Nomentatus 2 months ago

I think the necessary background fact here is that chlorophyll is a miracle chemical because it's safe. Not 'cause it's efficient. It's not efficient at splitting water, about 1%, but unlike so many other chemicals that can split water when hit with photons, it can perform the job while producing very few harmful free radicals. That's chlorophyll's secret sauce. Since green is a relatively high frequency that's intense in sunlight, it's safer to filter that color out. "Noise" here means a less smooth chemical process will produce more free radicals.

  • caper 2 months ago

    Interesting - why would fluctuation of the energy flow into the biochemical cascade cause an increase in free radical production?

    If this is the case then seems a lot more likely and evolutionarily sound than the efficiency interpretation; unless there is some second order effect of the rate of photosynthesis on its efficiency/completion that couple with some sort of initial energy barrier I struggle to see how smoothing fluctuations by using non-proximal wavelenghts would be more efficient than allowing fluctuations with greater absorption across the spectrum (and so greater net energy absorption). Some more basic survival mechanism like the free radical one you propose just seems to be more intuitive. With green colouration a circumstantial bedfellow of the other chemical properties rather than the master. Still speculative of course.

    Keen to hear your thoughts.

    • currenciessfe 2 months ago

      Eneregy is conserved. If it "misses" the reaction center, it will hit something else like a stray bullet.

      > Non-photochemical quenching (NPQ) is a mechanism employed by plants and algae to protect themselves from the adverse effects of high light intensity. It involves the quenching of singlet excited state chlorophylls (Chl) via enhanced internal conversion to the ground state (non-radiative decay), thus harmlessly dissipating excess excitation energy as heat through molecular vibrations. NPQ occurs in almost all photosynthetic eukaryotes (algae and plants), and helps to regulate and protect photosynthesis in environments where light energy absorption exceeds the capacity for light utilization in photosynthesis.[1]

    • Nomentatus 2 months ago

      currenciessfe 's answer above is better than this crude comment, but: just the extra heat randomizing reactions would be a problem.

  • throwaway0asd 2 months ago

    More specifically green is far higher in luminosity, which is about radiation power and not frequency.

    • sigmoid10 2 months ago

      It actually isn't. The dominant frequency of solar irradiation is dependent on choice of spectral variables and could just as well be said to be in the infrared, when plotted as a function of frequency. So with the same argument, plants would be better off reflecting that. Especially when you consider that absorption happens as transitions between energy levels (i.e. frequencies) in molecules. However, in truth it simply doesn't make sense to talk about point frequencies in a density distribution.


      • throwaway0asd 2 months ago

        The math to compare colors is more simple than that:

        Blue is a slightly higher frequency than both red and green but green has a dramatically higher luminosity. Simple arithmetic applied against that less simple luminosity formula allows for contrast comparisons.

        • sigmoid10 2 months ago

          We're still talking about the solar power density here though. Ofc blue is a higher frequency than green, noone disputes that. But you can't technically say green is high(er) in the solar power spectrum.

      • Razengan 2 months ago

        Hah I love these cycles of [dis]information and correction on Reddit/HN:

        > Commenter A: [cool fact]

        > Reader: Oh! Interesting!

        > Commenter B: Actually no

        > Reader: Oh...

    • Nomentatus 2 months ago

      The energy of (one photon worth) of electromagnetic energy does indeed increase with frequency. So green is more problematic than the same number of red photons. But you're right that if there were few green photons coming in and a ton of red, red might be blocked, and green not.

  • blowski 2 months ago

    For the novices like me, whats the benefit in producing fewer free radicals?

    • smiley1437 2 months ago

      Free radicals are extremely reactive and can form bonds in undesirable ways in cellular chemistry, which is generally bad for the organism, potentially causing all sorts of cell damage.

      Cells produce anti-oxidant defenses to regulate free radicals such as the delightfully named "Superoxide Dismutase" enzyme:

      • anonymous_sorry 2 months ago

        As an aside, there is poor evidence that consumption or topical application of anything artificially high in anti-oxidants does any good for healthy people, although you see "antioxidants" used to sell crap all the time.

