Cannabis Daily Light Integral

So I've been spending some time thinking about the optimum light levels our plants need based off of Light Cycle Duration and also what stage of growth the plant is in. According to my quick google searching, most mature 'High Light' plants require 12-18 Mols/ Day and 'Very High Light' plants need 18+ Mols/ Day of light for best growth, with cannabis being the latter of the two.

https://www.extension.purdue.edu/extmedia/ho/ho-238-w.pdf

I've also read on numerous 'forums' that flowering cannabis DLI saturation is between 20-30 Mols/ Day, but I haven't yet found any proper documentation backing that claim up.

But, if there is a hint of truth to this claim, it might explain a lot of the light stress that folks are seeing on their plants.

The formula for determining DLI:

• DLI (mol/m2/day) = average light intensity (μmol/m2/s) · time (in seconds) / 1.000.000

• DLI (mol/m2/day) = PAR · h · 3600 / 1.000.000

So, for example, say we have a 12 hour flowering schedule and you take a spot reading with a PAR meter and it reads 850 (μmol/m2/s).

So... (850 x 12h x 3600) / 1,000,000 = 36.72 Mol/ Day

So based of this observation, are the plants receiving too much light?
Could the same results/ plant health/ yield/ quality be achieved with less light?

I remember @captainmorgan saying that his canopy received about 550 μmol he had some awesome results. That is about 23.76 Mol/ Day.

I know that plants outside in direct sunlight can receive much higher DLI, but there are many other variables with growing outside. This discussion is more about indoor DLI requirements.

I hope to determine some sort of 'DLI standard' so we can have true target light levels to aim for.


https://en.wikipedia.org/wiki/Daily_light_integral
http://www.apogeeinstruments.com/daily-light-integral-measuring-light-for-plants/

I just go with what the photosynthetic process can handle.

PhotonFUD said:

I just go with what the photosynthetic process can handle.

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What is your experience with minimum/maximum light levels vs length of 'day'?

230-600 umoles is fine....has to be uniform though.

Spot reading is too quantitative and not qualitative enough....there are tweaks out there......

I also have been finding that my plants seem less stressed where I'm spot reading under 600 umol, while still fully developing. Putting them under 30 Mol for the day.

The colas getting 1100 umol aren't much bigger, but the colas getting 150-300 umol are much smaller.

42 max i think

subbed

weed-whacker said:

42 max i think

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42 max dli? with or without co2?

Max is when your leaves begin to droop towards the end of the daily light cycle.

did we ever find a source for cannabis dli under normal and elevated co2 levels?

i cant help but think that a super healthy large plant under maximum metabolic efficiency (proper temp, vpd and co2) cant make more use of a higher DLI, since the majority of gardens dont push the plants to their maximum it could be said that good producing garden with average plants would be maxed out at 30, but a super vigourous diale din pro grow (when everything goes right) could have advantage up to 45

some people claim they run their gardens at 1200-1500 ppfd but thats obviously at the tops

how can we quantify average light over the plant? with different canopy depths and densities it seems almost impossible

i mean if you went to the bottom of a branch like the bottom bottom where you still get nice buds but not popcorn, i bet it is as low as 200 ppfd and still making usable material

cdgmoney250 said:

So I've been spending some time thinking about the optimum light levels our plants need

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The problem here is that an "optimum" value will be different for different people.

If you want a higher g/W ratio then a lower intensity will be more optimal. You'll get less yield overall, but relatively more per watt. If you want a higher g/m2 ratio then a higher intensity will be more optimal. You will get more yield overall, but relatively less per watt. Each person will have their own compromise between these two which suits them best.

I read a report from a medical cannabis led test where they used 250umol/s/m2 as the average intensity and claimed 400umol/s/m2 was "high" intensity.

Wa while back I checked the YOR database with grow results for 175 grows and translated those results to a g/m2 related to intensity chart. That gave a chart pretty similar to the one from that chart that floats around mapping intensity to photosynthetic efficiency. I found it was a bit more linear in the 250 to 800umol/s/m2 range. As was also reported by other growers that they felt the chart from that research paper was to exponential. But then the paper only did tests on leaves and did not do actual grows to see the effect of average light intensity

Still it's not entirely linear of course and for example if you would get 1,4g/W at 800umol/s/m2 average, you would on average get 15% higher g/W at 500umol/s/m2 (ie 1.6g/W). So if you raise the intensity by 60% you wouldn't get 60% more yield, but it (and your g/m2 ratio) would go up by 40%.

It just depends what you are limited on (either space or electricity)

1 DLI = ~278 umols for 1 hour.

The best way to find out when you have hit your max DLI for the plant you are growing is by measuring the leaf temps. There will be a clear increase of between 1-3c once the plant has taken in what it can as that unused light energy is converted to heat. A simple example would be this:

PPFD at leaf is 560 so for each hour on, it is 2 DLI. At 12hrs 20mins, the leaf temp goes up 2c indicating that the plant is done for the day. The total DLI the plant can handle at this point in its life is roughly 25. Going past this will start to cause photo-inhibition.

