DLI important or not?

[OneHitDone]

Penetration should relatively be the same though. Why wouldn't it? If you start with half the light from the fixture, you have half the light everywhere. Since you have the light on for twice as long, you would see the same DLI everywhere as if you'd run it half the time with double the intensity.

I don't have the science to back it up but I would have to disagree with this theory.
Suppose you had a pool if water with 1000 little 1w led's hung over the top, then a single 1000W cob in the over another.
Which is most likely going to light the bottom of the pool with the highest intensity reading at the brightest spot?
It was this thinking that led @subcoolgrower to make the "HPS is the bigger dick" comment when comparing to led and spread and intensity.
What are your thoughts on "penetration" from that perspective?

 

[Yodaweed]

I don't have the science to back it up but I would have to disagree with this theory.
Suppose you had a pool if water with 1000 little 1w led's hung over the top, then a single 1000W cob in the over another.
Which is most likely going to light the bottom of the pool with the highest intensity reading at the brightest spot?
It was this thinking that led @subcoolgrower to make the "HPS is the bigger dick" comment when comparing to led and spread and intensity.
What are your thoughts on "penetration" from that perspective?

I also am on your side about the dimming, if you dim your lights you effectively lower the amount of photons , if you raise the light you keep the same amount of photons but decrease the intensity (essentially all the photons are still there and will make your plant grow faster) , it might cost a lil more for electric, but who cares when the veg time and growth rate are better.

 

[wietefras]

I don't have the science to back it up but I would have to disagree with this theory.
Suppose you had a pool if water with 1000 little 1w led's hung over the top, then a single 1000W cob in the over another.
Which is most likely going to light the bottom of the pool with the highest intensity reading at the brightest spot?

This is not about distribution of light. Although I'd argue that even that doesn't matter since light is accumulative, but lets not get too distracted. The idea is dimming a light to 50% and running it twice as long.

If you dim your COB to 50% of the light production, you will see half the intensity everywhere compared to when the COB is at 100%. There is no sudden extra diminishing at some point just because you start with less light.

So the DLI will be the same since the light is on twice as long as it was with the 100%.

It's indeed about the number of photons (since photons drive photosynthesis) and in both cases that number of photons is exactly the same.

 

[OneHitDone]

This is not about distribution of light. Although I'd argue that even that doesn't matter since light is accumulative, but lets not get too distracted. The idea is dimming a light to 50% and running it twice as long.

If you dim your COB to 50% of the light production, you will see half the intensity everywhere compared to when the COB is at 100%. There is no sudden extra diminishing at some point just because you start with less light.

So the DLI will be the same since the light is on twice as long as it was with the 100%.

It's indeed about the number of photons (since photons drive photosynthesis) and in both cases that number of photons is exactly the same.

But the argument is that you can have the same DLI at the top of the plants all day long but the one with the lower output (dimmed) fixture is going to be larfy shit down low and the high intensity with less day length will be denser.
At least that would be my prediction.

 

[wietefras]

But the argument is that you can have the same DLI at the top of the plants all day long but the one with the lower output (dimmed) fixture is going to be larfy shit down low and the high intensity with less day length will be denser.
At least that would be my prediction.

You have half the amount of light intensity everywhere, but for twice as long. So they get exactly as much light in both cases. That's the whole point of DLI.

Suppose you take a 12 hour drive going at an average of 50km/h. Or you take a 24 hour drive going at 25km/h. Which of the two gets you further?

 

[OneHitDone]

You have half the amount of light intensity everywhere, but for twice as long. So they get exactly as much light in both cases. That's the whole point of DLI.

Suppose you take a 12 hour drive going at an average of 50km/h. Or you take a 24 hour drive going at 25km/h. Which of the two gets you further?

Yes, but if you drive off the road and hit a tree half way to the destination - which hits with a harder impact?

 

[wietefras]

Yes, but if you drive off the road and hit a tree half way to the destination - which hits with a harder impact?

You are not supposed to throw the light fixture on your plants. Lightspeed is a constant too.

Different example then. Suppose you move 12 buckets of 10 liter water each. Or ... you move 24 buckets of 5 liter. How many liters of water do you get in both cases?

Photons is what drives photosynthesis. Absolute amounts of photons measured in mole per time unit. In the case of DLI, per day. The DLI will be exactly the same for each spot. Whether it's 800umol/s/m2 * 12 hours or 400umol/s/m2 * 24 hours. Or 100umol/s/m2 * 12 hours or 50umol/s/m2 * 24 hours.

Of course you will get larfy shit way down below, but the point is that there is no difference in 12 hours 100% light versus 24 hours 50% light since the DLI is the same for each individual spot. Some points will get more or less light, but compare between the two scenario's, it's the same.

