# LED grow light (blue and red)



## Aepoc (Jul 25, 2007)

I am interested in building a grow light with LED's for an indoor herb garden i plan on having over the winter. I recently read that plants only need two colors of light: some around the red wavelengths and some around the blue. I was wondering first of all if the plants would grow with a combo of red and blue LED's. Seccond I was wondering how much output I would need. Lastly does anyone know a reliable source for some colored luxeons?

I know that this isn't a flashlight but I put it in the LED section because I wasn't sure where else to put it.

Thanks in advance for your help.


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## enLIGHTenment (Jul 25, 2007)

See this thread: https://www.candlepowerforums.com/threads/169757

The Luxeon and Rebel colors most effective for typical plants are royal blue and red.


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## spaech (Jul 25, 2007)

Aepoc said:


> I am interested in building a grow light with LED's for an indoor herb garden i plan on having over the winter. I recently read that plants only need two colors of light: some around the red wavelengths and some around the blue. I was wondering first of all if the plants would grow with a combo of red and blue LED's. Seccond I was wondering how much output I would need. Lastly does anyone know a reliable source for some colored luxeons?
> 
> I know that this isn't a flashlight but I put it in the LED section because I wasn't sure where else to put it.
> 
> Thanks in advance for your help.


Hey there. I'm attempting this exact thing with some luxeon rebels (see the link in enLIGHTenment's post). People have used red & blue LEDs to successfully grow plants, though I haven't seen any cases using high power leds like luxeons or crees.

Currently I'm running just one red & one blue rebel together @ 700mA as a preliminary experiment, and my plants seem to be responding. They are bloody bright, even with just the two of them! I intend to ramp up the output tenfold once my stars arrive so I can mount the rebels properly. At this preliminary stage though it looks as though it should definitely be feasible to use these LEDs as grow lights. Very power efficient grow lights, at that!

Try here for sourcing rebels, they seem to be the cheapest & best stocked - I got mine there.


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## StandaT (Jul 26, 2007)

For exact wavelenght of light for different purposes look at this picture.


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## wakibaki (Jul 26, 2007)

Aepoc said:


> ..for an indoor herb garden...


 
LOL. Yeah.

w

I'm working this issue. The initial cost is somewhat higher than HIDs, but the TCO gets ever more favourable. One problem is the balance between Red/Blue required for best efficiency. This doesn't seem to be well understood. A few hundreds of watts in R&B LEDs + drivers + power doesn't come cheap to run experiments with.


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## Kinnza (Jul 26, 2007)

Most high power red leds have a somewhat short wavelenght emission (625nm dominant, about 632-633nm peak usually). And most manufacturers have only one color bin in the red. Lumileds has two bins, but the longer one isnt avalaible (ive requested it some times in the past). Cree offer the bin R4 (630-635nm dominant, about 638-650nm peak), wich is a bit better for plants.

In the blue range, any bin work fine. Royal blue is the most adecuate, but the difference is little, because, opposite to the red side, in the blue the increased photosynthetic efficacy is toward shorter wavelenghts, wich means less photons per emited watt.

Anyway, dont get fooled with photosyntetic pigments absortion spectra. What matter is the whole leaf absorbance, and its very flat (less than 2x the photosynthetic efficacy of best wavelenght against worst wavelenght along the PAR (400-700nm) range). Differences between 600 and 670 nm are little, below 10%. 

Notice plants adapt their photosynthetic system to use the best the light they receive (changing the percentage of each pigment at chloroplasts).

I think makes sense using a percentage of white leds, now that phosphors improvement had let to less losses at them. Cool white leds mixed with red leds may give a very nice spectrum for plants while allowing to check plants without a weird pink tone. White leds provide photons of all PAR wavelenghts, wich is good for healthy plants. Not neccesary, but useful. Aditionally, white leds emits some in the far red range (700-800nm) wich most plants needs at some development stages, and specially, long day plants to trigger flowering.

Check these articles for more info on this topic: http://ncr101.montana.edu/Light1994Conf/Contents.htm


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## wakibaki (Jul 26, 2007)

Good link Kinnza, thanks.

OK, so let's do a little ball-park figuring.

I'm going to introduce a few assumptions. 

For most instalations and plants a 400W HPS (e.g Grolux) is as large as can be practically utilized without a light rail or substantial installation. In the UK a basic lamp + reflector + ballast can be bought for UKP90 (180USD at time of writing). I'm going to use it as representative of a typical purchase.

Of course LEDs can be distributed, so it may be possible to use higher powers effectively, but we'll ignore that for the present.

A 400W HPS runs ~40,000 lumens or 100 lumens/watt (some better, some worse). Of course at least 50% of this is going the wrong way, and meets the reflector where it is probably reduced to 70%, some of which is still going in the wrong direction.

Then there's the green. We're going to save on all the useless (maybe) green light that we're simply not going to supply.

Production LEDs don't actually run 100 lumens/watt, lets say 70 although the numbers aren't directly comparable with the complex spectrum of the HID. First guess at the photon flux ratio R:B from what I've read so far is 5:3, let's say twice as many red LEDs as blue.

We want to run the LEDs @ 1 Watt, for a good compromise between output, efficiency and longevity. 