Grams per watt is a pretty useless measurement for comparing yields. Yield is commonly determined by area and length of time, eg x number of <weight> per acre per growing season.

If you are trying to figure it out for business cost then you should be looking at total power used over the entire grow not just what the light fixture uses from the wall. There are many overhead factors involved even with non-commercial hobby gardening that are often overlooked like fans, odor control, HVAC, etc.

Once the smarter folks who went to the full out efficiency end of the debate start posting 3,4,5+ g/W results there will probably be a significant shift to the 'less power more light' side of the fence. Only casualties will be heatsinks and possibly expensive meanwell drivers when PWM catches on.

cdgmoney250 said:

So based of this observation, are the plants receiving too much light?
Could the same results/ plant health/ yield/ quality be achieved with less light?

I remember @captainmorgan saying that his canopy received about 550 μmol he had some awesome results. That is about 23.76 Mol/ Day.

I know that plants outside in direct sunlight can receive much higher DLI, but there are many other variables with growing outside. This discussion is more about indoor DLI requirements.

I hope to determine some sort of 'DLI standard' so we can have true target light levels to aim for.

Click to expand...

I would say it depends on whether you are supplementing with Co2 or not because this is a major factor you will need to consider.

If you are growing at temps around 21 - 25 degrees Celcius then you will hit the point of diminishing returns without Co2 around +600 - 800PPFD.

If you want optimum, then in my experience I have found (strain dependent/supplementing with Co2) Avg;
- Start at 800PPFD week 1 of flower, then 1000PPFD in week 2 of flower, then crank it up to 1500 PPFD (in mid flower) then drop down to 1200PPFD in second to last week of flower and 800PPFD in last week of flower.
- Temps between 25 - 30 Degrees/c (increasing as light levels go up, decreasing as light levels go down)
- Co2 levels 700umol throughout the duration of the grow

Without Co2 supplementation, I would experiment on your strain/s around 500 - 850 PPFD.

And don't forget that you need to remember, that as your light levels increase, then you will need to increase grow-room temps accordingly and vice-versa.

Photon Flinger said:

1 DLI = ~278 umols for 1 hour.
Grams per watt is a pretty useless measurement for comparing yields. Yield is commonly determined by area and length of time, eg x number of <weight> per acre per growing season.

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People do both depending on what their limiting factor is.

There is something that invalidates any form o comparison. So then none will be useful. The fact is that g/W is very easy to measure and it's perfectly valid if you grow in both situations under mostly similar conditions.

If you are trying to figure it out for business cost then you should be looking at total power used over the entire grow not just what the light fixture uses from the wall. There are many overhead factors involved even with non-commercial hobby gardening that are often overlooked like fans, odor control, HVAC, etc.

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Even if you add additional electricity users, it's still g/W.

I recently helped someone replace 2 600w HPS with 1120w LED. I let them borrow my par meter and asked them to take readings before and after. The HPS was reading 1022 PPFD 16" below center and 678 PPFD near the side, approximately 16" off center. Readings were also taken 22" below center (752 PPFD) and 22" off center (330 PPFD).

Anyway, this person had one plant that was a late addition and he angled both of his HIDs onto the plant since he didn't need the whole space at the time. Got the biggest buds he's ever gotten. He does run CO2. His light levels at the canopy were likely between 1500 and 2000. Unfortunately I don't have a way to quantify the difference, but he was impressed.

If anyone is curious, the 51% efficient LED that replaced the HID at same reading points were 1408/820 and 1011/605. The bulbs were six months old so they didn't get beaten that badly, but still a major improvement.

Point is, if you hang your lamps too high you're wasting light and loosing yield. I haven't had a chance to play around with HID but one thing I've noticed with LED, especially using 90 degree reflectors is that the center point reading will be somewhat linear while the outer readings will stall for a bit. What I mean by that is for instance you are checking light levels at 12 inches and get maybe 1000 center and 600 side. Move down to 14 inches and your at 850/620 or something similar. Then at 18" it's 700/590. This happens on the side because although the reading is being taken further away which lowers readings it's also further inside the cone which raises readings. This is why you should get your lights as close as they can tolerate within reason. Moving up from 12" to 10 inches in the same example might produce 1200/430 or something similar as the side reading moves outside the cut off point of the reflector cone.

Rahz said:

I recently helped someone replace 2 600w HPS with 1120w LED. I let them borrow my par meter and asked them to take readings before and after. The HPS was reading 1022 PPFD 16" below center and 678 PPFD near the side, approximately 16" off center. Readings were also taken 22" below center (752 PPFD) and 22" off center (330 PPFD).

Anyway, this person had one plant that was a late addition and he angled both of his HIDs onto the plant since he didn't need the whole space at the time. Got the biggest buds he's ever gotten. He does run CO2. His light levels at the canopy were likely between 1500 and 2000. Unfortunately I don't have a way to quantify the difference, but he was impressed.

If anyone is curious, the 51% efficient LED that replaced the HID at same reading points were 1408/820 and 1011/605. The bulbs were six months old so they didn't get beaten that badly, but still a major improvement.

