Effects of light quality (spectrum) on plants

We were having a talk about how different lamps induce differences in photosynthesis and other factors of plant development. As I think this topic deserves its own thread, I open this and translate the posts that arised the question, in the Ceramic Metal Halide thread (http://www.icmag.com/ic/showthread.php?t=72215&page=190), in order to not highjack that thread and continue here.

People were talking about the output in lm of CMH and HPS, so I posted this:

"An optical watt (emitted light) of CMH only produces 285lm, vs 385lm of a typical HPS. So, its not the HPS emits more light, but more lm: the light they emits produces an higher brightness sensation for humans, but not for plants.

1000lm of CMH (4200K) holds near 16 micromols of photons. While 1000lm of HPS holds 11.5-12uE.

So 31000lm of CMH=496uE

49000lm of HPS=563 to 588uE.

So, the HPS emits more photons, but there is way less difference than lm rating leads to think. "

etinarcadiaego posted:

"right we agreed that HPs emits more lumens, which is a standard created by people to measure as you mention, perceived light. Check this out, a great read about lumens and what they do and don't measure.

I followed the rest of your post, but it didn't really quantify the amount of photosynthetic reactive energy emitted by a particular bulb, though I don't think that's what you had in mind."

My next post

"Great link, its difficult to find pages that explain those concepts well.

Yeap, I did not wanted to enter into the conflictive topic of induced photosynthesis by different wavebands and light spectrums, but just state the actual light emission of both lamps in the unit meangliful for plants, micromoles of photons per second (uE).

But the photosynthetic response of plants is basically flat to all absorbed photons into the PAR range (400-700nm), irrespective of its wavelenght. There are differences, but they are small, and mainly produced by the different absorbance of each wavelenght, as one absorbed photon usually has the same potential of induce photosynthesis whatever wavelenght it is.

Its impossible to state how much photosynthesis induces photons of different wavelenght in the practice, due the adaptative nature of plants. But its possible to state some orientative figures, based on the data of botanist experiments, for unsaturated photosynthesis.

Using the Inada curve, which sum the effect of absorbance and quantum yield, the 4200K CMH result on a efficacy of 75%, and a typical HPS spectrum (phillips Son T), an efficacy of 78%.

Using the McCree curve and the cannabis absorbance of photons (thus, a more accurate way), it result on a efficacy of 74% (CMH) and 80% (HPS) respectively, when applied to the baseline of photon emission. But in the practice, difference is smaller. And when using high light levels, the efficacy of the bluiser CMH is way less affected (in the negative way) than its than of HPS. And the effect of higher UV (below 400nm), with reduced but positive photosynthesis induction narrow the edifference even more, as noted by hoosierdaddy

So resuming, there is little difference in efficacy of photons inducing photosynthesis for both type of lamps, and the photon output of each is a very good sign of their potential. And always take in mind that there are other things apart of photosynthesis, that are impossible to quantify (leaves to calixes ratio, production of resin, effects over cannabinoid profile...) "

Note: I deleted the quote of the last post, as etinarcadiaego has paste it

Lol. good call, opening the new thread

And I thought I understood english........

I'll just re-paste my post for ya man!

Thanks for the info man! Very interesting!

knna said:

But the photosynthetic response of plants is basically flat to all absorbed photons into the PAR range (400-700nm), irrespective of its wavelenght. There are differences, but they are small, and mainly produced by the different absorbance of each wavelenght, as one absorbed photon usually has the same potential of induce photosynthesis whatever wavelenght it is.

Click to expand...

Hmm, just wondering, as I've read information to the contrary before on other forums (not technical data), where did you find this information? Though I've suspected it before, I have never found anything actually stating that photons of light, regardless of wavelength, stimulate the same photosynthetic response. I've read some things recently that seem to say this, but none seem to offer it as a final conclusion or state in clear not-uncertain terms, if you will. For instance, check this read out. I really liked it's description of the various processes and how each leads to another more in-depth reaction, though this goes FAR more in-depth than needed.

This here seems to support what you said, as it states that chlorophyll a & b, which as mentioned in the first link are there to aid one another so as to absorb as much light as possible, both begin a process which ends the same way, thus each has the same result . . .