Let's say that taking into account the savings in luminaire efficiency and green light and the losses due to the apparent poorer luminous efficiency of the LEDs err.. 140 red LEDs and 80 blue.

Plus drivers, heatsinks, optics or reflectors, a support, wiring and a 200W+ DC PSU.

Let's say $10 per LED and supporting stuff, and an old computer PSU (maybe a couple old laptop supplies) ...only $2200.

Against that, the LEDs have a lifetime 5 times or more that of the HPS, and there's the power saving and less waste heat, if the numbers are right. That would be 8760 kilowatt-hours (units) over 10 years of 12 hours on/off. 

So reckoning $30 per bulb the capital outlay on the HPS is $300 so if your electricity costs more than $1*1900/8760 = 21.7 cents/unit then you will be a winner after 10 years. 

If the numbers are right. 

w


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## Kinnza (Jul 27, 2007)

When thinking in lighting for plants, you need to avoid thinking in lm, because its a units for human, and gives little info about effect on plants. Its necessary use radiometric units, optical watts or better, micromols of photons (uE), because photosynthesis is directly related to photons count, not energy (both a blue photon and a red one do the same photosynthetic effect, although the blue one carry a lot more energy).


A typical 400w HPS, the Phillips SONT Plus, emits 670 uE (1,53 uE/watt, supposing a consuption of 440w, including ballast). About 20-25% of them get absorbed by reflector (and easily a 10% more if the fixture has a glass barrier). It means from 536 to just 435 uE avalaible for plants.

Say you use a LED fixture with 40% white leds and 60% red leds (the ideal would be using blue, red and white, but this is just to make calculations easier, as anyway its just an aporoximation). 200 uE provided with white leds and 300uE provided with red leds.

For example, using the Cree XR for white. The XO bin gives 311 lm/optical watt at normal operating conditions. Say you use the newest bins emitting 100lm/w, wich equal to 100/311=0,321W emited=321mW. 100lm/w emits 1,4 uE/w (14uE/Klm). So you need to install 200uE/1,4=143watts of white leds (considering optical losses negligible, although it may count for up to 5%).

The XR red, bin R3 at Tj=52ºC, brightness bin M (highest avalaible currently), gives 38,9lm (already derated for increased Tj over ambient, considering thermal resistance junction-ambient about 30ºC/W). At average consuption of [email protected], its 49,5 lm/w. At 38,4 uE/Klm, its 1,9 uE/w. 300/1,9=158w of red leds.

Total of 301 watts of leds, plus drivers losses (10% with very good drivers), 330w.

So you are saving 110w to achieve same radiance in photons. Using it 12h a day, it mean 482KWh a year. For me, its about 60€ (~80$) a year. The current cost of a 330w led system would make it impossible to compensate with that electric bill savings and relamping costs.

Im putting it in the worst scenario, as getting the light better distributed and spectral advantages (about 15-25% more efficacy of red photons against the yellow emited by the HPS) may count for a reduction in the uE required to achieve same photosynthesis. Taking this into account, and supposing 400uE of LEDs can have same photosynthetic effect than 500uE of HPS, then you will need to install 225w of leds (about 55% of required with the HPS). Electric bill savings would be of 845KWh in this scenario (about 100€~135$ a year in my case). In ten years of use, savings may count for near 2000$, allowing to recover the initial investment. But anyway, too long to considering it "cost effective".

Notice that the bins used are premiun ones, wich are very expensive when thinking on install so many watts of LEDs. When we mod a flashlight, we dont mind paying for a premiun bin, but it isnt the same when buying more than 200 high power leds. The only advantage, you dont need to do a group buy .

Said this, im doing a LED light fixture for plants, using stock cheap leds, but i dont think it worth the cost, just giving use to some old leds (2005, now near obsolete). I want to check how it work with plants, and whats exactly the photosynthetic gain of using LED photons.

If prices continue going down and perfomance increasing as they had done along this year, maybe next year or the next as much, cost scenario could be very different. I hope so.

Future is bright!


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## Aepoc (Oct 9, 2007)

Thank you all for your suggestions and information. This is plenty to get me started. I would like to hear any further information on how those plants do.


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## knabsol (Oct 11, 2007)

I´m in the process of building a light here. It´s going quite well so far. I´m using the luxeon rebels for this. How are your ideas with the cooling and so on?


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## Aepoc (Oct 15, 2007)

knabsol: where did you find your rebels. The euro store online that someone pointed out looks legit but i don't know if they ship to the states


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## knabsol (Oct 15, 2007)

I´m in europe (sweden) though I ordered them frmo the US. I ordered from www.luxeonstar.com which worked really nice and had good prices. I´m just waiting for my power supply now before I can fire it up.


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## VanIsleDSM (Oct 16, 2007)

Well I dunno what kind of herbs you're growing but this may give you some good information (obviously this is illegal to do unless you are a medical user or something and I don't condone it, but it's a good information resource to use for all plant growing)

70Watts of red/blue LED VS 70HPS.


First time:
http://www.icmag.com/ic/showthread.php?t=59699&highlight=led+hps

Second attempt:
http://www.icmag.com/ic/showthread.php?t=67108&highlight=led+hps

There are some things to consider, like when the lights go out the plants don't go right to sleep with LEDs.. there's more info in that first link about it.


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