        Maintaining the right balance between free radicals and anti-oxidants is the sort of thing biology is pretty good at on its own. Trying to put a finger on the scales in one direction or another is probably pointless at best.

        • Ekaros 2 months ago

          When thinking about it it seems pretty weird. Wouldn't most free radicals either enter via lungs or digestive tracts? And those will have plenty of stuff to react before any anti-oxidant can get to work... And anti-oxidants spreading through body on other hand seems bit worrying.

          • tpm 2 months ago

            Most free radicals are products of reactions inside the body and the body does have mechanisms to deal with them, even if not 100% sometimes.

    • teaearlgraycold 2 months ago

      My understanding is free radicals are literally atom sized bombs. Bombs are trouble because they lead to dangerously quick oxidation, transforming a solid into a gas in milliseconds.

      Now consider you are a cell. A lot of things you consider important are individual molecules. Free radicals are oxygen ions. So get a few of those ions inside of you and your important molecules are getting oxidized. They’re getting ripped apart. The same as a grenade in a trench. But at the indivisible scale.

    • Nomentatus 2 months ago

      Free radicals - in this case often oxyen or hydrogen on its own - are highly reactive as others have said. What that means is that they'll grab atoms from anything ripping pretty much any other molecules in the area apart, and releasing a punch of energy when they do that, which could do further damage.

    • pid_0 2 months ago

      Free radicals will cause cell damage and thus death or cancer

  • wuschel 2 months ago

    Would you have a reference to comparative studies re the “safety” of chlorophyll in contrast to some other energy transformers, say, mitochondria?

  • hun3 2 months ago

    > Since green is a relatively high frequency that's intense in sunlight, it's safer to filter that color out.

    What about (ultra-)violet light?

    • deepsun 2 months ago

      I suspect ozone layer filters it out.

      • hun3 2 months ago

        Ozone layer does not completely filter out UV-A (~400nm), and most certainly visible light.

leobg 2 months ago

I still don’t understand. How does specializing on blue and red remove the noise from flickering sunlight? After all, when it flickers (say, because of shades or clouds), doesn’t that affect all wavelengths equally? Why should green light be more unstable in that regard than blue and red?

  • layer8 2 months ago

    I didn’t quite get that either. It seems to be based on the fact that the intensity of sunlight varies with frequency: Green in the middle of the visible spectrum is the most intense, whereas blue and red fall of towards the edges of the visible spectrum, so are less intense. Maybe the noise is less for blue and red merely by virtue of those frequency ranges having less intensity.

    • caper 2 months ago

      I think it has actually more to do with "But they also needed to absorb light at different rates to buffer against the external noise caused by swings in light intensity." To create this buffering one would ideally have the the least proximal wavelengths, which will presumably be least similar in downstream rate of conversion/transportation and therefore smooth energy flow from the flickering, but which are still at near peak intensity. In this case that's blue and red visible light. The article notes they are at the steepest part of the intensity curve which is just a proxy definition for the above criteria.

      This of course still assumes that their model of generalised networks is analogous to the real biological cascades - otherwise could just be another coinciding superficiality rather than evolutionary reality ( Quick skim through the source paper on SciHub leaves me sceptical.

      • layer8 2 months ago

        I think I need an ELI5 on that.

        • krackers 2 months ago

          If I understood correctly, the implicit assumption is that different wavelengths of light will result in energy being produced at different rates. So having two far apart wavelengths results in one fast process and one slow process, with the slow process helping to buffer out any intermittent dips in sunlight.

          • layer8 2 months ago

            Got it, thanks for the clarification.

