Introduction: LED Grow Light

Picture of LED Grow Light

This is my first attempt at an instructable. This was also my first attempt at building an LED grow light using spare parts laying around the house. My main inspiration came from an instructable by DemonDomen, (

This is a fairly simple design, but would probably benefit from having a light sensor (something I didn't have easy access to.). I plugged mine into a light timer, which is now running my hydroponics setup. I was disappointed with how directional the light ended up being, go figure since I used parts from a flashlight, but it should still work well for seedlings.

Step 1: Gather Parts

Picture of Gather Parts

Parts List:

LEDs salvaged from a Maglite (LED conversion kit)
DC Wall wart**
Small Dowel (From the craft section of the Dollar Tree, originally for another project)
Scrap metal (PCI slot cover from cheap computer case)
Straw (Optional, not shown)
Electrical Tape (Not shown)

Soldering Iron & Solder
Drill Bit (And drill of course)
Knife or scissors (to cut straw)

**NOTE: Match your wall-wart with the power needs for your LEDs. I grabbed the closest I had on hand, (5V DC) and the circuitry running the LEDs overheated fairly quickly. I will be looking for a 3V DC PS next time I hit RS or Goodwill.

Step 2: "Arm" Assembly

Picture of "Arm" Assembly

I started by drilling (2) holes in my piece of scrap metal. The Dowel appeared to be about the same size as the little nub on the LED casing, so I made both the same size.

The idea was for the weight of the LED to make the metal catch on the wood so it would be adjustable in height, but still hold. Turned out the dowel was too small. A quick simple fix with a straw, and I had a perfect fit!

TIP: if you fold the end of the straw into itself and push it as far through the hole as you can, then you can simply push the dowel through the straw and it creates a tight fit. At least it worked for me :)

Step 3: Attach LEDs

Picture of Attach LEDs

The Maglite LED conversion kit came with a back plate that helps hold it in the flashlight (A battery leaked in my Mag and corroded the 3rd part of this assembly beyond my fixing it). I pinched the metal arm between the back plate and the LEDs, then bent the leads to hold it in place. (See the first three photos)

A quick (and not so great looking) soldering job attached my wall-wart to the LEDs.

To hold it all in place and keep the wire out of the way I wrapped the arm in electrical tape. I probably should have covered the wire leads as well.

Step 4: Final Assembly

Picture of Final Assembly

Stick the dowel in your potted plant, and you have yourself an LED grow light!

Since I don't have the proper power supply for my LEDs yet, I don't know exactly how good this really works.

As you can see in the last photo, I zip tied the wire to the dowel to help keep it corralled.

As for parts, since that will probably be where most of the comments will be aimed, I used what I already had laying around the house. I do believe you could build a better looking, if not better working, light with a little planning and shopping. If you have comments or improvements I would love to hear them. I would also like to hear about experiences from people who have tried LEDs for grow lights.




arnookie (author)2011-04-26

If you are thinking of building a diy grow light please take note of this.
Each and every led needs to be atleast 1watt each. Anything below that will be useless so don't use old leds out of toys or old boards, they simply will have too little Total lumens versus lumens per watt. You need atleast 10mm LEDs with 1watt per LED to supply enough light to the plant anything lower will not work. A good combination is a pannel made from 75% 1watt red high brightness leds, 20% 1watt blue high brightness leds and 5% 1watt amber high brightness leds. somewhere in the region of 660nm for red and 460nm for blue
There is also no effective difference in penetrative power for horticultural purposes between a 1W LED and a 3W LED. So anything over 1watt is just wasted. This means brightness has very little to do with the benefit you will get once you use 1wat leds. Don't confuse this with a pannel made from say 20 LEDs rated a 10watt as to one with 10 LEDs rated at 10watt. As the 20 watt pannel will use the useless 0.5watt leds verses the 10watt pannel that uses 10x10watt 1watt LEDs that are ideal. This has been tested and proven that 1watt single LEDs have great benefit to plants and anything less is just a waste of time and has no benefit at all to plants. The same applies with going brighter than 1watt has no benefit either.
Hope that may help some of you. Especially if you are growing indoors.
Also LEDs are more efficient than any other form of grow lighting available.
The commercially available LED growlights outperform all other growlamps from HID lamps to including high pressure sodium (HPS) and metal halide (MH) lamps.
So prepare to see other grow lamps become obsolete as LED growlight take over.

