I How does the electron come back down in energy level after absorbing a photon?

[jjschwartz1]

A common explanation for the origin of (some) color is that a material absorbs a, say, red photon and an electron moves from one energy level to a higher energy level, the difference in energy being the energy of the red photon. The material then appears bluish having absorbed the red light.

What happens to that excited electron? If it just falls down to the original energy level it will emit red light and the material won't have color. There must be other processes.

Thank you in advance for any insights.

 

[Vanadium 50]

Where did you get that explanation? It is certainly not the case for solids.

 

[jjschwartz1]

Among other more valid references, this youtube video produced by the American Chemical Society, beginning at 1:07,

 

[PeroK]

A common explanation for the origin of (some) color is that a material absorbs a, say, red photon and an electron moves from one energy level to a higher energy level, the difference in energy being the energy of the red photon. The material then appears bluish having absorbed the red light.

What happens to that excited electron? If it just falls down to the original energy level it will emit red light and the material won't have color. There must be other processes.

Thank you in advance for any insights.

I suspect the full answer to this question may be quite complicated and that different types of objects have colour for different reasons. One key point to note is this:

The light from the Sun or a lamp is largely in the visible (and infrared) spectrum. This determines the spectrum incident upon an object. Some of that spectrum may be absorbed. Note that visible light is relatively energetic, so the absorbtion will excite a molecule from the ground state to a relatively high excited state. Typically, a molecule has a large number of possible excited energy levels.

When the molecule reemits the light, however, it may do this in several stages, resulting in several emissions each of a lower energy (longer wavelength) than the original incident light. The object may emit light generally in the invisible, infrared part of the spectrum. It's possible that statistically very little light is re-emitted in the visible spectrum.

This would tie in with the thermodynamic picture of the incident light heating the body, as the light is absorbed, then the energy is radiated according to the blackbody spectrum, which would be largely invisible at normal temperatures.

 

[Vanadium 50]

Solids don't have orbitals in the way you are imagining. They have energy bands. The energy to move an electron from band to band varies with the size of the band. Further, electrons can gain or lose energy as they travel in a band.

 

[snorkack]

A common explanation for the origin of (some) color is that a material absorbs a, say, red photon and an electron moves from one energy level to a higher energy level, the difference in energy being the energy of the red photon. The material then appears bluish having absorbed the red light.

What happens to that excited electron? If it just falls down to the original energy level it will emit red light and the material won't have color. There must be other processes.

If the deexcitation takes place by emitting same frequency light (in the case, red), then the photons would be spontaneously emitted in random directions. Absorption and reemission would thus work as scattering, and the substance would be blue in transmitted light, but red in scattered light, including backscattered light.
A good example of a substance which is similar colour as gas and as liquid is bromine. Simple homoatomic diatomic gas too. Does a Br₂ molecule in gas have orbitals?
How much do the spectra of gaseous, liquid and solid bromine differ? And does liquid bromine have bands instead of orbitals?
For water, there is a nice comparison of spectra:
https://en.wikipedia.org/wiki/File:Water_infrared_absorption_coefficient_large.gif
but that´s somewhat more complex, infrared absorption, compared to a simple diatomic molecule.

 

[sophiecentaur]

Does a Br2 molecule in gas have orbitals?

Bromine is one of the few gasses with very visible colour. Could that be because it is dense and has high van der Waal's forces - meaning it is more likely to absorb light? That would tie in with the fact that solids and liquids tend to exhibit colour, where most gases do not.
There is a great temptation to discuss what goes on in solids and liquids by referring to a simple Hydrogen Atom model; in fact it's nothing like that because there are many more possible energy levels involved (bands not lines)

 

[DrClaude]

The origin of the color of the halogens stems from the excitation between the highest occupied π* molecular orbital and the lowest unoccupied σ* molecular orbital. The energy gap between the HOMO and LUMO decreases according to F2 > Cl2 > Br2 > I2. The amount of energy required for excitation depends upon the size of the atom. Fluorine is the smallest element in the group and the force of attraction between the nucleus and the outer electrons is very large. As a result, it requires a large excitation energy and absorbs violet light (high energy) and so appears pale yellow. On the other hand, iodine needs significantly less excitation energy and absorbs yellow light of low energy. Thus it appears dark violet. Using similar arguments, it is possible to explain the greenish yellow color of chlorine and the reddish brown color of bromine.

