DLI important or not?
- Thread starter KonopCh
- Start date
nfhiggs
Well-Known Member
Its not a threshold - its a curve.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?
cdgmoney250
Well-Known Member
You aren't taking into account photon transmission. Higher PPFD will transmit more photons into the mid-lower canopy. This will increase photosynthesis over a low PPFD situation, even if DLI is matched.
Big smo
Well-Known Member
I love this analogy. The curve ball is autos can't handle 1000+ppfd. So it's more like doing 25km/h because that's all your vehicle will do or can handle.
OneHitDone
Well-Known Member
Auto's can't handle 1000+ppfd?
They sure seem to handle full sun just fine
MrTwist1
Well-Known Member
There's a few variables to consider, but it is common knowledge that 600W HPS is more efficient than 400W... then that extra heat from having 2 less efficient lights is immediately an important factor too.
boilingoil
Well-Known Member
I won't argue over those points, but the response was to whether 1/2 of the intensity in 24 hours versus 12 hours of full intensity is equal.
Unless your running autos' then it's a moot point. As photos' would never flower under 24 hour of light.
MrTwist1
Well-Known Member
For what it's worth I agree with @wietefras that in theory 12h x 100W = 24h x 50W. Daily Light Integral is real.
As you say, it is not particularly relevant to flowering photoperiod plants that need 12h darkness... but the important thing to take away is that light energy is cumulative to the plant. If you wish you could have your lights produce more/less light at different times of day, yet still achieve the same DLI as if you just ran the same power all day.
boilingoil
Well-Known Member
In theory yes. But if that was true why do we have trouble with light penetration to the bottom of our plants even running high intensity lighting.
MrTwist1
Well-Known Member
Because of inverse square law... which is largely mitigated by having multiple sources of light in a reflective area, but still plays a part... But this thread isn't really about penetration, it's about DLI.
boilingoil
Well-Known Member
I'm not saying DLI is not relevant in a grow, it's just one part of the puzzle. But by you referring to intensity that's the ability of the source to drive the photon with more energy enabling it to travel farther with less degradation and the ability to do work, Cut that in half and you can have thousands of photons hitting the plant but if they don't have the energy to perform the work than what use are they really?
wietefras
Well-Known Member
Wow these "penetration" myths are really deep rooted.
You have exactly the same "penetration". Penetration is photons travelling between the leaves. Nothing about intensity of light matters for that path. Photons travel until they hit something. The distance they travel is not related in any way to the number of photons joining it on their journey. They don't lose energy along the way either. Every photon carries an exact amount of energy depending on their wavelength.
It's a myth that certain lights penetrate easier or "deeper" than others. All that happens is if you start with a higher intensity, you will have a higher intensity lower down too. Or vice versa, if you cut it in half up top it will be half down below too. If you run half the intensity in the same 12 hours then you'd have less "penetration" yes. In this case the light runs twice as long, so same number of photons and therefore exact same "penetration".
Read the article in the link I posted. It explains exactly how photosynthesis works in capturing photons. It's like filling a bucket with water. When it's full it tips and starts the process. Then it's empty and starts filling again for the next round. You get the exact same amount of full buckets in both cases.
It's all about absolute numbers of photons hitting a cell.
nfhiggs
Well-Known Member
I do not understand why people call it a "myth". Inverse square law is quite real and applicable to point source or near point source lights. Double the distance from the light source and you have 1/4 the number of photons per square inch. Natural sunlight is the same intensity (disregarding shading) from the top of the plant to the bottom of the plant - that is what is meant by "penetration". You simply don't get that with artificial lighting because they are so much closer - instead you have an intensity gradient that diminishes from top to bottom. The closer you can get to that natural ideal, the better. The only thing that is a "myth" about this is the idea that HPS is automatically "the best light" in this regard. There are different ways to achieve an improved intensity gradient - distributed multiple light sources with optics and/or reflectors can improve the light intensity gradient dramatically if implemented well.
wietefras
Well-Known Member
There is a huge amount of myth around "penetration". Like described above, that photons lose energy. That 5W leds penetrate deeper than 3W leds. That HPS penetrates deeper than anything else. etc etc etc.
Inverse square law is also one of the myths, but more in the sense that people think putting the lights closer to the plants will increase the amount of light hitting the plants tremendously. Hint, it doesn't. It only serves to focus the total amount of light on a smaller area while other areas will get less light.
But in this case inverse square law is not the issue at all. Or rather, I don't care how the light is lost, my point is the relative loss is the same in both scenario's (12 hours of 100% light or 24 hours of 50%).
The case here is as follows: We have a spot on the bottom of the grow room. We measure the light intensity at this spot. Now, if we cut the light production from the light source in half, what happens to the light intensity at the spot on the bottom?
A) Does the light there suddenly disappear completely?
B) Are we left with a quarter of the light intensity?
C) Do we get exactly half the light at the bottom also.
D) Something else.
boilingoil
Well-Known Member
I understand where you are coming from from the quantum theory side.
ChefKimbo
Well-Known Member
Slightly off-topic question, could this in anyway be related to the turgidity changes when the plants learn the light cycle. How some plants(and some don't) droop right before lights off and readjust right before lights on. Some plants don't do this, would that be an indication that DLI has not yet been achieved for that plant?
Hybridway
Well-Known Member
Good question...
wietefras
Well-Known Member
But can you explain how you would come to any other answer to my question than answer C?