The Freak (author)arnookie2014-10-15

You posting this nonsense everywhere right? This is plain wrong on so many levels. It might be true that a plant has a minimum and maximum light intensity per leaf area that it can absorb. I have never read about this but hey you are probably right on that, it makes sense to me at least. But this is in no way directly correlated to 'only 1W LEDs are useful'. If you place a 1W led on the moon and a 10W close to your plant, is this equal for the plant? It just doesn't make sense. Is it better to place 10x 1W LEDs close to your plant vs a 10W LED a meter or 2 away? Probably, yes. It is all about light intensity per area, not about 1W is better then everything else. Placing 500 0.9W LEDs next to your plant (equals 450W) compared to a single 1W LED, in your theory the 1W LED should do better. There is just no way this can be true since Watts is just a unit of current times voltage, why would the plant care about current and voltage to a light source? Plants like the sun, but no current and voltage there, just nuclear fusion. (Well actually I guess its a plasma of sorts, so electrons are flying around like crazy but hey lets not go there.) Nor is the sun a 1W LED. Shall I compare the 1W LED with the sun?

Yilgul (author)The Freak2016-04-01

that escalated quickly

The Freak (author)Yilgul2016-04-03

Yes guess so, but it annoys me that he comments these false statements on many instructables, resulting that there might be persons building stuff based on his statements. I don't mind him being convinced that he is telling the truth, just don't try to make other persons believe it.

arnookie (author)arnookie2011-04-26

Just to clear a point up. If you make a 100watt pannel with 100x1watt leds you will benefit. But if you use 200 0.5watt leds to make a 100watt pannel it will not benefit the plant at all. The same applies if you use say for eg 10x10watt leds to make a 100watt pannel then you are only really getting 10watts overall because the extra 9watt per LED is just wasted as the plant will not benefit. SO using 100x1watt LEDs will benefit the plants by 100watts. 10x10watt LEDs would not because 9Watt of each led is just wasted giving the plant just 10watt of usefull light. Sorry but thats just the way plants absorb light.

conscious (author)arnookie2012-03-12

Hey, can I ask you where did you get this idea that "anything below 1 W would not work and anything above 1 W is unnecessary"? I seriously doubt the validity of your claim. Try not to discourage others when you do not have the necessary expertise in the field.

arnookie (author)conscious2012-03-12

I can assure you what I stated is correct. Although people should take into account that new led technology is being made and some lower watt bulbs may produce a better nm spread and power. Although testing has shown this not to be the case so far. The results above were concluded after intensive tests and trials so I do know following this guide is a very very good idea.
I also do not discourage others from experimenting in any way they see fit. I do beleive after tests that the advice I gave is good and provides much better results. My main point being that a lot of sellers are producing LED grow lights that have little to no benefit to plants. My advice is mainly to stick to the 1watt led setups rather than the cheaper 0.5watt led setups that provide dissapointing results and can let people down.

conscious (author)arnookie2012-03-12

Thanks for taking my comment in positive light. I am still curious where you got the information; I want to verify it myself because it does not make logical sense to me. Plants need a certain luminous intensity or say a certain energy per unit solid angle (or say area) per unit of time for healthy growth and if that condition is met with proper wavelengths in any combination of LEDs or candles, I don't see why the plant should complain.

arnookie (author)conscious2012-03-12

Let me try explain this in as simple terms as I can. At a low watt say .5watt the plant can not absorb light as it will not penetrate and be absorbed. In tests it takes at least 1watt to penetrate and be absorbed by the plant leaf to be any benefit at all. Anything above 2 watt will also not be absorbed by the plant and will be wasted. Basically the plant can only use so much light. In this case that is 1watt. Going above that just becomes a waste of energy. Led's run cold so they can be place extremly close to the plant material. The only reason to go above 1watt is in a situation where the light needs to be further away from the plants. I would say to go up in wattage by 1watt for each foot away from the plants you put your lights. So if you want to grow plants with best economy put lights close to the plant within 1 foot and use 1watt leds. If you want the light 5 foot away use 5watt led arrays. This is because by the time the light reaches the plant it would only roughly get around 1watt from a distance of 5 foot from a 5watt leds.

1st_Balrog (author)arnookie2015-05-16

In my opinion, Watt and Plants have nothing in common.. what really matters is the Lumen per inch/foot/meter/[put your measurement in here].
Also Lumen is the better way of comparing old light bulbs vs new LED ones. e.g. a 100W old one equals a new LED with 15W from X or a 12W from Y (X & Y as producers), but all 3 bulbs give ~1600 Lumen, making them equal in brightness but different in Watt.
What you're right about is the different amount of LED's with the 75%,20%,5% types. 3 red ones and 1 blue (if you have no amber).

BarkerS1 (author)2015-05-13

Akin Yildiz (author)2014-04-20

hello everyone, this is a very cool simple design that gave me a wider vision on what I was already kinda putting together, please check it out... love and peace !

fredrikher (author)2009-10-09

good work with your LED growlight.

pullinsb (author)2009-03-26

Do these LEDs give the proper light spectra for growing? I would think the light would be too "cold" (blue) for good growth as opposed to a HPS light. Maybe?

