Introduction: Build Your Own 3120 Lumen LED Grow Light

Picture of Build Your Own 3120 Lumen LED Grow Light

I started this journey after after testing several of the low cost grow lights being imported from China. Every one I tested was over hyped, low powered junk. By the time I got tired of fooling with the Chinese junk 3 watt LEDs had come out and I realized that with the right cooling a lot of these could be mounted in a very small space. You can read more about this project on our web site.

Fast foreword 2 years and industry has finally released more affordable LED replacements for screw-in type light bulbs, including LED flood lights. And while in LOWES looking at LED light bulbs one day I wondered if my Grow Sun grow light had been out flanked by technology? I wondered of a lower cost LED based grow light could be put together out of production LED lights? Well, the answer is yes, you can put together your own high intensity LED grow light, and this article shows you how.

We decided to sell a fully assembled version of this grow light fixture. You can find more details HERE.

Step 1: Select the LED Flood Lights You Want to Use

Picture of Select the LED Flood Lights You Want to Use

I did a lot of shopping around the big box stores and picked out a LED flood light I liked. It's a SYLVANIA ULTRA LED flood light. The output is rated at 520 lumens at only 8 watts of power and because of the relative small size (2.5" across) I thought I could get 6 mounted to the housing I had in mind.

Step 2: Select the Housing

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The housing I had in mind is manufactured by LMB HEEGER in California. It measures 7" X 5" X 2" and I was pretty sure I could mount 6 LED flood lights in the box.

Step 3: Select Your Light Sockets

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The sockets I chose are the ceramic snap-in style & they are designed to mount in the same size hole you would punch in a box to mount 1" conduit. The hole is 1-1/8" diameter.

Step 4: Layout a Template

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I used MS Word to layout a quick drill template. You can use paint, another drawing program, or hand draw something. regardless you need a template to make the project look sharp at the end.

Step 5: Tape Template to Box & Drill Pilot Holes

Picture of Tape Template to Box & Drill Pilot Holes

Any time I'm going to drill a hole in metal I start with a pilot hole. A pilot hole acts as a guide to larger drill bits and you end up with a much sharper project at the end.

Step 6: Drill Holes in Rear of Panel

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I drilled the holes for the power cord, power switch, and grounding point. Because this is a metal box it's extremely important that you use a 3 wire power cord and properly bond the green safety ground to the box.

Step 7: Drill the Main Mounting Holes

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Then I drilled the main mounting holes. See how stright they are? It's because I used a template then I started the large holes with pilot holes!

Step 8: Mount the Light Sockets

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Once I completed the holes I mounted the light sockets and did a trial fit with the lights.

Hint: Because the aluminum chassis is flexible it's impossible to push the sockets in from the front. You have to put the socket in the hole, place the chassis on a table top face-down, then use a largish screwdriver to push the chassis into the socket.

Step 9: Wire the Chassis

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Because this is a light fixture you are supposed to wire with high temperature wire. I used Teflon coated 22 gauge wire. Why so small? Because the entire fixture is only going to draw 48 Watts & that's only 0.4 Amps at 120 VAC. 22 gauge wire is rated at 5 Amps.

Step 10: Connect the Internal Wiring to the Power Switch

Picture of Connect the Internal Wiring to the Power Switch

Connect the internal wiring to the power switch. I used a 2 pole, 2 throw switch because that's what I had. If you use only a single pole switch make sure it's wired to turn the black wire on & off.

Step 11: Wire in Power

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Attach the power cord ground to the chassis. I used a 3/16" aluminum rivet and a backup washer.

Whe connecting power make sure the power cord black wire is routed through the power switch and then on-to the brass colored screws on the back of the light sockets.

Step 12:

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Close the housing and test.

The lights on picture was taking under normal office light. Also, note that the lights run cool enough for me to hold them. Try that with a Sodium Vapor Lamp!!!

