New colors without shooting lasers into your eyes | Hacker News Reader

New colors without shooting lasers into your eyes

dynomight.net

568 pointszdw170 comments

For whatever reason, evolution decided those wavelengths should be overlapping. For example, M cones are most sensitive to 535 nm light, while L cones are most sensitive to 560 nm light. But M cones are still stimulated quite a lot by 560 nm light—around 80% of maximum.

The reason is simple: genes coding the long wave opsins (light-sensitive proteins) in these cones have diverged from copies of the same original gene. The evolution of this is very interesting.

Mammals in general have only two types of cones: presumably they lost full color vision in the age of dinosaurs since they were primarily small nocturnal animals or lived in habitats with very limited light (subterranean, piles of leaves, etc.) Primates are the notable exception, and have evolved the third type of cone, enabling trichromatic color vision, as a result of their fruitarian specialization and co-evolution with the tropical fruit trees (same as birds, actually).

So, what's interesting is that New World and Old World primates evolved this cone independently. In Old World primates the third cone resulted from a gene duplication event on the X chromosome, giving rise to two distinct (but pretty similar) opsin genes, with sensitivity peaks at very close wavelengths. As a note, because these genes sit on the X chromosome, colorblindness (defects in one or both of these genes) is much more likely to happen in males.

New World primates have a single polymorphic opsin gene on the X chromosome, with different alleles coding for different sensitivities. So, only some (heterozygous) females in these species typically have full trichromatic vision, while males and the unlucky homozygous females remain dichromatic.

Decent wikipedia article on the subject: https://en.wikipedia.org/wiki/Evolution_of_color_vision_in_p...

Types of opsins in vertebrates: https://en.wikipedia.org/wiki/Vertebrate_visual_opsin

> So, only some (heterozygous) females in these species typically have full trichromatic vision

Wow that's wild how heterozygousity can be that helpful. Makes you wonder if there are other genes like that.

Some human females have functional tetrochromatic vision.

https://jov.arvojournals.org/article.aspx?articleid=2191517

No I meant like if there is some other gene where the two different variants are synergistic to each other.

This is a good biological explanation. The physical explanation is, if the sensitivities didn't overlap, our spectral sensitivity would not be continuous. There would be valleys of zero sensitivity between the cones, and a continuous wavelength sweep would result in us seeing black bands between colors.

Gray bands, or more realistically just desaturated bands. There'd still be sensitivity to light through rods (black and white), and even if the peaks of wavelength sensitivity were highly separated there would still be some cone response to wavelengths that didn't stimulate them strongly.

This is only tangentially related, but I have always wondered why chlorophyll absorbs blue and red, but reflects green--green being sunlight's brightest component.

It's almost as if there was some evolutionary pressure towards being very visible in sunlight which is more important than evolving ways to collect as much sun energy as possible. When I guess at this I end up with something along the lines of reflected green being used as a signal to a neighboring plant: "I'm already here, grow in some other direction instead." There is some evidence that plants do this (https://en.wikipedia.org/wiki/Crown_shyness, https://onlinelibrary.wiley.com/doi/10.1111/1365-3040.ep1160...) but it's not clear that the need to do so is so strong that it would overshadow the drive to collect as much energy as possible.

Or perhaps there's something to do with the physics of absorbing light to drive a chemical reaction that makes it better to absorb at red and blue while passing on green (450nm and 680nm are not harmonics--so if this is the case it's more complex than which sorts of standing waves would fit in some chemical gap or other).

Red is nature's warning signal, and blue was already taken by the sky, so the only option left was green.

Just kidding of course, it is an interesting question.

Maybe it has something to do with keeping the albedo of the planet at a higher value.

This is fascinating, I’d never realized there is this seeming-paradox! Thanks for mentioning it

Have you looked into band-gaps?

Also remember that these are random processes with selection pressure keeping those who survive to reproduce. Assigning a will to such processes makes them and the results harder to understand- imho.

Theres probably something more efficient at converting light into simple sugars.

Maybe it was in response to an extinction level event that filtered sunlight for a long time, removing green but allowing primarily only blue or red.

It still doesn't explain the need to reflect green, though. They could have evolved to be black and absorb all energy.

Well I think the question then becomes can they use that much energy without cooking themselves alive? Maybe the entire spectrum is simply too much incoming energy to dissipate effectively and blue and red absorption are either more efficient or is easier to accomplish than green.

One, you're adding intent to a process that has no intent.

It's not reflected- it's just not used (and thus absorbed). If the plant has more energy that it needs already to produce offspring... what pressures exist to produce more?

It is reflected. That's why plants are green.

You seem to have missed the context of my reply:

> an extinction level event that filtered sunlight for a long time, removing green

The lack of green sunlight would not necessarily result in a mutation that reflects green. There is no evolutionary pressure for reflecting/not using something that doesn't exist. In fact, it would be adding intent to a process that has no intent.

It could also be to prevent overstimulation; "maximize energy" is not really the goal. A lot of plants can die from too much Sun unless their other inputs are just right (plenty of water, etc.).

Here's a recent take: https://www.quantamagazine.org/why-are-plants-green-to-reduc...

TLDR: Plants are running an energy-harvesting system that can only respond so quickly to changes in light input. Making use of green would cause variance to be large enough that the gains would not offset the losses. So, avoid green and have lower variance --> higher energy capture on average.

This video talks about it as well, it includes an interview with the author

https://m.youtube.com/watch?v=TgGoW5AIKEY

> Plants are running an energy-harvesting system that can only respond so quickly to changes in light input.

That would be easy to test, I suppose.

In fact, perhaps we're already doing so by letting plants live in our offices with 60Hz flicker, and perhaps higher frequency flicker caused by LEDs and PWMs.

In short, I'm not buying this theory just yet.

