LED Lighting - DIY Style

Geomancer

So I'm an Electrical Engineer by day, novice aquariest by night.

I've been thinking for weeks of something practical I could make at home that wouldn't cost exponentially more than just buying it pre-made off the shelf.

Then I had an epiphany! LED lights to grow plants! Genius!

So I went to my favorite parts supplier and lo and behold they did list kelvin ratings, awesome. So I searched for everything between 6000K and 7000K. Got lots of results. Perfect!

The question then becomes of intensity, and how on earth do you compare LEDs to incandescent (or even fluorescent) lights.

The brightest option was a 850 lumen LED at 6300K, 11.8W. Not bad at all. Now, if I look at a table of lumen's versus watts for incandescent lights that makes it equal to a 60W bulb (or 14W fluorescent).

Does that make sense in my logic? That's one heck of a lot of light coming from a single 12mm (half inch) diameter LED!

The issue, of course, is cost. These suckers cost $26 each! However, I was only looking at the top of the barrel. Lower intensity LEDs are of course less expensive and I'm sure I could find a more cost effective $/lumen. Still, a couple of those and it isn't going to be more expensive than buying a pre-made one (A 5 LED 19" @ 6500K marketed for growing plants is $136 and is only 12W).

Geomancer

Found another much cheaper alternative, less than $6 an LED however only 5500K. Here is its color spectrum, it is the one labeled "Cool White".





Another possible issue is heat dissapation. That would take a bit of consideration, but I still think I could come up with a cheaper alternative ;)

Geomancer

One final note that sounds cool. They drop to 70% of their luminosity at the 50,000 hour mark. At 10 hours a day that's over 13 years ^_^

Quantum

edit: new post answered my question

Quantum

Very little red in the cool white.


I would argue that lumen would not be the best way to compare light output unless the spectral output is the same. Irrandiance (watts persquare meter) would be the best way to compare, but not sure it if that info is available.


The 11.8 watt number for the LED is interesting. Is that power consumption? Any links to the sites where you are getting this info?

Geomancer

Yes, that's the maximum power rating.

I do my shopping at Digikey, although Newark is another big one. I find Digikey easier to find things though, both will sell electronics is small quantities.

I know lumens on their own isn't much use, but coupled with the kelvin rating should give some basis for comparison. I would hope that a 5500K LED for example would emit nearly the same 'colors' as a 5500K fluorescent? Lumens, power, and wavelength (or temperature) are all that's given typically in LED specs (well, that maters in terms of lighting). The lower power ones give their intensity in candle power (mcd specifically).

An alternative is to get wavelength specific LEDs and build an array of them, but I have a feeling plants aren't that specific, more of a range of wavelengths than just two very specific ones. That's why I went with ones rated in kelvin rather than specific wavelength.

zof

I hope you will start a DIY thread with a parts list and assembly if you go this method, would be interesting to see your results. Also make sure you stick around! I need a good electrical engineer to ask questions to once I find some stepping motors for my arduino..

Quantum

I hope it didn't seem like I was questioning you about the numbers you had listed, I just wanted to be able to go to the sites and look around rather than ask a bunch of questions.

This may be the case, but since the spectral output of fluorescent lights can be very limited, only emitting certain wavelengths and Kelvin temp technically only refers to incandescent (e.g. full spectrum) sources, the K rating of fluorescent lights can be somewhat inaccurate. As a result similar K ratings don't necessarily mean similar spectral output and trying to compare lumens of sources of dissimilar spectral output could be misleading regarding light energy output - it would be ballpark at best.

It would be easy if the radiant power numbers (in watts, which is why I asked about the 11.8 number) of the various light sources were availble - I mentioned irradiance earlier to try to avoid confusion between electrical power usage watts and light energy output watts, but since we are talking light source, radiant power is the better measure.

Regarding wavelength specific LEDs, the association between chlorophyll (a) and photosynthesis is very specific regarding wavelenth, but that is not to say that flooding plants with light of those wavelengths produces better growth. Full spectrum light (roughly equal in blue, green, and red) is generally recommended.

Geomancer

Not at all =) I'm confident in the electrical aspect, but the light aspect, well, I have no experience with that.

Yeah, that information is not provided, just the electrical power, a lot of which I'm sure is heat.

The datasheet for the small 6300K bright one that's fairly expensive at $26 each is:
http://media.digikey.com/pdf/Data%20...tor/W724C0.pdf
(also has a spectral graph, looks to be worse than the 5600K one to be honest.

The datasheet for the less expensive 5600K one is:
http://www.bridgelux.com/assets/file...3%20120311.pdf

I suppose the only way to know for sure is to try it and see what happens The 5600K ones are only $5.26 each.

rjwwrx

Interested to see how this works out. Good Luck