Point is, if you hang your lamps too high you're wasting light and loosing yield. I haven't had a chance to play around with HID but one thing I've noticed with LED, especially using 90 degree reflectors is that the center point reading will be somewhat linear while the outer readings will stall for a bit. What I mean by that is for instance you are checking light levels at 12 inches and get maybe 1000 center and 600 side. Move down to 14 inches and your at 850/620 or something similar. Then at 18" it's 700/590. This happens on the side because although the reading is being taken further away which lowers readings it's also further inside the cone which raises readings. This is why you should get your lights as close as they can tolerate within reason. Moving up from 12" to 10 inches in the same example might produce 1200/430 or something similar as the side reading moves outside the cut off point of the reflector cone.

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So you never grew with a HID light but somehow think LEDs are better?

Isn't that a little backwards, shouldn't you have first hand experience before ruling something out or anointing something better?

Also why the hell would you continue to use 6 month old bulbs, that just shows your inexperience with HID lights.

You may have read a little too quickly. I wasn't continuing to use a 6 month old bulb. My customer had lamps with 6 month old bulbs. They were 6 months old at the time of the switch out because he waited until they were 6 months old to switch them out for the LEDs. Make sense?

As far as whether I think LED is better, when I was growing I achieved anywhere between 1.2 and 1.6 GPW from the wall. In both cases I was achieving close to 3.5 grams per par watt. GPPW isn't a metric for light efficiency but rather how efficiently par watts are used regardless of light source. If I had been using HID I would have continued to achieve somewhere near 3.5 grams per par watt and my GPW would probably have been similar since the lamps I was using were 35% and 42% efficient respectively. The 35% efficient lamp performed similar to a SE bulb and the 42% efficient lamp performed similar to a DE bulb. Not surprising to me at all. This particular build used Vero29C at 1050ma so about 51-52% efficient so it's also no surprise that from the metric being measured it easily took first place.

Bottom line 1200w of HID was reading much lower than 1120w of LED. Interestingly that was even more true at the sides of the area and at lower readings, seeing as how the LED was providing almost twice the PPFD at 22" (605 -vs- 330). This should put to rest the idea that a big bulb necessarily provides better penetration. The array of 70w emitters had higher readings at every level and provided better "penetration" in the center and especially on the sides due to the the way the light is distributed.

If you're going to be disagreeable and cuss, probably best to comprehend the other person's post before you do. I didn't even say I thought LED is "better". Par measurements were took and the LED had better numbers. Make sense?

@Rahz I have done a run to try and find the maximum PPFD a strain could handle and was smashing it with up to 3500 PPFD while keeping the ambient temps between 25-30c. As long as the temps were kept in check, the plant can handle it. More relevant is DLI - the plants can handle the high intensity for shorter periods but once they hit their max DLI, damage starts to occur.

Apparently lettuce can handle up to 5000 PPFD in recent research but didn't increase yields.

There is a benefit though, you can use the higher intensity light to reduce your lights on time and increase flower period, which with FR speeds up the flower cycle. Still working on the particulars but I have reduced my lights on down to 6hrs using a 1500-1850 PPFD at the canopy.

Also since you seem fairly smart and a decent vendor, you should go take a look at using PWM current to drive the cobs. Not the PWM dimmer option on meanwells, they still provide stabilized current to the cobs. Do your research into it and see if you are able to source a LED driver with PWM output.

Rahz said:

You may have read a little too quickly. I wasn't continuing to use a 6 month old bulb. My customer had lamps with 6 month old bulbs. They were 6 months old at the time of the switch out because he waited until they were 6 months old to switch them out for the LEDs. Make sense?

As far as whether I think LED is better, when I was growing I achieved anywhere between 1.2 and 1.6 GPW from the wall. In both cases I was achieving close to 3.5 grams per par watt. GPPW isn't a metric for light efficiency but rather how efficiently par watts are used regardless of light source. If I had been using HID I would have continued to achieve somewhere near 3.5 grams per par watt and my GPW would probably have been similar since the lamps I was using were 35% and 42% efficient respectively. The 35% efficient lamp performed similar to a SE bulb and the 42% efficient lamp performed similar to a DE bulb. Not surprising to me at all. This particular build used Vero29C at 1050ma so about 51-52% efficient so it's also no surprise that from the metric being measured it easily took first place.

Bottom line 1200w of HID was reading much lower than 1120w of LED. Interestingly that was even more true at the sides of the area and at lower readings, seeing as how the LED was providing almost twice the PPFD at 22" (605 -vs- 330). This should put to rest the idea that a big bulb necessarily provides better penetration. The array of 70w emitters had higher readings at every level and provided better "penetration" in the center and especially on the sides due to the the way the light is distributed.

If you're going to be disagreeable and cuss, probably best to comprehend the other person's post before you do. I didn't even say I thought LED is "better". Par measurements were took and the LED had better numbers. Make sense?

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Not really because those par measurements don't include which spectrum is more desirable, HID lights grow better plants cause of IR.

You guys are obsessed with numbers but don't actually have any grow room experience, those numbers can be misread easily by inexperienced people like yourself.