But does this fixture produce enough light?
For comparison, a typical 2 tube 24" florescent grow light fixture produces about 1300 lumens of light.
This fixture produces 3120 lumens of light and you can fit three of these fixtures in the same space that a 24" flouescent fixture fits in.
In other words, with three of these fixtures you can produce 9360 lumens of light - about 7 times more light than two 24" florescent tubes, and in the same space!
I think this fixture produces enough light!

What about red and blue spectrum light?
At these light levels who cares?

Thanks, Tom Hargrave

Step 13: Select Mounting Brackets

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In a rush to get this instructable published I completely forgot about mounting, so I ran down to Home Depot and bought these mending plates for less than $3.00.

Step 14: Mount the Mounting Brackets

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Then I marked the locating holes, drilled the holes, riveted in the mending plates in place, and now I have corner brackets that I can use to hang the fixture with chains and S hooks.

Step 15: Test Light Under Shelf

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I can also attach the fixture to the bottom of a shelf with screws. Looks like I need to build two more....

Step 16: Select a CFL to Test

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After reading some of the great feedback, I went shopping for some alternate bulbs. I found some 1190 Lumen 6500K "daylight" CFL bulbs at Wal-Mart that were not too expensive.

One complaint I have about these lights is they are not a spot light design and the light will transmit from the sides, so in theory if the fixture is above your plants in a open room your plants will not receive as much light from these as they would from a more focused source like a spot light. But if you are going to grow plants in a closed box like I did in this instructable it probably does not matter.

My second complaint is they draw considerably more power - 6 of these will draw 120 Watts where six of the others will only draw 48 watts.

Step 17: CFLs in Fixture

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And here is what the lights look like on and off in my fixture.

Step 18: CFL Verses LED Light - Side by Side Comparison

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I did a side by side comparison by first mixing three and three. You can see that my camera "sees" some color difference but not much, probably because the sensor is swamped with light.

Then I re-arranged the bulbs - I put thee of one type down one side of my fixture and three of the other type in the other side of my fixture. I separated the two sides with a heavy piece of cardboard and turned the light on in a darkened room. You'll notice the color difference right away - that's the difference between a 3000K and a 6500K light source. But you'll also notice that the brightness appears about the same even though the LED light is rated at about half the lumens. This is because the LED bulb is a spot light design and all of the light is pointed down. The CFL bulb is a non-spot design and the light is spreading everywhere.

We decided to sell a fully assembled version of this grow light fixture. You can find more details HERE.

Thanks, Tom


IanA78 (author)2016-08-05

I read your full instructions AND all the comments with some interest. I have a PhD in physics and a new interest in grow lights. Specifically , I want to provide some extra light to a terrarium in a north facing spot in my house that receives only a small amount of indirect sunlight.

An important point here, often overlooked or sidelined, is that these lights produce a light that is more pleasing to the (human) eye. Whenever mentioned it has been a case of 'but the human eye is different to a plant's needs', but I am interested in simultaneously pleasing both my plants and my eyes! Sure, it must be true that by concentrating power output to the specific wavelengths that are used in the various photosynthetic processes must result both in better plant growth and lower operational cost, but such lights have the drawback of making the room look like aliens are visiting! That might be fine in a basement or cupboard for certain types of horticulture, but it is not going to cut it in my dining room!

The discussion here about LUX vs. Lumens is very true (i especially enjoyed the tangent about rays of sunlight being almost parallel by the distance of the Earth - something I assumed in so many problems I solved at uni!), but being a physicist, the photosynthetic response curves were completely new to me. Now I assume that the various elements of photosynthesis evolved long before the current variety of plants and these peaks in absorption (as indicated on the graph posted by 'Redbinary') are the same across the diversity of plant species? i.e. Algae, moss, flowers and vegetables all have very similar peak absorptions in the red and blue that are often quoted here and elsewhere.

From what I understand about photonics (e.g. from the photoelectric effect) is that so long as some of the photons are in the energy range needed for absorption (chlorophyll A & B absorption peaks), then the light will have some effect on the plants. Increasing the intensity of photons at these wavelengths will increase the effectiveness of the grow light but with the drawback that the emitted light becomes less aesthetically pleasing. However, if the intensity of the whole spectrum were boosted by the same amount, the intensity of PAR photons increase, yet the overall light remains white(ish) but gets brighter.

