Amount of light?

[Death The Cultivator]

@Son of Hobbes
Sir, if I may to chime in and correct a minor oversight and maybe give some food for thought...

1. PPFD is quantum flux expressed over an area over time, so the unit is umol/m^2/s. The umol/s is PPF that is the raw net amount of photons a fixture released as being measured in an Ulbricht-integration sphere.

2. The Light-Saturation-Point given by Fluence is extremely low at ~550ppfd and that's not supported by any study I'm aware of. But what studies did show is that it's different depending on the genotype but generally way higher than that, even before CO2.

3. Outside the sun, even in the mourning or evening hours is already so strong enough to fully light-saturate any leaf that has exposure to direct sunlight. Once you see the sun yellow then it'll be at high ppfd. Then long before midday its fluence will be so high that a photoinhibition sets in that is both the product of too high irradiance and a spectral blueshift. So studies have shown that many plants do better photosynthesis when the sun is not in the zenith.

4. PPFD undervalues the light influx as it only integrates photons ranging from 400-700nm by definition. But plants can use photons from UV to FR/IR, with especially the range of 700-750nm is still plentyful in the SPD and the capture of these wavelength carry great implications that weigh them even far better than any generic weight light.

So what I'm saying is that outside the plants receive way more light than what an incomplete metric as DLI states on paper.

Hope this helps you out a bit

Those DLI maps are inaccurate but the link below covers the entire US annually.

https://www.asianturfgrass.com/post/high-resolution-dli-maps-united-states/

Check that one out @Son of Hobbes

#3 I disagree for the most part. Far too many outside influences compared to the controlled environment indoors. If you check the link for the map provided we can pick a high light point in California and average their hours of light in the summer to 13. It averages out to around 1200ppfd, cannabis doesn't reach the threshold of inhibition until 2000ppfd and outdoors that's going to be affected by clouds and other environmental factors.

Then the consideration that even IF light hit for 2000ppfd, the sun isn't in a constant position so light levels and parts of the available light spectrum change throughout the day.

#4 I disagree with DLI being an incomplete metric for outdoor plants. Spectrum changes throughout the day, plants can differentiate between seasons by the available amount of certain light spectrums. That affects the amount of UVB/A and Far Red as well. Indoors we can use these spectrums for crop steering but they are minimal. Too much UVB would cause tissue damage, too much far red would cause excessive stretching.

 

[Son of Hobbes]

https://www.asianturfgrass.com/post/high-resolution-dli-maps-united-states/
Check that one out @Son of Hobbes

Oh I like this, you can put in your address and it pinpoints.

 

[Butrod]

. #4 - "traditional" PAR is 400 to 700 but ePar broadens the range from 400 to 750nm. I was looking at a PPFD map of a Vipar Spectra light and noticed that ePar was being measured. It adds ≈ 50 µmols - not a lot but I believe it's synergistic with red.

Yes, with all white light and even UV. There's even a broader metric "PBAR" (PhotoBiologically Active Radiation) that extends much further - 280-800nm.
Though designed to encapture the light shaping photomorphogenesis, still this energy can reach chlorophylls and fix carbon.

 

[Butrod]

Do you have links to said studies to support your statement? I mean that in favor of tweaking and altering the guide.

Here's an old one with a Mexican Sativa that is an unusually good photosynthesizer.

There's a bunch more, let me just go through my archive to search for the select excerpts

 

[Butrod]

Here's another one that is especially good to explain why it can be beneficial to even go further than the light-saturation-point in an indoor scenario because even when the tops get too much light then still the middle parts profit much from a higher photon influx.

It also illustrates how a leaf grown under high fluences are adapted to be able to process a higher fluence
Thus, the diagram gives different LSPs.

 

[Talonxracer]

Something else to consider is that the total amount of light(measured with a PAR meter) can be a rather deceptive number, it is important to also know where the spectral peaks are and that takes a spectrometer(another costly piece of gear).

 

[Death The Cultivator]

Here's another one that is especially good to explain why it can be beneficial to even go further than the light-saturation-point in an indoor scenario because even when the tops get too much light then still the middle parts profit much from a higher photon influx.

It also illustrates how a leaf grown under high fluences are adapted to be able to process a higher fluence
Thus, the diagram gives different LSPs.

I kind of like this one but I do wonder about a couple of things.

I don't find any mention of the particular method in which they cultivated outside of using DWC. Was there trellis?

1800ppfd or roughly 78 DLI to only net 519g per meter squared only works out to roughly 51g per square foot.

Two week veg? I see 14 days to root, transplant, topping after 10 days but not overall veg time.

I go to look at the light company, Lumigrow 650, and I'm not impressed. Vague metrics and a horrid excuse for a ppfd chart. This would have been more valuable using several different types of lighting. The company claims 40% efficiency over HID 1000W but which kind? Single ended? Double?

No real mention of plant height. I wish they had it in there? Do you see it? I see the initial height but not any final height.

Could you quote where they really explain how stronger levels of lighting influence the middle?

I think using that facilities standard operating procedures was part of the problem. 50g or so per square foot isn't super impressive imo. What size was the overall grow space per culture basin? I thought I saw 8x2 but I'm not sure.

 

[Butrod]

Something else to consider is that the total amount of light(measured with a PAR meter) can be a rather deceptive number, it is important to also know where the spectral peaks are and that takes a spectrometer(another costly piece of gear).

Agreed, the quantum meters or luxmeter have sensors that will not pick up much of the diffuse radiation present

 

[Talonxracer]

Two week veg? I see 14 days to root, transplant, topping after 10 days but not overall veg time.

I accidentally forced a plant into early flowering at 18 days and thought I screwed up royally, but I let the plant do its thing and ended up with a harvest that was massive! It is now my go-to schedule for the shorter life span autos

 

[N/A-Greengo]

I use this PAR meter.

Fall Color Sale - Phantom PHOTOBIO Advanced Quantum PAR Meter

This advanced quantum PAR Meter provides accurate and cost-effective measurement for all light sources used to grow plants. The PHOTOBIO by Phantom Quantum PAR meter is designed to measure PAR (Photosynthetically Active Radiation) flux in wavelengths ranging from 400 to 700nm. There is a...

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