B What Makes the Six Colors in Newton's Experiment Special?

[Lish Lash]

"So why is it that if you split a ray of light several times, you will end up with an irreducible color? Say you isolate the blue section of a spectrum emitted from a prism. Why does the blue frequency not separate into different frequencies of blue?"

The three types of cones in the human eye are bandpass filters that respond to broad, overlapping ranges of colors. The "green cone", for example, doesn't just detect green wavelengths, it responds to a wide range of colors from orange to yellow to green to aqua. The "red cone" also responds to yellow and orange, as well as red wavelengths, but in different proportions than the green cone. When both red and green cones respond with equal intensity (and there is little blue cone response) the brain interprets this combination as yellow.

The important point to understand is that an individual cone cannot distinguish among the different colors it responds to. For example, a green cones cannot tell the difference between blue-green and yellow-orange colors, and responds in exactly the same way to both. Likewise, a blue cone would respond in exactly the same way to two shades of blue that were close to the same wavelength. You would only be able to distinguish between them if one of the blue colors stimulated the green cone more than the other.

 

[sophiecentaur]

"So why is it that if you split a ray of light several times, you will end up with an irreducible color? Say you isolate the blue section of a spectrum emitted from a prism. Why does the blue frequency not separate into different frequencies of blue?"

The three types of cones in the human eye are bandpass filters that respond to broad, overlapping ranges of colors. The "green cone", for example, doesn't just detect green wavelengths, it responds to a wide range of colors from orange to yellow to green to aqua. The "red cone" also responds to yellow and orange, as well as red wavelengths, but in different proportions than the green cone. When both red and green cones respond with equal intensity (and there is little blue cone response) the brain interprets this combination as yellow.

The important point to understand is that an individual cone cannot distinguish among the different colors it responds to. For example, a green cones cannot tell the difference between blue-green and yellow-orange colors, and responds in exactly the same way to both. Likewise, a blue cone would respond in exactly the same way to two shades of blue that were close to the same wavelength. You would only be able to distinguish between them if one of the blue colors stimulated the green cone more than the other.

You have to draw a huge distinction between colour vision and spectroscopy. Human colour vision is very approximate and uses just three wide and sensors to analyse and classify approximately, the whole of the visible spectrum of light entering the eye. It treats single spectral lines and light with complicated spectra in exactly the same way. The brain uses just three signals to categorise all the light from an object. That sensation is what we call colour. A spectrometer, otoh, splits the light into regions of FINITE bandwidth. It's the same as a radio receiver or RF spectrum analyser. The notion of a 'single' frequency is a bit nonsensical in this context. It's just a bit of convenient Maths. Every measurement method has a Resolution Bandwidth that blurs the resulting analysis. Zero bandwidth means no energy admitted, meaning you couldn't measure it. The resolution of a "prism" is limited by the width of the slit. Too thin a slit would mean not enough light gets through. Catch 22.

 

[Simon Peach]

The initial question was about colours. As I said before there cannot be infinite colours, the range of the visible electromagnet spectrum is "Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), or 4.00 × 10−7 to 7.00 × 10−7 m, between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths)". So unless you're going to split a nanometre there cannot be infinite range of colours.

 

[jbriggs444]

The initial question was about colours. As I said before there cannot be infinite colours, the range of the visible electromagnet spectrum is "Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), or 4.00 × 10−7 to 7.00 × 10−7 m, between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths)". So unless you're going to split a nanometre there cannot be infinite range of colours.

What's the problem with splitting a nanometre?

 

[Drakkith]

So unless you're going to split a nanometre there cannot be infinite range of colours.

You can easily split a spectrum up into sub-nanometer wavelength. This is routinely done in spectroscopy.

 

[OmCheeto]

Why are there only 6 colors?
I recently read an article written by Newton which outlined the process and results of his "crucial experiment".
From what I understand, Newton says that light can continue to be split until it reaches the basic colors and then it simply stops. What is it about these frequencies of light that makes them so special? Are there six exact frequencies that are the base of all the colors? Or are there ranges of frequencies that Newton simplified to one color? I asked my physics teacher and he responded with, "I don't know..."

