Tetrahedral
Well-Known Member
Yes you can cut the leaves in soil or touching.
Tent getting hot 84⁰ f HELP!
- Thread starter Cvntcrusher
- Start date
ComfortCreator
Well-Known Member
The less stressful solution is to find a slightly lower lighting intensity (between when u run at 85 and then lower it to be at 80) and keep it there. Thats your environmental limit. I have similar issues, more light than my room can manage at times in summer. Solution is a little less light!
Cvntcrusher
Well-Known Member
I have no problem turning off my Cfls lol I just want my LEDs to be enough for her
NanoGadget
Well-Known Member
Again, spectrographs and my thermometer don't lie. HPS puts out more IR. IR tends to heat things up. It isn't half as complicated as you're making it. We could discuss spectrum if you'd like, we could discuss the effects of UV, we could discuss the changes and developments in led as a horticultural light source. Those are all valid discussions. None of that changes the fact that my leaf temps vary less from ambient room temps under my led, or that my plants universally prefer warmer ambient temps under said led.
Tetrahedral
Well-Known Member
No we should discuss leaf temperature sometime just not here.
LinguaPeel
Well-Known Member
So what is optimal leaf temperature? No one will say.
85 air temp without a fan is not hot. Plants are water cooled, leaf temp would be in the 70s under led, add a breeze and you got evaporative cooling, drops another few degrees. Going by all the bush beating that goes on around here I can scientifically confirm low 70s is optimal leaf temp under any light.
85 air temp without a fan is not hot. Plants are water cooled, leaf temp would be in the 70s under led, add a breeze and you got evaporative cooling, drops another few degrees. Going by all the bush beating that goes on around here I can scientifically confirm low 70s is optimal leaf temp under any light.
KingQuazy
Well-Known Member
Cannabis grows at a wide range of temperatures and in different environments. You'll want to look into CO2 at them temps. To get a better understand of what temperature and humidity levels do the the plants, you should study a bit on what is called VPD.
Tetrahedral
Well-Known Member
The optimum temperature is a discussion not a figure. You could vary humidity to vary the cooling rate.
Plants are clever, they reflect a lot of unwanted and how about the shaded, underside and stem temps.
I would like to say it's the air temperature minus it's cooling effect from water loss which includes increases from wind and both Inc/decrease from humidity.
There are a few types, cold norm warm and hot, approaching air temps for C4 hot plants above 30 hash marijuana must fall just there and below. Leaf temps in full sun should be lower than that. Outdoors you have wind rain overcast and so maybe some strains can manage hotter but in a more desert climate it's relentless heat and sun so specialization is high towards C4 and marijuana wouldn't last hence some weird Aussie types.
Did you say low 70's, I'll buy a figure at around there if you have mastered growing. Salts, drought, overeater, heavy defoliating now there's reason for a variation.
Can we work towards an ideal leaf surface temperature of our top canopy or are we stuck with the simpler air temperature approach, some hi tech bother some don't, their stuffs a lot more perfect than mine but their profit margins are bad they need that tiny gains I can pass and never notice.
How HP's and another comparable strength spectrum differs when growth rates are similar could only be by a small amount or we would hit death zone too quick the lights just wouldn't sell. A guess but do your ir thermometers pick up all the ir reflectance from the light not just it's output heat and so raise your readings artificially, I don't know that using an IR thermometer so close to a source of it is all that great but that's out there I never covered wild topics in colleges.
