User:Phacelias/notes2

From Talk page Chlorophyll
Talk Page Chlorophyll

Chlorophyll does not reflect green light
Chlorophyll does not efficiently absorb green light but this does not mean that it reflects green. It transmits green light. The misconception that chlorophyll would specifically reflect green light comes from school teaching. My extensive search in scientific literature did not provide any experimental evidence supporting the idea of reflection of green light by chlorophyll - but I would be utterly interested in seeing a reference in which chlorophyll is shown to reflect light. In my laboratory, I work a lot with thylakoid membrane preparations and plant extracts that contain chlorophylls a and b as the main pigments, and both become very dark green or almost black when they are highly concentrated. On black background, both tend to disappear. If chlorophyll reflected green light, they would make a green spot on black surface.

In the lack of earlier research I conducted, in my research group, an experimental study. We measured reflectance from green leaves and from similar leaves devoid of chlorophyll. In all cases, green reflectance of white or yellow leaves was higher than that of green leaves. The paper has now been published online in a peer-reviewed journal (Virtanen et al., Journal of Biological Education, https://doi.org/10.1080/00219266.2020.1858930). The results reveal the obvious: leaves are green because chlorophyll absorbs red and blue but does not block the green light reflected from the tissues, mostly from the cell walls.

I understand that Wikipedia should reflect the consensus, and one paper against a large body of contrasting evidence might only be mentioned as a discrepant voice, if even so. However, in this case, the consensus is not, at least in the light of my database searches, based on science. Therefore I feel that my argument should be taken seriously. Besides, the evidence in the Virtanen et al. paper is absolutely conclusive. I tried to edit the Wikipedia page in 2019 because I thought that this is a simple mistake and a real no-brainer. The edit was reverted because I could not cite any reference (and I think that was quite right). However, now that I have the reference, my edit on December 29, 2020, became reverted without any notice, and the reference was omitted.

The question whether chlorophyll reflects or transmits green light is not only of academic interest. For remote sensing of chlorophyll content, it is important to understand how the green color of plant leaves is formed. Similarly, some plant biological applications are based on reflectance measurements. It may also be important for school children to understand the differences between artists' colors that function like chlorophyll (only absorb - e.g. marker pens, some crayons) and colors that contain reflective stuff and therefore both absorb and reflect (some crayons, in fact also many watercolors). The video published as an attachment of the Virtanen et al. paper touches this point (and also shows that on a black paper, colors that only absorb but do not reflect, including green chlorophyll-containing acetonic extract of plant leaves, do not produce any image while light-reflecting crayons can be used to draw on black paper).

EsaTyystjärvi (talk) 16:05, 2 January 2021 (UTC)


 * Your addition to the article was reverted by who said in their edit summary that your edit was in good faith but was a conflict of interest (true, as you are one of the authors of the reference in question) and was WP:RSBREAKING. I disagree with the latter assessment, since although the publication of the article is recent it is not the sort of "breaking news" that is likely to spread potentially false rumours. Either one believes the science in your article (which I do) or one refutes it but can't be said to be a rumour! Subject to further comments by other editors who may read this Talk Page, I'll add back something along the lines that you did, as I certainly have no WP:COI. Mike Turnbull (talk) 17:42, 2 January 2021 (UTC)

Thank you - I am sorry that I did not pay attention to the abbreviations and did not try to find out what they mean. I agree that a citation to my own paper might raise a conflict of interest. However, I am concerned about the fact that the opposite view does not need any reference to scientific literature. The finding that chlorophyll does not reflect light is certainly not breaking news in the plant biology community! Otherwise I would have chosen a photosynthesis journal rather than an educational one :) EsaTyystjärvi (talk) 08:31, 3 January 2021 (UTC)


