H
hawkman
- 2,210
- 263
In relation to PAR what is the Par one needs for flower ? what is a average par on wants - do understand that the par does fluculate with distance - was is the normal par?
Ignignokt
- 350
- 93
H
hawkman
- 2,210
- 263
It does fluculate with distance - (each led is different and the Par's are generally given ) but don't know of the "perfect par" ? was wondering that myself
Icemud
- 88
- 33
From my research its based on a plants DLI....
For cannabis I have not found a significant source of information on the perfect PAR, however, using the above article from Purdue U and other sources like the Chandra study. It seems that the best DLI would be somewhere betweeen 22 to 65 mols/day of PAR light.
So how does that break down to PAR in micromoles per meter squared per second or PPFD.... well...
I wrote up a long article about plant lighting a while back on another forum, but I will share part of it here which explains how this breaks down...
What is a PAR measurement, and why is it useful?
A PAR measurement, known in the lighting world as PPFD or PPF
PPFD is Photosynthetic Photon Flux Density, and this measurement describes how many photons, fall on a square meter, every single second.PPFD is a useful measurement when determining how high to hang a light, how far will a light actually cover, and what size light you need for a certain type of plant and grow area. This is a directional measurement in which readings are generally taken on a surface that would represent the canopy of your plants.
PPF is Photosynthetic Photon Flux, and this measurement is used mainly to compare lights for their Photon efficiency. What I mean by this is PPF is a omnidirectional measurement and irregardless of direction, it measures all TOTAL photons emitted from a light. PPF is usually measured in an integrating sphere or Ulbricht Sphere which is a huge reflective sphere that measures light coming from a source at all angles and directions. This measurement is usually used more for HID bulbs than LED but can be used for both when comparing how efficiently a light source creates photons per watt, many times measured in the units Mols/Joule.
Other than comparing light sources for photon efficiency, this measurement of PAR light isn't used much. PPF is much more usefull for comparing HID bulbs, so you can see at a same wattage and same ballast, which bulb will product more photons in the PAR range vs another. Being that the bulb would go into a reflector and shape the output, PPF is used to compare the actual bulb's photon efficiency, but also could be used to compare one LED panel to another at a Same wattage. It wouldn't show you anything about coverage, or hanging height, just which panel at the same wattage produces more photosynthetic active photons.
When we are looking at picking the right grow light we are typically using PPFD. We want to know on a flat surface (our canopy) how many photons are falling here every second. As we described above, plants are photon counters, and so the more photons that are falling on a surface, the higher the rate of photosynthesis. This is why its very important for grow light manufactures to list PAR data, usually in the form of a 4'x4' grid, where at each 6" or 1' mark a PPFD reading is taken. This lets us know when a light is hung at "X" distance, then we can expect "Y" amount of PPFD to be available for the plants.
Now to measure PAR, you probably have seen in my video by now the Apogee Quantum Meter I am using. This device uses separate photodiodes to sense photons and basically counts them. As plants are photon counters, my quantum meter also counts photons, and this reading is displayed in the units Micromoles/Meter squared/every second, and usually written like this " 500umol/m2/s-1.
OK, so you now showed me your photon counter is 500umol/m2/s-1, but what does this mean to me?
So we have these PAR measurements, now what do they mean when talking about plants. The best way to look at this is that a plant has a certain"requirement" of the amount of photons it needs during the daylight period of growth. Each plant species has its own light requirements and you may even remember mom talking about this gardening when you were little, planting tomatoes in a sunny area of the yard where other houseplants didn't need as much light and would do fine in a windowsill.
In botany related applications this "light requirement is known as Daily Light Integral or DLI.
What is DLI
DLI is the amount of photons a plant need per day to be in optimal light for growth and photosynthesis rates and as I mentioned above each plant species is different. DLI is typically measured in Mols per meter squared, per day (very similar to PPFD) but instead of each second, this measurement is totaling all photons per daylight period.
A low light plant such as a fern only needs 6-10 mols/m2/day of photons to grow which is why ferns are commonly seen in dense forests under the canopy.
A high light plant such as Cannabis needs a minimum of 22 mols/m2/day of photons to as high as 65 mols/m2/day which is the range of optimal growth. Yes if you don't have that much light, cannabis will still grow,but you will typically see lower yields, less dense buds, lower THC percentages because the plant isn't operating at its best.
