Cannabis absorptance spectra: calculated and compared

[Bubbleblower]

If the photosynthetic performance of different light sources is to be compared, then the presently used metrics based on the quantum system are erroneous, not coherent and therefore fail.

Also photosynthesis extends further into the infrared region than previously thought and therefore the lighting metrics should be updated accordingly.

On topic is discussing Cannabis absorptance spectra, which isn't greatly affected by VPD, CO2, or container size to our knowledge (please cite published studies if we're wrong).

I got nothing specifically on cannabis. At the WUR they think these things matter and the container size is my own theory which was supposed to be discussed in the other thread.

 

[Beta Test Team]

I'm heading out now. I may edit for typos and cliarty later.

Some questions I have.

What is the optimum ppfd for cannabis? I have heard 1000-1500 umol/sec

There isn't really an optimum because the effects on photosynethic rate by irradiance (amount of light) depends greatly on various factors, including VPD (vapor pressure deficient), plant-water status, CO2, temperature, and probably most importantly, the total hours of light per day (DLI, ‘daily light integral’).

Right now there is no real agreement on an optimal range, either. That is something we plan to study once we acquire a photosynthesis meter in 2015.

Also, just like absorptance spectra, the ideal PPFD range for one Cannabis cultivar or variety may not be the same for another, for example, disparate landrace varieties

Some of the bigger problems with the study you refer to is the researchers only used red light (630 to 660 nm IIRC), and the VPD was pretty high (ca. > 2.0 IIRC), and the study period was far too short (60 minutes). So there is limited data we can draw from the findings of that main study, which found 1,500 PPFD is ideal for photosynethic rate.

And indeed, a main author of that study completed a very recent study on hydroponic growth of Cannabis at 700 PPFD.

In our experience with an ideal atmosphere (CO2, temp, VPD) between 500 to 800 PPFD is good for vegetative stage (in terms of great yields and flower quality), depending upon photoperiod (DLI) and environment (greater PPFD if the environment is more controlled). However, peak growth for us has been between 700 and 1,000 PPFD during flowering stage. Increasing DLI in flowering by increasing PPFD during flowering is good, relative to the DLI during flowering without increasing PPFD as compared to PPFD in vegetative stage. The source was white light, as Hortilux SuperHPS, and other lamps as well.

Another Cannabis study looked at irradiance on Cannabis but the author used PAR optic watts, not PPFD. So the findings are of limited use to us, however, we just thought yesterday if we can find the SPD for the lamp he used we can input that lamp data into our spreadsheet and create a PAR to PPFD conversion factor for his lamp. Then we can find the PPDF he used in his studies. This is what I'm working on later today. Otherwise, we can convert other lamps' PPFD to PAR W, and compare that PAR W to his PAR W:

The Effect of Electrical Lighting Power and Irradiance on Indoor-Grown Cannabis Potency and Yield
http://onlinelibrary.wiley.com/doi/...sCustomisedMessage=&userIsAuthenticated=false

However, that's mostly about PPFD (light as photons in the PAR range per second per meter squared), which is only half of the light equation. Equally (or more) important is DLI (the sum of PPFD over the whole day). To our knowable zero researchers have studied DLI effects on Cannabis, which is why that's going to be our first study in our new lab grade Cannabis research growth room we're starting to build next week! (We first have to do a break-in grow, though.)

In our experience between 30 and 55 DLI (mol/m-2/day-1 in the PAR range) is good for Cannabis in all growth stages. Like PPFD, only use higher DLI in well controlled environments, such as temperature, VPD and CO2.

Here's a quick way to convert PPFD to DLI; this is only valid for indoor or supplemental lighting greenhouses:

• (PPFD)*(hours of light per day)*(0.0036) = DLI

Thus far I have only written about irradiance, yet equally important is the uniformity of that irradiance over all the plants. Most indoor lighting for Cannabis is very non-uniform. So if the PPFD and DLI are ideal, yet the uniform is poor, total plant growth (from all plants as a mean) will not be as good as it could be.

What us the minimum/optimum CRI?
100 would be great but where does noticeable loss start.

This doesn’t matter for plant use of light. Ignoring this is safe.

What is the appropriate amount of UV?
Is there a level or a ratio that is optimum?

