Max PPF/PPFD with and without Co2

[plumsmooth]

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I've seen mention of up to 65 mol/d and according to purdue university studies on different plant species, most other light loving plants like sunflowers and tomatoes are recommended for a DLI between 22 and 30mol/day.



So for cannabis, bottom threshold for optimal growth and photosynthesis is a DLI of DLI of 22 would be:
24/0 schedule: 254.6 micromoles/m2/s-1
18/6 schedule: 339.5 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 are using 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: 1003.08 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 what about calculating the variance between light hitting the Tops vs the middle and bottoms? I Realize ideally I low stress Train my plants, train them etc... But sometimes we clearly have plants that the top 6 inches hits 1000 PPFD but then the rest of the plant in under 750 etc...???

 

[Week4@inCharge]

So what about calculating the variance between light hitting the Tops vs the middle and bottoms? I Realize ideally I low stress Train my plants, train them etc... But sometimes we clearly have plants that the top 6 inches hits 1000 PPFD but then the rest of the plant in under 750 etc...???

Hence the importance of an even canopy

 

[cdgmoney250]

This is why strategic defoliation is important as well. You could always add some side/inter-canopy lighting if you were concerned with lower bud yield. But really, training the plants for more tops early on is your best bet, regardless of your light fixture. I would guess fixtures with higher densities of chips would experience less drop in ppfd at same distance away, but I have not actually tested that theory with a par meter.

 

[ttystikk]

I would guess fixtures with higher densities of chips would experience less drop in ppfd at same distance away, but I have not actually tested that theory with a par meter.

Would you believe the opposite? The more concentrated the fixture, the more it acts like a point source of light and the more the inverse square law of light intensity applies. Having your lights spread out across the canopy reduces this effect.

 

[Greengrouch]

Depends, your ambient co2 might be higher than you think. If you’ve got gas heat/water/stove it most certainly is. If people and pets are usually in the house during lights on it probably is. You can get a meter on amazon and check, they’re not that expensive, you can even return it when you’re done. I don’t run co2 and my canopies at 1000+ most of flower, but I live in a 600sft apartment and I’m home all the time.

 

[Rocket Soul]

Would you believe the opposite? The more concentrated the fixture, the more it acts like a point source of light and the more the inverse square law of light intensity applies. Having your lights spread out across the canopy reduces this effect.

Yes, but it also will reduce peak ppfd at cannopy. I speced and made some lights: same 30ish watts per square foot as always. But fixture was as big as the cannopy (and in open space so no reflections): it did not perform very well as too much light fell outside the cannopy. When i narrowed the strip separation a little bit from 1.5m to 1.3 we finally saw the light start performing. That little tweak is only 15% but thats almost 100ppfd.
But in the centre underneath of that light theres very little ppfd falloff as you go lower due to crosslighting, just as you state.

 

[cdgmoney250]

Would you believe the opposite? The more concentrated the fixture, the more it acts like a point source of light and the more the inverse square law of light intensity applies. Having your lights spread out across the canopy reduces this effect.

No, I wouldn’t believe the opposite. Here is a quick little blurb from Google AI that is worded quite nicely regarding how the inverse square law works in regards to multiple light sources.

“When multiple light sources overlap, the inverse square law applies to each individual source, meaning the intensity of light at a given point is calculated by summing the individual contributions from each light source based on their distance, resulting in a combined intensity that is not simply the sum of their individual intensities at that point due to the falloff with distance; essentially, the closer light source will have a greater impact on the overall illumination at that point.

Key points about overlapping light sources and the inverse square law:

Individual calculations:
For each light source, calculate its intensity at a specific point using the inverse square law based on its distance from that point.

Summation:
To find the total intensity at that point, add up the individual intensities from each light source.
Distance-dependent influence:
A light source closer to a point will contribute more to the overall intensity at that point compared to a farther source due to the inverse square relationship.

Example:
Imagine two light bulbs, one close to a wall and one far away.
To calculate the combined illumination on a spot on the wall, you would calculate the intensity from each bulb individually based on their distance to the wall, then add those intensities together to get the total illumination at that spot.

Important considerations:

Light distribution:
The inverse square law assumes a point light source emitting light uniformly in all directions. If a light source has a directional beam, the intensity distribution will be different.”