Here is a brief quote "The different sidegroups in the 2 chlorophylls 'tune' the absorption spectrum to slightly different wavelengths, so that light that is not significantly absorbed by chlorophyll a, at, say, 460nm, will instead be captured by chlorophyll b, which absorbs strongly at that wavelength. Thus these two kinds of chlorophyll complement each other in absorbing sunlight. Plants can obtain all their energy requirements from the blue and red parts of the spectrum, however, there is still a large spectral region, between 500-600nm, where very little light is absorbed. This light is in the green region of the spectrum, and since it is reflected, this is the reason plants appear green. Chlorophyll absorbs so strongly that it can mask other less intense colours. Some of these more delicate colours (from molecules such as carotene and quercetin) are revealed when the chlorophyll molecule decays in the Autumn, and the woodlands turn red, orange, and golden brown."

This seems to state pretty clearly that light is absorbed by one or the other chlorophyll, depending the wavelenth as shown here:





And that the light is absorbed and begins a chain reaction, REGARDLESS of the wavelength it was absorbed at or by which chlorophyll. That fascinates me for one reason, which would be that it implies that I could grow a plant under a single light source emitting light at one specific wavelength, provided either chlorophyll a or b could absorb it (wouldn't matter which), and that I'd get a healthy plant as a result.

I don't know that to be untrue, but it certainly seems contrary to the beliefs of many who claim that MH which emits light at a shorter wavelength, lead to shorter, squatter plants with tighter inter-node spacing versus HPS with light at longer wavelengths which can lead to stretch. Unless it would be a result of the bluer MH light have greater intensity because of its shorter wavelength and thus greater energy (inverse relationship between wavelength and energy, right?) . . .

In spite of this evidence, I've read elsewhere on this site (wish I could find the thread) that shows an image with depicting various wavelengths of light and what each will lead to in terms of plant-growth response. Is this wrong then? I'm not sure where it came from, only that i've seen it and what it claimed . . .

knna said:

There are differences, but they are small, and mainly produced by the different absorbance of each wavelenght

Click to expand...

What are the differences? Based on the above chart, does this mean that a & b are in fact different in terms of beginning the photosynthetic process?

knna said:

Using the Inada curve, which sum the effect of absorbance and quantum yield, the 4200K CMH result on a efficacy of 75%, and a typical HPS spectrum (phillips Son T), an efficacy of 78%.

Using the McCree curve and the cannabis absorbance of photons (thus, a more accurate way), it result on a efficacy of 74% (CMH) and 80% (HPS) respectively, when applied to the baseline of photon emission. But in the practice, difference is smaller. And when using high light levels, the efficacy of the bluiser CMH is way less affected (in the negative way) than its than of HPS. And the effect of higher UV (below 400nm), with reduced but positive photosynthesis induction narrow the edifference even more, as noted by hoosierdaddy

Click to expand...

So what you're saying here is that the data actually favors HPS in terms of plant-usable-light emitted per watt of electricity used, though you go on to mention that the difference in real-life performance may be substantially less noticeable. What would cause that to be the case?

knna said:

And when using high light levels, the efficacy of the bluiser CMH is way less affected (in the negative way) than its than of HPS.

Click to expand...

I'm not sure I follow. Are you saying that when using more light (multiple sources, stronger point sources???) the CMH actually performs a little better?

You also mention that the UV light emitted by the CMH adds to making the difference less noticeable. I've read that the amount of UV emitted by a 400 watt CMH is nominal, is that incorrect?

Also, what you would attribute the difference in bud structure to plants (clones) grown under HPS vs CMH? I ask this in part because if the data does suggest that the photosnythetic response is not wavelength dependent, what would cause the structural difference, or is there none?

Hmm, just wondering, as I've read information to the contrary before on other forums (not technical data), where did you find this information? Though I've suspected it before, I have never found anything actually stating that photons of light, regardless of wavelength, stimulate the same photosynthetic response. I've read some things recently that seem to say this, but none seem to offer it as a final conclusion or state in clear not-uncertain terms, if you will.

Click to expand...