> green being sunlight's brightest component.

It actually peaks between magenta and blue: https://sunwindsolar.com/blog/solar-radiation-spectrum/

Green is only bright to us because of our cone sensitivities overlapping.

That graph shows sunlight in the upper atmosphere, but at sea level, the 400-450 nanometer blues are partially scattered out. The peak we see on the ground is broader, and centered more around 450-550 nanometers, a range that tends more towards teal or "Miami green". Wikipedia shows both spectra:

https://en.wikipedia.org/wiki/Sunlight#/media/File:Solar_spe...

I think this is also why the sky appears to be a deeper, darker blue at higher altitudes.

The chart I linked shows both upper atmosphere and sea level irradiance, for what it's worth. Though it's possible the chart simply isn't the most accurate. I only did casual research.

Doing more research, looking at [1] (the data source for that Wikipedia image), it looks like the peak is between 480 nm (cyan) and 540 nm (lime green) for "global tilt" and 480 nm to 580 nm (yellow) for "direct + circumsolar" (I have no idea what the difference is between "global tilt" and "direct + circumsolar").

Interesting. It seems like the chart in my original comment isn't as precise as I believed.

[1]: https://www.nrel.gov/grid/solar-resource/spectra-am1.5

> It actually peaks between magenta and blue

No, it actually peaks wherever you want it to peak, depending on how you plot it: https://www.oceanopticsbook.info/view/light-and-radiometry/l...

From the link, what appears to be the crux of the issue:

> Figure 1 shows plots of [solar] energy irradiance as functions of both wavelength and frequency. The red line is the solar irradiance at the top of the atmosphere. The green curve in the left panel is the corresponding blackbody irradiance for a temperature of 5782 K, reduced by the distance of the Earth from the Sun

> The peak of the blackbody irradiance spectrum is at 501 nm for a temperature of 5782 K. This corresponds to a frequency of ν = c/λ = 5.98 ⋅ 10¹⁴ Hz.

> The right panel of the plot shows the same solar data plotted as a function of frequency, along with the corresponding blackbody spectrum

> Note that when plotted as a function of frequency, the solar and blackbody spectra have their maxima near 3.40 ⋅ 10¹⁴ Hz, which is not the frequency corresponding to the maximum when plotted as a function of wavelength in the left panel. Indeed, 3.40 ⋅ 10¹⁴ Hz corresponds to a wavelength of λ = c/ν = 880 nm.

> In other words, when plotted as a function of wavelength, the solar irradiance is a maximum near 500 nm, in the visible, whereas the maximum is at 880 nm, in the near infrared, when the spectrum is plotted as a function of frequency.

[emphasis original]

> This occurs because the relationship between wavelength and frequency is not linear, so that a unit wavelength interval corresponds to a diﬀerent size of frequency interval for each wavelength: ∣dν∣ = ∣c / λ² dλ∣.

However, it continues:

> Figure 2 shows the solar photon irradiance [number of photons per second, as opposed to number of joules delivered per second] and the corresponding blackbody spectra

> Now the maximum is at 635 nm when plotted as a function of wavelength and at 1563 nm, in the short-wave infrared, when plotted as a function of frequency. The maxima are at still different locations if the spectra are plotted as a function of wavenumber.

This time the emphasis is mine. This contradicts the explanation given above, that the curve peaks in different places along different scales because those scales are nonlinearly related. The relationship between wavenumber and frequency is linear. Why does that lead to a different plotted peak?

Are we measuring wavenumber somewhere within the atmosphere (where?), rather than in a vacuum? That would mean that different frequencies of light had different velocities, complicating the relationship between frequency and wavenumber. But it would also be a strangely artifactual way to represent solar irradiance. What's so special about wherever it is that we standardized wavenumber measurements?

Irradiance is a density function - it's telling you how much energy or how many photons are hitting a given area per unit of the dependent/spectral variable (you can see this by inspecting the units in the plots, for instance).

This means that changes of variable come with an additional factor - the Jacobian. You cannot simply substitute the relationship directly into the formula for the one spectral variable, like you would for a "point function" (you need to account for the change of unit in the y-axis too, if you like, not just the x-axis).

It's not explained well but this is fundamentally what causes the moving peaks.

This subject is also a wonderful example why the maximum of a densitiy function has very little meaning. The amount of energy is an integral over the densitiy function, and if you look at the solar-spectrum, you'll notice, that the bulk of the energy is in the infrared.

Indeed, the value of a density function at any single point (maximum or not) tells you very little. What's important is how it changes over a range of values.

> Irradiance is a density function - it's telling you how much energy or how many photons are hitting a given area per unit of the [in]dependent/spectral variable (you can see this by inspecting the units in the plots, for instance).

Well, I can see that in the labels on the y-axis, but I assumed it was a mistake.

So you have a graph that tells you that, for light of wavelength 1000 nm, measured irradiance is 3.5e+18 photons per square meter per second per nanometer.

And since there "are" 1000 nanometers (?!?), this means that the actual irradiance is 3.5e+21 photons per square meter per second.

Or does the "per nanometer" really mean something less stupid than that? What's being measured? What kind of nanometers are those on the y-axis?

Not quite - the nanometres on the y-axis are "deltas" of your spectral variable. The density allows you to answer questions like "how much power am I getting per square metre in a range [A, B] of wavelengths". You would integrate your density between A and B to obtain the value.

For example, pick some small value "k" close to 0 in units of nm. Then in your example, the amount of irradiation contributed by the small window [1000-k, 1000+k] nm of wavelengths is roughly equal to k*3.5e18 photons per square metre per second (you can check that the units work out). The smaller k is, the more accurate the approximation. If you want to get an answer for a larger interval you can break it up into lots of k-sized pieces and sum the results up. Recall from calculus that this is exactly what integration is (yes, I know the truth is a little more complicated in general measure theory).