Thanks in advance,
JB

Being a brilliant mathematician, Newton probably figured out pretty quickly, that to name an infinite number of colors would take him an extraordinarily excessive amount of time out of his finite time here one earth, which would interfere with his further experiments.

I'm sure Newton, were he alive, would tell you; "There are more than 6 colors."

 

[FactChecker]

So unless you're going to split a nanometre there cannot be infinite range of colours.

But of course there can be infinitely many colors in a finite range. (In fact uncountably many colors.) There is no conceptual problem with splitting a nanometer. Any two frequencies with the slightest difference represent different colors.

 

[pixel]

So unless you're going to split a nanometre there cannot be infinite range of colours.

The D-lines in the spectrum of sodium are at 588.9950 and 589.5924 nanometers. These are two instrumentally resolvable lines. Spectral lines don't just fall on integer values of nanometers.

You could say these represent two different colors. But as others have alluded to, if we mean by "color" the human visual response to light, then these are not visually distinguishable.

 

[rootone]

The human visual sensors (light sensitive neurons in the retina), come in three distinct types.
These are distinguished by response to what we see as red green and blue wavelengths.
However the response is not to a precise wavelength, just are most sensitive to wavelengths in a general range.
That gives six possible combinations that our visual cortex can process, rg, rb, gr, gb, bg, br, to associate a colour to an object.
We also have sensors which don't particularly recognise wavelengths, but just total amount of light.

 

[jbriggs444]

The human visual sensors (light sensitive neurons in the retina), come in three distinct types.
These are distinguished by response to what we see as red green and blue wavelengths.
However the response is not to a precise wavelength, just most generally they detect wavelengths in a general range.
That gives six possible combinations that out visual cortex can process, rg, rb, gr, gb, bg, br, to associate a colour to an object.
We also have sensors which don't particularly recognise wavelengths, but just total amount of light.

Even if our cones provided only binary color recognition, two raised to the third power is eight, not six. In addition, I fail to see the distinction between gr and rg.

 

[rootone]

Even if our cones provided only binary color recognition, two raised to the third power is eight, not six. In addition, I fail to see the distinction between gr and rg.

That is mathematically correct of course, but I'm not going to argue with nature itself, or evolution.
My personal experience is that I see six identifiable colours in a rainbow.
Not seven, I can't tell the difference between violet and indigo using that scheme

 

[sophiecentaur]

That is mathematically correct of course, but I'm not going to argue with nature itself, or evolution.
My personal experience is that I see six identifiable colours in a rainbow.
Not seven, I can't tell the difference between violet and indigo using that scheme

That is a totally personal, subjective assessment of what you see. Under other conditions, you (despite what you claim) would almost certainly be able to distinguish between two sources of spectral colour, both of which would fall within the 'yellow' band. If what you say is true, why would they need 'millions of colours' for good quality digital colour TV?

 

[pixel]

That gives six possible combinations that our visual cortex can process, rg, rb, gr, gb, bg, br, to associate a colour to an object.

Not sure what you are getting at here. That there are only 6 colors?

 

[Algr]

Here we go:

I originally made this to taunt people on an artist forum who didn't have a proper understanding of color theory. But I think it's a perfectly valid approach to examining the psychological perception of colors. I honestly do see all these colors as nearly equidistant. It's hard to explain that given a trinary understanding of color. My understand is that language, and how you were taught color names as a child, can effect your ability to perceive colors. So we can blame the evil Crayola corperation for all this 6 color talk. ;)

But as for this talk about not being able to split colors further - who actually performed this experiment? Ref please? It seems to me that if you kept trying to expand a spectrum further, you would simply end up with something too dim to see the subtle changes of color.

