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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.
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Step 1: Select the LED flood lights you want to use

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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.
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ohbejoyful2 months ago

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 Yildiz11 months ago

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;

djimdy1 year ago

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)  djimdy1 year ago

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.

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)  djimdy1 year ago

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.

Surferdude1 year ago

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.

shadewolf1 year ago

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)  shadewolf1 year ago

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)

Dude, you missed what I was saying. Tom EXCLUDED the sun from the inverse square law. I simply said that it applies to ALL em waves, and the sun is a source of em waves. Your calculation should reflect cutting the distance in HALF, not by one foot. Its erroneous and misleading. If you want to compare apples to apples, add another SUN in your calculation, one that is TWICE the distance from the earth/measurement point... and guess what, we're back to the ISL.

My reply had two points. The first is that although light from the sun does indeed obey the inverse square law (ISL), the sun is so far away that any distance around your house (with respect to sunlight) is so small that it's unlikely you can measure the effect: the rays are effectively parallel. People sometimes mistakenly start measuring from the wrong place when using the ISL. You have to measure from the source. So, for the sun, that's a point 93 million miles away. The .0002 at the end in my example is one foot farther away. So if you move 1 foot farther away from the sun, the light flux is 99.9999999995699% of the original value.

The second is that, by not using a factor of two as you suggest, I'm showing the general way of calculating the effect of the inverse square law. It doesn't only work when you double the distance. The general relation is a power law. So if you have a lamp that's 2 feet from a plant, and you move that lamp one foot father away (now three feet from the plant), the energy flux on the leaves is now 4/9 of the original value. If you moved it to 4 feet from the plant (double the original distance), it would be the more familiar 4/16 or 1/4.

Tom Hargrave (author)  dougstrickland1 year ago

I agree that the inverse square law applies as much to sunlight as to any other radiation source. But for the purpose of growing plants the law has no measurable impact on light. We are 149,597,887,500 meters from the sun and the distance between a plant and a grow light is maybe 1 to 0.2 meters? Apply 149,597,887,500 and 149,597,887,501 into your formula and you will see that the brightness difference is so small that 1 meter further away from the sun does not matter. BUT 1 meter further away from a grow light has a huge impact on light brightness. Depending on your bulb & reflector design 1 meter away could be 1/4 of the original light brightness or less.

Tom Hargrave (author)  dougstrickland1 year ago

I agree that sunlight from the sun is spreading out just like sunlight from a lamp is spreading out. But because of our distance from the sun and the short distance between where someone would hang a grow light and the plant leaves sunlight light could be considered parallel.

This is a question of Lumens vs Lux. (As some have tried to clarify..) Lumens is a measure of the total light output of something. Lux on the other hand is light output divided over an illuminated area. (lumens per square meter)

With the sun, given its distance, intensity, and polarization, it lights the surface of your garden evenly. An electric light source however is closer, so it is spread across your garden unevenly.

Tom Hargrave (author)  dougstrickland1 year ago

Lumens is a measure of the amount of visible light radiated from a source. For example, these bulbs are rated at 520 Lumens each.

LUX is a measure of light brightness and LUX is equal to one lumen per square meter.

This attached picture shows how the two measurements compare. The light source may be 3120 Lumens like my project, but as the distance increases between the light source and your plants the LUX decreases as the light spreads out.


First, you just repeated what I said.

Second, the illustration you shared represents beam angle, something beyond this discussion. A more representative image follows.

The problem is that you are coming from a growers POV, where a basic understanding of Optics would be more helpful. Since optics require more complex calculations, and dependent on measurements that growers do not typically have instrumentation for, empirical evidence is more likely to be produced and shared.

As a lifelong photographer, scientist, and grower living in Sonoma County, I assure you that I come by this knowledge through formal education in Physics, hands on experience, and the scientific method.

Tom Hargrave (author)  dougstrickland1 year ago

Actually, I was not responding to you I was responding to the same person you were responding to & that's why my answer is essentially the same. At the time your response was not in the order it's in now.

maxhuey1 year ago

Just wondering about the LED lamp you purchase lat your local "Big Box Store"... where are these lamp made?

What is the country of origin of the material used to manufacture the lamp and where is it assembled?

Tom Hargrave (author)  maxhuey1 year ago

The box is marked "Made In China"

Thank you, I have made my point on your initial comment about Chinese Junk Products.

You see, most people in North America including me have the same impression as you do about Chinese junk, but if you had traveled to China, you will quickly realized there are no "Junk Products" in China. In fact everything they use are much heavier duty than us here in the western world.