Does that help? It's a bit like a continuous probability distribution, in the sense that to get an actual probability out of it you have to integrate. Formally a mathematician would say that a density corresponds to a "measure" over the space of all possible values of your spectral values.

I may have been a bit lazy there and imagined the distribution as Gaussian despite having seen charts that indicate otherwise. I'm glad you pointed that out.

But the question remains... Why do plants reflect light so well at the frequency where my cone sensitivities overlap? Mere coincidence would be believable, but it seems to also hint at something about the relationship between myself and those plants.

We often hear about the relationship between perception of red and berries (food). Perhaps for survival in very dry areas: green == plants == water?

You have a kind of cone with maximum sensitivity in green, because that is what plants reflect, not the other way around.

You have another kind of cone with maximum sensitivity in blue, because that is what the clear sky provides.

So a mammal looking upwards (or forward for a tree-dwelling animal) can distinguish easily leaves from sky.

Monkeys and us have another kind of cone with maximum sensitivity in red for 2 reasons, blood is red and many mature fruits have reddish colors (including orange and purple).

The redness of blood matters not only for noticing wounds, but also for detecting emotions on the faces of mates or adversaries (due to increased blood flow; for some monkeys the emotions may be seen not only on faces, but also on other hairless areas, e.g. buttocks).

> something to do with the physics of absorbing light to drive a chemical reaction

Exactly that. Blue does two steps of the process, while red does only one. There's a cost for synthesizing all that machinery, so absorbing green would just be not worth it.

> 450nm and 680nm are not harmonics

In fact they're in 3:2 ratio with 1% margin. But they don't have to be. Take a look at fluorescence: it converts one wavelength to another, and they don't have to be multiples of each other. Once photon gets absorbed onto a chemical, the electronic structure of the molecule decides what will happen to it.

Chlorophyll a, which is the pigment that actually uses solar energy to split water, absorbs red light and violet light. Thus its color is blue-green, as it can be seen in some lichens that have only symbiotic cyanobacteria.

This is most likely a historical accident, with no special meaning.

Most algae and plants have auxiliary pigments, which absorb other parts of the solar spectrum and then transfer the energy to chlorophyll a.

The land plants and the green algae use mostly chlorophyll b as auxiliary pigment, which absorbs light in a blue band adjacent to the violet band of chlorophyll a, and in a red band that is distinct and adjacent to the red band of chlorophyll a.

Thus the addition of chlorophyll b increases considerably the amount of captured energy.

The algae that are dominant in oceans, e.g. diatoms and brown algae, have more auxiliary pigments, so that many are dark brown, even close to black.

Unlike for marine algae, for land plants, capturing more solar energy is not desirable, because they already have difficulties in avoiding overheating and excessive loss of water. So the pigments used by them are good enough for their needs.

I don't think the mystery goes away when you consider the other photosynthetic pigments. chlorophyll-a, chlorophyll-b, lutein, B-carotene, zeaxanthin, lycopene... they're all active between 450 nm and 550 nm. And then chlorophyll-a and chlorophyll-b have secondary activity between 650 nm and 700 nm.

The the lack of photosynthetic activity between 550 and 650 is still suspicious. I've learned from other commenters here that my assumptions about the gap corresponding with peak solar energy weren't on solid ground, but there is a gap.

Perhaps a different way to frame the question is: why do the chlorophyll pigments have two peaks, while the others appear to have only one? Perhaps they have an evolutionary past which involves absorbtion from a star besides sol?

Most organic pigments have 2 or more absorption bands, but this is not always apparent for humans, because the second band is located in near ultraviolet or in near infrared.

Like I have said, in marine algae you can find a variety of colors, as already seen in their names, e.g. red algae, yellow algae, brown algae. Most of them have strong absorption for green light, due to the auxiliary pigments that they happen to use.

Only the green algae and their descendants, the land plants, do not absorb green light and as a consequence they are competitive with the other algae only in places with abundant light, i.e. in very shallow waters or on dry land, where they can get all the energy that they can use without damage, so they do not need better coverage of the solar spectrum.

The energy of the captured photons does not matter much, because even the red photons have enough energy.

The captured photons are not used for "photosynthesis", which is a misnomer whose origin lies in a time when the mechanism of "photosynthesis" was not known.

In oxygenic phototrophs, a part of the captured energy is used to oxidize some manganese atoms so strongly that they can oxidize the oxygen from water, converting it into free dioxygen. The hydrogen from water is bound into a reduced organic substance (NADPH), which will be used later as a reducing agent (without needing light) to make carbohydrates from carbon dioxide.

The rest of the energy of the captured photons is used to pump ions through the membrane of the chloroplasts. The energy stored in an ion gradient will be used later to power all organic syntheses.

The ionic pumps could work even with infrared photons, as they do in phototrophic bacteria that live under algae, so they have modified chlorophylls whose red absorption band is shifted into infrared, away from the red band that is removed from solar light by the algae sitting above. However, those bacteria cannot split water, the energy of infrared photons is too low for that (splitting water needs around 1.25 eV, while red photons have over 1.5 eV).

You're totally right, thanks for being patient with me. It should have been obvious, but I hadn't initially made this connection:

> Only the green algae and their descendants, the land plants, do not absorb green light

The earlier sources that I found had a bias towards land plants.

I'm much happier to accept as mere coincidence the fact that land plants evolved from a specific kind of algae (i.e. one that might have adapted for absorbtion of light at a certain depth and therefore shows a preference for absorbing blues over greens) and not some other kind which would've had different preferences.

Initially I thought that each of the green pigments I listed had evolved separately on land and it seemed rather spooky that they shied away from green. But that's likely not where they evolved, so now it's not spooky.