        • caper 2 months ago

          There is slight possibility I'm interpreting like I'm 5, so don't take this as gospel and please anyone else issue corrections, also it's a gross oversimplification but here goes:

          First a brief outline of the actual experiment. Rather than directly measure all of the processes that occur within a plant to effect photosynthesis (from photons hitting a leaf and water being drawn from the ground to the creation of some sort of molecule used for transporting energy in plant cells e.g. ATP) the researchers cited in the article created a mathematical model of part of the process that directly concerns chlorophyll: absorbing photons and transferring the energy to the next stage. They don't specify what the next stage would be, they simply modelled a network of nodes from input (representing the initial photon hitting), via nodes representing different stages of chlorophyll, to a generic output.

          The models assumed two things indicated by prior research: 1) there is an upper threshold of energy production beyond which deleterious back reactions occur i.e. chlorophyll make too much power do nasty thing to plant 2) there is a lower threshold of energy production beyond which eventual power output is inefficient (nonlinear decrease in output) because the rate of energy transfer out of the network [from the chlorophyll stages to the next part of photosynthesis] is fixed by electrochemical processes i.e. chlorophyll make too little power makes actual photosynthesis even worse

          Given those assumptions an ideal chlorophyll stage would operate between the thresholds. In a static environment, that is one in which the rate and state of photons entering remains constant, this could be easily achieved. In a noisy environment, when the light source fluctuates as a result of shadows etc., then a system that relies on one absorption rate will see a direct corresponding fluctuation in power output - fewer/more photons in means less/more energy out and importantly the rates of power in to power out would be directly linked. This noisy environment could cause a drop below / rise above the 2 thresholds above and therefore bad/inefficient operation. Given this noisy environment is inevitable an ideal chlorophyll stage would smooth out the fluctuations in input energy so the output doesn't spike in direct relation to input spikes. Think here of adding capacitors to smooth current fluctuations. This smoothing can be achieved by having two (or more - this is limited by biological/chemical realities here) different concurrent input sources that flow energy through the system at different rates given they both produce the same output. Krackers has more clearly explained this bit than I did initially - although I must add the differing energy production rates is my interpretation of what's implied by the authors because they don't explicitly explain.

          I have ignored here the internal noise of the system which the paper attributes to protein dynamics driving fluctuations of intermediate excitation energy transfer events for simplification and because it doesn't effect the main thrust.

          • layer8 2 months ago

            Thanks for the detailed explanation. The relation/mechanism between the flow rates and the buffering isn’t entirely clear (beyond what Krackers surmises), but at least I have a rough picture for how it works now.

    • Maursault 2 months ago

      > Green in the middle of the visible spectrum is the most intense, whereas blue and red fall of towards the edges of the visible spectrum, so are less intense.

      The Sun appears yellow and orange because green, blue and red light is scattered by the atmosphere; in space, the Sun appears white like other stars. The questions are, if green is the most intense frequencies output by white stars, why are there no green stars? And why aren't plants yellow and/or orange?

      Also, I find that gathering, preparing and eating food is expensive, inefficient and time consuming. How do I get chloroplasts? Why is no one working on this?!

      • layer8 2 months ago

        All stars have approximately a blackbody curve as their spectrum. The sun’s spectrum happens to peak around green, and our eyes are calibrated to interpret that as neutral (white). Other stars can only have that peak shifted towards blue/violet (when hotter) or towards yellow/orange/red (when cooler), which to our eyes correspondingly looks more blue/violet or more yellow/orange/red. If our sun peaked at red or blue, we would probably be able to see green stars.

      • currenciessfe 2 months ago

        The color of noon sun light on earth is literally the definition of white balance (6500K). So it doesn't appear yellow, unless you talk about sunset.

        • AuryGlenz 2 months ago

          It appears yellow if your eyes are adjusted to the color of the blue sky.

      • dgoldstein0 2 months ago

        There are no green stars because stars don't just emit one wavelength, they emit a range that has a peak somewhere. If the peak is green, they also emit similar amounts of red and blue light, and all combined the result looks white. Whereas there totally are blue stars and red stars out there, because those colors are at either end of the visible spectrum, and so you can get a lot more blue than red out of a star or vice versa.

imtringued 2 months ago

I have heard this theory. A plant that absorbs light perfectly would appear black and only the first few layers of cells would get any light at all. Chloroplasts only absorb a small portion of green light and reflect it so that the green light can penetrate deeper into the plant so that every cell gets some energy and even go through leaves and then be captured by a second layer of leaves so that the occluded leaves don't die.

leeoniya 2 months ago

the explanation is actually quite difficult to google.

