Is my led too close?

Discussion in 'Newbie Central' started by Tokintoucan, Jun 11, 2017.


    Tokintoucan Active Member

    noticed a patchiness today, top of one in particular, noticeably lighter shades of green on the top, is my led too close? Viparspectra 900w (400 actual) was at 24 inch, moved it to 26, any other idea what could cause this? Thanks in advance

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    Kcbscrogger Well-Known Member

    They look fine to me it's just new growth is a little lighter, my 600w viparspectra is at 18 inches during veg. Good luck
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    furious248 Well-Known Member

    You can go for a good 12-18 inches start around 18" away to begin with but you could probably move it a bit closer after they adjust. They don't run as hot so there is the ability to keep the led lights closer to the canopy but break them in slowly. I still don't run mine any closer then 12" even tho it seems it could sit flush with the tops and still not burn em.
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    Tokintoucan Active Member

    The recommended height in the manual for vegging is 26" to 30"? The patchiness is only present on one plant and seems to be at random but only on the top (not necessarily new growth) I know it's not the best pic but yeah the back right seems to be the affected one

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    furious248 Well-Known Member

    My bad, i thought they were beginning flower. Distance is about right for veg but it still looks a bit like bleaching (from what i can see) has vertical growth stopped ? Do the leaves feel thicker?

    Maybe a sulfur deficiency ? But would need a second opinion

    NanoGadget Well-Known Member

    Do you foliar feed or mist your plants?

    Tokintoucan Active Member

    I don't. Would this be the cause

    NanoGadget Well-Known Member

    I was just wondering. Sometimes people who spray their plants have issues with water droplets on the leaves acting like a lense and burning them.
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    NoFucks2Give Well-Known Member

    You can put it as close as 6" if you want. Depends on the area you are covering. As long as the light spreads across the canopy.

    If that light can do both veg and flower, I'd turn them both on. IMHO the veg flower thing is a myth, there is no science to back it up. To reverse the elongation you only need a little bit of blue with red. Red is very good for veg.

    If you remove the plexiglass cover, you will get an extra 10% photon flux.
    Last edited: Jun 12, 2017
    Tim Fox

    Tim Fox Well-Known Member

    they look great,, 18" for veg and 12 after they have hardened off,, like mid flower

    Tokintoucan Active Member

    I have considered this. It does have a flower switch too, would this speed things up? Also how long would you recommend till flower? This is the current situation

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    NoFucks2Give Well-Known Member

    My background is electrical engineering and programming. I currently am a consultant to the University of Florida Horticulture Department that does all their LED research. I design and maintain their LED fixtures. I do not grow cannabis, at least not since the 70's where they were grown under growlux bulbs. I asked the professor that leads the LED research about grow spectrum and his reply was "we do very well with deep red and deep blue". The veg / flower thing is likely a misinterpretation of Phytochrome Response and not photosynthesis. Far Red (730nm) can be used to signal the lowering growth stage but using the photoperiodic timing (light on less hours per day) is a much safer method. Elongation of the stem can be triggered by far red or no blue in what is know as Shade Avoidance Syndrome (SAS). It has noting to do with veg or flowering photosynthesis. If you can turn on both veg and flower that is the way I would go.

    I am not an expert on growing cannabis. I do have many books on the subject written by experts and self proclaimed experts.

    The opinion on when to start flowering I liked the best because I like simple was by Ryan Riley in the book Growing Elite Marijuana said when your plants are half the size you want them to be, begin the 12/12 photoperiod and never let the plants see any light what so ever during the off cycle.

    The veg / flower switch is something I do not believe in as there is no science to back it up. My opinion is to get the plant as many photons as possible preferably around 450nm (deep blue) and 650nm (deep red) which are the most efficient bands for photosynthesis. And preferably 1-3x more deep red than deep blue. Stay away from UV, IR, and Far Red. Bottom line it is not important, just get them as many photons as you can afford. IMHO
    Last edited: Jun 14, 2017
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    KRSTEK Active Member

    6" with a 900w ?:o:shock: U told him to FRY IT with both veg and flower on @ 6" ? Serious?
    I WOULD NOT DO THAT:!: Unless you want liek teh Light Burnz:!:
    If my 600W in Flower managed to slightly burn a plant at 13" , at 6" he might as well pull them out now even, with just VEG light on 6" it is still TOO close.

    "The recommended height in the manual for vegging is 26" to 30"?"
    OK I suggest you start at 26", go down 1" per day, if the leaves start to lose colour in other words pale (bleached effect) then raise them 1" until you find the distance they like.

    BTW RED is good for Bloom - Flower....