 

[KonopCh]

Yea, but in this scenario quallity and yield is different.

 

[wietefras]

@KonopCh

Why? What do you think the point of DLI is then?

When number of photons is what drivers photosyntheses. Why whould it matter if a plant receives 800umol/s/m2 for 12 hours or 400umol/s/m2 for 24 hours?

The amount of photons received in both scenario's is the same up top and down below as well. Of course you will have less light below, but it';s the same in both cases. In fact, for every point the number of photons will be exactly the same in both scenario's. Photons is what drives photosynthesis.

Explain rather than just saying "it's so", because if you try to explain then perhaps you will understand.

 

[StonerCol]

Automatics also need a certain rest phase, but only 4-6h.

Are you sure about this? I've heard so many people say that they don't require a rest phase. I'd be interested to read any evidence you may have of this.

 

[StonerCol]

When number of photons is what drivers photosyntheses. Why whould it matter if a plant receives 800umol/s/m2 for 12 hours or 400umol/s/m2 for 24 hours?

I'm no botanist but there is one thing I know: All systems/processes have an inherent level of efficiency and amount of inefficiency.
No system/process is 100% efficient.
So, where does the threshold lie? There must be a point at which the efficiency of the plants processes drops off?

 

[boilingoil]

@KonopCh

Why? What do you think the point of DLI is then?

When number of photons is what drivers photosyntheses. Why whould it matter if a plant receives 800umol/s/m2 for 12 hours or 400umol/s/m2 for 24 hours?

The amount of photons received in both scenario's is the same up top and down below as well. Of course you will have less light below, but it';s the same in both cases. In fact, for every point the number of photons will be exactly the same in both scenario's. Photons is what drives photosynthesis.

Explain rather than just saying "it's so", because if you try to explain then perhaps you will understand.

You make good points here,but by physics standards said photon of light energy will have a diminished effect. Sure you'll get the same photon count by your analysis but the excited state of the photon will be less.

 

[boilingoil]

I'm no botanist but there is one thing I know: All systems/processes have an inherent level of efficiency and amount of inefficiency.
No system/process is 100% efficient.
So, where does the threshold lie? There must be a point at which the efficiency of the plants processes drops off?

Like this! At max our plants are only 4-6% efficient at converting their inputs to plant mater.

 

[wietefras]

You make good points here,but by physics standards said photon of light energy will have a diminished effect. Sure you'll get the same photon count by your analysis but the excited state of the photon will be less.

But where would this "diminished" effect come from?

The photons carry the energy. Each photon absorbed increase the energy by a certain amount no matter how many photons are raining down. When more photons hit the plant per interval, the whole process just goes faster.

See: Photosynthetic Stages and Light-Absorbing Pigments https://www.ncbi.nlm.nih.gov/books/NBK21598/

In fact photosynthesis is actually more efficient at 400umol/s/m2 than say 800umol/s/m2, because photons can no longer all be absorbed and actually used.



If a lower intensity would actually "diminish" the efficiency, this chart would look completely different.

But of course if you run at 400umol/s/m2 for 12 hours then you'd get less photons on the plants and you will lose in yield and quality. Which is compensated by running the light twice as long.

 

[StonerCol]

Like this! At max our plants are only 4-6% efficient at converting their inputs to plant mater.

Fair point but if you double or triple the amount of light, that 4-6% becomes larger in absolute terms. At what point/amount of light can the plants no longer process it? Just as a simple example: If a plant can process 1000 photons per second then 1001 photons per second is too much. If that makes sense?

 

[boilingoil]

Not by the laws of Physics. Sure the Photons still carry energy but at a reduced state. Just the laws of physics.

 

[StonerCol]

Not by the laws of Physics. Sure the Photons still carry energy but at a reduced state. Just the laws of physics.

That doesn't make sense to me. If you add an extra 3 lights (All the same spec) then you'll have more photons.

 

[Bubblin]

Interesting read, thx Bob.
http://blog.surna.com/a-62-light-schedule-could-increase-plant-growth

 

[boilingoil]

That doesn't make sense to me. If you add an extra 3 lights (All the same spec) then you'll have more photons.

Ok, But I'm able to produce the same if not more from my 4x4 grow area with a single 600 watts of HPS as I can with 2 400 watt HPS in the same area, Why is that i ask you? I know why, it's because the photons carry more energy.

 

[boilingoil]

I also am on your side about the dimming, if you dim your lights you effectively lower the amount of photons , if you raise the light you keep the same amount of photons but decrease the intensity (essentially all the photons are still there and will make your plant grow faster) , it might cost a lil more for electric, but who cares when the veg time and growth rate are better.

It's more about the available energy stored in the photons.