There is something also to keep in mind regarding the inverse square law and light fall off. The further you get from the light source, the difference in intensity becomes incrementally smaller and smaller.



Here is a helpful video from the photography department at BYU that explains the difference in light levels at different distances.

The thing to keep in mind is that the inverse square law applies to every individual chip whether it’s a COB or a mid power chip that would come on a board or a strip. The quantity and spacing/orientation of the chips will have a cumulative effect on light levels further from the source due to light beam overlap and the inverse square law. @rocketsoul beat me to the punch with his explanation of reducing spacing between his strips and the 15% increase in ppfd levels at further distances from the level light.

 

[Rocket Soul]

No, I wouldn’t believe the opposite. Here is a quick little blurb from Google AI that is worded quite nicely regarding how the inverse square law works in regards to multiple light sources.

“When multiple light sources overlap, the inverse square law applies to each individual source, meaning the intensity of light at a given point is calculated by summing the individual contributions from each light source based on their distance, resulting in a combined intensity that is not simply the sum of their individual intensities at that point due to the falloff with distance; essentially, the closer light source will have a greater impact on the overall illumination at that point.

Key points about overlapping light sources and the inverse square law:

Individual calculations:
For each light source, calculate its intensity at a specific point using the inverse square law based on its distance from that point.

Summation:
To find the total intensity at that point, add up the individual intensities from each light source.
Distance-dependent influence:
A light source closer to a point will contribute more to the overall intensity at that point compared to a farther source due to the inverse square relationship.

Example:
Imagine two light bulbs, one close to a wall and one far away.
To calculate the combined illumination on a spot on the wall, you would calculate the intensity from each bulb individually based on their distance to the wall, then add those intensities together to get the total illumination at that spot.

Important considerations:

Light distribution:
The inverse square law assumes a point light source emitting light uniformly in all directions. If a light source has a directional beam, the intensity distribution will be different.”

There is something also to keep in mind regarding the inverse square law and light fall off. The further you get from the light source, the difference in intensity becomes incrementally smaller and smaller.

View attachment 5443593

Here is a helpful video from the photography department at BYU that explains the difference in light levels at different distances.

The thing to keep in mind is that the inverse square law applies to every individual chip whether it’s a COB or a mid power chip that would come on a board or a strip. The quantity and spacing/orientation of the chips will have a cumulative effect on light levels further from the source due to light beam overlap and the inverse square law. @rocketsoul beat me to the punch with his explanation of reducing spacing between his strips and the 15% increase in ppfd levels at further distances from the level light.

I think the both of you are saying the same but with different words, at least thats how i understood you both. Of course inverse square law applies to each diode but the cumulative effdct is that light falls of slower but is less intense at a given height. Hard to explain in words but ive seem it myslef comparing high power cobs and fotop boards (900x280mm) woth par meter in hand: the cobs would need a higher hanging height but also the rate of light dropp was proportionally higher than the bugg boards: the more you bring the sensor away from right up close the more cross lighting you get. But also depends on having the sensor under the middle of the board.

 

[cdgmoney250]

I think the both of you are saying the same but with different words, at least thats how i understood you both. Of course inverse square law applies to each diode but the cumulative effdct is that light falls of slower but is less intense at a given height. Hard to explain in words but ive seem it myslef comparing high power cobs and fotop boards (900x280mm) woth par meter in hand: the cobs would need a higher hanging height but also the rate of light dropp was proportionally higher than the bugg boards: the more you bring the sensor away from right up close the more cross lighting you get. But also depends on having the sensor under the middle of the board.

I’m not sure we were both saying the same thing, but it gave me the chance to illustrate my thought and it sounds like you have seen the effect in action.

That’s all I was getting at, was that with more quantity of individual point sources (chips), depending on spacing, power, etc. you would likely see an overall higher average ppfd at the further distances (higher hanging heights) due to the overlap of all the beam angles and the cumulative flux effect. Maybe this could be helpful in designing lights that could be have better ppfd numbers at higher distances, so as to have higher light levels hitting the mid/inner canopy, without totally frying the tops of the colas.
That’s what I was thinking anyways.