"why are plants green?" -> because chlorophyl

"why is chlorophyl green?" -> because it reflects green and absorbs everything else

okay, you have to search:

"why did plants/chlorophyl evolve to be green"

  • maven29 2 months ago

    I think you have to skip Google and go for Google Scholar instead if you want to escape pop-sci publications and pointless blogposts.

    • sh4rks 2 months ago

      Or worse, Quora "answers"

  • alar44 2 months ago

    Yes, you need to search for the answer you are looking for.

acdanger 2 months ago

I read - I think here[0] - that green light doesn't penetrate water as well as other wavelengths. So there was no advantage to evolving to absorb the full spectrum.


  • klabb3 2 months ago

    > that green light doesn't penetrate water as well as other wavelengths

    As a diver that sounds weird. Red is the color that disappears quickly with depth. Blue is preserved the most.

    Additionally, land based plants have had some serious time to change color if more energy was beneficial, which clearly must be the case?

  • moffkalast 2 months ago

    > there was no advantage

    Well there is one disadvantage even: overheating.

  • aaaaaaaaaaab 2 months ago

    This doesn't explain why terrestrial plants didn't evolve some way to utilize e.g. UV radiation. It should be possible in theory, since we know of radiotrophic fungi:

    • posterboy 2 months ago

      Ironic if those are the result of mutation caused by the UV radiation. If UV causes cancer in humans it's probably not good for fungi DNA.

      I think some indoor gardens do add low UV but I don't know exactly

    • lightedman 2 months ago

      John Lydon did some research with UVB radiation and cannabis that you might find interesting. This was done back in the 80s.

Silverback_VII 2 months ago

I always thought that it's because that they are descendants of a bacterium that was forced to use the less profitable part of the light spectrum(blue & red) because the main part was already occupied by other bacteria. By reflecting green from the sun, they reflect the strongest wavelength.

  • anonymous_sorry 2 months ago

    This is the hypothesis I remember being taught 20 years ago. Rhodopsin, used by phototrophic archea, evolved first and has a broad absorption peak in the green (giving it a purple colour). Chlorophyll evolved to absorb light either side of this peak, in the red and blue.

  • kzrdude 2 months ago

    So, are there multiple competing explanations being offered for this in general, and none of them have ever become entirely settled?

    • kingkawn 2 months ago

      Welcome to true science

      • kzrdude 2 months ago

        That's fine, but there seems to be explanations spread around that are not really established. Or said otherwise, chains of people who forgot how to say "we don't know".

        • kingkawn 2 months ago

          I know. The thing you’re objecting to is fundamental to our process of coming to know.

  • currenciessfe 2 months ago

    But that would only make sense if the bacteria were stacked on top of each other.

    Otherwise there is plenty of space under the sun, even in water.

  • fluoridation 2 months ago

    The peak of the solar spectrum seems to be in the blueish zone, though.

osigurdson 2 months ago

>> There are plants that don’t appear green but…

Seems like a fairly casual dismissal of data points that aren’t fitting the hypothesis.

  • planetpluta 2 months ago

    I think the rest of that sentence tries to explain the dismissal:

    >> There are plants that don’t appear green, like the copper beech, because they contain pigments like carotenoids. But those pigments are not photosynthetic: They typically protect the plants like sunscreen, buffering against slow changes in their light exposure

    The reason for non-green is not related to photosynthesis but some other process

    • osigurdson 2 months ago

      This what I mean. The reason why some data points do not fit the hypothesis is thrown in rather casually, without any references.

fallingfrog 2 months ago

Has anyone plugged in the spectrum of a red dwarf star to see what color plants on a planet orbiting one would be? He states that the code is all available. I’m really curious.

Yaa101 2 months ago

Interesting, apart from more efficient solar panels it could hand us a solution to better protect our skins with colored sunblock.