https://chem.libretexts.org/Bookshe.../8.13.01:_Physical_Properties_of_the_Halogens

 

[snorkack]

Bromine is one of the few gasses with very visible colour.
There is a great temptation to discuss what goes on in solids and liquids by referring to a simple Hydrogen Atom model; in fact it's nothing like that because there are many more possible energy levels involved (bands not lines)

And solids and liquids are too complex compared to hydrogen atom.
Halogens are a good next step to look at - just two atoms and a symmetry because the atoms are identical. Just a few extra degrees of freedom compared to hydrogen atom.
One obvious degree of freedom to look at is the internuclear distance.
Something I recalled in pondering it is Franck-Condon principle.
Movement of nuclei is slow compared to excitation of electrons.
Therefore, when molecular orbitals are excited, they are often excited to vibrationally excited states of the electronically excited state of the system.
I said "system" because I am not sure whether to call it "molecule". When a halogen molecule has one electron excited to antibonding orbital, is it excited to a bound (and therefore quantized) state of the molecule, or an unbound continuum state of two dissociated atoms propelled away from each other by repulsion of their opposite wavefunction orbitals?

 

[sophiecentaur]

https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/Inorganic_Chemistry_(LibreTexts)/08:_Chemistry_of_the_Main_Group_Elements/8.13:_The_Halogens/8.13.01:_Physical_Properties_of_the_Halogens

What about the attenuation of the light with those strong colours? Could there be something to do with the probability of photon/electron interaction (i.e. do other gasses just absorb EM of other frequencies just as much?)
PS or is it to do with the fact that the absorption is broader band so more electrons are stimulated by photons of a range of frequencies? That could make sense to me.

 

[sophiecentaur]

Solids don't have orbitals in the way you are imagining.

That's a popular misconception.

 

[Vanadium 50]

Can you suggest a better one-sentence explanation?

 

[sophiecentaur]

That's a popular misconception.

The word "orbital" is hardly accurate to describe the way an electron 'moves' anywhere but in a simple molecule. What would it 'go round' in the middle of a block of plastic or a crystal? Or through a piece of copper.

 

[snorkack]

The word "orbital" is hardly accurate to describe the way an electron 'moves' anywhere but in a simple molecule. What would it 'go round' in the middle of a block of plastic or a crystal? Or through a piece of copper.

But you seem to agree with Vanadium 50 on the issue.
When Vanadium 50 captures an electron and turns into Titanium 50 in a block of solid metal vanadium, is the electron taken from 1s (or even 2s or 3s) orbital of the specific Vanadium 50 atom? Or is it taken from a conduction band of metal vanadium?
When Vanadium 50 captures an electron and turns into Titanium 50 in a molecule of VCl₄ in frozen VCl₄ (melts at -25 degrees), is the electron taken from 1s (or even 2s or 3s) orbital of the specific Vanadium 50 atom? Or is it taken from a molecular orbital, shared with the 4 Cl atoms but not the other VCl₄ molecules, bound by dispersion forces alone? Or from a band of the solid (and nonconductive) VCl₄?
VCl₄ incidentally can also be excited by visible light - it is bright red. It can also be observed as a gas, because it boils at 148 degrees.

 

[sophiecentaur]

But you seem to agree with

There is no "but" involved. I agree with his (@Vanadium 50 's) and your ideas but I question why the term "orbital" is ever used to describe anything but the very basics of the Hydrogen Atom - particularly when QM stresses that the shapes that you see in the associated graphics are probability densities.
Having learned my Physics without an A Level Chemistry past I was just confused by the term Orbital when nothing goes 'around' anywhere. I'd be surprised if no one else would have been helped by the use of a better term.
Too late to change now, though. (The term AND me!)