What is potentially of worth here then, is that it MAY be possible to deliver enough red and blue wavelength (PAR) photons to benefit the plant but where the other wavelengths, far from being useless, result in a light which isn't painful to look at! Given the low cost of LED lighting, I'd pay a bit extra for the light and room to look nice, especially since I have very limited space and only one 18 inch square terrarium to illuminate - my considerations for a nice room with healthy plants are very different to those of a commercial grower who wants maximum yield at minimum cost and it seems that many of the detractors on this post are in the latter category. Such disagreements are like comparing apples to oranges.

So, rather than saying this light is for reading or other tasks (as suggested in one comment), so long as these LED lights provide some photons at the wavelengths of interest, you could say it is a 'supplemental to natural light' grow light. Only experimentation will tell you whether or not the number of white LED fixtures necessary to noticeably boost growth would result in a set up so bright that your room looks like a floodlit stadium!

With the last comment being some months ago and it now being the height of summer, I hope that you have been able to test out these lights and that you may be able to let us know whether your set up provided a high enough intensity of photons at the key wavelengths to have an effect on your plants.

AlanD105 (author)IanA782016-11-17

Hello, I too am like you I am learning about this process. What I have learned regarding the human spectrum and plant spectrum is regarding the PAR (Photosynthetically active radiation). Which is about the chlorophylls and carotenoid response to light waves, specifically measured in nm. I have found lots of research that indicates that the light plants need is hardly ever pleasing to people. If I understand it correctly our vision is much more blue and plants are non-flowering plants are red and green with a smattering of blue. Now to make even more confusing you have to worry about light heat temp and light irradiance. The heat part is hopefully obvious but you dont want to bake your plants. Get it bake. hehehe. Anyway, irradiance is the strength of each light wave group from the distance of the emitter, that says how much of each wave band will be however strong at a specific distance. My research indicates that lumen and watt are more relevant for human sight and less effective for grow lights. I could definitely be wrong but I have read all the research put out by Cornell and they clearly say " (Don’t use these units for referring to greenhouse lighting):"

Sadly it is next to impossible to carry around a spectrometer to measure light bulbs at Home Depot, and they go out of their way to not break down the light bands even for grow lights.

Hope this helps.

goykhman (author)2016-04-13

The output is rated at 520 lumens at only 8 watts.


..or 1560 lumen at 24 watts, or 65 lumen per watt


LED, $2.50 apiece if one buys four, 800 lumen at 8 watts or 100 lumen per watt

Fluorescent, $3.25 apiece if one buys four, 1600 lumen at 23 watts or 70 lumen per watt

Dr_Traigh (author)2016-02-13

You made a great project and I'm going to buy the stuff to do this today.

I've been reading the comments, and wow man. Chill out and maybe try the project before spouting all kinds of hate about full spectrum lights and raving about how useless all the wavelengths other than red and blue are. Apparently you're all scientists, so do some science. Maybe don't blindly follow online charts and papers, and perhaps do your own experiments? You know, science? Test your hypotheses.

If full spectrum LEDs work for the author, and they work for me, then the project is a success (Scientific Method, and all that...). If not, then I guess I'll have 6 more LED bulbs to make my place that much more efficient.

bhb420 (author)2015-10-22

some plants need different spectrums for different stages like our 4 seasons when the sun closer and futher we are getting different spectrums as the 4 seasons so unless you want to waste time and money on house plants that dont produce and give back your normal house lighting is fine maybe open the blinds but brightness on single spectrum house/flood light isnt whats going to make a healthy plant and that set up would be too bright for normal house plants now on the smokeable kind of plants you would want high uv's with lots of blue white and purple specs for vegi stage and for flowering whites orange reds and about 3 weeks til harvest time you would also introduce med to high uv to increase potencey and thats opitional so check the specs and research the plants to see witch type of specs they like and at what lumination and for how long

bhb420 (author)2015-10-22

man before any of yall go out and a bunch of flood lights from the hardware store do your research first those lights are only giving off one spectrum maybe 2 and some plants need sertian spectrums to be heathy or even to bloom flower or produce fruit yeah if you want to spend money