    Peac3 :blsmoke:
    Last edited: Jun 14, 2017
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    NoFucks2Give Well-Known Member

    All that matters is the heat from the fixture not get the leaves too hot. That fixture is NOT anywhere as powerful as they try to make it sound. It's a shame that buyers give vendors bonus points for being inefficient. Cannabis can easily handle 1500 µmol/m²/s. There is something very wrong if an LED fixture burns at 13". Watts don't mean a thing.

    When reading Reviews of LED grow fixtures, I often see the term Watt used. Misused more than Used. When someone uses the term “True Watts”, I know they do not know. There is no such thing as a True Watt. True Watt is a marketing term. As with most marketing terms that use the word true or truth, it is neither.

    An LED grow fixture has many Watts.
    Wall Watts
    Power Supply Watts
    LED Driver Watts
    LED Electrical Watt
    LED Thermal Watt
    LED Radiance Watt

    If there were a Watt of importance it would be the Wall Watt. The main criteria for the evaluation of a grow fixture is how much electricity goes in, and how much light comes out. In this evaluation the amount of electricity is typically specified in Joules, as in PPF per Joule, not Watts.

    More specifically than just the amount of PAR, what is more important is the amount of light phonton energy that reaches the plant leaves, PAR is measured in moles/m2/s, Watts/m2 /steradian, or Lumens/m2 /steradian.

    Energy takes many forms in a grow fixture:

    Photometric, Luminous Energy (Lumen Second)
    Radiometric, Radiant Energy (Joule)
    Electrical Energy (Joule)
    Thermal Energy (Joule)
    Photon Energy (Moles)

    Each form of Energy listed above there are many more measures. Volume, Density, Intensity, Illuminance, Irradiance/Illuminance, and Radiance/Luminance.

    Not to be, as often is, confused with Flux (moles/s), Intensity (moles/m3), Density (moles/m3/steradian), or Irradiance (moles/m2). Note about steradian: A steradian is a unit of volume. Because light spreads as it travels and takes on a cone shape, the steradian is used. The steradian is just that, the volume of a cone.

    Photon Radiance is the number of photons (moles) hitting (incident) a surface area (m2) in a given amount of time (seconds) at a specified photon travel distance. If a vendor does not specify the height when using µmol/m²/sec and if using µmol/m² it also is nearly meaningless.

    PPFD (Photosynthetic Photon Flux Density), is a measurement of Radiance, not Density. Why is it called Density? Because someone didn't think this lighting measurement was confusing enough? No, it is more likely someone was already confused enough that they used the term Density where it was actually Radiance. Happens all the time. PPF and PPFD are not standardized Units of measure. There is no standards body over seeing the technical characteristics of PPF(D). Anybody can use the terms however they desire.

    PPFD measures the Transmittance of light. Transmittance being the effectiveness of transmitting the Radiant Energy.

    Then there is the Quality of light. The Quality is the result of light Absorptance, Reflectance, and Photosynthesis. Quality is based on the Spectral Radiance. More specifically the Spectral Radiant Flux, in wavelengths (or frequency), received by the leaf surface.

    As Watts relate to LED grow lighting, the Electrical, Thermal, and Radiant Watts are too dynamic to be meaningful in the evaluation of a grow fixture.

    The Electrical Watts are divided in to a ratio of Thermal and Radiant Watts. A lighting electrical engineer will choose an efficient LED, with good efficacy, with the highest Radiance Watt to Thermal Watt ratio.

    The most important parameter of an LED fixture, in my opinion, is the temperature of the LED. Secondly is the amount of current flowing through the LED. It is the temperature (and current) that gives LEDs their dynamic characteristics. It's the amount of current flowing through the LED and the fixture's thermal management that produces the LED's temperature.

    When current flows through an LED a voltage is created across the LED's anode (in) and cathode (out). This voltage, referred to as the Forward Voltage, when multiplied times the current gives the instantaneous Wattage. I say instantaneous because it is so dynamic it will change.

    When the LED Current flow is increased, it's Radiant and Thermal Flux increase. How much they increase depends on the LED's temperature. As the LED temperature rises the Radiant Flux decreases.

    In grow lighting, the thermal management of the LED's temperature is the most important criteria in the fixture's design. Temperature is the number one factor in how much light is generated.

    The Forward Voltage of a Red LED is about 2 Volts, a Blue or White LED about 3 Volts. While the LED Datasheet specifies the Typical Forward Voltage, there is nothing typical about it. The is nothing typical about any LED characteristic.