"Junk Products" came from greedy western businessmen who decided to pay as little as possible for products that barely works so that they can make bigger profits. Just look at the TV infomercials for wild claims. Because of that, the Chinese businessmen simply geared they business toward the majority of western consumers who likes buying cheap junk products.

Talk to any western corporate buyers and they will tell you that if you want to buy product "A" from a Chinese manufacturer, they will show you 5 "A's" that looks exactly the same but the first one would be $50 and the last one would be $500. Can you guess which "A" these western corporate buyer will choose?

It is unfortunate that "most" western consumers can not understand "you get what you paid for" principle so they simply blame it on the Chinese for producing junk products.

To stretch this further, you probably know that the whole world has been blaming China for most of the pollution in the world as you would often see this in the news like CNN and such. But, if you think deeply, we in the western world are actually the blame for all these pollution by the way we consume and waste. Look at this another way, if all these products are manufactured in North America, can you guess where the pollution will be coming from?

I hope this will let you and many other readers understand the real facts. Let's not blame others for our own fault.


You can say that the pollution in China is the western world's fault, but that is a grossly over-simplified view. If the same products were made in the US, they would not result in the amount of pollution that is coming out of China, we have environmental controls in place that result in less pollution from our manufacturing processes. In addition there is a culture of conservation of resources in this country that generally helps to keep our air and water clean, which can not be said for China. Having lived in developing countries (or some would say 3rd world countries), I can say that cultural priorities are very different. When many people in a country are concerned about whether they have food or not, they are often less concerned about litter, smoke, and other forms of pollution. In addition, in a quest to raise their socio-economic situation (while likely having little education about pollution) they do what they have to in order to produce the products that the rest of the world consumes. There are of course exceptions in both the developing world and western world, however look at the levels of air pollution in the big cities of China where much of the manufacturing is done and then compare to similar areas in the US. China's lack of pollution controls is by Chinese governmental and business choice, not based solely on western world demand for product.

Let's not forget that most of their plants that pollute the most came from the U.S., which means those corporate b45t4rd5 ARE responsible, because they sold those plants (and our jobs) off to China.

And how did those jobs get sent to China, by free trade agreements that were passed by American lawmakers that were elected by the American people. We only have ourselves to blame, not the corporate b45t4rd5. Elections have consequences.

except for those that were bought by those corporations, along with the votes that ultimately stripped us of our rights and our jobs.

That is true 15~20 years ago,

I have traveled to China just 10 years ago and saw the amount of progress they had done to control pollution. Many system are among the highest standard in the world. Unfortunately, it is the shear volume that still cause the pollution. No country in the world can handle that kind of volume and still have clean air. Look at Wal-Mart alone, can you find anything in there that is not from China? Have you been to industrial belt in Midwest and southern US to look at the pollution a just few tiny factories (compared to factories in China) does to the air? and this is not even 0.01% of the volume output in China. An average Chinese person uses less than 20% of the energy a typical north American person use.

We need to control our own wasteful habit here in the western world. It never help blaming others for problems we created.

The average Chinese person, compared to the average US person is not an apples to apples comparison. What was done to adjust that percentage for access to products/energy, socio-economic status, etc. I'm quite sure it wasn't adjusted. Simply because they live using less energy on average does not mean that given access to more that they wouldn't use it. Then figure that you have over a billion of them. When you have millions of people that use the same amount of energy as people in the US and then you have millions that don't even have access to it your average is not going to be the same. I bet if you adjusted for socio-economic status, and size of home and you then compared that energy consumption would be much closer. I will admit that we need to change our wasteful habits but we also can't take responsibility for what another country chooses to let happen in their own turf. If the US and it's desire for product is so terrible, why did the Chinese CHOOSE to pollute their country to cater to us? Also, with a growing middle class in China, do you really think that the Chinese People are not going to increase their own per capita consumption.

Tom Hargrave (author)  maxhuey1 year ago

I understand that the Chinese are willing to produce any quality we want to buy. Matter of fact, most of our "high quality" cell phones are "Made in China". But unfortunately there is a lot of junk coming out of China and not all of it is driven by greedy Western businessmen. From my experience most products that are bought on-line from China are junk or at least not up to the buyer's expectations.

Yes, for the most part, that is correct, many Chinese businessmen had learned from experience, that most western consumers shop by price. I ( a shopaholic) also shop on line often, at least once a week if not more, but I shop wisely on line, had yet to buy any products not up to standards. Once in a while I get a product damaged by shipper and the seller from China replaced it even though its not their fault.

I have even gotten to know some sellers personally and had visited them them when I traveled to Asia.

Thank you for posting that max, very interesting take.

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.
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.

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.

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).

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)  Coffeinated1 year ago

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.

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 Arcana1 year ago

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?

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.
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