LED grow lights... input please.

[jabzab]

i think they mean the efficiency of the photons being absorbed by the plant. Im looking into pulsing for energy saving reasons, since energy is only required 1% of the time compared to 100% of the time. Yes the current will have to be raised 2-3X higher so that will increase the power used to about 2-3%. In the graph it shows that photosynthesis occurs at the same rate (100%) as long as the pulse is less than 100us.





so the paper based its research around determining if photon efficiency was higher when pulsed, and i did some reasoning of their research and came to the conclusion that if photosynthesis occurs at the same rate when using alot less energy, then why not use this to our advantage???

If you want to take graphs and not bother to read the caption, and ignore conclusions, go ahead.

jabzab Reviewed by jabzab on 04-24-2008. LED grow lights... input please. Hello guys, I'm exchanging eMails with a representative from a LED company. I asked him if they could produce a custom light for growing, and here's what he told me: Our options are as follow: 940nm, 850nm, 660nm, 630nm, 610nm, 590nm 570nm, 530nm, 510nm, 470nm, 460nm, 400nm and a total of 64 LEDs in the bulb. Rating: 5

[physicsnole]

read the paper again, and if you still disagree with me, read it again. in fact keep reading it until you realize what the captions and conclusion are really talking about. i don't know what else to do to try to explain this to you without getting to technical, i don't know how far in calculus you got so i don't wanna waste time spewing out intense mathematical calculations that nobody will understand. I can assure you that i understand the math and physics talked about in that paper and that it does still apply for our purposes. maybe we wont get a 99% increase in efficiency, and maybe 1% duty cycle isn't the most efficient for growing, but its a start, and thats what im hopefully going to find out.

[jabzab]

Let's have a look at the graph again, with the caption. You see how it says increasing photons per pulse, and the total amount of photons emitted remained constant?

If you have a light on constantly, lets hypothetically say it emits 100 photons per second.
If you have the same light on half the time, it will obviously only emit 50 photos per second on average.
So say if you wanted the light off half the time, but want 100 photons per second, you could get two of these lights, or drive it at a higher current, which corresponds to giving off 100 photons per second.

If you have a look at the graph which shows relative luminous flux vs forward current for CREE XE-Rs, you need more than twice as much current to double the light output.

Conclusion: It's less efficient to pulse.

I can't make it any simpler.

[devilgoob]

It's not the photons you put out, it's how they're used.

Photosynthesis isn't continuous, it goes in steps, so when you pulsed light at 5khz, then I assume in the mean time they are still using the light the pulse gave them while the light is in the duration of the off cycle. Or they are recycling the light...as in sunflecks.

It's been proven with tomatoes...........lol.........

physicsnole wouldn't be screwing with hundreds of dollars of equipment and designing circuits if he didn't know what he was doing.

n00bs that come in here without reading up or going off other's opinions need a life, but after physicsnole is done with this and you see the results YOU will become the n00b that wants to be like him.

PLUS If you'd read the chart....it's 4.6 umolc02m2s1 for continuous light and just as much with the pulsing BUT at a certain pulse duration. I don't get why posting a graph that you can't understand has anything to do with being knowledgeable.

[physicsnole]

think about average power used from AC instead of instantaneous DC power during those pulses. since there are capacitors and inductors in the power circuit the pulsed energy is taken from them, and then the AC "slowly" gives the power back, making the average AC power used lower. indeed there is still alot of testing needed with pulsing. i couldn't tell you one PWM frequency or duty cycle that works, cause i havent done it yet. And on the cree graph the derivative of the line for the white/blue looks constant past 250mA, however i am sure that it tapers off at a point, as most components do. this max point will have to be determined with testing. if we can reach the saturation point of photosynthetic quantum yield by experimentation then we can see if the LED array or whatever other light source we use produces "too much" light, in which we can then pulse the light to reach the saturation point, but not exceed it. to tell you the truth pulsing might not bring any advantages to the table; if the LEDs cannot reach the saturation point even when overdriven. But if they can reach tose saturation levels then we can limit the use of the LEDs (on time) to save energy. The theory is there, just needs to be tested. oh and pulsing is not less efficient, it is just as efficient as continuous light. Finding the right frequencies of PWM and flux could prove to lead to a nobel prize. one thing is for sure, plants do not need continuous to perform photosynthesis at the same rate as with continuous light.

and the fact is this is not a simple topic. we can put it into simple words, but that just destroys the value and information the theory provides. if you still dont believe me, fine, the test will prove who is right and "wrong"

[physicsnole]

http://www.plantphysiol.org/cgi/reprint/88/1/158.pdf

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http://www.biophysj.org/cgi/reprint/16/1/93.pdf

http://www.ecaa.ntu.edu.tw/weifang/led/360204hs.pdf

MAKE: Blog: Super efficient grow light

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[jabzab]

I made it as simple as possible, but you still don't understand. I'll leave you to it.

[jabzab]

Scrap that, I think physicsnole does actually understand the point I was trying to make now. devilgoob, you've proven you don't have a clue

[physicsnole]

im glad you realized that:thumbsup: thank you for understanding i understand where u come from

[Opie Yutts]

I understand that jabzab understands that physicsnole now understands that jabzab understands that physicsnole has a clue.

I've always understood that.