 

[DaTario]

When the molecule reemits the light, however, it may do this in several stages, resulting in several emissions each of a lower energy (longer wavelength) than the original incident light. The object may emit light generally in the invisible, infrared part of the spectrum. It's possible that statistically very little light is re-emitted in the visible spectrum.

A process that is possibly important in explaining the phenomenon of color by subtractive synthesis is the fact that once excited, the electron decays and emits a photon in a superposition of momentum states (Weisskopf-Wigner theory for spontaneous decay). In practice, this means that the red photon is not generally directed toward the same retina that collected the other incident and reflected photons. In many cases, this photon must head toward the sample of matter itself, giving rise to reabsorption or thermal processes.

 

[snorkack]

A process that is possibly important in explaining the phenomenon of color by subtractive synthesis is the fact that once excited, the electron decays and emits a photon in a superposition of momentum states (Weisskopf-Wigner theory for spontaneous decay). In practice, this means that the red photon is not generally directed toward the same retina that collected the other incident and reflected photons. In many cases, this photon must head toward the sample of matter itself, giving rise to reabsorption or thermal processes.

If the only effect is reemitting the photon in a random and new direction, at the same frequency, over time small relative to reaction time and with 100% efficiency, it looks like scattering. And selective scatterer of e. g. red light should be red in reflected light, blue in transmitted light.

 

[ketoenol]

If the electron decays and emits light, that's known as fluorescence (or phosphorescence, depending on the exact mechanism). These are interesting phenomena, but most condensed materials do not appreciably fluoresce. Instead electrons relax through other mechanisms, which I will admit I don't fundamentally understand at a quantum level, but the end result is that the energy just gets turned into heat. This is of course very in-line with our experiences: if you go out in the sun, you get warm!

 

[DaTario]

If the only effect is reemitting the photon in a random and new direction, at the same frequency, over time small relative to reaction time and with 100% efficiency, it looks like scattering. And selective scatterer of e. g. red light should be red in reflected light, blue in transmitted light.

Notice that you are describing some color issues of the sky. When sunlight enters the atmosphere, it scatters more intensely blue light. At the end of its journey (ray of sunlight in the atmosphere) it shows us a red sky.

 

[sophiecentaur]

Notice that you are describing some color issues of the sky. When sunlight enters the atmosphere, it scatters more intensely blue light. At the end of its journey (ray of sunlight in the atmosphere) it shows us a red sky.

It's important not to confuse the mechanism of scattering and the mechanism of absorption. In absorption, the energy of a photon is absorbed and then re- emitted. With a gas the molecules can be regarded as independent and the frequency of the affected photons is the characteristic frequency of an available transition between two available states. A well defined absorption line / band results and there is very little energy involved. The re-radiated energy can be in any direction . In condensed matter ( solids and liquids) the photon interacts with many of the molecules and the absorption spectrum will be very broad. The Pauli Exclusion Principle is an explanation of the effect in many interacting molecules.

Scattering is a broad band phenomenon in which the whole visible spectrum is affected by the molecules and there is often a clear visible colouration effect. Google Raleigh scattering to find out the way the photons are affected; it is directional, depending on the size of the scatterer and is not like the well known Hydrogen Atom absorption operates.

 

[BVirtual]

@jjschwartz1: Your question might be interpreted to be about where color comes from. Or about how atoms have structure, multiple ground state orbital shells with only two possible electrons each, and the nucleus. Other posters added "electron capture" by the nucleus, which is not a process that directly generates "colored" light, but does change all the colors that an electron moving between "orbital shells" might emit as a photon.

This post to your question focuses on the orbitals, not the nucleus, so I add only those details. Every Periodic Table element has thousands of possible orbital shells that an electron might occupy. There is only one ground state or the lowest possible energy for an electron in any one orbital. All other orbitals available to this one electron in its ground state orbital are all higher in energy. There are for most elements around a thousand known energy levels, that is a thousand known orbitals. That is the basic structure. I will not go into nesting, shapes, and other structure properties, as for "color" only the energy level is of concern. I will say one thing about higher energy orbitals, the electron spends more time further away from the nucleus, thus the higher energy. Partially ionized electrons are attracted to the positive protons in the nucleus. In order to spend more time further away from the nucleus, the electron must have more energy.