Its general botanic knowledge, well stated and proved decades ago and measured repeatly along the following years. In this article of LI-COR (manufacturer of quantum meters used in most botanic studies) you can see the most used curves of photosynthetic response, from Inada (upper one on first page), that represent average photosynthesis induced for 1W of each wavelenght of incident energy, and below, it, the curve from McCree, that represents the photosynthesis induced by an equal amount of photons absorbed by the plant.

But unfortunately, its specialized knowledge, and many people uses incorrectly the chorophills absortion, that is way easier to find and understand, and use it to extrapolate photosynthetic response. But the problem is chlorophills absortion in lab (dissoved on a solvent) is very different to photosynthetic response of live plants. Peaks are similar (not the same), but relative effect of wavelenghts into the PAR range (400-700nm) is very different for both, so using the chlorophills absorbance is very misleading.

The cause is chlorphills absorb better one or other wavelenghts depending of its position on the leaf and to the protein to which its binded. When extracting chlorophills of leaves and dissolving it in a solvent, many things changes from the response in the live plant.

Plants are designed to use the best as possible all the light they receive, and it would be very stupid (inefficient) to waste many of the light reaching them. Plants doing it would be extinguished long ago, and plants using all the avalaible light survive them.

Photosynthetic systems are configured in a way that many chlorophills works together, with different orientation and configurations, and associated with other pigments, in order to absorb as more photons as possible. Chlorophills absorb photons by resonance, in a way that they are able to absorb mainly on two wavebands into the PAR range, one being the main (in the red) and the other, secondary, by armonic resonance, on a shorter wavelenght. Chlorophills are arranged in a way that those chlorophils having the absorbing peak for lower wavelenghts (thus, absorbing photons with higher energy), transfer that excitation energy to other chlorophills with absortion peaks on longer wavelenghts. The central chlorophills absorb directly on the longer wavelenght of the group, but most of their energy comes transfered from other chl absorbing on shorter wavebands.

By using millions of chlorophill molecules, plants are able to use photons of all wavelenghts. Some a little worse than others (typically, those on the green range), but only a little. Differences are small.

A plant change how much of each photsynthetic pigment is in each leaf depending of the light its receiving. For example, plants grown under HPS have tipically double the percentage of chl b than sunlight grown plants, in order to use HPS's yellow light the better.

Photosynthetic pigment arnt distributed homogeneously in the leaf, but near the epidermis there is more concentration of pigments specialized on absorbing red light, a little deeper more concentration of those absorbing blue, and on the inner part of the leave, of those specialized on absorbing green.

The adaptation of plants thus produce changes on their morphology, in order to use the light the better: a red rich spectrum produces leaves larger but thinner, so this way the plant may have more pigments absorbing red and less pigments for other wavebands.

All changes on the morphology of the plant are called morphogenesis. Morphogenetic effects are different of photosynthetic response, although they are interrelated

Thus these two kinds of chlorophyll complement each other in absorbing sunlight. Plants can obtain all their energy requirements from the blue and red parts of the spectrum, however, there is still a large spectral region, between 500-600nm, where very little light is absorbed. This light is in the green region of the spectrum, and since it is reflected, this is the reason plants appear green.

Click to expand...

This a false statement. Any empirical measurement of light absortion of plants shows a reduced absortion in the green range, but its very far from "very little light absorbed between 500-600nm".

For example, cannabis light absorbance:



At the worst wl into PAR, about 540-550nm, aprox 13% of light is reflected back, for only 7-8% reflected back on the best wavelenght. A 5% difference cant be said to be a large one.

And with a ligh absortion of about 76% at 540-550nm, vs 92% on the best absorbed wl, about 460nm, it cant be said neither that very little light is absorbed. A little less than red and blue, yes, but green is still absorbed pretty well.

Ill continue tomorrow (time to sleep), but you can read a thread about this topic in the meanwhile: Lighting concepts

hmm, I have a feeling this is going to get interesting.

something id be interested in discussing, if it were to so venture in that direction, would be the (potential) effects of spectra on the terpenoid profile of the plant.