GeorgR (author)2015-07-04

How exactly is this a grow light? It's 6 normal "Living room" LEDs as far as I see, you're basically wasting most energy on the green spectrum plants don't even need. If I just assume that each of the lamps above is $10 (which they for sure, if not much more), make your project at least $60 for the lamps PLUS the entire DIY work. Sorry, but then even a cheap 300W+ China LED grow light which can cost as little as $70 (6 Spectrum with 3W or 5W LEDs) seems a much better choice to me than your DIY project there. And might ironically even be cheaper ultimately.

Tom Hargrave (author)GeorgR2015-10-02

Yes, it's a project based on normal living room LED lights but that was the plan all along - to build a grow light from material you can buy from LOWES. This is a "grow light" because of the high concentration of light from one source. You won't find a off the shelf light that produces as much light in such a small space.

altainta (author)2015-09-29

Very creative i found only 2-3 sources over the net who suggest using simple LED bulb as a grow light.

are flood light and spot light are different ?

What are the different names for the LED flood light

What should one what out for before buying ?

Can you suggest more alternative buy (on the LED bulb ) with amazon uk / us ?

the product you made is sufficient for how many plants ?

Tom Hargrave (author)altainta2015-10-02

We are in the middle of a LED light revolution, with light technology evolving so fast that even models introduces three months ago seem obsolete. My best advice is to limit your selection to floodlight style LED bulbs, then buy whatever produces the most lumens per watt, then set up as many lights as you can afford.

"How many plants" depends on what you are growing. The light I made grew two tomato plants just fine with some help from an outside window. The same type plants in the same window grew too tall too fast, so I know the lights made a difference. We don't grow pot here, it's still illegal in Alabama.

BarkerS1 (author)2015-08-05


My name is Susana Barker, i am a housewife but I like the
high-tech very much. I want to find a best led to grow all tree in my garden. I
like this article very much, this article is very helpful for me, i will share
this post to all my friends. The best same site, I found at Google: Thank
for shared!

GeorgR (author)2015-07-04

Also, just as a side-note, LED technology, for growing but also for lights at home is fortunately progressing like crazy the last few years. I believe that today you can actually get "decent" LED grow lights without spending too much money. I constantly read about people warning about cheap "China LEDs"...but then I bet any money that pretty much ANY manufactured has them produced in China and uses the same parts and LEDs, saying that your $800 super-grow light might necessarily not be that different than the $100 "cheap" one, I mean ultimately most of this stuff is made in China...just rebranded and then you pay premium just for a name. My $0.02

Tom Hargrave (author)GeorgR2015-07-09

Be careful when value shopping because but there are a lot of cheap grow lights on the market that don't produce much light and are grossly misrepresented.

Also, this article was written just before the bottom fell out of the consumer LED market. Right now you can buy a LED flushmount ceiling fixture from LOWES for about $36 that I believe would make a great grow light. I also believe that these are a better deal than any specialty grow light you can buy.

One advantage of building a fixture like the one in this article is with the right LED spot lights you can generate a lot of lumens (light concentration) from one spot and this would be important to some growers.