Converting DLI to PPFD
Now how do we get from DLI Mol/m2/day to PPFD or micromoles/m2/second.
The formula to convert this would be:
You would use this formula...
PPFD x 0.0864 = DLI
OR
DLI / 0.0864 = PPFD
So lets look at cannabis, knowing that cannabis needs at least (Minimum for optimal growth) 22mol/m2/day DLI at minimum for optimal photosynthesis lets break it down.
22 / 0.0864 = 254.6 micromoles/m2/s-1 (PPFD)
This is the amount of photons you need every second, averaged over 1 square meter, for the whole 24 hours if usuing a 24/0 daylight schedule (no dark period).
So what happens if you are using a 18/6 veg period or a 12/12 flowering light schedule... simple...
If using a 12/12 flowering schedule, you are only using 12 hours of the 24 hours of the day, which means you would take the 254.6 Micromoles/m2/s-1 and multiply it by 2, since you are reducing the amount of daylight by 1/2 (12 hours), then each hour of the daylight period you need double the amount of photons... so in this example you
would need 509.25 micromoles/m2/second.
If using a 18/6 schedule, you are using 3/4 of the amount of daylight with 18 hours on, 6 hours off, therefore you would multiply the 24hr PPFD by 1.5 because you are using only 3/4 of the day, or 1 1/2 times the 12 hour requirement. In this example a DLI of 22, under a 18/6 schedule would amount to 381.5 micromoles/m2/second.
So for cannabis, bottom threshold for optimal growth and photosynthesis is a DLI of DLI of 22 would be:
****Going lower than these numbers will still grow cannabis, however yields, bud density, potency and THC percentage may suffer.
24/0 schedule: 254.6 micromoles/m2/s-1
18/6 schedule: 381.5 micromoles/m2/s-1
12/12 schedule: 509.25 micromoles/m2/s-1
For Cannabis, the Top threshold for optimal growth and photosynthesis is a DLI of 65 moles per day.
***extremely important notice, only go up to these amounts if you areusing supplemental CO2, do not go this high if you are not using supplemental CO2 as you will actually slow down photosynthesis and waste energy.
24/0 schedule: 752.31 micromoles/m2/s-1
18/6 schedule: 1128.465 micromoles/m2/s-1
12/12 schedule: 1504.6 micromoles/m2/s-1
The generally accepted guidelines for artificial light PPFD in flowering are this:
in a 12/12
PPFD of at least 510 micromoles/m2/s-1 for the low end of optimal intensity
PPFD of at least 800-1100 micromoles/m2/s-1 for perfect optimal lighting without additional CO2.
PPFD of at least 800-1500 micromoles/m2/s-1 for perfect optimal lighting WITH additional CO2.
So now that we know what all these numbers mean, how to we interpret these PAR charts or 4'x4' grids with PAR readings?
Typically if a Lighting company presents a PAR chart "4'x4' grid" with measurements, you will see a bunch of readings all over the place.
Even though PAR measurements are in micromoles/METER/second this is with a constant and even light source what the average would be... grow lights, especially LED's do not have an even footprint and intensity can change rapidly over just 6" or 1" away from the center of the light. This is why these 4'x4' PAR grids are important because the light source is not even, it shows us the Actual area that will produce the OPTIMAL amount of PHOTONS for driving photosynthesis at each point of the grid.
So now knowing for flowering you need to see a grid with a bunch of 510's all over it or higher for flowering, you can see exactly how far a light will spread to OPTIMALLY drive your plant. Also, usually when a company makes these grids, they do it at heights of 12", 18", 24" and 36". By comparing the charts, you can tell at what height a certain light will spread providing 510's or higher and at what height would be optimal to hang the light. The closer the light is to the canopy/or meter, the higher the amount of photons that will be hitting it, but the narrower the coverage area will be (less light is scattering). The further away you move the light, the more photons that scatter leaving less to hit the canopy resulting in a larger coverage area but less Photon Density (PPFD).
Now if you don't see 510's or higher across your chart for your light, does that mean it wont work...NO.. it will just produce less photosynthesis which typically results in more airy buds, less potency and THC, and lower yields.
