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LED Distance From Canopy

Discussion in 'LED and other Lighting' started by thatsmessedup, May 19, 2012.


    thatsmessedup Well-Known Member

    To figure out the optimal distance the led panel should be from the canopy, I think this makes sense. Most led panels have 4 to 11 spectrum's of light. Its my belief that your plant will grow best when it receives all these bands simultaneously. Also light degrades with distance so you will want to keep the light as close as possible. So basically, you want to keep the light as close as possible while blending all the bands of light.

    So we want to take the distance from the furthest apart leds and find out the distance in which they blend
    optimal led to plant distance.jpg
    To do this we need to use a little math. I never took trigonometry so please correct me if my math is wrong.
    So with this I can see that my led panel will blend all its bands of light at about 9.5". Therefore keeping my light at 9.5" above the canopy is optimal.

    Please chime in with your input and let me know what you think about my theory.
    guod likes this.

    ghettorigger Member

    the blackstar uses 60 90 and 120 deg lenses so depending on how they divided it up it could be closer. I'm a bit baked but i think there was a shorter way to do that math, you got me curious so i am going to dig out my book and look it up haha...

    ahh baked math

    FranJan Well-Known Member

    Does the size of the diode matter in your equations? Distance between each LED on the panel? Whether the LEDs are in clusters or laid out in a square/rectangular/circular pattern? Would wattage matter? Angles and lenses come to mind too. I always think about there being a formula that's simple then questions like those pop up and I come to the realization that I really really suck at mathematics. And 9 1/2 seems close for a BS500 to be to any plant, but I've never owned one. Good Luck with this by the way.

    hölynpöly Member

    How do the leds blend anyway?? If I put my hand close to the leds I can see areas of different colours, this is obvious. In the middle they seem somewhat mixed but I can still differentiate different colour areas on individual leafs. And then when I look on the floor I can see a rainbow of colours. Is there Interference happening with different wavelengths of light emitted , please tell me, if your high enough this should be easy [​IMG]
    Greengenes707 likes this.

    thatsmessedup Well-Known Member

    My goodness!! your right!! why do I see distinct color on my floor, when my floor is obviously far enough to blend the different bands. When I crack my tent I can see separate blues and reds. Interesting indeed. Well after some thought its because all the leds have a particular position on the unit above, so only certain leds will be in the correct position for its light to make it through the slits or foliage.

    ^^I was assuming the smallest angle was 60 for the bs500 so that's what I used in the equation. I also wonder how the light falls off with distance. I know its the inverse square law but is it more like a round bulb or more like a laser. My guess is somewhere in between.

    thatsmessedup Well-Known Member

    Does the size of the diode matter in your equations? No

    Distance between each LED on the panel? Don't think it matters as long as you measure from the outside leds. My equation assumes your plants are directly under that mark. So if you want your leds on the right to touch the plants on the left you will need to raise the light.

    Whether the LEDs are in clusters or laid out in a square/rectangular/circular pattern? Would wattage matter? If the leds are in clusters, just measure from the center of one pattern to the center of the next pattern. No wattage does not matter in this case. Im not saying you can actually put your plants that close, just that they can get that close and still have all the wavelengths needed to grow. But taken that led do not create that much downward heat, as long as they do not bleach the plant, my guess is closer is better. Coverage does not matter in this scenario.

    Angles and lenses come to mind too. I always think about there being a formula that's simple then questions like those pop up and I come to the realization that I really really suck at mathematics. And 9 1/2 seems close for a BS500 to be to any plant, but I've never owned one. Good Luck with this by the way.