Aadieu (author)2015-05-19

uhm NO

cheap closeout multisocket strips bathroom strips (those things u see over mirrors a lot) and/or 2:1 Yconnectors and/or 4:1 splitters

2015 prices paid:
$3 / 950 lumen LED bulb for COOL WHITE/DAYLIGHT 5000-6500K
$0.25-0.59 / 1200-2400 lumen CFL for SOFT WHITE (cfl deals too nice to go led for 2700-3000K, also cfl soft whites have 65-70 lumens/watt, which while nowhere near led 5000k's ~100, is just a hair worse if it all than the 60-80 lumens/watt out of common cheap soft white fixtures and connectors are pricier than bulbs these days, and good CFLs sit in the 23-40w/1200-2400 lumen ranges vs led's 9-11w / 600-950 lumens, making mixing in some cfl good common sense)
$2.50 / Yconnector 2:1 splitters
$5/ closeout 3 bulb strip fixtures, even had a semblance of a reflector albeit bronze coloured

currently running clusters of hanging yconnects, havent installed the 3 socket strips yet. bulbs totalling ~200w, half LED half CFL by wattage, put out measured lows of 10,000k edges to average 30,000- 40,0000k lux AT FOLIAGE for most plants in a black and yellow aero tote. measurements supported by the most robust growth seen at the brightest spot.

no leaf burn. cheaaaaaap. and puts out the kind of foliage surface lux people look for out of MH and HPS (desirable range often stated as 25k-50k - my 30k-40k for most positions foliage fits right in with that), simply cuz led can be run point blank and cfl a mere 2 inches away or so, and thus their lumens actually deliver. while mh lumens dissipate since its temp requires running it from way far off..

Tom Hargrave (author)Aadieu2015-05-23

Congratulations, that's a great find! But not everyone finds closeout items to fit their projects.

Coffeinated (author)2014-03-05

I don't think the LED Lights were a good choice. The lumens just don't matter alone. If you want a nice 200 gram steak, you won't be too happy with 2 kg sausage, would you? Like that, light with 3000 K does not have the right wavelengths of light that plants need. With normal fluorescent light tubes, you want to go as high as possible, like 4800K or 6400 K, which I use, or you can mix 2 6400 with 1 4800. But light tubes give off a whole mixture of wavelengths, that is well known. LEDs work completely different and no one knows which wavelengths your lamps have. That is why professional LED Grow Lights use red and blue LEDs in a certain mixture.

Tom Hargrave (author)Coffeinated2014-03-05

I put a tremendous amount of research into lighting and plant growth. I learned that plants are sensitive to all light wavelengths not just blue and red. I also learned by doing my research that the light sensitivity graphs that are scattered all over the net are somewhere between misrepresented data and outright lies. What I discovered through research is the graphs that show high sensitivity to red and blue light and almost no sensitivity to green light misleading. Find the real light sensitivity data and you will see that the bottom 2/3 of any graph that shows only red and blue has been cut-off and that plants are sensitive across the entire range of visible light with red and blue being the most sensitive areas.

Costarus (author)Tom Hargrave2014-03-05

Alas, but this is not so. Just 130 years ago a scientist Timiryazev studied this process. Important only the red and the blue part of the spectrum. Green indifferent. Sometimes add a little white. For the aesthetics of the human eye. But plants are indifferent. The white light is wasted much energy.

I successfully grow salad lamp 20W (15W red LED and 5W blue.). This is enough for the area of 40 x 40 cm

Aadieu (author)Costarus2015-05-19

20w "daylight white 5000k" led, as long as pointed correctly, can output absolutely INSANE amounts pf lux at 40cm x 40cm

RedBinary (author)Costarus2014-03-09

Thanks! I'd be interested in you doing a write up on this!

Tom Hargrave (author)RedBinary2014-03-09

As in, you want to build one or you want me to loan you one so that you can use the light and report to the rest of us?

I had originally intended this to just be a project to share, but based on the initial interest in these instructions I wonder if we should start selling light kits?

RedBinary (author)Tom Hargrave2014-03-09

Here's a variation on the graph Costarus posted

Tom Hargrave (author)RedBinary2014-03-09

I've seen this chart in many variants but what the publishers don't tell, or at least what the original publisher does not tell is the lower part of the chart is cut off and the range is re-scaled. Find the actual data and you'll see that plans sensitivity to green is not close to 0 as the chart leads you to believe, but plants are about 1/2 as sensitive to green as they are to red. The problem is this chart has been posted on the net and has gained traction and is now taken as "the gospel truth" for lack of a better term. I'm sure you've seen the insurance commercial - the one where the lady states "if it's posted on the internet, it must be true?"