    As the LED Current increases the Forward Voltage increases. As the Current and or Voltage increases the Wattage increases. As the Wattage increases the Thermal Flux increases and the temperature will likely increase, depending on the Thermal Management. As the Current raises the temperature the temperature lowers the Forward Voltage which lowers the Wattage. The lower Wattage decreases the Thermal Flux. Unfortunately the reduction in Forward Voltage is insufficient to cancel out the increased Thermal Flux and the temperature rises without significant Thermal management.

    As the Wattage increases the temperature determines the ratio of how much of that Wattage is dissipated as light and heat.

    Why this is so important in LED grow light fixtures is because Red (Deep Red 660nm) is the dominant LED Photosynthetic color.

    Red light is produced by a particular type of LED or by converting blue light to red light using a phosphor converter. Most white LEDs are blue LEDs with a phosphor converter.

    White and Blue LEDs are made differently than a Red LED. It's not important but LEDs are made using Indium, Gallium, Aluminum, as a Phosphide, Nitride, or Arenide. Blue LEDs are typically Indium and Gallium Nitride (InGaN). Red LEDs are Aluminum Gallium Indium Phosphide (AlGaInP) or Gallium Arsenide (GaAs). The point being Red and Blue LEDs are different in more ways then just their color.

    The thing about Red LEDs is how much the temperature affects the Radiant Flux.
    A red LED can easily lose 50% of its radiant flux to heat. And that is with half way decent thermal management keeping the LED temperature at or below 85° C.
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    KRSTEK Active Member

    I'll back up this example with another example based on Personal Experience.
    I have the V600 it's similar to your V900, when a plant is in flower and has matured well in veg it can handle 14-18" with a v600 without issues - usually. If however a plant didn't mature well or took some form of damage in veg and starts to flower, it can suffer light burn at 14-18" cause this is what happened to one of mine. I had to adjust the light in the grow room just for 1 damn plant, now it's perfectly fine.
    This is why I say gradually introduce it to the light height a little bit each day.
    Last edited: Jun 14, 2017
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    KRSTEK Active Member

    I'm not talking about heat, i'm talking about LIGHT BURN = TOO MUCH LIGHT....Heat damage is a different subject.

    Here look it up this basic example:

    Futhermore with all due respect, you stated you don't grow it, I suggest you give it a try again - ALOT has changed since the 70s , some things you have to see and feel for yourself to realise it isn't always as they make it out to be. Plants like all living things react to their surroundings, they are alive, they show us signs to say "I need water" "It's too hot!" etc etc and these aspects often get over looked far too often.
    Last edited: Jun 14, 2017
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    NoFucks2Give Well-Known Member

    That is why I mentioned the 1500 µmol/m²/s. If there are optics that concentrate the light that can be a problem. I did not see optics on this fixture. I am not a fan of optics, they have a transmittance loss of at least 9%. A common problem with a fixture being close to the canopy is the lack of uniformity. That is why I originally also mentioned

    NoFucks2Give Well-Known Member

    If I did, I would still have to say I do not. I do work for the Horticulture LED Research Dept. at the University of Florida designing and maintain their LED lighting. They have $Millions in USDA grants that would be at risk if associated with cannabis. If that counts for anything. And they typically do not run high intensity experiments.

    I use a radiospectrometer to measure the µMoles of photons hitting the canopy so I'm safe there.

    There is no way, none, nada zilch, that the V900 compares to traditional 1000 watt HPS/MH while consuming only 418 watts.

    The Cree engineers created a horticulture reference design to match a Gavita Pro 1000W HPS. Cree engineers very likely know what they are doing and spared no expense in the most efficient design possible. The used mostly XP-G3 LEDs which are the most efficient LEDs on the planet. They used Mean Well HLG power supplies and it still draws over 550 Watts. It has 144 XP-3G White and 48 XP-E Photo Red (deep Red) LEDs. Epistar are no match for XP-3G, XP-E, or a CoB.

    I attached a PDF of the Cree design. I estimated the parts alone would cost me nearly $1000. The heat sinks alone were about $250.

    So a $250 fixture is going to compete with that?

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    NanoGadget Well-Known Member

    All I'm going to say here is that I've bleach the shit out if the tops of my colas at 14 inches with my CLW Solar Storm 440 which draws 350 watts at the wall. If I'm not mistaken 5he OP said he runs a Vipar 900 which pull about 400 at the wall. If we assume that it runs at approximately the same efficiency as mine and puts out similar PAR levels then 6 inches is way too close.
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    HydoDan Well-Known Member

    The only light you can run that close is a cfl.. I have light burn on a tomato plant 6" from my 35 watt led strips.. And am also losing all the fan leaves from one strain due to light burn at 16".. 6" is too close..
    Real world experience not growing on paper..
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