There is no proven ideal amount of UV-B as photon flux (umol/m-2/s-1 from 280-320 nm) or DLI, and the same goes for UV-A. This is an area we plan to study in 2015, as well. If you haven’t read my comments in Shaggy’s thread about UV-B you may like to:
https://www.icmag.com/ic/showthread.php?t=293184

Somewhere in the ballpark of 0.1 to 5 kJ/m-2/day-1 UV-Bbe is the target range. The best study on this topic thus far used the older UV-B action spectrum of higher plants by Flint, and found around 6, 8, and 14 kJ/m-2/day-1 of UV-Bbe all proved very effective at increasing THC.

UV-B increases not only THC, but also some secondary metabolites like some terpenes and flavonoids.

Potential UV-B DNA and cellular damage is mitigate by strong PAR irradiance (as PPFD, at least 10% of the sun's peak PPFD of about 2,000). For example:

Effects of prolonged UV-B exposure in plants
http://www.ubrisa.ub.bw/bitstream/handle/10311/491/Effects of prolonged.pdf?sequence=1

Effects of Ultraviolet-B Radiation on Photobiology
http://www.vitamindwiki.com/tiki-download_wiki_attachment.php?attId=534

The spreadsheet we're writing will convert the figures from that study to UV-B and UV-A photon flux, as well as the new Flint and Caldwell UV-B and UV-A action spectrum for higher plants (weighting the photon flux irradiance).

 

[Beta Test Team]

If the photosynthetic performance of different light sources is to be compared, then the presently used metrics based on the quantum system are erroneous, not coherent and therefore fail.

Yep, YPF may be quite inaccurate. That's why PPFD is the preferred metric in plant science.

Wait...what? Are you suggesting that use of photons (quanta) for light measurement isn't correct for plants? If so, please have that discussion in a different thread.

Also photosynthesis extends further into the infrared region than previously thought and therefore the lighting metrics should be updated accordingly.

PAR is only about strong effect on photosynethic rate by EM. It's been known for well over 50 years that wavelengths above 700 nm affect photosynethic rate. See Sager, et. al., 1988. That's why PPFD is used, it's the definition of PAR irradiance.

Our spreadsheet uses Sager, et. al. adjusted McCree RQE to calculate YPF. That updated RQE accounts for 330 to 782 nm (not 400 to 700 or 360 to 760). I have uploaded it to MEGA for you if you haven't read it yet (it's too big to upload to this post):

Photosynthetic Efficiency and Phytochrome Photoequilbria Determination Using Spectral Data
https://mega.co.nz/#!m40HFQbB!wtujIooa14CZOUy7RS2inQBX2lQU2-qgoSmsyr9dwXM

YPF is only tangentially useful in most cases, as YPF/PPF. Using YPF in the field is a non-starter too, due to the very poor quantum response of YPF sensors. All those reasons, as well as that McCree only used 150 PPFD to make his RQE (and other factors) is why PPFD is preferred in plant science.

On topic is discussing Cannabis absorptance spectra, which isn't greatly affected by VPD, CO2, or container size to our knowledge (please cite published studies if we're wrong).

I got nothing specifically on cannabis. At the WUR they think these things matter and the container size is my own theory which was supposed to be discussed in the other thread.

Any scientific citations or even simple evidence is what I was asking for, not about Cannabis (unless you had some ). What's WUR (Wageningen UR)? And why do they think those three factors greatly affect absorptance?

Absorptance is a very specific thing. I think maybe it's being used too loosely in this thread. It’s strongly affected by things like plant-water status and nutrient status (especially N), but even different Cannabis genotypes (cultivars or varieties) haven’t been found to have hugely different absorptance spectra.

Most higher C3 plants have pretty similar absorptance spectra, they are generally not wildly different from Cannabis over the whole PAR range.

 

[Bubbleblower]

What's WUR (Wageningen UR)? And why do they think those three factors greatly affect absorptance?

Yes, Wageningen, they have a goldmine of information. They don't report opinions, but just state facts or observations. I don't understand why you ask that question, if this is something with semantics it's only confusing.

In search of the ideal amount of PPFD and in relation to the Rubisco break it would be interesting to know if cannabis suffers from midday depression.