Get away from the "light fixture marketers" and turn instead to sources hosted by educators (Universities & such) and you see the real plant light sensitivity curve. It took a few minutes to wade through the HPS, MH and LED marketing sites to get to university hosted sites but right away I found a chart of the actual plant light spectrum sensitivity. It's the second image I uploaded. The image shows a dip around green but the dip is no-where around 0!

Also, the human eye sensitivity to light bell chart in this graph is dead wrong. I added the correct graph that does show our eyes are more sensitive to green but is nothing like what's in the previous chart.

RedBinary (author)Tom Hargrave2014-03-10

Not to pick nits, but since you infer that I'm gullible and only read marketing drivel: the scaling of the charts are different. Yours aren't really labeled well and contain no citations whatsoever. Regardless, it appears that in your second chart the black line is chlorophyll blue absorption wavelengths with the peaks at A and B just as in the one I've posted , while I have no idea what the green line is. You've also taken issue with "human eye sensitivity peak: perceived white light" in the chart I posted and then posted a chart showing almost identical sensitivity, just scaled differently.

As far as scholarly articles here's one of the several I looked at before posting:
an excerpt of which is "Upper curves: Diethylether solutions of chlorophyll a (Chl a, solid line) and chlorophyll b (Chlb, dotted line) show distinct absorption peaks in blue and in red regions of the visible spectrum (redrawn from Zscheile and Comar’s (1941) original data)." as well as "Leaves absorb visible light very effectively (>90% for all wavelengths combined; solid curve).Wavelengths corresponding to green light are absorbed less effectively (absorptance drops to c. 0.75). Beyond 700 nm (infrared band) absorptance drops to near zero, and forestalls leaf heating from this source of energy."

Tom Hargrave (author)RedBinary2014-03-10

I did not intend to infer that you are gullible, my comments are for everyone to read & not just you. Unfortunately there is a lot of marketing hype on the net and I'm just stressing, or maybe over stressing that point.

RedBinary (author)Tom Hargrave2014-03-09

Actually, I was replying to Costarus' comment. I'd like to see more about what he's using for the targeted wavelengths. After my comment I did a little looking around online and this appears to be the current "state of the art".

After my admittedly cursory reading around I am curious how much of the 425-465nm and 640-660nm spectrum is being emitted in the configuration you've used. I understand that your goal is to open up the area to less technical people, but I've found some of the red/blue LED grow lights online for around $20 each.

Tom Hargrave (author)RedBinary2014-03-09

Buy them, use them, please let us know how well they work!

I bet when you get the lights in they will be powered by small power supplies that can't deliver any real power. These are the type lights I mentioned at the beginning of my article.

maxhuey (author)Tom Hargrave2014-03-09

years ago, I was using exactly the same 1000 watts HPS lights that every other commercial grower is using, most growers were getting 0.5 pound ~ 1.1 pound of harvest per light, I was getting just over 2.0 pound per light, there's a lot more to growing than just lights. If you do it right on the entire process, simple HPS works just fine.

Aadieu (author)Coffeinated2015-05-19

other way around.

ALL white leds emit significantly in the entire visible spectrum, with high blues and reds, and comparatively lowrr green and yellow. meanwhile, fluoros and cfls emit three HUGE NARROW SPIKES in R G B and barely anything else

kainxavier (author)Coffeinated2014-03-05

Lumens can matter alone just fine. HPS or MH grow lights dont have nor need a perfect full spectrum to grow from seed to fruit because of the pure amount of lumens they output. If you're serious about growing, you switch between the two to simulate summer/fall sunlight though (spectrum as mentioned). The point is, lumens CAN cut it. However, I dont know how much you'll really grow with only 3000 of them.

slo5oh (author)kainxavier2014-03-06

Lumens are not the important number when it comes to growing. LUX is the correct identifier. Believe it or not, there is real science behind this. You need to provide plants the correct color ranges for photosynthesis and enough LUX to make it happen. Science says these are in the red and blue range. (see chart above from costarus)