 * ✅ The relevant changes have now been made to this article and to Chlorophyll a and Chromophore. Mike Turnbull (talk) 15:07, 6 January 2021 (UTC)
 * I have difficulty in understanding the statements that chlorophyll does not efficiently absorb green light and that chlorophyll does not reflect light. The lightwaves that are not absorbed are reflected, so everything that is green reflects green and everything that appears red reflects red and absorbs all the other wavelengths. It is as simple as that. The question is then, has purified chlorophyll a green appearance? Has it a green color? Then it doesn't absorb green and hence reflects it. If it has no color it reflects all wavelengths of the visible spectrum. If it absorbs all lightwaves it should be black but it isn't, see photograph of purified chlorophyll. Chlorophyll_Extraktion.jpg Phacelias  (talk) 11:50, 28 July 2022 (UTC)
 * The other possibility that you have not considered is that chlorophyll transmits green light. In the example shown, the solution of chlorophyll is transmitting green light, not reflecting it. Leaves reflect green light because it is transmitted through the chloroplasts and then scattered and backscattered by interaction with cells and intercellular spaces. Plant surfer 13:33, 28 July 2022 (UTC)
 * Hi . I think that the best way to explain this is to look at the absorption spectrum (on this Talk page top right). You'll see that neither chlorophyll a or b absorbs very much at 600 nm (~ green) while they have a large maxima centred around the purple/blue end of the visible spectrum and a smaller maximum near the red/yellow end. So these natural dyes look green, having subtracted most of the other colours from white light. Your extraction flask shows the standard green colour both from the light transmitted though the solvent layer containing the chlorophyll and reflected from that layer. The discussion above in this section was about leaves and it is worth reading 10.1080/00219266.2020.1858930 in full. It is open-access. Mike Turnbull (talk) 13:33, 28 July 2022 (UTC)
 * Hi @Plantsurfer and @Michael D. Turnbull. Thank you for your quick reply. In the photo on the right, the flask contains chlorophyll and no other plant or leaf structures that might transmit or reflect or absorb whatsoever. Maybe I don't understand what you mean with 'transmitted'? You want to suggest that it is the solvent that reflects green light? I have read the discussion and I don't agree with the outcome. I don't think you can change Wikipedia content in an article of High importance because of one scientific paper that states a 'new' result. This paper is full of contradictions. It might be mentioned at the end of a paragraph, if you really want to name it, but as it is now we risk to mislead the reader. Phacelias  (talk) 14:12, 28 July 2022 (UTC)
 * What you are seeing is well explained at Absorption spectroscopy and in particular in the diagram top right in that article. The flask does indeed contain chlorophyll and chlorophyll absorbs certain wavelengths of white light. What is not absorbed is transmitted (that's the word used in the caption of the diagram I'm referring to and has its normal dictionary definition of "to allow to pass through"). We see green because green is what passes through, the other colours of the white light having been absorbed. Mike Turnbull (talk) 14:37, 28 July 2022 (UTC)
 * Hi Phacelias In simple terms, transmitted light is light that passes through an object, like through a window. Reflected light is light that is backscattered off the surface of an object. In the flask, the solution is transparent, and the green light is transmitted through it, not reflected off it. Plant surfer 14:36, 28 July 2022 (UTC)
 * @Michael D. Turnbull and @Plantsurfer How do you explain the green colour of the chlorophyll extract? Why is it green?
 * I read the paper. The short conclusion of the paper is the following: "In conclusion, plant leaves are green because green light is less efficiently absorbed by chlorophylls a and b than red or blue light, and therefore green light has a higher probability to become diffusely reflected from cell walls than red or blue light. Chlorophylls do not reflect light." This is one of several contradictions. If green light is not or less efficiently absorbed in chlorophyll, that just means that chlorophyll reflects part of the green light. If this green light is scattered by cell structures, doesn't mean that chlorophyll does not reflect light.
 * The paper ends with the following acknowledgments: The authors thank the Quora social network service and Wikipedia for inspiration. Interesting. Phacelias  (talk) 15:10, 28 July 2022 (UTC)
 * if you look through a sufficiently thin leaf at a bright light you'll see that the light looks green. That's because, as the paper says, chlorophyll absorbs red and blue light more than green, so the green passes through. If you look at the top of the leaf under these conditions, it too looks green, because, as the paper says, the cell walls (not the chlorophyll) reflect the light that isn't absorbed, in all directions. Peter coxhead (talk) 16:17, 28 July 2022 (UTC)