 

[sophiecentaur]

The term 'primaries' has a specific meaning. It is the least number of colours that can be mixed to produce all the others. So, with Additive Mixing (Using Lights, as in TV), you only need RG and B. There is no need for Yellow.
When mixing paints and pigments, the three primaries are Yellow, Cyan and Magenta. Other pigments are often used, to allow for brighter or more saturated colour display.
I suggest you read up about the existing theories on colorimetry. They are well based and have stood the test of time. Do that before trying to come up with an alternative theory of your own.

 

[sophiecentaur]

I honestly do see all these colors as nearly equidistant

I'm not sure how you are concluding that the colours are 'equidistant'. The CIE Colour space diagram is the standard way of plotting the chrominance values of colours and the distance between to 'just perceptibly' different colours depends on where they are in colour space. The 'Macadam Diagram' in this link (In the Tolerance section) shows how our resolution between adjacent colours varies over colour space. Those Ellipses (scaled by a factor of 10, to make it more obvious) show that, in the greens area, we are much less fussy than in the reds and pinks area. We are particularly sensitive to differences in skin tones as we use that information to judge emotions. I guess that there are few examples of highly saturated green colours in nature so we do not need to be able to distinguish there. Leaves of different shades of green will all have desaturated colours, where our colour vision is more discriminating. The details must all be down to evolutionary advantages and cost.

if you kept trying to expand a spectrum further, you would simply end up with something too dim to see

Yes. That is absolutely correct. The narrower the bandwidth, the less energy is admitted (that applies to RF signals as well) and the resulting signal can become too low to 'measure' or detect. This is 'why' our light sensitive cells use very wide band analysis filtering. If you use a spectrometer to look at fine details of the spectrum of light from stars, you will be limited by the actual amount of light power that arrives in a very narrow range of wavelengths that fall on your detector (or film).

 

[Algr]

The chart is my response to the "six colors" in the title of this thread. Take a look at the triangle at the bottom of the chart. Compare it to the square above and to the left. These are easily more different than red is from orange, and yet most people would have difficulty assigning names to them. They are both "Blue". We see one as darker than than other because our eyes aren't very sensitive to blue light. I'm well aware that yellow isn't really a primary (for additive color) but it seems to have a psychological identity so unlike its components. There is good reason why traffic lights are red-yellow-green, and not red-green-blue.

Apparently Isaac Newton would have called the primary color in the square "indigo" and the secondary in the triangle "blue". In modern language, the blue triangle is "Cyan".

 

[sophiecentaur]

The chart is my response to the "six colors" in the title of this thread. Take a look at the triangle at the bottom of the chart. Compare it to the square above and to the left. These are easily more different than red is from orange, and yet most people would have difficulty assigning names to them. They are both "Blue". We see one as darker than than other because our eyes aren't very sensitive to blue light. I'm well aware that yellow isn't really a primary (for additive color) but it seems to have a psychological identity so unlike its components. There is good reason why traffic lights are red-yellow-green, and not red-green-blue.

Apparently Isaac Newton would have called the primary color in the square "indigo" and the secondary in the triangle "blue". In modern language, the blue triangle is "Cyan".

Like I already said, you should try to read some stuff on modern colorimetry (1930's actually) and on the tristimulus theory of colour vision. (Google and learn) There is loads of information about this theory which is the basis of colour TV and film. TV colour fidelity is pretty damn good these days so your theory will need to be a bit more than one diagram with coloured squares and triangles. You need to account for the response of the eye to pale brown, khaki and the colour of facial skin as well. It is not a trivial subject.

 

[Algr]

I don't really have a "theory" these are just observations.

 

[sophiecentaur]

I don't really have a "theory" these are just observations.

The diagram you presented implies that you have tried to systematise what you have observed. The CIE colour diagram has a place for all the colours you (we) experience and shows how they fit into a universal system that works well. You are right to say that many nontechnical but highly creative users of colour use their own naive (I use the term in a non-judgemental way) models. I know that approach can produce excellent results, despite its technical flaws and they have been doing it for thousands of years.
I still recommend that you look into the present state of knowledge of Colorimetry. It could help you with reconciling your subjective observations with the accepted system. It may involve some brain ache, though!