 

[PetFlora]

Plant knowledge cannot be learned in a microcosm

Some of the 411 you site has long been refuted

Your blinders are in the way of higher learning

Peace out

 

[Beta Test Team]

[FONT=Arial, Helvetica, sans-serif]What's WUR (Wageningen UR)? And why do they think those three factors greatly affect absorptance?[/FONT]

Yes, Wageningen, they have a goldmine of information. They don't report opinions, but just state facts or observations. I don't understand why you ask that question, if this is something with semantics it's only confusing.

I asked because I didn't know what you meant by “WUR.” I know about Wageningen UR. And I asked the second part because I want to know.

Could you please post why they think that about absorptance? I'm simply asking for data to backup the claims made, that's all. It's not that I don't believe you, I just want to see the data and sceince. We want to know if something we're doing is questionable.

In search of the ideal amount of PPFD and in relation to the Rubisco break it would be interesting to know if cannabis suffers from midday depression.

Yes, Cannabis does, just like other higher C3 plants. Which is often onset by high VPD and high PPFD (around noonish outside in the summer).

Also, I'm sure you're aware that Rubisco activase can be strongly inhibited once temperature exceeds about 90'F and CO2 about 1,500 ppm, and that for highest rate of photosynthesis Rubisco must not be limiting, therefore, because Rubisco activase is used for 'active Rubisco,' Rubisco activase must not be inhibited to miantian sufficient active Rubisco for high rates of photosynthesis all day long.

But this is far off topic, so that’s the last I’ll write about that in this thread:

Rubisco Activase
http://5e.plantphys.net/article.php?id=81

Robust Plants' Secret? Rubisco Activase!
http://www.ars.usda.gov/is/AR/archive/nov02/plant1102.htm

Rubisco activase constrains the photosynthetic potential of leaves at high temperature and CO2
http://www.pnas.org/content/97/24/13430.abstract

 

[Beta Test Team]

Plant knowledge cannot be learned in a microcosm

Some of the 411 you site has long been refuted

Your blinders are in the way of higher learning

Peace out

Please post scientific evidence or data refuting what I wrote about Cannabis absorptance. We honestly want to know if there's scientific evidence against what we're doing here.

And if you have valid scientific evidence or studies refuting claims I made about the other topics I wrote about please let me know. Maybe send me a PM or start that new thread we spoke about ('advanced lighting concepts')?

Thanks (and I mean that)

 

[Ranger]

Oh yea, Ranger, and others, here's a really great review on some of these topics you may like. Such as how yellow can inhibit plant growth (used to be thought green light was the cause, but it's yellow), green light effects on photosynthetic rate, VPD, root space (we use <=1 g/L), etc.

I uploaded for you because it's not free:

Horticultural lighting − present and future challenges

nah, it's all good man, just genuinely sorry for getting off on a different subject and i do appreciate the data man.

many thx

 

[Beta Test Team]

Updated absorptance spectra calculation workbook to v1.1:

In this is updated to version 1.1 we fixed a bug in v1.0 (missing nm 418), this version also has our data and knna's data removed so users can more easily create their own absorptance spectra:

https://mega.co.nz/#!K0Ez3IqC!99CDrTEcnwMuhbVROIpeaBQkWT7HIV4C0VVIyZVqQXQ

 

[3dDream]

Plant knowledge cannot be learned in a microcosm

I also think it is impossible to fully recreate nature in a room. You keep arguing about 1000 factors, but people are trying to discuss one topic: light and weed. You have yet to add anything to this thread other than mud in the water. Get over yourself.

 

[Beta Test Team]

UV-B

UV-B

With all the discussion about UV-B, UV-A, far-red and infrared we thought we should extend our absorptance spectra graph to match the data we're using in our lamp analyzer workbook.

And we're glad we did! It's really helpful to visualize using a graph. And the first thing that stuck out to us is how our UV-B and UV-A absorptance spectra mirrors the higher plant UV-B and UV-A action spectrum by Flint and Caldwell (2003).

All these data are being used in our spreadsheets.

For this post we made a mean graph for Cannabis as before (from early veg to late flowering), however, this time we used cubic spline interpolation (math) to calculate absorptance below 400 nm.

It took quite a while to get this correct but we're happy with the end result. Granted, there is an error margin (as always), but we think it's likely below 2% per wavelength (at least from 400 to 850 nm).