 * @Peter coxhead yes, that is what the paper says. But in the first place it is the Chlorophyll that reflects the green light, independently of the fact that you look under or above a leaf with respect to a light source. That reflected green light may yes or no be transmitted or scattered or reflected by de cell walls. That is of no importance to the fact that chlorophyll reflects green light.
 * How can cell walls by themselves reflect green light? What is the mechanism, where are the pigments in the cell walls that reflect the green light? I never heard of that before. Phacelias  (talk) 17:21, 28 July 2022 (UTC)
 * nowhere that I can see does the paper (or any others) say that chlorophyll reflects green light. It absorbs blue and red more, so the light that is left appears green. This light is reflected by the cell walls. Your comment implies that you need pigments to reflect light. This is simply not the case; consider a mirror or the reflections you get off the surface of clear water at certain angles. Sorry, but you are simply wrong, as others here have tried to explain to you. Enough from me. Peter coxhead (talk) 06:38, 30 July 2022 (UTC)
 * Hi @Peter coxhead, you write: “nowhere that I can see does the paper (or any others) say that chlorophyll reflects green light. It absorbs blue and red more, so the light that is left appears green. This light is reflected by the cell walls.” The paper states in the last sentence that Chlorophyll does not reflect green light. This is not true, this is false and shows the low quality of this paper.
 * Now you are wrong, since reflection by a mirror is a completely different chapter.
 * I will quote 3 texts, one from national geographic, the Max Planck Institute again and the article in Wikipedia about pigments.
 * A pigment is a molecule that has a particular color and can absorb light at different wavelengths, depending on the color. There are many different types of pigments in nature, but chlorophyll is unique in its ability to enable plants to absorb the energy they need to build tissues.
 * Chlorophyll gives plants their green color because it does not absorb the green wavelengths of white light. That particular light wavelength is reflected from the plant, so it appears green.
 * From National Geographic
 * Chlorophyll a absorbs violet and orange light the most. Chlorophyll b absorbs mostly blue and yellow light. They both also absorb light of other wavelengths with less intensity. However, none of them absorbs green, so the leaf looks green because that light is reflected to our eyes instead of being absorbed by the leaf. Since there are no other strong pigments present in leaves, that is the whole story.
 * From Max Planck Institute
 * Like all materials, the color of pigments arises because they absorb only certain wavelengths of visible light. The bonding properties of the material determine the wavelength and efficiency of light absorption. Light of other wavelengths are reflected or scattered. The reflected light spectrum defines the color that we observe.
 * Pigment
 * Now the color of an object is determined by what is absorbed and what is reflected. Your blue shirt reflects blue because that is the color/wavelength that is not absorbed. Your shoes are red because that is the color that is reflected and not absorbed. All other colors/wavelengths like green and blue are absorbed by your shoes. It is so simple, please make an effort. So this is the same for chlorophyll. The paper states that chlorophyll does not reflect green light. The author seems to think that this is a new discovery that should be announced to the scientific world. If this were true it would be worth two papers in Science and Nature. But it is not true, see also the absorbance spectra of the chlorophylls. Phacelias  (talk) 08:10, 30 July 2022 (UTC)
 * I'll make one last attempt (against my better judgement). Your quotes above with my emphasis:
 * "Chlorophyll gives plants their green color because it does not absorb the green wavelengths of white light. That particular light wavelength is reflected from the plant, so it appears green." – does it say reflected by chlorophyll? No.
 * "the leaf looks green because that light is reflected to our eyes instead of being absorbed by the leaf" – does it say reflected by chlorophyll? No.
 * Peter coxhead (talk) 06:19, 1 August 2022 (UTC)
 * @Peter coxhead The fact that chlorofyll reflects green light is demonstraded by its absorbance spectrum: what is not absorbed is the color (wavelength) that is reflected and is the color that we see. Now compare the pigments chlorophyll of green leaves and heme of platelets that makes our blood red. These are both pigments, and pigments reflect a certain color of light (wavelength); Chlorophyll_c1.svg chlorofyll reflects green and the heme Heme_b.svg reflects red. These are very similar pigments a part from the metal in its center Phacelias  (talk) 07:24, 1 August 2022 (UTC)


