LED light height question

Maybe someone there can run this by Robert, as I know he has at least some experience with LED’s. One piece of information I simply can not find - what is the best height to run my LED? It is a top of the line Pro Grow 260. The freaking manufacturer doesn’t even give a recommendation!! I read every where from touching the canopy to 3-4 feet. I don’t have a light meter for PAR meter. Obviously I am watching my Auto seedlings very closely to attempt to intuit what is right.
Also for Robert - run both spectrum’s all the way through, or switch? I know all the underlying theories about light saturation points, and wavelength usage, etc. I would just like a comment from someone who I trust. As always, thank you all for all the help you render me!



(Learning is growing. You know what they call something that has ceased to grow? Dead)

I’m not familiar with the pro grow 260 line. I did just google it to get an idea how their rig is set up. This is the thing with High Output LED systems. With many, the plant can grow right up against them with out being harmed or burnt, however, often that is not the most efficient use of the light. Most LEDs I’ve looked into usually don’t recommend getting the light closer than about 18" or about a half meter from the plant. And the reason why is because of the way each little led is emitting a kinda pin point of light and it needs some distance to spread out to cover a larger area. This distance will vary depending on the type of lens diffusion over the individual LEDs.

Here is a good trick to try and find out the maximum close distance you should let your LED get to your plant:

Take a nice pure white square or rectangle of cardboard or something similar about the same dimensions as your grow’s floor space under the light. Or you could just use the floor with something white covering it. Then move the light really close to the white rectangle, you will see at a certain closeness the light points become very individual and not overlap each other as much, this is too close as it will not give the plant an equal amount of all spectrum of light. Back it off until the white rectangle has a mostly uniform color and mixture of all the light spectrum, this is about the closest you want the plants to get. Another thing to keep in mind is if the canopy is going to be scrogged to the same dimensions, then you also want the even coloring to cover all the white rectangle and not leave the edges unlit.

One other thought. Most LED systems state a coverage area, something like 3’x3’ at a 3 foot height and 4’x’4’ at 4 foot high or 2’x3’ at 3’ high and 3’x6’ at 4’ high. Your optimum light distance would probably be the shorter measurement and is the distance the light was designed around. Something to think about, there may only be a small few infra red and or ultraviolet LEDs and we can’t see this light with our naked eyes. Some camera phones, security cameras and other digital cameras can see this spectrum and will show it as white light on the display screen. These lights would be placed sparingly in an even distribution and usually in the center as the one or few LED’s has to supply its spectrum to the whole canopy. So when a manufacturer states that distance, that is the distance closest that it would still have all spectrums evenly represented on the “white rectangle” so to speak.

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Also I found this on a system that uses aprox. the same watts from pro gro:

Pro Grow LED® (PGX5-300) Product Specifications:

“Minimum distance above plant canopy: 18¨+ (Due to the power of the diodes employed in this unit please follow this guidline for optimal results)”


Thanks, Mac’!! Great thinking, great ideas. LED’s are a whole other animal than HID or HPS. It is a little difficult for an old codger like me to remember that instead of one light bulb, one must think of 30 or 60 lights working in unison. Angled so as to get am even mixture of their respective outputs. You’ve really given me some thoughts to ruminate on. I know LED’s are no your ‘bag’, so I really, really appreciate the help! The white paper test is brilliant. (You must not consume Cannabis, because my Gummint has thought me that it makes people stoopiid. :wink:

Actually Jodie I do use LEDs and I like them, but I built my own system. Latewood and I both agree that most are way over priced and won’t save you much money in the short term as the initial investment is so much more than HIDs. As I built mine at cost with parts from the same Chinese factories that the name brands manufacturers get their parts, I was able to build a 600 watt HID equivalent for about $100 USD and so I see the savings immediately. Maybe I’ll write an article on LEDs but there is as much variables in a LED rig, if not more, than in growing, lol, that might be a whole different web page all on its own.

You can see our thoughts on LEDs in this thread as well as a great chart showing price/cost comparisons, including electrical bills, based on well respected name brand systems here:


That is way cool that you built your own rig. I’m very much a research fanatic, mostly because I have been so poor, but also I like to know what’s what. When I was in prison, and on parole, I couldn’t read about anything to do with growing, because it was too painful emotionally. Both because of what was done to me, and because growing is the closest thing to a religion I have. So LED’s were a complete surprise to me a couple of months ago. I went with Pro Grow - I actually got a really good deal on the 260 because they were phasing them out for newer models. $240 I think it was. Their promotional material seemed the most adult, science based I found. The lack of any appreciable heat, and not having to be scared shitless I would get a drop of water on a hot HID bulb (yes, more than once!) attracted me. Right now I am doing a side-by-side comparison with seedlings out in the sun, and under the LED. I’m journaling the grow, but I dislike posting such until it is done. I think the 1 watt chip-sets are probably not good for mature plants. Mine has 3 watt chips. And Pro Grow has an outrageously good guarantee (I think it is two years bumper-to-bumper.)
I’m going to get a settlement from the VA in August-October for disability, an outrageous amount of money to me, so in the very near future I am going to have ever little doo-dad and thing-a-ma-gig I desire.
Seriously, you cats are continuing to amaze me with your dedication to the art of growing. I was thinking the other day while walking (always my best thinking time) how I happened to pick your firm over all the others on the WEB. I think it was because your’s seems the most adult to me. No almost naked women (which I love, just not advertising things like seed!) no cartoon drawings, no real hype. Just well written information, and your own outrageous germination guarantee. I feel blessed I found you. :wink:

Thanks Jodie, that’s exactly how I felt when I found ILGM the first time, lol. A great selection of traditional award winning strains at about one of the most reasonable prices anywhere on the web, an excellent guarantee, and “no B.S.” straight forward knowledge, it’s why I stuck around.

Oh yeah, my system is built out of 3 watt chips. 1 watt and lower, and the Christmas light type 13 watt rigs, are not good for mature plants, no penetration through the canopy at all. As LEDs live so long, I have yet to try the new 5 watt LEDs that a lot of the companies are upgrading to and like you said as why you got such a great deal on the previous generation’s technology. The good thing about sticking with the 3 watt tech right now is that it has kinda become proven technology and the manufacturing of 3 watt LEDs have become very consistent and reliable. 5 watts systems are a little more likely to have individual LEDs burn out early. But I am curious to start experimenting with them and see how much better their penetration will be.

Another question, Mac’. What is your take of the selective spectrum’s I have on my light? I am unconcerned with the electricity it draws, only keeping the girls happy. Just to establish a baseline, I ran it on only the blue for the first 7 days, and then turned on both blue and red. I plan on finishing flowering, say, the last three weeks, with only the red. Very interested in you thoughts in this regard. Thanks, Brother!!

It actually can select ‘only blue’ or only red? No mix in ratio of red vs. blue?

OK, here’s my thoughts on this…

There is only one sun. Although during the sunset or in the winter, as the light is angled through and filtered through more atmosphere, it does become a little redder in appearance, the actual difference of the relevant spectrum that plant’s leaves can use is so minimal that it is actually unimportant.

There may be some truth the plant finishes faster with more red as it thinks it is winter and needs to hurry up and finish, but there is very little evidence of shorter flowering time with more red light vs. blue light.

It used to be when using incandescent lights for growing indoors, the problem was the plants would most often get sick because of not getting enough light from the blue end of the spectrum. You’ll notice most “professional” florescent plant lights come with a 6500k light. You can flower under these lights without any problems and they are considered cool or blue white light. However they actually have plenty of red light in them but as it mixes with the other colors we just see it as white light. A perfect mix of red, blue and green light makes white light.

The truth is plants respond to lights of varying colors because there are several different plant pigments which are capable of absorbing light and transferring the energy to chlorophyll which catalyzes photosynthesis. Plants may grow in green light, but efficiency in the use of the total light energy will be small because plant absorption of green light is very small.

As is well known, plants will grow best if given a mixture of blue 450 nm light and red 650 nm light (a ratio of bout 20%-30% blue and the remaining LEDs red, seems to be best – I actually like to mix in some pure white LEDs, the equivalent of 5000K-6500K white color rating). BTW, 5800K is supposed to be the light color of high noon. This white color rating has some photosyntheticly active green and yellow/orange spectrum – as well as the blue and red spectrums. And as an added benefit – your plant appears a more normal green, if you have enough of the white LEDs mixed in, similar to the appearance under HPS or MH and it seems a little less stressing on the eyes and makes it easier to read the plant’s health by the color of the leaves.

Plants grown in all red light will grow to be overly tall and leggy and ones grown under all blue light may be low-growing and stocky. Overall, red light is more important and efficient in photosynthesis.

So does more blue equal more vegetative growth and more red equal better flowering? No, if the minimum amount is available then more of only one spectrum is not necessarily better. For example if 20% blue keeps the inter-nodes short during veg, twice as much blue will not make even shorter nodes. In the same way increasing the amount of red required for flowering will not necessarily equal bigger flowers. Overall intensity/lumens/LUX, up to a certain point, is what makes for more intense growth. But of course, for those that don’t know, there is such a thing as too much light and it will cause photoinhibition.

So why do people use MH that seems to have more blue light in vegetative growth and HPS that seems to have more red light for flowering?