Color, or a light photon is created/emitted from two types of electrons, a free electron not currently in any of the atom's orbital shells (think coming in from infinity), and an existing high energy orbital electron changing to a lower energy orbital. For energy conservation an electron changing to a lower energy orbital emits a photon with energy equal to the energy difference between the two levels. This type of electron in the high energy orbital is called "partially ionized."

Now comes the interesting part. Lots of "colors" are possible from these thousands orbitals, as each orbital has a different energy level. Most emitted photons are in the radio spectrum, such is black body radiation. When an object is heated, the electrons can be in higher energy levels, and when they change orbitals to one lower, they will emit Infrared photons. When the object is greatly heated like a light bulb coil, the electrons are boosted into even higher partially ionized orbitals, might even be emitted as a free electron, later to be recaptured by the same or other atoms. The colors emitted at these higher temperatures are Visible light.

There are other ways to excite electrons to higher energy levels, but the basics are enough for the super interesting part.

A high energy orbital's electron while called partially ionized can change to ANY lower energy orbital, and emit different frequencies of photons. If this new lower energy orbital is not the "ground state", the lowest possible energy level, then the electron can change AGAIN to another lower energy level. The electron emits another photon. This level change continues until the electron reaches the lowest *available* energy level. This series of changes is called a cascade. Most times these cascades have energy differences so low that only radio waves are emitted, no visible light.

Laser beams work with such cascades. The partially ionized electron enters into a special type of semi-stable orbital, formally called "meta stable," as this electron in this special orbital can stay there for seconds, hours or even days. Also, due to how laser photons impact an atom's orbital, in a process called stimulated emission, the impacting photon causes the atom to emit another photon of the identical frequency, and even in the identical direction of the first photon. A very special behavior inside a laser optical cavity only.

Well, I have now undoubtably written an overly brief summary, that is too short for proper understanding by the lay person. However, the thread reader should now understand the level of complexity in an atom's "orbital." It is super complex. A whole textbook is needed. A starting point is JANUS software that has hundreds of numerical values for many possible transitions for most of the Periodic Table elements. If you view its primary interface you likely will recognize the graph with axes of neutron count and proton count. While there may be only around a thousand orbital energy levels per element, there are factorial times more transition energies, the energy difference between any two levels.

A few years back, 8 to 10, I read a paper of scientists claiming to have solved the QED equations for electron motion in orbital. They made assumptions like the electron was actually in orbit around the nucleus, where the orbit obeyed the QM waveform for each orbital shape. They wanted to calculate the "speed" of the electron, so made many assumptions. They found the electron would have to move at above 99% of the speed of light. Whether there is a basis in "reality" for such an orbiting electron was not a conclusion of the paper. But it is interesting that the QED math could then be solved for simple cases and come up with the emitted colors.

I hope you have enjoyed learning more about how colors are made, from an atom's many orbitals.

You wrote over half a year ago:

> The material then appears bluish having absorbed the red light.

Yes, that is possible, but not in all cases. This bluish color does not come from emitted photons from orbital electrons. It is from the academic topic called "Art" and its "Color Theory" as perceived by the human brain. Which might be even more complex than what I wrote.

> emit red light and the material won't have color.

Ah, the color is red, as that is the emitted color.

 

[sophiecentaur]

Color, or a light photon is created/emitted from two types of electrons

As part of a well informed post, this equating of a photon with a colour is a definite error. Colour should't be part of any description of a physical mechanism. Yes; we do experience colour but that's all in our heads and Physics has no place for it. A photon has an energy which corresponds to a frequency / wavelength. A suitable mix of frequencies will stimulate a sensation of a colour.
The only way to measure the effect of a substance on passing light is with a spectrometer. The eye is totally unreliable.

 

[BVirtual]

I believe there has been a misreading of my quoted sentence. Clarifying posts is important. Pardon the length of this one, as I do believe the details matter.