There's also a chance that the primary photosynthesiizers on each happened to be purple for a while (purple earth) and the ancestors of plants absorbed red/blue and ignored green because they were getting leftovers. Also, even now, iirc the limiting step in oxygenic photosynthesis is by far rubisco's incorporation of CO2, so there's no immediately obvious fitness function that would be optimized by just increasing the efficiency of light harvesting.

There was a proposed theory on this the spread of absorption created more stability in the power generation of plants over different conditions. This was supposed to be a more important factor than being able to absorb the peak and highest energy.

https://www.science.org/doi/10.1126/science.aba6630

I think this paper is what I was looking for, thanks. I may have to reread it after becoming more familiar with the chemical/physical nature of:

> Photoexcitation energy is rapidly transferred through an antenna network before reaching the reaction center

I didn't know that. With this in mind, perhaps a better formulation of my question is not:

> Why are plants green?

But instead:

> Why are green photosynthetic pigments more common than others?

Based on my read of this paper, the answer to that would be that a pigment which absorbed only a single narrow band of light would be prone to being either over or under powered most of the time. Absorbing red and blue, but not green, provides more opportunities to deliver constant power at the reaction center despite varying light conditions.

I didn't see any mention of this so thought I would add:

This sounds like https://en.wikipedia.org/wiki/Retinal and https://en.wikipedia.org/wiki/Purple_Earth_hypothesis. Going through history, there have been times where the Earth has had oxygen spikes https://en.wikipedia.org/wiki/Geological_history_of_oxygen (Examples https://en.wikipedia.org/wiki/Great_Oxidation_Event or https://en.wikipedia.org/wiki/Neoproterozoic_oxygenation_eve...) Cool image showing how this process is unstable: https://en.wikipedia.org/wiki/Great_Oxidation_Event#/media/F...

You might be interested in the different photosynthesis cycles: https://en.wikipedia.org/wiki/C3_carbon_fixation https://en.wikipedia.org/wiki/C4_carbon_fixation https://en.wikipedia.org/wiki/Crassulacean_acid_metabolism https://en.wikipedia.org/wiki/Alarm_photosynthesis - this one was only discovered in 2016!

Research into these may have profound impact on climate change.

I'm pretty sure that line of the article didn't mean to imply that we don't know, or aren't sure, only that it goes beyond the scope of the article and isn't directly relevant to the topic at hand.

To me it looked like the circle outline had a shimmering aura, it felt very magical. This was a incredibly delightful experience so I just want to say thanks for posting it.

When the circle was around the halfway point of shrinking the color looked the most vivid for me, so be sure to wait the whole duration.

Similar, an extremely bright and magnificent teal-ish green with a vibrant yellow edge was dancing around the edge of the circle

You can also look at the background about halfway through and get a large circle of the new color, the same size as the original circle.

To me, it seemed to be a visual equivalent of that auditory trick where a note seems to descend or ascend in pitch indefinitely. The outer aura of color seemed to be shrinking constantly.

The Shepard Tone - https://en.wikipedia.org/wiki/Shepard_tone - brilliantly used by Hans Zimmer in the Dunkirk score.

At the end, the green circle had a very intense grainy, hypersaturated quality for me. Not like the shimmering aura that shrinks with the red circle, but still there was something magical going on.

I looked away, and then back to the screen, and the effect was gone. It was only in my head. Wow.

A super fun, delightful experience indeed.

I, too, had this view. It was flecked with blue. Like a linen sheet it had those lines.

I had to zoom in to double-check the blue dots weren't there!

To my eyes, it looked like TV snow made up of blue and green particles! Twas quite delightful.

I looked away, then back, and the effect was gone—but then reappeared after a second or two, only less pronounced.

The aura was a very brilliant green, which reminded me of an hallucinogenic experience I had. I was sat with friends in the city centre, my brain altered by chemical substances, and I spotted a guy 100m away with the most brilliant and beautiful green shoes. It was an amazing sight, standing out from everything else.

Sober, I later realised that they were normal green shoes, but in my no-brain-filter state, I was able to appreciate that we have many more green cones in our retina than red or blue, and normally the mix dial for green in our brain is kept pretty low not to overpower the other colours. The animation once again raised this dial to show how powerful is our raw perception of that colour.

(The evolutionary reason is that we spent a lot of time in vegetation or on trees, and it's very useful to be able to distinguish things and perceive small movements in a sea of green.)

Yes, this reminded me of a similar experience camping with friends where we could only describe the foliage as “ultragreen”. An incredibly vivid blue-green tone that suffused the whole island where we were staying. Been looking for explanations since

Ultragreen is a great way of describing it. That's exactly it.

The one with a red circle on a brown background had a really interesting effect; before the circle starts to shrink, the background becomes the same colour as the circle, then moving your eyes made a bright red or green circle appear, each on their opposite side.

Do you have red-green color blindness ? The background is clearly green.

Edit : Apologies, I just now see the other ones.

I got that, as well as a seemingly random set of changes in apparent brightness. The Magenta one seemed to produce patches of bands in my vision as well, think like blown up versions of edge detection kernels.

Same thing for me, although, it looked more like an aura rotating around the red circle with a cyan-ish glow with a hint of teal.

As the circle was about to disappear, the blue-green was super saturated for me and persisted for a good minute if I kept locking onto the white dot. Another thing you can do, is at night time (lights off) look at the red circle like before, and when the timer runs out close your eyes and keep it dark. You will see blue-green glow very strongly.

Serious pleasure

A bit unrelated but I found this interesting: water is transparent only within a very narrow band of the electromagnetic spectrum, so living organisms evolved sensitivity to that band, and that's what we now call "visible light".

http://hyperphysics.phy-astr.gsu.edu/hbase/Chemical/imgche/w...

Interesting, given that most life is water based, most life will respond the most to this spectrum.