HPS spectrum is not as well balanced, but it has the highest radiant flux density of any man-made light source (with the exception of newer high output LEDs which may have a better spectrum specific flux density and better photonic flux, and induction plasma which may have overall better radiant flux with a more balanced spectrum). And MH has a more complete and balanced spectrum but doesn’t have as high of radiant flux and as a result has less penetration and lumens per watt.

As florescent and MH have more blue light and not as intense of light is required for veg, this is why florescent and MH are used for veg, and as flowering tight nugs requires intensity and penetration and blue light is not as important for flower, HPS is preferable – and has enough of blue to prevent growth dysfunction.

So I would imagine intense balanced blue and red light through the entire life cycle is best and as such I’d probably run both on, through the entire life cycle. A proper ratio is probably best for the entire life cycle. And at the very least I certainly would be running the full spectrum/maximum lumens/intensity pretty much all through flower and right up until the very end.

I found the sweet spot right at about 26’ with my XTE 200 advance Led Light . If you have a smart phone , there are light meter apps for lux and lumens you can download on your phone to also help measure height . I used the blue and white spectrum only during vegging and the heats was almost dead on at 18’ and the growth was phenomenal . When you switch to flower , you want to raise the height at least 8-10 inches and lower as plants become use to the high intensity at about 24-26’ and you should be fine . If they stretch ah little , which they will , I measured from the top of my pot and not the plant to 26’ and they took off . Also add 20 % daily until you reach full spectrum switching from veg to flower and you should be okay . But that smart phone app really helps just like a standard par meter . Happy growing !!!

Oh yeah , in vegging I didn’t have to used inline fan at all almost but I have a small 2x2x5 tent , it was not until I switched to bloom full spectrum I had to move air in & out the tent to control temps at 76.3 F and 46 - 48 % RH . Just my experience with High intensity Led lights 5 watt Cree lights .

I have been wanting, make that needing a light meter for some time and have just been to cheap to buy one. Thanks for the tip here. Keep it green.

By the way I am running 2 XTE 350 and I really like them. I have them on a white widow crop right now and just finished 17 plants of Gold Leaf and White Widow. A little pricey but top quality. I am thinking of buying an XTE 100 for my mother plants.

Right now I’m running the XTE 200 , but I bought the XTE 350 just to have an extra light . But that app works great for me measuring light distance and how much light is to the canopy .

Just started researching a home made LED Set-up
and wanted to ask What you think of these. The
optimal nM’s are off a little but not sure how close
one can get with what’s available.

Also Cost seems high at 2.95 Ea.

350 Lumen 10 Watt Super Bright, Red LED
200 Lumen 10 Watt Super Bright, Blue LED
1000 Lumen 10 Watt Super Bright, Cool White LED Module

Spec’s for the Red LED:
10W High Brightness 620-625nM Red LEDs
(a little less then the 650nm)

Spec’s for the Blue LED:
10W High Brightness 460-465nM Blue LEDs
(this time a little High on the 450nm)

Spec’s for the White LED:
Color Temperature: 6000-6500 (is this the color rating ?)

Case Temp. <45C max.
10W High Brightness 620-625nM Red LEDs.
Max Reverse Voltage: 5V
160deg. View angle.
Output: 350 lm,
Forward Voltage Drop: 6.7-6.8VDC
Forward Current: 900mA max.
Sq: 20mm H: 3.5mm WT: .011

Chlorophyll absorption peaks are 430 nm (blue) and 662 nm (red) for chlorophyll a, and 453 nm (blue) and 642 nm (red) for chlorophyll b. Chlorophyll b is not as abundant as chlorophyll a, and merely helps in increasing the absorption range.

You might think about using the white, the average color of the sun is about 6000K, its actually closer to 5800K.

5000K to 6500K is the color of sunlight with various other conditions, including just before sunset and still bright(5000K) and overcast and kind of bright(6500K). Yes, the more exact color might change depending on altitude, possibly latitude as well as season, as this will change the amount of atmosphere the sun goes through and more atmosphere may further yellow or redden the hue of the sunlight, not unlike the way sunsets are more orange or red than the way the sun looks most pure white at high noon(5800K) when it is passing through the least amount of atmosphere.

You might think of getting some of the 50 watt LED flood lights and make something from them, most of the electrical work would be already done fore you.

Something like a few of these:



BTW, I’m finding if you can get about 2 actual watts or more per dollar, you are getting a good deal on a good LED. This light actually probably uses closer to 40 actuall watts and it comes with the heat sink and transformer already in the lights.

In your 3x3 space, I’d bet 4 or 5 of these would do wonders! If you could get 9 to fit in the previously suggested layout, you’d have one awesome light for your area.

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