Allow me to clarify by adding the concept of "color names." Both human perceived and spectrum measured light have color "names."

A careful reading of the words

Color, or a light photon is created/emitted from two types of electrons

can be read a different way from sophicentaur. Notice in this sentence there is no mention the eye ball.

I am responding here to the assumption that colour is something only seen by the eyeball. This 'assumption' is proven false by the fact that "Visible Light" as observed by a spectrometer measuring frequency 'bands' have "color names." Keep reading.

These electron generated colors are a subset of human perceived color. That is, the colors seen by a human have more "colors" than actually present in the Visible Light spectrum, like the color "white", or differences in saturation, hue, shades of pascal and other variations.

Also true is the Visible Light spectrum can be a superset of colors, as some are unseen by some humans, like Near Infrared, Near UltraViolet, and people who are color blind. <smile>

Of course, sophiecentaur is also right that one way a physicist can view spectrometer output is not in a rainbow splash, but in a graph of intensity versus wavelength. To say this is the only valid way to interprete the output of a spectrometer I suppose can be considered true.

I believe this graph can be mapped by frequency to color names. Orange is hard to find as its band is so very narrow. Turquoise is not present.

There are many computer/math algorithms that convert between types of color cubes. Also, there are no algorithms that are successful in converting all color cubes definitions to a single frequency of Visible Light as emitted by electrons. Why? There is no possibility of a one to one mapping between these sets of colors to just one frequency. Visible light as created by electrons is very limited in range compared to what the human perceives. Human colors can have an one to many frequencies mapping, even then this mapping fails.

Physicists have no use for the human perceived colors. Physicists must limit themselves to those frequencies in the continuous band of photon frequencies known as Visible Light to just a very limited subset of "named colors."

Every photon 'band' comes with a set of names.

AM, TV, FM, CB, SW, Portable Phone, Cell Phone, microwave, radar
Far Infrared, mid infrared, near infrared
Visible Light names here... in other words subset of "color" names
Near Ultraviolet, Mid Ultraviolet, Far Ultraviolet
Soft X-Rays and hard X-Rays
Gamma Rays and Cosmic Rays

The quoted sentence I wrote only referred to the limited subset of color names from the Visible Light band.

It is true that all perceived colors by humans are from varying intensities of one or more frequencies of Visible Light as generated by electrons. This set includes superimposing, absence, and other such effects. Except the color Black, which physicists believe is the absence of light, but never the less does have a color "name." <grin>

 

[BVirtual]

I need to clarify a post I did days ago where I wrote:

This bluish color does not come from emitted photons from orbital electrons. It is from the academic topic called "Art" and its "Color Theory" as perceived by the human brain. Which might be even more complex than what I wrote.

I stated "Color Theory" from "Art", and this is not fully accurate. I looked up Color Theory (again) and while it is more complex, the "Art" Color Theory does not include several topics mentioned before I posted, such as brain perception of color, the absence of absorbed light by the substance's atoms' orbitals and other scientific issues dealing with both of the foundations and complexities of these two topics. Any more information would be off the topic of the thread, imho.

 

[sophiecentaur]

Notice in this sentence there is no mention the eye ball.

I am responding here to the assumption that colour is something only seen by the eyeball. This 'assumption' is proven false by the fact that "Visible Light" as observed by a spectrometer measuring frequency 'bands' have "color names." Keep reading.

Colour is, by definition, an experience of humans. Other creatures may analyse the spectrum of the light they see and classify the experience in the same sort of terms that humans do but, if their analysis curves are different then the classification will be different. It's very vague and misleading to say that a particular animal 'sees blue' if it has a different passband of wavelengths and different sensors. There will be a totally different set of numerical values that classify a particular spectral content.

Newton studied colour (see New Scientist Article) and his conclusions were a bit limited because he worked on the corpuscular theory of light. He worked on the principle that there were only seven colours (he had mystical reasons for this). It was only later that Huygens and others developed the idea of wavelength (a numerical quantity) and Physics made great advances after that. Most coloured light is not actually a single wavelength; most colours have many spectral components.