    IlovePlants Well-Known Member

    Just going to throw out something I was thinking of. Branding. If you were going to attempt to formulate a perfectly lit room, really the most important thing about TESTING out whether or not assumptions are correct is consistency. All tests must be conducted limiting the maximum amount of variables. There are a few ways to do this. Product consistency, or new parameters. Most LED lights output a "block" of light. What I'm getting at is that 9.5 inches is probably too close, as you didn't factor in how many diodes are going to be putting out light onto a plants photocells. Light is thought of as a wave of particles (which has been demonstrated) and much like a wave or a particle, your density is going to increase as two lights overlap each other. Determining whether the beams of light will oppose each other or attempt to move together. LED's power and weakness lies in this property. The light its self has amazing consistency, but the plants underneath it do not. Most likely if you leave the lamp at 9 inches you are going to see; stress, dead plants, and completely happy plants. Some plants like really intense light from leds, but you shouldn't ruin your garden on the idea that you want the maximum amount of exposure for a plant, what the hell is the maximum that your plants can take? Do you know how many umol's of PAR light you are outputting at 9 inches? Are the same colors all operating on the same lenses? Are oranges by blues? Are reds by 12000k whites? How many spectrum per square inch? How many spectrum per square foot? How many watts are the diodes? (Reds are generally run with less wattage) INTENSITY!

    Or you could test your light for it's intensity before you decide to put it right on top of your plants. That light supposedly has a 3'x4' range. It just seems a bit tight is all.
    Best of luck in your growing endeavors,

    foreverflyhi Well-Known Member

    damn, this is serious shit.
    Ive asked countless people, and countless people have asked me how far do i have my lights from my canopy.
    if you look at my current grow, the smurfberry that has the most LST done to it and is the shortest plant, seems to be getting decent penetration from over 24 inch, but at the same time i have other plants that are in diffrent distance from the led, and all are doing just as great if not better...

    i think your equation makes sense, but i wouldnt go any equation, TRIAL AND ERROR WILL ANSWER ALL THESE QUESTIONS WE ARE ASKING :weed:

    im high, and i think i just confused myself.:shock:

    thatsmessedup Well-Known Member

    I figured Id get something going as no one really has an answer or formula for a proper distance. Hopefully sometime down the line we will have an answer to this simple question.... "How close or far to put the leds". Its easy with hps, as close as possible.

    puffenuff Well-Known Member

    Everything here makes sense, the closer the better but still want colors to blend. From my led grows, the buds closest to the lights are also bigger and denser. I like to get my leds as close to the canopy as possible. I'm even willing to sacrifice some bleached tips. I also think that the colors blend within a couple inches from the leds due to the patterns they use. I could be wrong though, I've just never held my hand under my panels at different spots and seen different color blends, the color blends appear to be uniform across the panel at the same heights right up to the panel's glass.

    Scotch089 Well-Known Member


    Would love to hear more input

    SnotBoogie Active Member

    A few things I thought of, which could definitely be wrong:

    One. I dont have a certain answer to why your eyes perceive different colors. Would love to know.

    Two. You want to measure not the distance between the furthest lights, but the furthest of different colors. this brings an interesting new factor into playing "LED sudoku".

    Three. Its important to weigh up the advantages of a perfectly mixed spectrum at canopy level with the need for light penetration. it could be a valid trade-off is more light is getting to the lower levels of the plant.

    Four. While the angle of most LEDs is given in the specs, if you look at the actual spec sheet you will see a graph showing output over the complete angle. a 90 degree LED for example, give off around 50% of the specified output at the edges of its specified output angle. This could also factor be factored in with some clever maths :P

    I thought of some other stuff and forgot it in the process of writing this, ill come back when i remember! :D

    guod Well-Known Member


    Endur0xX Well-Known Member

    thanks thatsmessedup, that was a good thread ... at the time you forgot to include that it isnt only the blending between 2 diodes but between many diodes ... therefore the best blending of spectrum would have been further than 9.5'' for your bs500.

    I think anyone growing christmas trees can keep their lights slightly closer but in a scrog situation it's probably best to keep the light further.

    thatsmessedup Well-Known Member

    ^^ Im sure its not perfect but about the the measurements i used... I measured from one edge of the panel to the center of the panel. I did this because on the blackstar 500 the pattern is repeated twice. Therefore using half the distance seemed reasonable.

    somebody1701 Well-Known Member

    You only see the distinct colors through the canopy. If you just had your light pointed at the floor without anything in between you wouldn't see the distinct colors.

