is sponsored by the Würth Elektronik eiSos group.
When talking about plant growth then we can not avoid talking a bit about biology
which loves to throw around complex technical terms like chlorophyll,
beta carotene, phytochrome and much more.
That is why I want to keep this biology excursion as simple as possible and recommend everyone who
would love to learn more about the subject to check out the Würth Elektronik website
or the video description where you can find very detailed application notes with tons of details.
And with that out of the way let's get right to the first quiz question:
“Why do most plants look green to the human eye?” I mean with my example here I am using a light
source which roughly represents the visible light spectrum of the sun and as you can clearly
see our plants appears to be green in colour. The reason is of course that the wavelengths of
the green light which lay between 490 to 575nm are for the most part not required
by the plant organism and thus mostly not get absorbed but instead reflected.
However the other wavelengths which represent the remaining colours are apparently more essential
for the plant since they clearly get absorbed. The plant uses this light to mainly drive
its photosynthesis which takes carbon-dioxide and water and turns it into oxygen and glucose
which the plant organism also uses for its own energy supply to grow.
And with that thought in mind we can turn our attention to the 4
different LED types that I received. Their colours are called deep blue,
hyper red, far red and daylight. And the first 3 LEDs colours are special
because their emitted wavelength peaks correspond with the absorption maximum of the plant,
which is basically the spot where they can absorb the most light.
And needless to say the fourth daylight LED covers a bigger spectrum.
This is also mandatory though because the plant not only needs
additional other wavelengths for other processes besides photosyntheses
but also because our eyes can more easily see how the plant develops in this light.
And with that being said the fundamental theory should be clear
and explain why those particular LEDs can be used for an accelerated growing process of a plant.
That means it was time to face problematic electronics related question like how many
LEDs of which type should we use, how do we supply the right amount of current, how can we cool them,
how can we dim their brightness and so on and on. Luckily most of those questions were easy to solve
by a bit of clever thinking and having a look at the datasheets but since I had absolutely
no experience regarding horticulture LEDs, I had no idea how many of which type to use.
But I was also partly lucky with that question because as it turns out Würth Elektronik carries
a lighting development kit that not only comes with a driver PCB but also a horticulture panel.
And I said partly lucky because while the LEDs were in stock, other parts of the kit
were apparently sold out and thus I had no chance of getting the kit at this point.
Thanks to its manual though I at least got a reference point on how many LEDs of
which type to use and thus I continued by designing a replica of this PCB.
And even though I was happy with my final design I was still a bit worried about the LEDs.
You see the LEDs are high power ones which means that even though they are small,
they can emit quite a bit of light and thus obviously demand a bit of current as well
with a nominal value of 350mA. The consequence is that it produces a noticeable
power loss in the form of heat. And of course we have to somehow spread this heat elsewhere,
otherwise the lifetime of the LEDs could get shorten.
And luckily does my PCB manufacturer offer aluminium PCBs for one layer designs,
which mine should be, and thus I used this option to get my hands on those
promising looking aluminium PCBs which will *spoiler warning* keep my LEDs nicely cool.
And of course I also didn't miss the chance to include an error into the design.
But besides that everything worked out just fine; spreading the solder paste with the stencil was
no problem and also using hot air to reflow solder the LEDs turned out to be successful
even though I think using a hot plate for reflow soldering would have been
more appropriate for such an aluminium PCB. And once I was certain that all LEDs functioned
correctly, it was time to think about a circuit that could supply them with a constant current of
350mA and that I could also pulse in order to dim the brightness between 0 and 100%.
I of course chose an Arduino to create the PWM dimming signal and also 4 LED
step down modules from Würth Elektronik. These modules are in a nutshell small
switched mode power supplies that require very few complementary components around them
in order turn a variable input voltage into a constant output current.
And since we can adjust the brightness by pulsing the DIM pin;
everything should work out just fine. That is why next after creating the
fitting schematic, I designed a second PCB as a driver PCB around the just described components.
As soon as the PCBs then finally arrived at my place, I once again used the hot air technique
to solder the LED drivers into place and then switched over to a normal soldering iron
in order to secure the remaining SMD and also THT components to the board.
The result did look promising but before I could test anything I firstly had to write a bit of
code for the Arduino that generates the 4 PWM signals which I then obviously had to upload.
After then checking the PWM signals; it was time to connect all the LEDs and power the whole system
with 19V and as you can see I think my soldering technique was not suitable for the LEDs after all.
But luckily while I was about to fix this problem, the lighting development kit from
before was back in stock and needless to say it comes with a horticulture LED panel
that I can use and best of all it even comes with a lens that focuses the light better.
Now the kit also came with its own LED driver PCB which seems to be more sophisticated than mind
and even supports Bluetooth but I decided against using it because mine works just fine.
And just like that the electronics sides of things came to an end and
it was time to start the actual experiment which began by selecting suitable seeds.
I decided on Arugula because it not only grows fast but also because its delicious and nutritious
which fits well with the topic of horticulture which is all about the efficient,
profit-yielding and sustainable production of food for a growing population in the future.
So I prepared 6 containers with seeds of which 3
will have to live with only the sunlight while the other will be continuously lit up
by the LEDs through the help of a rustic wood construction that I build beforehand.
But here comes the question how the individual light channels should be mixed together
and let me tell you that there is no universal answer to that because every plant comes with
other light tendencies and thus an individual fine adjustment is kind of necessary.
It is also noteworthy that during different development stages,
the plant requires different wavelengths. But since we are only doing a simplified
experiment here and because the manual recommends a blue red mixing ratio between 50 50 and 90 10,
I made my life easy and went with the middle value and adjusted the remaining
LEDs to get a nice to look at end result. And just like that I started the experiment.
It is mentionable that all plants were watered with the same amount and I also took care to
guarantee an almost constant temperature along with some fresh air from time to time.
And after the first days there wasn't really much of a difference noticeable between all the plants.
But after only a week the difference became apparent and became more and more obvious as the
days passed by. And after a total of 21 days so 3 weeks we can definitely not deny that horticulture
LEDs do in fact accelerate the growth of plants and by the way the Arugula also tasted great.
Of course in comparison to this faster growth we have to take the energy costs
and costs of purchase into account, but I think that when fine adjusting all the
parameters for such an indoor greenhouse, it can be a promising agrosystem for the future.
And since building such a horticulture lighting system is pretty easy to pull off and you can
always ask for free samples from Würth Elektronik, everyone can try it out even today in their homes.
With that being said all initial questions should be answered and I hope that not only I but also
you before the screen learned something new. If so don't forget to like, share,
subscribe and hit the notification bell. Stay creative and I will see you next time.