Probably the best way to persuade you that colour is distinct from what a spectrometer will measure is to challenge you to find a spectrometer with a scale that's marked in 'colours'. To specify a colour value (human perception and matching colours), three numerical quantities are involved. At a very basic level, we can use the RGB values in TV systems. You can process the whole set of values that a spectrometer will give you and analyse them to give an approximation to the colour experience of human vision. This is miles away from the energy carried by a single photon. Trying to use the term 'colour' in this context is not helpful.

There is not a lot of point in arguing in favour of the use of colour in quantum physics. You won't find it used in serious publications. Can you find an example of a credible paper or textbook? Just stick to wavelength (or frequency or, indeed energy) when quantifying a photon. It does make sense.

 

[BVirtual]

Summary:
I have included some degree of lay person understanding of the word color.
You object. I am fine with your position.

If you want to continue to advocate for all physicists to stop using color names, and do so in Physics Forums, for students and children to learn that the colors of the rainbow, as separated by the water droplet refraction by frequency/wavelength/energy, which is identical to spectrometer prisms, are not to be "named", but referred to by frequency or wavelength number ... be my guest.

Such outreach to junior physicists is admirable. <smile>

--

Your definition of color is what is 'common.' It can be found in all dictionaries.

I have no idea why your viewpoint is so important to you. Nor why you feel I must be convinced, as you have appeared to misread or not read, and not understood, the many ways I have already agreed with your some of your position. I think you best address children, teenagers and young adults, not me.

---

I think you said it best, when you wrote "quantifying a photon."

Physicists are known for doing two things, quantify and qualify. Usually in the reverse order. Right?

I am doing the qualifying part first with my post. I will leave the quantifying to you.

Except for my need to do full spectral analysis of my fusion device, and especially the Gamma Ray energy spectrum, not just a simple Geiger Counter telling me ionizing radiation is present and giving a single numerical value.

---

I think your issue can come down to lay person use of names of color versus what you want experts to do in their use of color names.

You advocate physicists to not use names of colors, but use a frequency number.

I agree with "quantifying a photon". What about qualifying? Do physicists ever get to qualify photons?

---

Seems there is a semantic interpretation issue going on?

You seem intent to persuade me "color" is different from what a spectrometer measures, which I already posted a great deal on agreeing. Color cubes are all about human perception of color and not about spectrometers, as evidence by the lack of one to one mapping, which is a most solid point I made, and you have repeated.

You repeated a lot of key points I posted. These points were arguments I used support your position, to point out perceived colors do not map to spectrum frequencies . Which is something you did not originally raised, but I did, to support your position.

---

Even humans disagree on what frequencies are in each "color NAME BAND." Most 'city' people see 5 greens or so, while native tribes living in the forest will name more than 20 green colors by different names, even over 30 different greens. And each member of the same tribe will have agreement between them.

---

You used the term RGB and I qualify that term as follows:

RGB color cube does not map well to spectrum colors, to repeat myself. I researched the math algorithms for this years ago, and found two, and implemented one. It is not one to one. Better than computer science based RGB color scheme is the artist HSL color cube talked about below:

ChatGPT QUOTE:

The Three Main Dimensions of Color:​

1. Hue – the basic type of color (e.g., red, green, blue).
2. Saturation – the intensity or purity of the color.
3. Brightness (or value/luminance) – how light or dark the color appears.

----

I am referring to what is also a common meaning of color (from ChatGPT, which might be lying...)-;

Physically: Color is determined by the wavelength of visible light, which ranges approximately from 380 to 750 nanometers.

----

Let's examine your viewpoint from what I have perceived you are saying:

Let me ask you that when a spectrometer uses a prism to split an incoming beam into a spectrum, that you believe there are no colors present in that spectrum? No red. No violet.

And names do not count, like Infrared and Ultraviolet? There are no spectrum bands by those names? Is that what you are telling me?

That the Sun is not yellow nor reddish, and stars made of Hydrogen are not bluish? That astronomers are not physicists?

What I will not do is attempt to eliminate from the jargon of all physicists the names of colors. I do not have that type of power.