Tetrahedral
Well-Known Member
An old assesment but how could the physics and real life situation be any different to this based on what we know about basic leaf temp so far;
The use of LED technology is commonly assumed to result in significantly cooler leaf temperatures than high pressure sodium technology. To evaluate the magnitude of this effect, we measured radiation incident to and absorbed by a leaf under four radiation sources: clear sky sunlight in the field, sunlight in a glass greenhouse, and indoor plants under either high pressure sodium or light emitting diodes. We then applied a common mechanistic energy-balance model to compare leaf to air temperature difference among the radiation sources and environments. At equal photosynthetic photon flux, our results indicate that the effect of plant water status and leaf evaporative cooling is much larger than the effect of radiation source. If plants are not water stressed, leaves in all four radiation sources were typically within 2°C of air temperature. Under clear sky conditions, cool sky temperatures mean that leaves in the field are always cooler than greenhouse or indoor plants-when photosynthetic photon flux, stomatal conductance, wind speed, vapor pressure deficit, and leaf size are equivalent. As water stress increases and cooling via transpiration decreases, leaf temperatures can increase well above air temperature. In a near-worst case scenario of water stress and low wind, our model indicates that leaves would increase 6°, 8°, 10°, and 12°C above air temperature under field, LED, greenhouse, and HPS scenarios, respectively. Because LED fixtures emit much of their heat through convection rather than radiative cooling, they result in slightly cooler leaf temperatures than leaves in greenhouses and under HPS fixtures, but the effect of LED technology on leaf temperature is smaller than is often assumed. Quantifying the thermodynamic outputs of these lamps, and their physiological consequences, will allow both researchers and the horticulture industry to make informed decisions when employing these technologies.
Introduction
Light emitting diodes (LEDs) have shown to be a disruptive technology in all areas of illumination. Large (>200 watt) LED fixtures have become commercially available for both sole source (growth chamber) and supplemental (greenhouse) plant lighting. At the same time, the more traditional high pressure sodium (HPS) technology has also improved in efficiency by as much as 60% [1]. Though the spectral effects of different light sources have been studied, there have been few studies on the thermodynamics of these new lighting systems. The thermal properties of fixtures are of consequence both for researchers, as differences in leaf temperature and transpiration can change experimental outcomes, and for the horticulture industry, as heating and cooling costs may be different under different sources and hot lamps may damage plant tissue.
The energy balance of leaves has long been studied in field conditions and a well-developed family of models is used to determine transpiration and leaf temperature over a wide range of environmental conditions, including controlled environments [2–5]. These models are well developed, and are used to predict values that are hard to measure directly, such as leaf temperature and evapotranspiration [6]. Models also provide the opportunity to compare individual parameters while keeping all other environmental conditions exactly the same. This facilitates comparison of radiation sources.
Although linearization of energy balance models, such as the Penman-Monteith equation, has been widely used, modern computing allows for more precise numerical solutions of leaf temperature. Widmoser [7] discusses the advantages of using numerical solutions.
A recent analysis showed that the conversion efficiency of electricity to photosynthetic photons of the most efficient commercial scale LED fixtures was equal to the most efficient HPS fixtures at 1.7 μmol photosynthetic photos per joule of electrical input [1]. They thus generate the same amount of thermal energy per photosynthetic photon. LED fixtures, however, dissipate much of their heat away from the plane they illuminate, while HPS fixtures dissipate more heat toward the plane they illuminate.
Elevated temperature reduces the lifespan of LEDs, so they are thermally-bonded to heat sinks where the thermal energy is removed by natural or fan-assisted convection and directed away from the plants they illuminate.
Conversely, HPS lamps operate at higher temperatures and thus generate more longwave radiation in the same direction as the photosynthetic radiation. This thermal radiation can be reduced using a barrier such as glass, but this reduces the photosynthetic radiation by about 10% (S1 Fig) and thus lowers the efficiency of the fixture.
The difference in how LED and HPS technologies dissipate thermal energy indicates that use of HPS fixtures will result in higher leaf temperatures. It is easy to misjudge the magnitude of this effect because HPS lamps are a far more concentrated light source than LEDs. Comparisons need to be made on the basis of equal photosynthetic photon flux (PPF).
Compared to sunlight and HPS lamps, LED fixtures emit almost no near infrared radiation (NIR; 700–3000 nm), but this radiation is not well absorbed by plant leaves. Photosynthetic (400 to 700 nm) and longwave (3,000 to 100,000 nm) radiation are about 95% absorbed, but non-photosynthetic solar NIR is only about 20% absorbed, and has a smaller effect on leaf heating. Unabsorbed radiation is either transmitted or reflected.
Right below this was the black dog shit of leaves at 100f, typical old let's sell LEDs and hope no one takes the study above with any seriousness especially the part about it being reflected and transmitted.