It's hard to admit, but even if your light works for a grow light, there are MUCH better ways to do this.

kainxavier (author)slo5oh2014-03-06

Metal halide (predominately blue) and
high pressure sodium (predominately red) bulbs have been the standard
for indoor growing for how long? Neither of them give off a perfect
red/blue spectrum, yet you can grow from seed to fruit under either
because of the sheer amount of lumen output. As I pointed out in
another post, people that really want the best results start with metal halide bulbs and finish with high pressure sodium to simulate the change in seasons.

most reviews of red/blue LED's were for the longest time, poor. They
simply didn't provide the lumens even though they were the optimal
spectrum colors. They're definitely better as of late through
technology improvements (IE More juice!). But still, I stand by what
I've said that you'd be better off with true high power LED's like the
Cree cxa3050 (something I'm currently building with myself).

Coffeinated (author)kainxavier2014-03-06

Of course, as long as the right wavelengths are at least there, you can just give off more light and it will eventually be sufficient at some point. But that is of course not the best way. To get back at my steak/sausage example, if I give you 2 kg meat of which 50 gr are the steak you want, of course I can just give you that four times so you have 200 gr steak. No problem.
Metal halide and sodium pressure lamps are just easy to get, and known technique.
If you would try to grow plants with a green laser, even 100000 Lumens would not be okay for your plant, it just would get quite hot. So if my lamps give off just the right spectrum, I can save energy because I don't have to emit the waste, the useless light.
So, with mixed spectrums, lumens can kill it, but that's not the clever way.

Tom Hargrave (author)Coffeinated2014-03-06

As I stated earlier and I will state again. Because one of the goals of this project is to make it build-able by
anyone with local hardware and you aren't going to find a 50w LED spot
light at your local Home Depot, Lowes or Menards store.

Also, the person most likely to build this project is looking at buying or building a "grow light" to grow a few plants indoors or start seedlings for his garden. The folks shopping for HPS or MH grow lights as well as those looking for high wattage red & blue LEDs is probably not going to be interested in building one of these lights.

Tex Arcana (author)Tom Hargrave2014-03-09

I'm interested, but not for a grow light. We have a large torchier that we've owned for 20 years now, and has seen everything from a 300w T3 halogen, through a 150w PAR38 reflector, to a twin-circline T8 fluorescent fixture (there worst of the bunch in terms of light quality, thanks to the incomplete spectrum, but the best in terms of heat output). This idea might just work for me.

Tom Hargrave (author)Tex Arcana2014-03-09

The trick will be to adapt a fixture to screw into your floor lamp. Maybe you can build something from a screw in base, a box and 4 sockets, kind of like a 1 to 4 adapter that you screw into your fixture?

Tex Arcana (author)Tom Hargrave2014-03-16

In case you didn't figure it out, I did all of those adaptations. so, yes, it'll be something akin to yours. is the fixture, except I pulled everything apart and flipped the base, to act as a reflector as well as allow it to sink into the fixture more. I'll likely use that plate, and see how an array of LEDs will work I'm guessing I need at least 4000-5000 lumens to make enough light, the 500w T3 worked great, but the heat output and power consumption don't make it worth it.

Tom Hargrave (author)Tex Arcana2014-03-16

Interesting, that's a picture of an old Circle-line fixture. I'd like to know know things ultimately work out.

Tex Arcana (author)Tom Hargrave2014-03-17

precisely. cost me $5 after my employee discount, the bulbs cost more than the fixture. I'll get pics of the fixture shortly.

ohbejoyful (author)2015-02-18

Love this - very easy to follow, and you make it sound very doable.

I would still prefer LEDs over CFLs, since CFLs contain mercury and thus cannot be discarded in the trash. They must be taken to a hazardous waste collection site (Home Depot takes them here in PDX, and there is also a county collection site).