Given the fluid inside your eyeball is mostly water, this is probably very related.

It’s interesting (kinda optimal) that different cones explore near both edges.

I thought it was mostly that those are the wavelengths output out by the sun.

But I guess it could be both.

The sun is very close to a black body radiator, so all wavelength. The atmosphere and water filters a lot.

It is actually quite strange that plants are green -- that's the wavelength the atmosphere lets through particularly well, so would be particular good to be absorbed instead of reflected, for energy production. It seems nature hasn't come up with a good, cheap way to move the absorption into that wavelength.

Or it could have another reason: https://www.quantamagazine.org/why-are-plants-green-to-reduc....

Well, black-body radiation is still peaked around a certain range of wavelengths depending on the temperature, it's not just equal power at all wavelengths.

Light visible to humans is at the peakiest bit of the sun's black body spectrum, see here image here: https://i.sstatic.net/kRUju.png

Green isn't just the wavelength the atmosphere lets through the best, or the wavelength humans are most sensitive to, it's also the peak of the sun's black body spectrum.

I like to joke that while nitrogen gas is the most common thing around us, we are blind to it. Of course, that's a feature, since it allows us to perceive everything else further away, instead of stumbling through a perpetual fog.

This location-dependent tradeoff is something to think about when it comes to "false color" images in astronomy. If some aliens described Earth as "a boring uniform nitrogen-colored ball", we'd probably be a little offended at their ophthalmo-centrism, and tell them that the fault lies in their eyes, not in our planet.

Is there a camera that would show me what our world looks like through the eyes of these hypothetical aliens? Would love to see it.

It would probably be some application of spectral imaging [0], highly dependent on what data you choose to capture based on your assumptions about how the aliens see.

Even if you have a mathematical "photo of a planet of nitrogen gas clouds", that leaves the problem of how to present it to humans, since we have no concept of what "nitrogen gas color" is supposed to be.

https://en.m.wikipedia.org/wiki/Hyperspectral_imaging

As OP said, most astronomical pictures, even in the visible, target specific wavelengths and are thus "converted" for human vision. It's also obviously the case of any picture in wavelength beyond visible light. Keep in mind that there is also massive processing to clean the pictures, not just a translation of the wavelengths

visible light is also the last octave before you hit ionizing radiation. it’s very energetic. good for harnessing in chemical processes. not so energetic that the electrons leave the party.

A guy copied&pasted this comment to X and got 42k likes lol: https://x.com/sridatta/status/1947180254684237851

At least he gave credit to HN, so the diaspora could find the source. The article is interesting. I think more needs to be said about how our eyes perceive color w.r.t. led lighting.

> If you refused to look at the animation, it’s just a bluish-green background with a red circle on top that slowly shrinks down to nothing. That’s all. But as it shrinks, you should hallucinate a very intense blue-green color around the rim.

I do not believe I have any kind or amount of colorblindness, so imagine my surprise when extremely confused I pulled the image into MS Paint, used the Color Picker tool, and found that indeed, the background has quite a bit of blue in it.

Anyhow, I cannot reproduce the illusion cited. For me the circle just blurs out and I start seeing orange.

If you make the outer colour yellow using the custom colour option, and the inner circle red, do you see a an aurora-green halo? Or if you make the outer circle yellow and the inner circle green, do you see a red halo?

> If you make the outer colour yellow using the custom colour option, and the inner circle red, do you see a an aurora-green halo?

You mean this, right? https://dynomight.net/img/colors/generate.html?inside=ff0000...

The background turns green (???) eventually, kind of like as if ink started to spread across it.

Or you meant full yellow (255r, 255g, 0b) and full red (255r, 0g, 0b)?

> Or if you make the outer circle yellow and the inner circle green, do you see a red halo?

I used the controls this time and made the background full yellow (255r, 255g, 0b) and the inner circle full green (0r, 255g, 0b). Also adjusted the countdown speed, I realized I wasn't patient enough to wait out the 60s before ever (but that also it didn't need to be so long).

During countdown the entire image turned green. Whenever my eyes would move a bit, I'd see either a 3D shadow depth effect or a yellow aura around the circle. When the circle started getting smaller I just saw the yellow aura. Whenever I'd drastically move my eyes, the entire background would revert to yellow, but would quickly go back to seeing green.

I don't really see them being unusually saturated though, but maybe I just don't have a good grasp on what to expect. Maxed out R/G/B or C/M/Y all strike me as super saturated from the get-go.

Do you have a setting on that shifts the screen colors towards red in the evening to avoid blue light?

For the first question, I see a green halo.

For the second question, I see something in between what you and blincoln see. The halo I see is definitely orange, not red. During countdown, the outside of the circle became greenish-yellow, but I could distinguish between the circle and outside the circle.

I did see the illusion but I just did a double-take. That image looks just straight green to me. I suppose I could imagine it being greener somehow, but blue!?

I have a slight deuteranomaly. I did see the illusion. Pretty!

Yeah, I don’t think I have any color blindness but that looked super green to me. I think I am fine at distinguishing two colors, but i am not the best at realizing the component colors I am seeing.

It sounds like you have red-green color blindness. What result do you get when you take this test?

https://www.colorblindnesstest.org/cambridge-color-test/

100% accuracy, 25/25 correct. That said, some of them were extremely difficult, way more than others. Not sure if that's intentional, so I might still have color vision deficiency per se.

I also did the Farnsworth-Munsell 100 hue discrimination test, got a score of 28 on that - ideal being 0, and above 4 meaning something is amiss. So I don't really know what to make of this lol

Redid these tests together with a colleague. Either they are fake or they are badly coded. We double checked the ordering with a color picker and we both ordered by hue angle just fine, yet various tests would keep reporting poor results. Eventually, tests would then flip and start reporting really good scores. Got 2s and a 0 at some point.