    MoReJew-ce Member

    To answer your question of why our eyes perceive colors, it's a result of different wavelengths being absorbed and reflected by objects. The wavelengths absorbed are not perceived while the ones reflected beam into our pupil and the light wavelengths are refracted to hit the cones in our retinas. Cones are a type of photoreceptor cells embedded in the retina which is the rear lining of the eye. Humans have 3 different types of cones from what I remember... and they absorb different lengths of light, activating electronic signals to the optic nerve located in the rear of the eyeball. These electronic signals, triggered in a Morse code style (if you'd like to simplify it) indicate these familiar colors in our brain and it is how and why we interpret colors. Some insects and other animals such as birds actually have cones that allow them to see in shorter wavelengths which we cannot. Pretty amazing imo.

    As for the LED discussion, from my experiences, closer placement of high intensity LED can end up being harmful. I've experienced significant stunting by placing larger panels within 4-5" of a plant before. Yet, using a UFO style 7 band at 3-4" caused significant thickening. It's really a lot to do with intensity, and as a few have mentioned, is best learned through trial and error. If you're using two panels that draw ~300 watts each, I'd remain 9-12" away at the closest. For larger fixtures, I'd obviously go further, and for anything under roughly 200w draw, you'd prolly be safe around 6" at the closest. Personally, it's better to give distance earlier in flowering, then slowly adjust closer to increase where it's needed. Earlier in flowering, they don't gain much benefit by very close panels. The optimal distance will display tight nodes and will later give way to dense, sugary fruit.

    The best experience I've had with LED panels has been with many smaller wattage panels surrounding the plants from multiple angles. Blending is important, but the plants are absorbing from multiple leaves so there's little chance that it'll only get a single band. Light of different wavelengths may blast one leaf, and to the side of that on the same node, two different colors are being absorbed. The energy is combined to produce the glucose or whatever, but they don't need that perfect mix of wavelengths on every leaf photosynthetically producing food. They can get it from multiple areas, as long as it's all one plant of course.

    Just to mention, the nature of light and our brains allows us to perceive these reds, purples, blues, etc. but the truth you are all over looking (besides the last post on the first page) is that the ACTUAL wavelengths are more of the spectrum than what you're seeing. So that pattern you talk about looking at, is only in your mind, and would look slightly different to another person looking at the same spot. The perceived wavelengths and the actual broadcasted wavelengths are two completely different things. Even though you think there's only a specific type, reality is that there's multiple spectra emitted and blended that you do not perceive.

    Just thought I'd offer some late info..

    bicit Well-Known Member

    Honestly, I think you're over complicating your trig. Tan(Theta B)=b/c, solve for b. 5.5*Tan(60*)=b=9.53"

    stardustsailor Well-Known Member

    Easiest & most straight forward solution : Phosphor Conversion White LEDs .

    Or else prepare to calculate ,evaluate and design for :

    - Tightly placed monochromatic LEDs .

    -Diffusion optics

    - Maths regarding wavelength dispersion ,
    thus monochromatic LED arrangement based on the actual wavelength emitted.

    Greengenes707 likes this.

    Greengenes707 Well-Known Member

    I hate to burst everyone here's bubble...you guys are talking about what is best for the LED light...how many of you are growing LED lights???...not growing with...but growing led lights??? As in plant a diode and a black star sprouts up???

    The correct distance from the canopy is what gets you an average of 700-1000umols. Or 1000+umols center and ~300umols on the very edge. If you light doesn't blend right when supplying that intensity/amount of quanta...then the light wasn't designed correct and you will never get maximum results.

    And like SDS said....phosphorus conversion whites and forget about it.
    bicit, mc130p and AquariusPanta like this.

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