  • delecti 2 months ago

    I'm not sure the same consideration applies to sunblock. The article makes the case that plants always "want" to let through the same quantity of light, but not necessarily the same proportion, while we ideally want to block 100% of UV all the time.

    • dieselerator 2 months ago

      I think this might be a good place to add this reminder:

      "Vitamin D is made when UV (more precisely, UVB rays) react with a compound (7-dehydrocholesterol) in the skin. The best rays for UV synthesis have wavelengths between 270–300 nm." [1]


      • lightedman 2 months ago

        270nm is UVC territory. Did you mean 280nm instead?

        • dieselerator 2 months ago

          That is a fair question. This is what I find. [1]

          Ultraviolet B UV‑B 280–315

          Ultraviolet C UV‑C 100–280


          My read is "UVB" is the popular medicine way of saying UV is needed for the body to synthesize vitamin D. It was not considered necessary to point out part of the useful spectrum is in "UVC" territory.

      • hinkley 2 months ago

        Also kills microbes on surfaces.

  • greenthrow 2 months ago

    Solar panels are already much, much more efficient than photosynthesis.

    • _alxk 2 months ago

      That doesn't preclude that further optimisation of solar panels could stem from research on photosynthesis.

      • akira2501 2 months ago

        Perhaps.. but part of the reason plants "lack efficiency" compared to our solid state electronics is that they need respiration to exchange input and output products with the environment and the entire plant needs to be laid out in such a way that it can maintain a root structure while being advantaged with respect to competing vegetation.

        The two problem spaces are similar in that they use light, but exceptionally different in almost every other respect.

        • lazide 2 months ago

          Also, sunburn is a real problem (aka excessive sun) without enough water or other nutrients for them.

eimrine 2 months ago

Do plants need a green light when growing in an artificial conditions?

stevyB 2 months ago

Sun emits the full spectrum of visible rays. The chlorophyl in the plant absorbs light with red and blue frequencies for photosynthesis and reflects the unused rest, this is what we see as green.

dvh 2 months ago

Because sun is green.

  • VierScar 2 months ago

    Sun white

    • cdumler 2 months ago

      The sun is classed as a green star[1]. As a black-body object, it emits the most light in the green spectrum. We see white because we evolved to distinguish color based on our star; however, our ability to detect variance in brightness in colors is far more limited.

      We, in fact, use this to our advantage. View screens transmit exactly brightness in narrow red, green, and blue such to fool our eyes into believing we see colors there that are not in fact there, such as red and green light to simulate yellow light.


      • thehappypm 2 months ago

        But chlorophyll doesn’t absorb green, it absorbs other colors !

        • caper 2 months ago

          Blue and red are the maxima but chloropyll does absorb green light too - just less of it (and possibly less efficiently). The article claims "[plants] absorb only about 90% of the green photons." which seems to be a typo and should be absorb 10% or reflect 90%. I'm having great difficulty obtaining complete absorption spectra from the literature - nobody seems to have bothered investigating since the 1950s ( with most modern papers seemingly content with declaring the red/blue maxima and not giving the full range.

          The paper I linked shows nonzero absorption for greenish wavelengths approaching 10% towards yellow - which would marry with my interpretation of the article's typo.

          • krackers 2 months ago

            Fyi all your posts seem to be dead on arrival, I've gone ahead and vouched for them but you should email dang and see if your account has been flagged for any reason.

    • kzrdude 2 months ago

      After passing through the atmosphere, the sunlight is strongest in the green (of the visible spectrum).

      • wyager 2 months ago

        The sun barely looks different from an artificial blackbody of the same temperature. The atmosphere is not a big consideration here.

        • kzrdude 2 months ago

          Aha. When looking at a spectrum recorded through the atmosphere, that's how it has to be reported (so that's my thinking, why I would say it like that).

    • tuatoru 2 months ago


      What color was it when plants evolved?

      • posterboy 2 months ago

        On a planetary scale that's like yesterday.