You can also look at these charts to see how you would hang multiple lights, by combining 2 charts together... lets say 2' out from the center of your light, the chart is only reading 250 micromoles/m2/s-1, well you know if you added a 2nd light and combined their outputs, with them spaced apart 2 feet from each other, then that center point between them (the 250 micromole/m2/s-1 mark) would double, now making that area optimal for flowering in a 12/12 schedule.
This is why it is important that companies provide this information, so we can all make accurate decisions on plant lighting for our plant species, photoperiod usage, and making sure to have a even light footprint over our canopies.
*When choosing a lights by PAR measurements we are looking for a PPFD of 510 umol/m2/s-1 or more across the entire canopy for optimal flowering results, less will still work but not at optimal levels for best results
*Having a 4'x4' grid with PAR measurements at different heights is the best way to judge a plants actual optimal footprint/coverage area based on plant type and photoperiod. Also aids with hanging height and
blending of multiple panels/lights.
For cannabis I have not found a significant source of information on the perfect PAR, however, using the above article from Purdue U and other sources like the Chandra study. It seems that the best DLI would be somewhere betweeen 22 to 65 mols/day of PAR light.
So how does that break down to PAR in micromoles per meter squared per second or PPFD.... well...
I wrote up a long article about plant lighting a while back on another forum, but I will share part of it here which explains how this breaks down...
What is a PAR measurement, and why is it useful?
A PAR measurement, known in the lighting world as PPFD or PPF
PPFD is Photosynthetic Photon Flux Density, and this measurement describes how many photons, fall on a square meter, every single second.PPFD is a useful measurement when determining how high to hang a light, how far will a light actually cover, and what size light you need for a certain type of plant and grow area. This is a directional measurement in which readings are generally taken on a surface that would represent the canopy of your plants.
PPF is Photosynthetic Photon Flux, and this measurement is used mainly to compare lights for their Photon efficiency. What I mean by this is PPF is a omnidirectional measurement and irregardless of direction, it measures all TOTAL photons emitted from a light. PPF is usually measured in an integrating sphere or Ulbricht Sphere which is a huge reflective sphere that measures light coming from a source at all angles and directions. This measurement is usually used more for HID bulbs than LED but can be used for both when comparing how efficiently a light source creates photons per watt, many times measured in the units Mols/Joule.
Other than comparing light sources for photon efficiency, this measurement of PAR light isn't used much. PPF is much more usefull for comparing HID bulbs, so you can see at a same wattage and same ballast, which bulb will product more photons in the PAR range vs another. Being that the bulb would go into a reflector and shape the output, PPF is used to compare the actual bulb's photon efficiency, but also could be used to compare one LED panel to another at a Same wattage. It wouldn't show you anything about coverage, or hanging height, just which panel at the same wattage produces more photosynthetic active photons.
When we are looking at picking the right grow light we are typically using PPFD. We want to know on a flat surface (our canopy) how many photons are falling here every second. As we described above, plants are photon counters, and so the more photons that are falling on a surface, the higher the rate of photosynthesis. This is why its very important for grow light manufactures to list PAR data, usually in the form of a 4'x4' grid, where at each 6" or 1' mark a PPFD reading is taken. This lets us know when a light is hung at "X" distance, then we can expect "Y" amount of PPFD to be available for the plants.
Now to measure PAR, you probably have seen in my video by now the Apogee Quantum Meter I am using. This device uses separate photodiodes to sense photons and basically counts them. As plants are photon counters, my quantum meter also counts photons, and this reading is displayed in the units Micromoles/Meter squared/every second, and usually written like this " 500umol/m2/s-1.
OK, so you now showed me your photon counter is 500umol/m2/s-1, but what does this mean to me?
So we have these PAR measurements, now what do they mean when talking about plants. The best way to look at this is that a plant has a certain"requirement" of the amount of photons it needs during the daylight period of growth. Each plant species has its own light requirements and you may even remember mom talking about this gardening when you were little, planting tomatoes in a sunny area of the yard where other houseplants didn't need as much light and would do fine in a windowsill.
In botany related applications this "light requirement is known as Daily Light Integral or DLI.
What is DLI
DLI is the amount of photons a plant need per day to be in optimal light for growth and photosynthesis rates and as I mentioned above each plant species is different. DLI is typically measured in Mols per meter squared, per day (very similar to PPFD) but instead of each second, this measurement is totaling all photons per daylight period.