LEDs made all this up for sales, some may just be finding out about all the studies and figures that disqualify them from ever entering a serious academic institution lol
The use of LED technology is commonly assumed to result in significantly cooler leaf temperatures than high pressure sodium technology. To evaluate the magnitude of this effect, we measured radiation incident to and absorbed by a leaf under four radiation sources: clear sky sunlight in the field, sunlight in a glass greenhouse, and indoor plants under either high pressure sodium or light emitting diodes. We then applied a common mechanistic energy-balance model to compare leaf to air temperature difference among the radiation sources and environments. At equal photosynthetic photon flux, our results indicate that the effect of plant water status and leaf evaporative cooling is much larger than the effect of radiation source. If plants are not water stressed, leaves in all four radiation sources were typically within 2°C of air temperature. Under clear sky conditions, cool sky temperatures mean that leaves in the field are always cooler than greenhouse or indoor plants-when photosynthetic photon flux, stomatal conductance, wind speed, vapor pressure deficit, and leaf size are equivalent. As water stress increases and cooling via transpiration decreases, leaf temperatures can increase well above air temperature. In a near-worst case scenario of water stress and low wind, our model indicates that leaves would increase 6°, 8°, 10°, and 12°C above air temperature under field, LED, greenhouse, and HPS scenarios, respectively. Because LED fixtures emit much of their heat through convection rather than radiative cooling, they result in slightly cooler leaf temperatures than leaves in greenhouses and under HPS fixtures, but the effect of LED technology on leaf temperature is smaller than is often assumed. Quantifying the thermodynamic outputs of these lamps, and their physiological consequences, will allow both researchers and the horticulture industry to make informed decisions when employing these technologies.
Introduction
Light emitting diodes (LEDs) have shown to be a disruptive technology in all areas of illumination. Large (>200 watt) LED fixtures have become commercially available for both sole source (growth chamber) and supplemental (greenhouse) plant lighting. At the same time, the more traditional high pressure sodium (HPS) technology has also improved in efficiency by as much as 60% [1]. Though the spectral effects of different light sources have been studied, there have been few studies on the thermodynamics of these new lighting systems. The thermal properties of fixtures are of consequence both for researchers, as differences in leaf temperature and transpiration can change experimental outcomes, and for the horticulture industry, as heating and cooling costs may be different under different sources and hot lamps may damage plant tissue.
The energy balance of leaves has long been studied in field conditions and a well-developed family of models is used to determine transpiration and leaf temperature over a wide range of environmental conditions, including controlled environments [2–5]. These models are well developed, and are used to predict values that are hard to measure directly, such as leaf temperature and evapotranspiration [6]. Models also provide the opportunity to compare individual parameters while keeping all other environmental conditions exactly the same. This facilitates comparison of radiation sources.
Although linearization of energy balance models, such as the Penman-Monteith equation, has been widely used, modern computing allows for more precise numerical solutions of leaf temperature. Widmoser [7] discusses the advantages of using numerical solutions.
A recent analysis showed that the conversion efficiency of electricity to photosynthetic photons of the most efficient commercial scale LED fixtures was equal to the most efficient HPS fixtures at 1.7 μmol photosynthetic photos per joule of electrical input [1]. They thus generate the same amount of thermal energy per photosynthetic photon. LED fixtures, however, dissipate much of their heat away from the plane they illuminate, while HPS fixtures dissipate more heat toward the plane they illuminate.
Elevated temperature reduces the lifespan of LEDs, so they are thermally-bonded to heat sinks where the thermal energy is removed by natural or fan-assisted convection and directed away from the plants they illuminate.
Conversely, HPS lamps operate at higher temperatures and thus generate more longwave radiation in the same direction as the photosynthetic radiation. This thermal radiation can be reduced using a barrier such as glass, but this reduces the photosynthetic radiation by about 10% (S1 Fig) and thus lowers the efficiency of the fixture.
The difference in how LED and HPS technologies dissipate thermal energy indicates that use of HPS fixtures will result in higher leaf temperatures. It is easy to misjudge the magnitude of this effect because HPS lamps are a far more concentrated light source than LEDs. Comparisons need to be made on the basis of equal photosynthetic photon flux (PPF).