We had to estimate one data point for the cubic spline interpolation (370 nm) from the trend line of the data we created using the graph by Daughtry and Walthall (they listed down to 400 nm). Otherwise, all the data points (by 25 nm step size) we used for interpolation were from our analysis of the graph by Daughtry and Walthall (1998).

The graph is a bit large because its waveband is so wide (280 to 850 nm), so I uploaded to this post and our gallery:

 

[Beta Test Team]

Slight misfire with the newest graph in the last post.

We had to do a little last minute hand editing to smooth out and correct the graph for data points 650 through 750 nm, which were previously too great when using only interpolation (at 2 nm step size).

This version is the most accurate absportance data we've yet produced.

Here's the corrected version:
https://www.icmag.com/ic/showpost.php?p=6593407&postcount=125

 

[HUGE]

Question.

Why the upswing in absorptance as you reach the end of the uvb area? I have been following your posts and I seem to remember you citing that you wanted more uva and blue par than uvb to help mitigate the damage from uvb. Am I missing something or reading the graph wrong?

 

[Beta Test Team]

Question.

Why the upswing in absorptance as you reach the end of the uvb area? I have been following your posts and I seem to remember you citing that you wanted more uva and blue par than uvb to help mitigate the damage from uvb. Am I missing something or reading the graph wrong?

Thank you for asking this question, I should have made these points sooner.

Short version:
I think you're misreading the graph. What it shows is only the relative percent of photons absorbed by leaves. It doesn't speak to what the plant does with those photons.

So while the graph shows lower absorption of UV-A photons than UV-B photons, we still want considerably more UV-A photons than UV-B photons when it comes to how plants use the absorbed photons.

And it’s important to note the UV-B and UV-A data was created with math, not studying light at that wavelength range. So it’s probably safe to assume less than 5% error margin for 280 to 399 nm. For 400 to 850 nm less than 1% to 2% error margin should be assumed, we think.

Long version:
Leaves use light in three ways: [1] they reflect it (mainly green), [2] they absorb it (what our data is about), and [3] they transmit it (passes through the leaves, mainly far-red and IR).

Absorptance is calculated by assuming out of 100% of light (photon flux density; PFD) at each wavelength (e.g. 400, 450, 500 nm, etc.) light absorptance (absorbed photons) is what is left over after one accounts for reflectance (reflected photons) and transmittance (transmitted photons).

Leaves use absorbed photons in three main ways: [1] for photosynthesis, [2] for reactions other than photosynthesis (i.e. phototropism, photoperiodism, photonasty, and photomorphogenesis), [3] and as heat (photons not used are converted to heat – which not always a good thing).

Therefore the absorptance spectra we're creating does not say anything about how the absorbed photons are used by the plant. Only that they are absorbed.

To your question, you may be assuming the graph shows how much light (PFD) we want at each wavelength relative to other wavelengths, but that's not what it’s showing.

What it's showing is UV-B photons have greater absorption out of the total photons striking the leaves vs. UV-A photons. So this doesn't say anything about how the photons are being used. The reason leaves absorb greater percent of UV-B than UV-A (relative to total UV-B and UV-A, respectively) is due to and accessory pigments in the leaves.

If you look at a graph of the action spectrum of UV-B and UV-A for higher plants (Flint and Caldwell, 2003), you'll see UV-B has much greater effect on plant growth than UV-A. There is a strong downward slope from 300 nm to about 350 nm (I can make a graph for you if you’d like). Flint and Caldwell's action spectrum is regarding plant growth (inhibition, specifically), while McCree's is about photosynthesis.

So the reason we want more UV-A relative to UV-B is (at least) four-fold: [1] UV-A has lower absorptance (photons are less readily absorbed vs. UV-B), [2] UV-A has reduced effect on plant growth (that is, to elicit a plant growth effect more UV-A is needed than UV-B), [3] UV-A mitigates UV-B damage to leaves, and [4] UV-A is found in much greater concentration (PFD) in sunlight than UV-B (regarding evolution).

Therefore, even though Cannabis absorbs more UV-B compared to UV-A on a relative percent basis we want more UV-A PFD than UV-B (at least 5 times more, better is 10 times or greater, specifically > 375 nm) to prevent damage to the plants from UV-B. And the same goes for PPFD, assuming the PPDF has sufficient blue light, greater than about 200 PFD should be used (which won't be an issue with Cannbais growers). White light sources (like MH, and some HPS) emit enough UV-A so that you can simply worry about PPFD (because if you provide enough PPFD there will be enough UV-A, too).