I would say on the cannabinoid profile, but I feel that research is probably lacking in this specific area, but a more diverse terpenoid profile should yield a more diverse cannabinoid profile, and information on that topic may be more readily available....or so I hope.

You're the man Knna!

Thanks for dropping by since, you've forgotten more about light and plants than I'll ever learn. LOL Your posts go in my archives for all time Thank you!

Stay Safe!

I have definatley nocticed blue spectrums promote femality in plants, as well as keep internodes closer, but will not obtain density like full spec hps. I also notice blue spectrum adds more frost. I did an experiment where i put blue cfl's over a-11 in addition to the hps, and they were much frostier on those buds after harvest than the ones with out the blue spectrum.

you forgot to mention that most of the light for example at 500nm which is "absorpted" actually turns into heat

amoril said:

hmm, I have a feeling this is going to get interesting.

something id be interested in discussing, if it were to so venture in that direction, would be the (potential) effects of spectra on the terpenoid profile of the plant.

I would say on the cannabinoid profile, but I feel that research is probably lacking in this specific area, but a more diverse terpenoid profile should yield a more diverse cannabinoid profile, and information on that topic may be more readily available....or so I hope.

Click to expand...

Im more than interested on this topic. Mi priority righ now is to find the spectrums that promote the highest photosynthesis, by measuring plant matter acumulation under different light qualities.

But if we want to optimize MJ growing, we must study how light affect terpenoids and more specifically, cannabinoids, aswell as effect over resin production.

Unfortunatelly, there is very little reliable info about this topic and we should study it if we want to know more. But the problem is the requeriment of expensive equipment for doing it.

Hash Zeppelin- keep in mind that cfls give off UVB. It might not be the blue.

3dDream said:

Hash Zeppelin- keep in mind that cfls give off UVB. It might not be the blue.

Click to expand...

standard cfls dont give much UV light, at all. Even the reptile UV bulbs, which radiate more UV light, only claim a 5%-10% of the total energy in the ultraviolet spectra.

its my understanding that the phosphor coating on the standard CFLs for household use blocks all appreciable amounts of UV light.

etinarcadiaego said:

And that the light is absorbed and begins a chain reaction, REGARDLESS of the wavelength it was absorbed at or by which chlorophyll. That fascinates me for one reason, which would be that it implies that I could grow a plant under a single light source emitting light at one specific wavelength, provided either chlorophyll a or b could absorb it (wouldn't matter which), and that I'd get a healthy plant as a result.

Click to expand...

Take in mind that apart of photosynthesis, light produces other offect on plants.

Some plants species may grow under monochromatic light sources, as wheat, and at less degree, cannabis (it grows, but not aswell as with more complete spectrums). But most plant species needs light at least on some wavebands along the PAR range.

Most plants needs at least some blue to grow healthy. And blue plays an important role in the signaling that plants uses to decide what internal distance to develop. The more blue, the shorter internodes, although its not lineal. From no blue at all to a little blue, the effect shortening internodes is very pronounced, while as blue goes increasing, the aditional shortening of internodal distances goes lowering, until a point where more blue dont get any further reduction.

But blue is not the only signalling waveband that plants uses to decide the internodal distance, but phytochromes photoequilibrium plays an important role too. The wavebands that affect most phytochromes are 660+-20nm (Red Phy) and 725+-20nm (Far Red Phy).

So usually we need to consider the full spectrum in order to know what plants reactions to expect.

Originally Posted by knna
And when using high light levels, the efficacy of the bluiser CMH is way less affected (in the negative way) than its than of HPS.

I'm not sure I follow. Are you saying that when using more light (multiple sources, stronger point sources???) the CMH actually performs a little better?

You also mention that the UV light emitted by the CMH adds to making the difference less noticeable. I've read that the amount of UV emitted by a 400 watt CMH is nominal, is that incorrect?

Click to expand...

No, what I say is that Inada and McCree curves used to give an orientation about induced photosynthesis are refered to relatively low light levels, for unsaturated photosynthesis. And things changes when using higher light levels, as most MJ growers do.

Independent of spectrum, C3 plants have reduced photosynthesis efficacy as the irradiance (light reaching leaves) incresases. But that reduction varies with the wavelenght, and the shorter the wavelenght, the lower that reduction.