Compared to sunlight and HPS lamps, LED fixtures emit almost no near infrared radiation (NIR; 700–3000 nm), but this radiation is not well absorbed by plant leaves. Photosynthetic (400 to 700 nm) and longwave (3,000 to 100,000 nm) radiation are about 95% absorbed, but non-photosynthetic solar NIR is only about 20% absorbed, and has a smaller effect on leaf heating. Unabsorbed radiation is either transmitted or reflected.
Right below this was the black dog shit of leaves at 100f, typical old let's sell LEDs and hope no one takes the study above with any seriousness especially the part about it being reflected and transmitted.
LEDs made all this up for sales, some may just be finding out about all the studies and figures that disqualify them from ever entering a serious academic institution lol
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LEDS should run hotter.. check leaf surface temp.. its probably only 78
Cvntcrusher
Well-Known Member
So what are you saying brother?
That's everything is cool because even though my tent says 84⁰ or 87⁰ my plant isnt that hot. Especially because plants are water cooled by their roots.
Yes.. and they cool through the leaves when they transpire.. Now, if your room is 84 and the RH is below 60.. you will have a less than optimal growth rate due to VPD imbalance.. which includes a list of other 'side effects'.. stay above 50% you'll be ok..
Cvntcrusher
Well-Known Member
Dude I cannot get my rh up to save my life. I put water on my heating pad in there and it doesnt do anything. I have a humidifier/AC blowing in there. Still cant get it to stay above 40. Itll jump almost to 50 when the lights are out. But then right back down to 35%
Also I was using this chart. So I figured my higher temps are fine with lower humidity....
Tetrahedral
Well-Known Member
It's a common fact that lower humidity encourages the plant to drink more and if that more is present you will not suffer at low humidity or even loose yeilds.
Where that chart starts to make sense is when your low in water, the plant cannot bring enough water to compensate the pressure needed.
Everyone takes that chart and similar too literally, it doesn't represent what happens in real life and seems more suitable for a cooler weather plant that needs humidity compensation because it can't handle the water needed at warmer temps - we are growing a warm species it's obviously evolved a better response to low humidity in heat as that's the sort of climate in the wild we went and got the first seeds to homegrown with.
Tetrahedral
Well-Known Member
I grow as low as 30%, there is no slowing of growth rate more like a faster rate, check the stem of your plant, looks like big hose lines running up the stem to the leaves, water it then cut the stem of and watch water form droplets quickly.
The plant is designed to supply a lot of water to its leaves, it's a fast grower and this resolves any humidity problem. Most info seems generalized, start focusing on this species because the more water the more it can grow.
I'm ok at growing no pro but is this not obvious to others? I find vdp great for lettuce but marijuana didn't grow in VPD conditions so might explain why it's a big drinker of water probably also why it eats nutrients at a fast pace too.
Tetrahedral
Well-Known Member
I never seen anyone mention the data on hemp transpiration thresholds, very keen to thrust a chart saying I need between 0.6 and 1.1 but hemp can go up to above 2.0 because it can transpire fast.
That's the simple answer to stop making an industry based on buzzwords and people not suited to gaining research grants.
That's the simple answer to stop making an industry based on buzzwords and people not suited to gaining research grants.
It is a thing.. if you have something that works for you, thats wonderful.. botanical science states that the rate plants transpire is affected by VPD. Its not new science, its new to cannabis.. its discovery is related to the need for optimization of $500k of HVAC equipment in multi million dollar grow facilities.. the science was brought to 'Chad and Brad ' through thoes companies who installed the tech in commercial vegetable facilities and labs..
You don't have to optimize your water bill, feeding schedule, and c02 generation ( LP or Propane ) .. but at 30k a month in overhead, its a good idea.
Tetrahedral
Well-Known Member
Wondering if you read what I said about VPD?
Where was I saying it isn't a thing?
Basically saying most of these charts and growers are not describing VpD in relationship to marijuana's transpiration threshold.
Are you after a real conversation or not?
KingQuazy
Well-Known Member
Yeah all that intelligence decimated with one ridiculous statement.
These VPD charts are Cannabis specific, first of all.
Second of all, masters of the VPD will grow circles around us. Your weed fucking SUCKS compared to the JB and they will look you dead in your eyes and say "VPD" when you ask them the "secret".
Tetrahedral
Well-Known Member
Come back to me when you work out the transpiration threshold of different plants.
Until then I've given facts and figures from studies thanks!