A low light plant such as a fern only needs 6-10 mols/m2/day of photons to grow which is why ferns are commonly seen in dense forests under the canopy.
A high light plant such as Cannabis needs a minimum of 22 mols/m2/day of photons to as high as 65 mols/m2/day which is the range of optimal growth. Yes if you don't have that much light, cannabis will still grow,but you will typically see lower yields, less dense buds, lower THC percentages because the plant isn't operating at its best.
Converting DLI to PPFD
Now how do we get from DLI Mol/m2/day to PPFD or micromoles/m2/second.
The formula to convert this would be:
You would use this formula...
PPFD x 0.0864 = DLI
OR
DLI / 0.0864 = PPFD
So lets look at cannabis, knowing that cannabis needs at least (Minimum for optimal growth) 22mol/m2/day DLI at minimum for optimal photosynthesis lets break it down.
22 / 0.0864 = 254.6 micromoles/m2/s-1 (PPFD)
This is the amount of photons you need every second, averaged over 1 square meter, for the whole 24 hours if usuing a 24/0 daylight schedule (no dark period).
So what happens if you are using a 18/6 veg period or a 12/12 flowering light schedule... simple...
If using a 12/12 flowering schedule, you are only using 12 hours of the 24 hours of the day, which means you would take the 254.6 Micromoles/m2/s-1 and multiply it by 2, since you are reducing the amount of daylight by 1/2 (12 hours), then each hour of the daylight period you need double the amount of photons... so in this example you
would need 509.25 micromoles/m2/second.
If using a 18/6 schedule, you are using 3/4 of the amount of daylight with 18 hours on, 6 hours off, therefore you would multiply the 24hr PPFD by 1.5 because you are using only 3/4 of the day, or 1 1/2 times the 12 hour requirement. In this example a DLI of 22, under a 18/6 schedule would amount to 381.5 micromoles/m2/second.
So for cannabis, bottom threshold for optimal growth and photosynthesis is a DLI of DLI of 22 would be:
****Going lower than these numbers will still grow cannabis, however yields, bud density, potency and THC percentage may suffer.
24/0 schedule: 254.6 micromoles/m2/s-1
18/6 schedule: 381.5 micromoles/m2/s-1
12/12 schedule: 509.25 micromoles/m2/s-1
For Cannabis, the Top threshold for optimal growth and photosynthesis is a DLI of 65 moles per day.
***extremely important notice, only go up to these amounts if you areusing supplemental CO2, do not go this high if you are not using supplemental CO2 as you will actually slow down photosynthesis and waste energy.
24/0 schedule: 752.31 micromoles/m2/s-1
18/6 schedule: 1128.465 micromoles/m2/s-1
12/12 schedule: 1504.6 micromoles/m2/s-1
The generally accepted guidelines for artificial light PPFD in flowering are this:
in a 12/12
PPFD of at least 510 micromoles/m2/s-1 for the low end of optimal intensity
PPFD of at least 800-1100 micromoles/m2/s-1 for perfect optimal lighting without additional CO2.
PPFD of at least 800-1500 micromoles/m2/s-1 for perfect optimal lighting WITH additional CO2.
So now that we know what all these numbers mean, how to we interpret these PAR charts or 4'x4' grids with PAR readings?
Typically if a Lighting company presents a PAR chart "4'x4' grid" with measurements, you will see a bunch of readings all over the place.
Even though PAR measurements are in micromoles/METER/second this is with a constant and even light source what the average would be... grow lights, especially LED's do not have an even footprint and intensity can change rapidly over just 6" or 1" away from the center of the light. This is why these 4'x4' PAR grids are important because the light source is not even, it shows us the Actual area that will produce the OPTIMAL amount of PHOTONS for driving photosynthesis at each point of the grid.
So now knowing for flowering you need to see a grid with a bunch of 510's all over it or higher for flowering, you can see exactly how far a light will spread to OPTIMALLY drive your plant. Also, usually when a company makes these grids, they do it at heights of 12", 18", 24" and 36". By comparing the charts, you can tell at what height a certain light will spread providing 510's or higher and at what height would be optimal to hang the light. The closer the light is to the canopy/or meter, the higher the amount of photons that will be hitting it, but the narrower the coverage area will be (less light is scattering). The further away you move the light, the more photons that scatter leaving less to hit the canopy resulting in a larger coverage area but less Photon Density (PPFD).