I should note it’s important to quantify UV-B and UV-A using weighted PFD, using Flint and Caldwell’s work from 2003.

Later this week we’ll work have data regarding peak PFD of biologically active UV-B and UV-A outside at various locations, also as DLI (UVba PFD summed over the whole day).

(I hope that was easiy to understand, if not, please ask for clairification.)

 

[Beta Test Team]

Question.

Why the upswing in absorptance as you reach the end of the uvb area? I have been following your posts and I seem to remember you citing that you wanted more uva and blue par than uvb to help mitigate the damage from uvb. Am I missing something or reading the graph wrong?

I wanted to try and make the point more clear, as to why there's an increase in absorption of UV-B photons relative to UV-A photons. I mentioned chlorophyll and accessory pigments (light-harvesting) only in passing above.

For UV-B and UV-A, it's accessory pigments that do the photon absorbing (though some chlorophyll could be absorbing near PAR). Example of an accessory pigments for UV range are anthocyanins (flavonoids).

Below is the absorbance spectra for an anthocyanin (malvidin 30 glucoside), as well as chlorophyll A and B, and you can see how UV-B photons range are greater absorbed vs. UV-A photons (by the anthocyanin). This is a good example showing why our graph looks the way it does. However, our graph isn't perfect, and we already have some ideas about how to increase its accuracy a bit.

From a small meta-review of some literature it seems there are generally more UV-B absorbing pigments (that is, those with greater relative absorption of UV-B than UV-A). That is likely why the spline interpolation we used created the graph below 400 nm the way it did.

https://en.wikipedia.org/wiki/Anthocyanin

 

[Bubbleblower]

Question.

Don't listen to that guy unless you want to ruin your plants instantly.

Flint and Caldwell's action spectrum is regarding plant growth (inhibition, specifically).

It's about the effects of ozone depletion like plant growth inhibition or DNA damage.
Their spectrum shows what is bad for a plant!!!!!

And yours supposively what is good.

So who is completely wrong, Flint and Caldwell or you?

 

[Beta Test Team]

Do me a favor and stop posting in all of our threads, please. Otherwise, have some facts and data next time, and stop with the hysterics. If you can prove us wrong do so, but use facts and science, not your emotion.

I already wrote that Flint and Caldwell is the action spectrum of plant growth, and in the case of UV-B that's inhibition, UV-A (the only nm they tested was 366) showed positive growth if I recall correctly. Maybe you didn't understand that, or you don't understand how an "action spectrum" is defined.

The reason I wrote about Flint and Caldwell regarding their curve is it does mirror our UV-B and UV-A. I made no other points on that matter.

Like I wrote to HUGE, the graph we made does not show how the photons are used. Only how they are absorbed. Please stop trolling us if you don’t understand the science and math. However, if you do understand it (which you don’t seem to), and find problems with our work, please, let us know.

Thank you.

 

[Beta Test Team]

Also, your claim below shows just how much you don't understand about this thread and the science under discussion. Please, read up on the science (absorptance of photons) and if you find problems with our work let us know, politely.

The graphs we're making and the data we have do not show "what is good [for the plant]." They merely show how photons are absorbed on a relative basis. That's all, nothing else.

I have made no claims that that data shows "what is good [for the plant]." And if you think I have, I am sorry that I wasns't more clear.

And yours supposively what is good.

 

[Bubbleblower]

Photosynthesis = GOOD
DNA damage = BAD

Your spectrum = VERY BAD

I seem to remember you citing that you wanted more uva

That was me. What he said was this:

UV-A may have UV-B damage mitigating effects

If you're using white light for PAR range irradiance then your plants are probally fine

So I guess he changed his mind since then after I disagreed and after Googling some more studies he is now linking to.
Almost every single post he makes claims that are untrue or unproven and he cites a million studies that are not relevant at all. He could have fooled you. If he says anything it is up to us to refute His word and if you do he'll just ignore it and burries it under more words. The sad thing is we can't even discuss these very interesting topics anymore.

 

[HUGE]

Thanks I completely understand now. Much appreciated.