The result is that a bluish spectrum that produce less at low light levels, may produce more at high levels.

In general, it means we must be very carefull when taking conclusions about spectrums, because the final effect depend of both spectrum and irradiance level.

This produces eternal controversies between growers that get better results with one or other lamp, because they didnt realize both may are right, because they are using different irradiance levels.

Growers using very high light densities, past 75W/sq ft of HID, very often get better results using blue enriched lamps, and those using lower densities, as 40W/sq ft, get better result using standard HPSs.

About UV, regular lamps, not designed to emit UV, uses glass envelopes that blocks most of UV. These glasses tipically blocks off almost all UV below 370nm, thus their actual emission of UVB (below 320nm) is very, very small. But between 380 and 400nm, that is off the PAR range, there is still photosynthesis induction. Lower than that induced by PAR photons, but positive. And those photons and their associated induced photosynthesis arnt accounted into the figures of PAR photons or PAR watts.

HPSs emits very little into that range, while MHs, do. So the difference for PAR photons between both is larger than the actual difference inducing photosynthesis.

Also, what you would attribute the difference in bud structure to plants (clones) grown under HPS vs CMH? I ask this in part because if the data does suggest that the photosnythetic response is not wavelength dependent, what would cause the structural difference, or is there none?

Click to expand...

Photosynthesis and light signalling are separate tasks, and pigments doing them are different.

Photosynthesis is produced mostly using Chlorophills and Carotenoids. While light quality sensing, that determines photomorphogenesis and photoperiodism is a task of Phytochromes, Criptochromes and many others, some still waiting to be identified.

knna said:

Im more than interested on this topic. Mi priority righ now is to find the spectrums that promote the highest photosynthesis, by measuring plant matter acumulation under different light qualities.

But if we want to optimize MJ growing, we must study how light affect terpenoids and more specifically, cannabinoids, aswell as effect over resin production.

Unfortunatelly, there is very little reliable info about this topic and we should study it if we want to know more. But the problem is the requeriment of expensive equipment for doing it.

Click to expand...

so, Im off work today, and since youve been able to get the wheels turning in my head this morning, Ive been reading

anyhow, I stumbled upon something that, while not specific to cannabis, shows an interesting pattern in spectral efficiency in photosynthesis...at least, i think it is LOL.

the two charts show that with increasing intensities (w/m2) of light, the red and green spectra seem to fall off in effectiveness, while the blue continues to be an efficient photosynthetic catalyst.

http://ncr101.montana.edu/Light1994Conf/1_3_Tikhomirov/Tikhomirov%20text.htm

this would be the article, so you can see the charts in context....although I think a few of you have previously seen them

edit - this actually goes hand in hand with that knna is saying just above me, about effectiveness of blue light. beat me by seconds

knna....

first off....awsome info bro..thank u for shedding some real light on the topic for everyone

What's your opinion on people who try to use 10k/uvb during the last few weeks of flowering?

If uvb does promote thc or whatever its claim to glory is...would it be only beneficial if the plant recieves this light from the start to end? So in other words...if your goal is trying to implicate uvb for its benefits...what would be the best way in your opinion to use it?

.....Gojo chime in here bro....this is so ur type of thread

amoril - I don't know. I can tell you that I keep my cfls very close to plants and have had buds turn blue due to exposure. Here's some info from the fda site:

Do CFLs emit UV?

All fluorescent lamps emit some UV. Typical fluorescent lamps, including CFLs, which consumers would encounter, emit very low levels of UV. In order to measure any UV radiation from these lamps, very sensitive measuring equipment must be used.
What is the wavelength range of the light radiation that is emitted by CFLs?

Since CFLs are designed to provide general illumination, the majority of the light emitted by CFLs is localized to the visible region of the spectrum (approximately 400-700 nm in wavelength). In addition, typical CFLs emit a small amount of UVB (280-315 nm), UVA (315-400 nm) and infrared (> 700 nm) radiation.
How do I know that the level of UV is acceptably low from a CFL?

