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Mike sent in another one of his projects. This time it's a super efficient grow light for your plants. As usual, Mike has included all the schematics, parts list and PCB layouts to make your own. If you want to skip the fun part, you can also purchase one completed.
A grow light made from red and blue LEDs being pulsed. This light fits inside a Altoids container and requires less than 1.1W of energy to grow a 6"x6"x6" space. Lights can be chained to grow more plants. Total lumens = 111. Plants need primarily red (680nm) light to grow and a small amount of blue (440nm) light. By pulsing the LEDs at 720Hz or higher the plant can achieve maximum growth with a minimal amount of energy.
How to make a Super efficient grow light
I'm not sure I get the value of the 720 Hz pulsing. Pulsing means less actual output. Why not just use fewer LEDs for the same total illumination? The high frequency pulsing seems more of a way to fool your light meter into giving a false read--or so I would guess.
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This is total overkill. I would rather use the board space occupied by the controller for more LEDs. Pulsing the light gives no advantage over continious light with the same photon flux:
http://adsabs.harvard.edu/abs/1994PhDT........53T
Since the power of LEDs in pulsed mode is usually lower then in continous mode due to surge current limitations, pulsing costs intensity and therefore growth rate. And 110 lm? What? Pack 10 5 W Luxeon K2 and get like 5 times as much! I would just adjust the ammount of light needed by the number of LEDs to use.
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The adsabs.harvard.edu... link is informative from a PhD point of view. The link talks about "transformed" tomato and tobacco plants under red LEDs - "transformed" means? Further, the question of mixing blue LED light affects growth how? Finally, I can conceive of using pulsing as a way to allow/extend battery usage (which may be convenient) - would pulsing then be so much an issue?
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Here's a link to a full PDF about pulsed vs. continuous light, University of Wisconsin. https://mywebspace.wisc.edu/tsharkey/web/My_papers/Tennessen%20Bula%20and%20Sharkey%20Pulsed%20light%201995.pdf
Choice quote: "The photosynthetic apparatus integrates the pulsed light and uses it as efficiently as continuous light. [...] in both the sunfleck work of Pearcy and colleagues and the work reported here, in no case were equal numbers of photons used more efficiently when provided in pulses than when provided continuously."
Of course this research is 14 years old, and I'd be interested to see if Mikey Sklar has references to updated information about this.
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@ clifford
AFAIK, pulsing extends battery life by putting out less light. While our persistence of vision may be fooled and not notice the difference between high frequency pulsed light and continuous light and and the pulsed light may fool some light meters, the actual energy transmitted is less than from a continuous source if all other parameters are the same, .i.e. there is no way to fool the plant into thinking it is getting more energy than it is.
So, this looks like a super inefficient way to make an LED light source for growing plants. (Maybe just a way for the DEA to track illicit growers by specialized chip purchases :-) (Probably not, but one wonders why all the high tech for no actual gains in energy input to output ratio.))
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This is the paper I used for the research about pulsing. Their research on potato plantlets is quite detailed and shows that above 720Hz the plants did not seem to detect a difference between that and full on driving the LEDs. They also explain the lower frequencies 220Hz and such can be used to save additional power. Give it a read and see what you think.
http://www.ecaa.ntu.edu.tw/weifang/led/360204hs.pdf
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@ MS,
Damn you and your well cited, fact-based logic! Thanks for the citation.
TTreatment no. & treatment code Daily light-on Hours
1. LED-CNF-100-8/16 8 × 100% = 8.
2. LED-CNF-100-12/112 12 × 100% = 12
6. LED-IP720-50-16/8 16 × 100% = 8 [there is a 50% duty cycle for the pulsed LED, but they have an odd way of writing it in the table]
What they didn't do was compare 16 hours of continuous LED light to 16 hours of pulsed light operation, so although we have comparison of what is supposed to be identical photon flux we don't have comparable "light in operation" day cycles.
Next, each treatment was only applied to three samples--a fairly small data set, all though the trend across the treatments appears consistent, but I suspect that they were ordered post hoc to make for a prettier chart.
But, I must say the study is intriging and I'd love to see independant confirmation of the results. Perhaps a Maker following the plans will do so!
Thanks for the response.
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