Akin Yildiz (author)2014-05-05

we don't need so much power, it's all about the angles, i have a 7W plant arm with no fan - no heat sink... check it out. you can attach these plant arms to any pot !

can be powered via USB, rechargable battery or solar even !

visit my profile;

djimdy (author)2014-03-31

Aside from (or in addition to) Lumens and LUX, could someone add information about CRI ? It would seem that higher CRI would mean more balanced light. So to that end why not build up shop lights with high-CRI, high Lumen T8 bulbs that also use low power?

Tom Hargrave (author)djimdy2014-03-31

The higher the CRI rating the more natural color rendering appears to your eyes, with 100 being the same color rendering to your eyes as natural sunlight. But this does not mean the light is producing the same spectrum as the sun or that a high CRI rating is the best light for your plants. Here is a good article about CRI.

djimdy (author)Tom Hargrave2014-03-31

Thanks for the educational link. It doesn't seem to make sense to me, however, that if a light produces the same spectrum as the sun it may not be the best for one's plants unless plants actually prefer higher or lower K lighting (i.e., with either higher or lower visible wavelengths filtered out, respectively). Is that the case?

Tom Hargrave (author)djimdy2014-04-01

Science discovered a long time ago that plants process some light colors better than others. And if you have control of the brightness of different colors why not tune your light source to benefit your plants? Anyways, that's the theory and the reason you see oddly colored grow lights. This project is all about building a grow light from off-the-shelf lights and my theory is if you get the light bright enough the plants will grow well anyways.

Surferdude (author)2014-03-18

This paper ( ) gives you the actual data in addition to the graph (on page 4). Although it's only for one type of plant (bean), it has a pretty good discussion and the concept is what's important. Note that it's based upon photons, not lumens. The curve measures how many photons are required to produce CO2 at each wavelength, not just what seems to be absorbed. Since this reaction and the production of ATP form the basis of the energy flow into the plant, it's what's really important. The long wavelength red is about 1/3 more efficient than green, so you're right that the curve doesn't drop to 10% as in the absorption spectrum, but the definition of lumens is so heavily weighted to the green that it makes the miscalculation even worse (as argued by Coffeinated, above).

If you add up the red, green, and blue in the chart you show for cone sensitivities in the retina, you end up with a curve that has an even more pronounced peak (because of the overlap with the red and blue sensitivity curves). That doesn't really matter though, because the lumens you're talking about are a measurement standard, not the actual response of your retina. That curve does have a peak in green, so light from bulbs intended for use as general purpose lighting get more "credit" for photons that have a wavelength that is not as useful to plants, as demonstrated by the photosynthetic action spectrum described in the paper.

shadewolf (author)2014-03-05

Forgive my ignorance about light meters, because I haven't tested it yet. If I was to make 2 of these units and put a light meter under both of them lit up, does that mean I'll get 6240 lumens right beneath them or will it still be 3120. Ie, adding extra 520 lumen bulbs pumps up the lumens on the meter when tested? Are the bulbs additive in brightness, or will they each show just 520 lumens of light when tested at say 4 inches away under the centre of each light?

Tom Hargrave (author)shadewolf2014-03-05

Total light produced will double and the brightness definitely will increase but measured lumens will depend on where you measure. Unlike sunlight where the light is pretty much a parallel beam because of our distance from the sun, lumens will decrease as you move away from any bulb.This is because with any light source but the sun, light spreads as you move further away from the source. Professionals who grow under artificial light understand this and they measure their light levels at the leaf level.

"This is because with any light source but the sun, light spreads as you move further away from the source"

That's not true Tom. The Inverse Square Law applies to all electromagnetic waves, of which the Sun is one.

The illustration below is the correct one.

Tom is right on this one. The inverse square law requires that you measure from the source, not from some arbitrary point. In this case, the difference in intensity (L) at point b, 1 foot farther from the sun than point a, is something like L(b) = (93,000,000^2)/(93,000,000.0002^2)*L(a). For a lamp it's very different. In that case you're maybe 2 feet away, so one foot farther away the intensity would be L(b) = (2^2)/(3^2)*L(a)

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