Development of a Growth Light (Wavelength of Light vs Photosynthesis)


So I started a competition at work, the ”Chili Challenge”. I planted seeds from the same fruit and after they where big enough I handed out the 12 plants to my co-workers.

The competition has three diffrents parts that one can winn.

  • Biggest single Chili fruit
  • Most fruit (in gram)
  • Commitment

So the first tow are pretty strate forward, the third one (du to that we ar all Engineers and Developers) The person that has the best commitment, in form och ”what you do for your plant”. Every person has to document what they do, such as, building a soil measurement sensor (as I have done) or just that you play Red Hot Chili Pepper to your plant on a daily basis. We all wore which person that had has the best commitment.

Now, I need to get my small plant to grow, and in a good way, not to fast so it gets to thin, and not to slow so the season ends without any fruits.

So, I am going to develop a very own Growth Led Light (GLL)

In order to develop the best DIY Growth Led Light (GLL) I have to do my research in this subject and get conclusion where to begin and what to do! The following part will be written in Swedish…


Lets start from the beginning, the first question is what is photosynthesis?

It is the process, which plants and some protistans and some bacteria use the sunlight and its energy to produce sugar.

The cellar respiration converts the sugar into  Adenosine Triphosphate (ATP), which is a form that living things stors energy. It consists of a nucleotide, which three photo phase groups.


For all you who love chemistry this is what happens

6H2O + 6CO2 ———-> C6H12O6+ 6O2I have just studied basic chemistry at the university, but i thing its says that six molecules of water plus six molecules of carbon dioxide produce one molecule of sugar plus six molecules of oxygen.


Why not black leafs?

I have thought about this sense I was a kid, why just reflect the green and not use the whole spectrum?

(Due to the fact that black is the most light absorbing color, in physics we talk a lot about an ”absolute black body” that emits most energy)

As it is stated, the life begun in the sea, so the earliest organisms that used photosynthesis were  aquatic bacteria. This type of bacteria is still in out oceans.

It is said that nne of these, halobacterium halobium, grows in extremely salty water,  it makes use of the bacteriorhodopsin pigment. The chlorophyll system developed to use the available light, as if it developed in strata below the purple bacteria and had to use what it could get.

There the ”leftovers” was in the spectrum of that the green pigment were most efficient, hence, Green bacterias.

This yields another question, why did they not turn black when they got up on land? (Why are land plants still green?)

Well, as I have come to understand, when the bacteria emigrated up to land, there where so much more sunlight and therefore there was no need to evolve more, the green pigments worked well. Now, there are still som plants that has more darker and lighter pigments, but over all, most of them are green.

Wavelength to saturate the Plant

So, there are several parts in the photosynthesis and I want to maximize it in the palant. Different wavelength gives diffrent ”levels” of photosynthesis.

When we talk about pohotosynthesis (PhS)

Studies has shown that one can devide them in to separat ”groups”, this are the main

  • chlorophyll a
  • chlorophyll b,
  •  β-carotene



this three basic parts has its max effecansy at diffrent wavelengths.

This is where I state what wavelengths I want for my LED’s shall be.

LEDs used in this project

In order to furfill the photosyntesis we need to use the wavelenght that is optimal for Photosyntesis A, photosynthesis B.


Follwong wavelenghts of LED’s are used in this project


  • UV                        365nm
  • BLUE                   470nm
  • GREEN               528nm
  • RED                     565nm
  • RED                     625nm
  • RED                     730nm
  • WHITE               6500K

Lamp Design


PCB Design



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