The Illuminating Engineering Society of North America (IESNA) has published a series of standards relating to radiation emissions from general purpose lighting. If a CFL were to exceed allowable levels of UV (according to IESNA RP 27.3), its packaging would be required to be labeled with a caution label. This standard, which was developed with the assistance of the FDA, requires lamp manufacturers to provide a suitable caution if one is needed. At typical use distances, UV levels from CFLs fall below the level of general concern for normal, healthy individuals and therefore carry no such warning.
How close can we safely get to an operating CFL?

Unless you are one of the few individuals who have a medical condition (such as some forms of Lupus) that makes you particularly sensitive to either UV or even visible light, you should be able to use these lamps at the same distance as you would use traditional incandescent lamps. However, a recent study from the United Kingdom Health Protection Agency has found that there are measureable levels of UV from single envelope CFLs when used at distances closer than 1 foot. As a precaution, it is recommended that these types of CFLs not be used at distances closer than 1 foot, for more than one hour per day.
How do I know if I am particularly sensitive to either UV or visible light?

Only your physician can make such a diagnosis. The vast majority of people do not suffer from such UV or visible light sensitivities.
Are there precautions I can take to reduce the small levels of UV from CFLs still further if I should wish to do so?

The glass used in CFLs already provides a UV filtering effect. In addition, any additional glass, or plastic, or fabric used in lighting fixtures that is between you and the CFL will further reduce the already low levels to still lower levels since these materials act as additional UV filters. Increasing the distance between you and any radiation source, including CFLs, will also reduce the small level to a lower level.

However, if you still wish to take additional steps then you might wish to purchase the type of CFL that has an additional glass or plastic cover that enclosed the CFL to make it appear more like a traditional incandescent lamp. These covers provide an additional reduction of the low level of UV to a lower level.

Click to expand...

amoril said:

standard cfls dont give much UV light, at all. Even the reptile UV bulbs, which radiate more UV light, only claim a 5%-10% of the total energy in the ultraviolet spectra.

its my understanding that the phosphor coating on the standard CFLs for household use blocks all appreciable amounts of UV light.

Click to expand...

3dDream, Im aware that there is UV light in cfls. My point is that the amount emitted is hardly enough to change the outcome of the crop, distance not really being a factor since the amount is dwarfed by the overall light of the bulb.

we're talking about anyting actually able to contribute, not strictly the presence of the wavelength. As I said earlier, bulbs that are marketed to emit a higher percentage of UV radiation toss somewhere around 2 watts of energy (10%) into the ultraviolet spectrum.

to be listed without a regulation, its going to be less than that. I have a hard time accepting that a CFL bulb, say 26w 6500k, is putting out more than 1 watt of ultraviolet light. Even at an inch, that isnt much. Sure, the plant could respond to it....

but ive put UV bulbs an inch from plants with no discoloration, and an inch from seedlings with no ill effects. I dont see how a "safe" bulb can offer an effect the "hazardous" bulb doesnt.

having said that, I do advocate the use of a full spectrum, including ultraviolet. Im of the school of thought that mimicing the sun's spectrum as closely as possible is the best avenue for indoor growers.

"ive put UV bulbs an inch from plants with no discoloration, and an inch from seedlings with no ill effects."

My reptile bulb will literally cook a plant if it is too close. Maybe your bulb was too weak? The 10.0 reptile bulbs I use expire in 6mo. Also, the 42w cfls will bring out color in bud. I have had flowers that were 1/2 blue due to the exposure (although I am assuming it's the uvb, it could be something else in the light). I am in a small space where plants are inches apart from the lights, this might account for what I see and you don't.

amoril said:

Im aware that there is UV light in cfls. My point is that the amount emitted is hardly enough to change the outcome of the crop.

Click to expand...

In the issue of safety, just want to point out here that most of us work with these lights in micro-spaces so it's not uncommon to find yourself working with your head less than 12" from them. Please protect your eyes and use an alternate source of light when possible. Too much time spent with your eyes that close to these lights WILL cause damage. The PL-L's I use will cause my vision to have a slight haze to it after a month or so of unshielded exposure when I'm working in there each day.

Took me a bit to figure out what was causing it.

Good thread.