 * Nasir-al_molk_-1.jpg in Shiraz, Iran]] Several other editors have urged you to consider that light that is not absorbed does not need to be reflected; it can be transmitted, meaning that it can pass through unchanged. This is the case for chlorophyll. Maybe it will help to consider the appearance of a stained-glass window when viewed from inside a darkened building. In the image shown, the green panes absorb the colors that are not green from the white sunlight, and the green passes through to the inside where it can be viewed directly or seen to light up objects in the interior with green light. This is not reflection; this is transmission. –MadeOfAtoms (talk) 10:15, 1 August 2022 (UTC)
 * @MadeOfAtoms Thank you for the beautiful image. I do see what you mean with transmittance. You are a physicist, nice to meet you here. I am out of arguments also because I don’t want to repeat myself. I will contact Dr. Angel Rubio from the Max Planck Institute and hear what he thinks about the publication of EsaTyystjärvi and the statement that chlorophyll does not reflect green light and I will let you know. Thank you for your contribution.
 * P.S. The only argument I want to leave here, is that when an extraction of a spinach leaf is made on chromatography paper, the green colored part contains chlorophyll. If the chlorophyll would transmit green light would we say that it is the white paper that reflects the green light transmitted by chlorophyll? Just like EsaTyystjärvi says that it is the cell walls that reflect the green light? I don’t think so. Phacelias  (talk) 06:03, 2 August 2022 (UTC)
 * @Phacelias Your logic is false. What is not absorbed is not necessarily reflected. It can alternatively be transmitted. Chlorophyll is not opaque, and is not like a mirror. It is a transparent substance. Transparent means light passes through it. Green light passes through it. Red light is absorbed. The internal structure of a leaf is complicated, full of materials (cells, cell walls) with different refractive indices and interspersed with air spaces. The consequence is that light cannot pass through a leaf in a straight line - it is bent into tortuous paths, some of it scattered back from where it came. The green light that is transmitted through chlorophyll is refracted and reflected by cells and intercellular spaces multiple times before it exits the leaf. Some of it ends up being backscattered towards the light source. You can call that reflection if you like, but it is a misleading and simplistic description of what actually happens. Some of it is forward scattered, appearing to pass straight through the leaf, but the actual light path is far too complex for that to be the case. Plant surfer  23:18, 2 February 2023 (UTC)
 * In summary 'reflected by a leaf' does not equate to 'reflected by chlorophyll' Plant surfer  23:41, 2 February 2023 (UTC)
 * @Plantsurfer I have no single reason to think, to suppose or to state that chlorophyll would transmit green light rather than reflecting it. So the statement "Hence chlorophyll-containing tissues appear green because green light, diffusively reflected by structures like cell walls, is less absorbed." in the first paragraph of the article is not true. It has no sense to name the structures: it would be like saying that my red blouse is red because the pigments in it transmit red and the tissue of my blouse scatter the red light. No, what we say is that my blouse is red just like chlorophyll is green. Chlorophyll is the pigment and the leaf contains it, that's why the leaf is green. No transmittance by chlorophyll and reflection by leaf structures needed. Phacelias  (talk) 02:49, 3 February 2023 (UTC)
 * No, chlorophyll does not reflect green light. Cell walls are transparent. They can reflect green (or any other colour of light) light at certain angles of incidence in the same way that clear glass can. But most of the light that impinges on a cell wall will be transmitted through it, not reflected off it.  Plant surfer  17:47, 28 July 2022 (UTC)
 * Yes, chlorophyll reflects green light, you are mistaken. Please, can you tell how it comes that the Chlorophyll extraction in the photo on the right is green? How is that possible? And you know that it has nothing to do with transmission. It is just the chlorophyll that does not absorb green light. Phacelias  (talk) 18:15, 28 July 2022 (UTC)
 * Proposal
 * Hi @Michael D. Turnbull and @Plantsurfer,