Now either we both fluked it the first few times or these tests are genuinely not trustworthy. I find that pretty unlikely, but what I do think I know is that I do not have CVD after all.

I just came to comment this after doing this test and scoring 80+ twice. Went to another site and scored 0. The previously linked site really seems to have some issues with this test.

This one seems to have worked for me: https://www.xrite.com/hue-test

I believe they are simply describing the color components, just like you don’t “see red” in a soft orange color.

Did you wait for the black bar to finish, and the circle to start shrinking? Takes a very long time. The effect happens at the edges and disappears if you remove your focus from the center dot.

I have mild achromatopsia and can see the effect in all color variants I tried.

> I pulled the image into MS Paint, used the Color Picker tool

The RGB values used are also indicated in the filename.

What you are seeing (in the static image) is normal. Have you noticed that (0, 255, 0) looks way brighter than (0, 0, 255) regardless of your monitor calibration? For the same reason, non-red images can have quite a bit of blue in them while still subjectively registering as "green".

https://en.wikipedia.org/wiki/Luma_(video)

Just in case... Maybe you didn't wait long enough? I saw nothing so I came to the comments expecting a lot of others to day the animation is broken. However, it turns out it's a lot slower/longer than I thought. I saw the little bar on the left shrink to nothing and thought that was it and exited, but that's just the start. The full animation is the red circle shrinking all the way until it disappears. There is no illusion until the circle shrinks quite a bit.

Many years ago [1] I was led to a marvelous site explaining many subtleties of human color perception, including the three cone primaries. The author called this pure-M-cone response "psychedelic aquamarine"; the page is offline but the archive has a capture [2]. I haven't seen this color referred to by that name elsewhere, but I think it's a good name.

I think I can see psychedelic aquamarine and the other cone primaries by closing my eyes and rubbing my eyelids while pressing in gently but firmly.

[1] https://news.ycombinator.com/item?id=813656

[2] https://web.archive.org/web/20160306132951/https://casa.colo...

Incidentally the linked Skytopia page is that of Daniel White, who originally described the Mandelbulb: https://www.skytopia.com/project/fractal/mandelbrot.html / https://www.skytopia.com/project/fractal/mandelbulb.html

I was at a physics conference once and the RGB cable for the presentations was a bit faulty and one of the color channels wouldn’t work, and this presenter’s slides were all tinted cyan. After a bit of jiggling it finally worked and the slides went back to normal, but everyone heard an old professor on the first row go “on no, now they’re purple!”

You found the person who'd been looking at the presentation the whole time, and not down at their phone.

Painters have been aware of this distinction for years. I encourage interested readers to get a good artist's book on color or just head for your local art store and explore the differences between pthalo and viridian greens (or any of many other surprisingly different tonal clashes).

It is incredible to see a concept going from 'optical table of sensitive equipment fraught with numerous safety concerns' to 'here is a 1 kB svg animation, stare at it for 1 minute' in 3 months.

Enjoy your forbidden color, you earned it!

The article however concludes: “So do the illusions actually take you outside the natural human color gamut? Unfortunately, I’m not sure. I can’t find much quantitative information about how much your cones are saturated when you stare at red circles. My best guess is no, or perhaps just a little.”

FTA:

> The idea for that animation is not new. It’s ~~plagiarized~~ based on Skytopia’s Eclipse of Titan optical illusion (h/t Steve Alexander), which dates back to at least 2010.

Incidentally, it’s also a demonstration that you shouldn’t use high contrast in typography. When you start the test you can clearly see the lines of text retained on your retina.

The same with MacBooks in dark mode, once you turn around you can see large horizontal lines separated at regular intervals that are maybe due to the refresh rate of the screen (or something else, if someone knows)

In my experience these are after exposures from lines of text. They get blurred together into indistinct lines because your eye focus moves between words, superimposing them.

I did a custom combination of yellow outer field, blue inner circle, and got a vibrant purple halo, which is not what I expected. I assumed it would be "yellow++", based on what I know about the human eye's colour sensitivity.

I didn't expect a strong effect, because the overlap between blue and red/green is so much less than the overlap between red and green, but bright purple is close to the opposite of what I expected. I'm genuinely puzzled.

That is interesting - I tried the setup you suggested and actually did see something that could be described as yellow++, with maybe a hint of gold/orange

It was also very intense, like staring into the sun. I observed this for both of the two default yellow tints that I could choose via the (Windows?) color picker

I have no idea why this would differ between individuals

Edit: link below with FFFF00 for yellow

https://dynomight.net/img/colors/generate.html?inside=0000ff...

Thank you.

I retried it first thing in the morning, in the dark, with my phone screen at minimum brightness, and no contact lenses in, and I got the expected result - vivid gold for my original setting, vivid yellow for yours.

After putting my contacts in, under medium ambient light, with my phone screen at medium or full brightness, I get the purple ring, but now that I'm looking for it, I can see an outer ring of gold or yellow as well.

The effects is much less pronounced if I put on my reading glasses (while still wearing contacts), so I think it must be an artifact of the contact lenses, probably in combination with the conditions they're supposed to correct (nearsightedness + astigmatism), as well as age-related inability to focus on tiny details with my contacts in.

Can you share settings and/or a link so an exported SVG?

https://dynomight.net/img/colors/generate.html?inside=0000ff... is the one I was using.

https://dynomight.net/img/colors/generate.html?inside=0000ff... was suggested by another commenter.

But as I mentioned in a parallel thread, I think the effect is caused by an imperfect optical path. Without my contacts in, there's no purple ring.

I am curious how these work for people with common kinds of colorblindness. The author mentions at the end that they likely don't work for that case, but they don't seem to have spent much time thinking about it.