Now if you don't see 510's or higher across your chart for your light, does that mean it wont work...NO.. it will just produce less photosynthesis which typically results in more airy buds, less potency and THC, and lower yields.
You can also look at these charts to see how you would hang multiple lights, by combining 2 charts together... lets say 2' out from the center of your light, the chart is only reading 250 micromoles/m2/s-1, well you know if you added a 2nd light and combined their outputs, with them spaced apart 2 feet from each other, then that center point between them (the 250 micromole/m2/s-1 mark) would double, now making that area optimal for flowering in a 12/12 schedule.
This is why it is important that companies provide this information, so we can all make accurate decisions on plant lighting for our plant species, photoperiod usage, and making sure to have a even light footprint over our canopies.
*When choosing a lights by PAR measurements we are looking for a PPFD of 510 umol/m2/s-1 or more across the entire canopy for optimal flowering results, less will still work but not at optimal levels for best results
*Having a 4'x4' grid with PAR measurements at different heights is the best way to judge a plants actual optimal footprint/coverage area based on plant type and photoperiod. Also aids with hanging height and
blending of multiple panels/lights.
The Dawg
- 116
- 63
Insert Clap Moji
AvidLerner
- 296
- 63
Thanks. Long read but the results are excellent to grasp.
Understanding PPFD is helpful.
Understanding PPFD is helpful.
Icemud
- 88
- 33
Thanks Avid! I'm glad that you got something good out of it :)
I wrote it a while back because the concept of par, plant lighting, measurements seemed to be very misunderstood by growers, and very exploited by unscrupulous LED companies. I wanted to help others know the truths about it because so many were learning "fake info" from LED companies who were distorting the facts to sell lights.
Dunge
- 2,233
- 263
Pondering on the art of pruning.
Did a bit of reading from the science side, yielded a few new frames in my mental cartoon called, "Photosynthesis, Now What".
Found this:
Capacity for the storage of assimilates and most of the carbohydrates that are not needed for the leafs own metabolism enter the sieve elements of the vascular system. The role of higher-plant long-distance phloem transport is therefore not only the supply of assimilates to all kinds of sink tissues but also the removal of fixation products from the source tissues to avoid accumulation of metabolites and feed back inhibition on the photosynthetic machinery.
These products then seem to flow via osmotic transport through the phloem directed by what they call the source and sink method.
I'm trying to imagine the flow at the base of a fan leaf, and how its proximity to a bud will impact "assimilate" distribution to the bud.
As to PAR, how much passes through a good leaf, and is available to veg below?
This all leads to the ultimate question, Which big fans need removal, and when?
Did a bit of reading from the science side, yielded a few new frames in my mental cartoon called, "Photosynthesis, Now What".
Found this:
Capacity for the storage of assimilates and most of the carbohydrates that are not needed for the leafs own metabolism enter the sieve elements of the vascular system. The role of higher-plant long-distance phloem transport is therefore not only the supply of assimilates to all kinds of sink tissues but also the removal of fixation products from the source tissues to avoid accumulation of metabolites and feed back inhibition on the photosynthetic machinery.
These products then seem to flow via osmotic transport through the phloem directed by what they call the source and sink method.
I'm trying to imagine the flow at the base of a fan leaf, and how its proximity to a bud will impact "assimilate" distribution to the bud.
As to PAR, how much passes through a good leaf, and is available to veg below?
This all leads to the ultimate question, Which big fans need removal, and when?
Ignignokt
- 350
- 93
Indeed, this was what I found when I went to purchase LED lamps. I found one exception to this, a lamp that uses a remote phosphor (essentially a plate with an imbedded phosphor) that uses Stokes Shift https://en.wikipedia.org/wiki/Stokes_shift to generate the PAR light output. The LEDs are all the same, so a failure doesn't shift the spectrum at all.
The other thing was they specified the output - Efficiency: >2.0 μmoles per watt
Icemud
- 88
- 33
You mean like quantum dot technology?
AvidLerner
- 296
- 63
Numbers are meaningless if they are not connected to some form of reference. it is nice to know a PAR of 700-800 is good not because it is a higher number but because it references a specific growth pattern.
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