I decided to build my own LED (light emitting diode) grow light since i didn't want the pre-build led light because it favors red over blue wavelengths.
I will split this post into 2, first some theory about LEDs in general, growth leds, and some physics 101 that is of interrest when building your own led light.
Light emitting diodes:
The principal leds depends on electroluminescence, which means light through electricity and was first discovered in 1907.
The whole principal in a nutshell is, electrons are excited to a higher orbit and releasing light when going back to the ground state.
The Color of the led depends on the level the electron is excited to, lesser orbit means a higher wavelength (energy is a to the power -1 function of wavelength), the materials used in leds to create different colors are:
(GaSb), GaAs, indium phosphide (InP), and silicon-germanium (SiGe)
Reason LEDS are becoming more common is that they are way more energy efficient then an incandescent or fluorescent light because of the required energy less is transferred to heat, and more into light (which is also heat but another wavelength which we consider useful)
The earliest lifeforms on earth could not produce their own energy, but gladly they evolved.
The first plants that used photosynthesis to produce energy were cyanobacteria and eventually they evolved further, and somewhere between a few milion years ago and now, carnivorous plants became to exist.
Every plant uses photosynthesis, which is: using light to make usable energy.
Plants do this by capturing electrons (light) by having chlorophyll. The 2 main chlorophylls in plants are Chlorophyll a and chlorophyll b.
In these chloroplasts there are Photosystems (I and II), which can "capture" electrons and divert them to make all kind of molecules (like making O2 from CO2 and ATP => making energy aka photosynthesis)
But the rate at which plants can use electrons is depending on the wavelength (also commonly known as color):
Therefore it can be concluded that giving plants the light they can use most efficiently (most usable electrons per watt of energy) is the light at the maximum absorption.
So became the LED grow lights.
I have to say i have found very few commercial grow lights that consider these peaks (they come close but as u can see a 20nm change can mean 60% less efficiency), that's one of the reasons i made my own.
Another reason is that comercial lights favored red, and i wanted more vegetative growth (which comes from blue light) instead of potgrowers which want flowering (achieved from red light).
First i decided on which leds to use and which power supply, then calculated which leds could be grouped together (voltage wise), the 420-450 and 6000k leds were similar in voltage 4.0-4.2 V.
Plan of the build:
Then i started drawing up -a more or less- evenly disributed array of leds, aiming for ~50 watts in power usage, done this a few times, determining what was the best way soldering and led distribution wise. the final design is as follwing:
Where the (+) means positive, and (-) negative, this way i have most of the positive wires in the middle and negatives on the outside, easier wiring this way with ~50 leds.
The used materials: thermal glue, star board heatsinks, soldering iron, leds
When not glued yet, use the thermal glue to glue the individual leds to a star heatsink
Glue them to your heatsink (in my case an aluminium plate)
O wait, i needed a layout
finally done, glueing the leds and soldering the wires in between (the 420-450 and 6000k leds were in sets of 3, the 660 and 630 leds in sets of 5 (due to difference in voltage), ceramic resistors were soldered into each set.
This is the complete panel except 5 660nm leds, so actual intensity will be higher, as a reference, full sun is 1800 microEinstein, 2x6500k 18w t8's measured 250 mE at 20 cms away.
Due to high energy prices here (~25 eurocents per kWh) i cut the whole in half so i ended up with 3-3-3-5-5 ratio of 420-450-6000k white-630-660 nm led, these are my helis under them at about 20-30 cms away with the single 22w lamp covering an area of 40x80 cm's:
This setup is cooled by a 8 cm diameter fan, and the aluminium plate i used as "board" only gets about 10 degrees above ambient temperature.
So in all, leds, and especially well designed leds can be a very good subsitute for CFL's when it comes to growing cp's, yet there are a lot of unknowns and research needs to be done in order to truely understand the effects of differences in wavelength on cp growth.
Please feel free to ask questions regarding grow LED's and i will do my best to find the answer!