Would it be possible to generate ones that _would_ work for specific kinds of colorblindness? Or is the entire concept doomed due to the specific way(s) that colorblind eyes are messed up?

The animation worked for me, I'm red-green colorblind.

The red inside, reddish-orange outside was a little strange - I'm not colour blind, but have a really hard time distinguishing shades. As soon as I focused on the white dot, the red circle started to blend with the background and disappeared completely (was just one single colour for me). Only when it started shrinking did I hallucinated a faint green aura around it until it was gone.

I have deuteranomaly, and the hallucination worked for me, and it did appear like a crazy saturated blue-green ring around the shrinking red circle.

I suspect, however, that those of us with deuteranomaly probably see a different blue-green than normal-sighted folks due to the bent color cones.

The real question is, what about the folks with Deuteranopia (no working green cones at all)?

Deuteranomaly, though, is still probably the best place to start since that's the big one that affects (some say) up to 10% of all males. Every other form of colorblindness affects a much slimmer percentage of the population.

I have red-green weakness but only saw a lighter green around the circle as it became smaller.

I saw this as well.

Didn't work for me. I notice that the color around the circle changes, but it's just a palish blue-something, not a new color, certainly not intense. Too much overlap, I guess. Perhaps it works when changing the background to blue?

I fail on the first page of the Ishihara (?) test. When using those colorblindness filters in photoshop/-like apps, the protanopia and deuteranopia filters do very little for me. No 'real' diagnosis. I can see red and green though, but the shape needs to be big, and the color should be quite saturated. Reading resistors is really hard.

The color (at least to me) doesn't actually look blue-green, but rather cyan-green. This "tertiary" color halfway between cyan and blue (#00FF80) is apparently called "spring green":

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

I wonder whether there is a physiological explanation for this.

There is: https://news.ycombinator.com/item?id=44635782

I'm talking about the newly induced color, not the one of the background.

The description of the induced colour is subjective, of course. And cyan is in the blue direction from green.

But equally, yellow is in the red direction from green, and surely yellow-green is different from red-green. Although... Perhaps "red-green" is just another name for yellow, and "blue-green" just another name for cyan.

"If you’re colorblind, I don’t think these will work, though I’m not sure."

Should work for anomalous trichromats (by far the majority of people with color deficiencies) but probably with less intensity.

"Folks with deuteranomaly have M cones, but they’re shifted to respond more like L cones."

I don't think this is true. What would the difference between deutan and protan then be?

"Why do you hallucinate that crazy color? I think the red circle saturates the hell out of your red-sensitive L cones. Ordinarily, the green frequencies in the background would stimulate both your green-sensitive M cones and your red-sensitive L cones, due to their overlapping spectra. But the red circle has desensitized your red cones, so you get to experience your M cones firing without your L cones firing as much, and voilà—insane color."

I think only people with missing L cone (Protanopia) or M cone (Deiteranopia) would not experience the phenomenon at all.

Maybe this could be used as a new type of color deficiency test?

I didn't see anything, probably because my M cones were also saturated more than a normal person. (though it is also possible I did it wrong?)

All of this resembles techniques of Op Art, for instance Fangor's works:

https://www.beloosesky.com/artists/wojciech-fangor

This is really cool. Tangentially, it's an example of an important life lesson, "work smarter not harder". To see the impossible color, you could build a super-expensive, super-complicated laser to directly stimulate the exact cells; or you could desensitize the other ones with an optical illusion that works on a personal device (effectively zero cost and minimal complexity since it uses existing technology).

Not to say the laser is a waste, despite the above I'd argue it's very useful. It lets us test how effectively the above actually works, and has other applications.

This optical illusion isn't some brand new thing. It's been widely known since I was a child, and surely hundreds of years before that.

The laser system results in a stronger perceptual effect than you get from the illusion alone. We didn't have the technology to build it until recently. I'm certain the people who built it knew about the illusion, and it's probably what inspired the experiment in the first place.

That is a notion that is far easier to make in hindsight.

Open the experiment animation and refresh the page multiple times to refresh the countdown while looking at the white pixel (from the same point of view) to get an even more impressive effect.

Is this just my device, or is there no way to use this roll-your-own SVG generator to actually roll your own? I can only pick from a tiny subset of preset colors, most of which seem super random and desaturated and not what I want. There's no FFFF00 yellow, for instance. Is there some way to enter an arbitrary RGB color that I am not seeing? If not, why on Earth write such an interesting article, advertise this custom SVG generator and then build the interface that way? :/

Does tapping on the horizontal color box to the right of the sentence “Select any color” under heading “Inside Color (Circle)” open a color picker? If not, perhaps your browser has a defective <input type=color> implementation, i.e. Firefox for Android [1796343]?

Woah... did anyone else experience a noticeable desaturated sense of color after coming out of a couple rounds of those things? Like the world was in sepia tone?

Not across my whole vision since I was using a phone, but yes.

The color I saw reminded me a lot of the kind I see when I close my eyes after accidentally looking at something too bright. I wonder if they could be related?

Using psychedelics, specifically 2C-B and LSD, you can also see very saturated colors you don't normally see in daily life. I see very saturated magentas.

I wonder how much of this is ‘seeing’ and how much is emergent in the brain due to the drug. I suspect the latter, but that’s just opinion.

“how much of this is ‘seeing’ and how much is emergent in the brain”

Yeah… it’s gonna be hard to distinguish those in the best of circumstances.

Seeing is also an illusion by the brain, all colors are in your head.

I realise that, I’m just speculating on when the effect emerges. Whether it’s because of changes in the cones (which are the tips of nuerons) or a later emergent property.

Most likely an emergent property. Psychedelics affect serotonin pathways, I don't think that cone cells and the first layers of neurons behind them have serotonin receptors.