 

[DaveC426913]

That gives six possible combinations that our visual cortex can process, rg, rb, gr, gb, bg, br, to associate a colour to an object.

I don't get this. The brain doesn't process in pairs like this.

It processes the relative values of all three types - simply: rgb.

 

[Electron Spin]

In my current reality there are 3 primary colours..

But... That's just mine...

Hello Dave!

 

[sophiecentaur]

I don't get this. The brain doesn't process in pairs like this.

It processes the relative values of all three types - simply: rgb.

I couldn't find that post from routone, for a suitable riposte and I have already suggested that he / everyone should do some reading about the pretty well established tristimulus theory of colour vision. This thread is not going anywhere whilst people are still posting with Primary School ideas, based on mixing paints and crayons. Personal theories, based on no evidence are discouraged on PF, surely.
Edit: I wondered whether this response is too grumpy but I have reconsidered it to be appropriate.

 

[rootone]

I'm not proposing a personal theory,and I will look into the established theory you mentioned.
My earlier post was really just a stab at a guess as for why traditionally artists, (of greater talent than schoolkids) thought in terms of 3 primary colours.
3 primary colours and their possible simple combinations gives a total of six easily identifiable colours.
That idea does correspond to what is now known to be the physical nature of light receptor neurons (rod cells) in human eyes.
I do know of course that visible light is not intrinsically in 3 bands,and what we are talking of here is human perception, not the nature of light as such,

 

[sophiecentaur]

My earlier post was really just a stab at a guess as for why traditionally artists, (of greater talent than schoolkids) thought in terms of 3 primary colours.

The 'Primaries' used by artists are not the RGB primaries, used in additive colour mixing. The whole system is different for producing the required range of colours because using pigments / paints / inks is subtractive. Very few artists try to paint with just three primaries (Cyan, Yellow and Magenta) because you can only produce saturated results (strong colours) by reducing the available luminance. One primary masks the other, reducing the total light available. If an artist (or printer* designer) wants to produce high fidelity and bright colours, it is necessary for them to use extra colours ('spot colours' are used for well known colours - such as the Coca-cola Red).
I can't understand why you insist on limiting your colorimetric rules to just six colours. The last time I experienced this limitation was in programming the BBC Microcomputer which had only binary values for its RGB video signals. People with normal colour vision can recognise and remember many more than your six colours and many colours are not part of the spectral set (Newton's six or seven). Why are you still defending this inadequate colour system? We normally try to work with appropriate accuracy in any other fields of Science and Engineering.
PS, it's the Cone receptors that are responsible for colour perception.
*Dot matrix printers tend to use interleaved coloured dots where possible so they can achieve high saturation without compromising too much on luminance.

 

[DarkBabylon]

Your monitor is able to make 16 million colors. Of course this is using 3 colors varying in intensity (256 for each). In the human visible spectrum alone you can have virtually infinite. Now take into account you can mix colors together. But wait there's more: X-rays, Ultra violets, Gamma rays, Radio, Microwave, infra-red...
The problem is, our eyes have a limited range that they can distinguish, rendering many of the wavelengths redundant.

 

[sophiecentaur]

rendering many of the wavelengths redundant.

No so much "redundant" as indistinguishable from their neighbours. All wavelengths contribute energy to what the colour sensors 'see'. The point has already been made that the ability to distinguish between adjacent colours will depend on the actual light level. It's the same old problem of Signal to Noise Ratio you need enough energy arriving on the three sensor to be able to assign a 'value' to their response so that your brain can do the sums and come up with a definite colour.
The Cones need much higher incident light levels in order to do this than the much more sensitive Rods. We always take clothes into a bright area to assess whether or not we have a good enough match. Daylight is best because the illuminant will affect the actual colour we decide we're seeing. CFL bulbs and old Fluo tubes are really bad for colour appreciation.

 

[DrClaude]

The OP has long been answered. Time to close.