Jux (author)pullinsb2009-03-26

That's something I'm not sure about myself. I would love to hear feedback from people about that. One idea I have heard before is that a combination of red and blue LEDs "should" work well, since plants reflect the green spectrum. Some of the comments on DemonDomen's project talk about some of this, including adding IR and UV light.

sammons (author)Jux2009-03-28

no, no no, UV is bad for plants, and does not help plants grow at all. If you are into growing the magic herb though. a little UV in flowering is said to remote higher THC because the resin is actually a defense mechanism against UV. as fat as IR goes, plants do absorb small amounts of specific IR light, but does not seem to be as significant as 660nm Red. so if you are after efficiency, just stick with 660nm for the red end

FeedTheGrid (author)sammons2009-04-24

660nm Red is good knowledge to have. Thanks, sammons. FTG

FeedTheGrid (author)2009-04-24

Great concept, Jux. Keep 'em coming! FTG

sammons (author)2009-03-26

Good instructable, as far as photos and comment go. But your design needs work. For starters you are going to need many more LEDs for the plant to even notice it. photosynthesis takes more energy than that. Research has shown a ratio of red blue should be in the region on 1 blue 9 red. the red is best off being at 660nm, and your blue LED should be 440nm or there abouts. Unfortunately the standard everyday red and blue are not these wavelengths.

LED driver circuits are really easy. if you are using just a few small 30mA LEDs then a tuned resistor is the way to go. calculate by Ohms Law. Target Current = 30mA, Voltage of resistor is supply voltage minus voltage of led string (number of LED's in series times the voltage drop of that led). Ohm's Law states that V = I x R, thus R = (5 - 3) / 0.03 = 66.6 Ohms, but the closest available resistor is a 68K so you would use that. giving I = V / R = 29.4mA

using P = IV the resistor dissipates 29.4 x 2 = 14.7 Milliwatts of energy

to use higher power LED's, for those that are a little more serious, you can use an LM317 or similar adjustable linear regulator setup in current regulating mode.

:o) Phil

Jux (author)sammons2009-03-28

I certainly see you point about not enough LEDs. With how bright mine are, I could see them working for a little while with seedlings, but once they start growing leaves... who knows. I haven't been able to find a good PS for it yet. Quick question on your voltage numbers: I've read that it can be bad to run your LEDs in series, because if one of them dies, the rest get over powered.. or something to that effect. Sound about right? and how would running them in parallel change your calculations? I may be over simplifying something I don't completely understand anyway.

sammons (author)Jux2009-03-28

OK, do not try too hard looking for a power supply. any old power supply will probably do. Just try find one with a high voltage like 12-24v. then calculate how many led's you want. work out the power they will consume, and make sure you power supply has more power than that. i.e. if you find a 12v 1A power supply. then it can supply 12watts. That's like 90 or so LEDs you can use on that power supply . Laptop power supplies are great because they are commonly available in 16v 19v 20v and sometimes more and are usually around 60 to 90 watts. That's good because the less driver circuits you have to make the better. about the LEDs in series. that's no problem if you run your series of LEDs through a current driver circuit. i.e. get a LM317 (pretty cheap). look up the datasheet and you will see the pinout. ADJ, output and input. you connect this inline (see photo) to one of the LEDs in series to control the current along that series string. that way if one of the led's blows and goes closed circuit. then you don;t fry the rest of them. your LM317 will just get hotter. not only that, it has an inbuilt thermal shutdown so even if many of them blow (because you have been driving them too hard, then you won't cook your power supply, the driver will just shut down. for more info on using your LM317 go

Jux (author)sammons2009-03-29

awesome! thanks for the info! :)

santa7 (author)2009-03-26

Hm it may be smart to have a resistor on those leds, and pulse them to ensure they don't burn out. An expansion to this project would maybe ad a clock to switch it on and off or light sensitive resistors to shut off when there is sunlight.

Jux (author)santa72009-03-26

The Maglite LED conversion kit I used has the resistors and circuitry built into it. I didn't think to show that part, but it might be a good picture to add. Thank you.

sammons (author)Jux2009-03-28

the Maglight kit has a switch-mode current regulator circuit. The batteries inside a torch usually don't have the voltage required to run the LEDs. so the regulator is a dc-dc converter. to keep the power to the led constant. you could use this but it is not a very cheap option.

Jux (author)sammons2009-03-29

Your right. The only reason mine was cheap was because I salvaged it.

kostya (author)2009-03-27

Few days ago I read an article on using LEDs to grow vegetables in a spaceship.It is published in March issue of the Russian scientific popular magazine Science and Life. They did a number of experiments to find out which leds would be the most efficient for this purpose. The winners are white powerful leds. Thanks for a nice instructable.

Jux (author)kostya2009-03-28

Very interesting. I will have to see if I can find that article. Thank you!

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