 * Please read the following: "Chlorophyll a absorbs violet and orange light the most. Chlorophyll b absorbs mostly blue and yellow light. They both also absorb light of other wavelengths with less intensity. However, none of them absorbs green, so the leaf looks green because that light is reflected to our eyes instead of being absorbed by the leaf. Since there are no other strong pigments present in leaves, that is the whole story."
 * Citation from The Max Planck Institute Research News: The true color of Chlorophyll.
 * I want to delete the added text in the edit in the article Chlorophyll concerning the Revision of 14:53, 6 January 2021 made by @Michael D. Turnbull. What concerns me most is the legend in the figure about reflection in leafs which got my attention some months ago. I will adapt that text too and will delete the reference and put it somewhere else in this article. Any suggestions? Phacelias  (talk) 07:17, 29 July 2022 (UTC)
 * Oppose: You clearly do not understand the interaction of light with leaves or with chlorophyll. It is much more complex than you appear to think. [User:Michael D. Turnbull|Michael D. Turnbull's]] edit was accurate and appropriately sourced. Plant surfer  10:34, 29 July 2022 (UTC)
 * The Max Planck statement is correct and tallies with what I said above when I pointed you to the absorption spectrum. Indeed, the quote explains what you said you [had] difficulty in understanding the statement that chlorophyll does not efficiently absorb green light. There is no need to alter the current text in the article, which is already accurate. However, if you wish to propose some alternative text you believe would improve the article, please specify it here, perhaps in the form of an WP:EDITREQUEST so that a WP:CONSENSUS for your change can be sought. Mike Turnbull (talk) 11:23, 29 July 2022 (UTC)
 * @Michael D. Turnbull yes, I will specify it here, but not as an edit requests because these are for controversial changes an editor wants to make while the problem is that the edit you made in the past was controversial. You or User:EsaTyystjärvi herself should have made the request.
 * The page you linked for edit request states the following: “Edit requests are requests for edits to be made to a page where editors cannot or should not make the proposed edits themselves. Requests should be accompanied by a clear and specific description of the requested change, and consensus should be obtained before requesting changes that are likely to be controversial.”
 * (1. Your edit was controversial and mine would bring it back to the scientific consensus. 2. We are both editors so we both have the right to make changes.)
 * I don’t see why we “cannot or should not” edit the page ourselves, but if that results in editing back and forth it is useless of course. Either you convince me of the valid affirmations of EsaTyystjärvi that is that chlorofyll does not reflect green light and we leave it as it is, or I will have to convince you of her erroneous conclusions and change the text in the article. So I'd rather see another publication with the same conclusion as the one of EsaTyystjärvi if you want to convince me. Phacelias  (talk) 12:12, 29 July 2022 (UTC)
 * I don’t see why we “cannot or should not” edit the page ourselves, but if that results in editing back and forth it is useless of course. Either you convince me of the valid affirmations of EsaTyystjärvi that is that chlorofyll does not reflect green light and we leave it as it is, or I will have to convince you of her erroneous conclusions and change the text in the article. So I'd rather see another publication with the same conclusion as the one of EsaTyystjärvi if you want to convince me. Phacelias  (talk) 12:12, 29 July 2022 (UTC)

I said perhaps in the form of an WP:EDITREQUEST, not that you couldn't be WP:BOLD if you wished,. However, I would point out that my edit that you have taken issue with was made in January 2021. This article has 286 page watchers and 39 editors who have made recent edits (according to the page information). So you are likely to be in a minority in seeing that edit as problematic. Also, please note that is male. Mike Turnbull (talk) 13:25, 29 July 2022 (UTC)


 * Thank you for being helpful. Esa seems female for who comes from Italy where almost all female names end with -a and male with -o. Sorry about that. I realise that the edit we are talking about was done one and a half year ago, and that nobody has seen the problem. I wish I were bold enough. Phacelias  (talk) 17:17, 29 July 2022 (UTC)