"Seeing" starts pretty much at the retina level and along the optic nerve. Lots of signal processing and data compression going on there. I wouldn't be surprised if hallucinogens affect those areas as well.

Everything is quite intense that way with 2C-B, very very rich, but in a more psilocybin way than LSD. 2C-B is super weird, I find it hard to pinpoint what it is about 2C-B that is so unique among the phenethylamines/tryptamines.

Interesting colours coming out of it - a while back I suspected I have https://en.m.wikipedia.org/wiki/Tetrachromacy since I was able to describe colours more vividly that others, and certain plants for me like Verbena have a glow around them.

I'd love it if there was someone with tetrachromacy who also knows a bit about color theory and perception and can talk about it!

How do you describe the experience scientifically? Do you get a whole bunch of extra colors you'd want to give a distinct name since they're so clearly different from the standard trichromatic colors?

Is a computer screen annoying because it can only produce a subset of the colors you can see?

Do you notice that you have a fourth parameter or dimension in the colors you see, so would want a 4th component in RGB, HSV, etc... color sliders? E.g. for our HSL, would the fourth parameter be hue-like, saturation-like, lightness like or some completely novel other thing? If hue like, do the hues also form a 2D sphere or torus like topology similar to how our trichromatic hue forms a circle?

I'd expect at least twice or 3x as many named colors, since for every regular color (red, green, blue, yellow, orange, purple, pink, grey, brown, black, white, ...) , you'd have a fourth dimension altering it that can be low, medium or high in value ...

E.g. for our yellow, you'd have yellow with not the extra signal, a bit of the extra signal or lots of the extra signal. Is this the case or not? Perhaps the overlapping reduces it, but as said in the article trichromats also have overlap yet we definitely see a lot more distinct colors than dichromats.

You can ask this lady: https://concettaantico.com/

Some people with two X chromosomes have this ability. And all birds.

If you are bored, try to get Gemini/claude to make a color wheel for birds or tetrachromats.

An aside: Recently I learned that birds are reptiles. That hurt my brain and I’m still recovering. Especially since the modern dinosaur exhibit claiming this fact contradicted the 1980s era reptiles exhibit down the hall (both at the British museum).

What are birds? We just don’t know.

Dinosaurs are birds. Birds are reptiles.

Also, reptiles are technically fishes, and so are we, but we are not reptiles.

I think I would make a color triangle, except I would remove blue from it, and instead have the corners be three different colors in the red-green part of the spectrum. I guess 530, 545, and 560nm.

Do tetrachromats have the same three "standard" cones plus a fourth? Or are they all shifted around?

Telenor's net nanny (which I didn't ask for) has decided that dynomight.net is dangerous and DNS blocked it.

Ran into the same thing. Changing to a non-default DNS fixed it.

So change your router settings to offer a different default DNS via DHCP? Maybe configure your device(s) to use some other specific DNS servers rather than the ones offered via DHCP?

For the site operator: the domain is present in the Spamhaus DBL (Domain Block List), which is presumably why these lovely gents are having issues, might wanna check that out.

Thanks for pointing this out. I submitted a request to spamhaus but it's an auto-responder black hole that tells me to contact my "IT department". (My personal blog, oddly enough, does not have one.) They don't explain why this domain which has no ads, sells nothing, and never sends email would be listed.

If/when we get BCI that inject a UI into our central nervous system, I’m sure this will get overused. :)

This reminded me of the works of James Turell. I saw an installation where you observe the sky at dusk or dawn through a circular hole in the ceiling. The ceiling itself was illuminated with saturating colors and there were auras happening around the hole.

What is the animation supposed to be like? I see just a black bar on the left narrowing, but nothing else happens. The red circle and green background and white dot didn’t change. (iOS 26 beta, iPhone 15)

After the black bar finish narrowing the red circle gets smaller slowly

After the black bar disappears, the circle start shrinking and on the boundary you can indeed an intense azure/green colour.for me quickly flickering the eyes left and right did temporarily increase the patches of intense colour.

It's not the animation itself that does anything magical, but the afterimage (I think that's what you would call it?) your eye produces after you stare at the dot for long enough. The black bar is just a countdown timer for the impatient.

But try to maintain laser focus on the central dot, not letting your eyes move or blink if you can help it. Once the black bar depletes, the circle should start shrinking, and around its periphery (like an eclipse) should be some incredibly vivid, super saturated colors.

The bar is counting down time to wear out the receptors in your eye (you need to be staring at the center the whole time). THEN the illusion begins.

I just want a display with a primary at 460nm. That's all I ask.

I don’t understand why you need the animation. If you point at the green background after staring the red one for a while, you can see a whole circle of the saturated color.

I agree, that you dont. As far as I can tell, the effect comes from superimposing an after-image on some other image.

You clearly demonstrated that you don't need the animation. However, it's a convenient way to keep you staring in the same place and not have to do anything else to cause the effect.

Now we need to know from the people that experienced the laser how different this hallucination feels compared to that. Very cool stuff!

The green I see around the red circle is exactly the color of a green traffic light bulb when lit, which has a hint of blue to it and is not actually pure green.

Yeah good catch. I see those light the same way.

TFA does describe the actual colour as a bluish green, described as (0, 170, 85) in the filename. The expected illusory colour is quite different.

How is a negative afterimage "a new color"? I didn't get it. A fatigued cone will show you less, not more.

Cross your eyes like a magic eye image when it's shrinking and the vivid color will expand to a larger patch.

It's enough to stare at anything for a few minutes without moving eyes to get similar effects and hallucinations.

We see with good resolution only a small part of our visual field. Perhaps the brain starts to "invent" what's there it we don't give it information by constantly moving eyes.

As a more advanced version, they say that fire kasina practice may produce very interesting visual effects.

To get 'speed up' the effect, move your face close (to the red) then away from your screen.

its turquoise

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