Pluto was a planet. <grin>

I wish you the greatest success in focusing physicists on strictly numerical values, and to forget color names.

Regarding your quantum physics needs, I agree 100%.

For textbooks that use color names just look at any K12 textbook.

 

[sophiecentaur]

not to be "named", but referred to by frequency or wavelength number

Quoting the perceived colour of incident light can often be more or less useless on its own in Physics. Yet numerical data can often be supported and conveyed by subjective terms. e.g. fast, slow, red, blue, hot, cold.

I have no idea why your viewpoint is so important to you.

I constantly read nonsense in the popular press and even casual scientific writings. That sort of thing is taken as gospel by many people. Most of the stuff you read on PF attempt to keep to the straight and narrow path (i.e. Physics). There is a misconception that introducing the term 'photon' into a poor description will make it more 'understandable'. Most people have no clue about the nature of the photon which they are happy to include in what they say. So it really does bother me.

Except for my need to do full spectral analysis of my fusion device, and especially the Gamma Ray energy spectrum, not just a simple Geiger Counter telling me ionizing radiation is present and giving a single numerical value.

Does your fusion device produce much visible light with distinct monochromatic colours?

Color cubes are all about human perception of color

They are barely adequate for objective applications. Colour TV was developed from the Tristimulus theory and the CIE colour space is a way through to tolerably good colour reproduction using additive mixing. The various areas in the CIE chart are often described in terms of the perceived colour names but the signal channel uses numerical quantities to produce the wanted 'colours' at the other end.

RGB color cube does not map well to spectrum colors,

Of course not because the triangle the RGB primaries does not enclose them. The curved line round the top portion is defined by the (average) sensitivity curves of the human eye.

ChatGPT QUOTE:

Best to avoid that. I believe PF has a view on it.

Let me ask you that when a spectrometer uses a prism to split an incoming beam into a spectrum, that you believe there are no colors present in that spectrum? No red. No violet.

That's a straw man argument. The output of a spectrometer is numerical. It is of course true that conversations about spectrometer output may often use colours. But what about the James Webb Space Telescope? Most of its images are in the IR and far IR. What colours would you use to describe the em frequency content of those images. Optical astronomy uses colours in discussions for convenience, when possible.

And names do not count, like Infrared and Ultraviolet?

All appropriate names are useful but life is full of occasions where numbers are needed to give the right message. "I drank a lot of beer last night" is not enough info for the guy who has to present the bill.
Even elementary quantum theory can't be done without maths and numbers. In fact, looking at the series of emitted wavelengths from the dear old H atom, there are many that are out of our visual sensitivity.

And on and on. . . .

 

[BVirtual]

The output of a spectrometer is numerical.

When looking at arguments involving a spectrometer, one has to wonder if there is not a fallacy in use, by treating the spectrometer as a black box, and not including the numeric output is convertible to a rough approximation of the input.

The series of numbers can be converted back to a colored spectrum for 'quick' analysis, perhaps confirmation that the captured data did do the needed job, or not. This quick analysis is first by quality and then by limited quantitative use. It would be more like a bar chart where each bar progresses from red to blue. What I like about the output is the absorption lines appear as black bars (with adequate resolution).

This contrasts as a teaching aid to students who often just look at the colors, without any understanding of the intensity of each 'bar/line' is of great value. Which is where your argument about quantitative analysis is good.

Apply a math algorithm to convert the bars to a more nature based rainbow like spectrum.

In addition, internal to the spectrometer is a prism or modern models use a grating. The incoming light beam is spread by wavelength onto a single bar scanner. This scanner has individual cells that capture photons, and counts the generated electrons, thus converting a small spread of light frequencies into a single intensity number (per cell). The numbers output are not for a single frequency. Spectrometer method is approximate. Resolution on the frequency axis is determined by several factors, like distance of the scanner bar from the grating, and number of cells per inch in the scanner bar.

I do have a right triangular black plastic box with an eye hole at one end, to observe the color spectrum from a grating. It has a numerical guide consisting of the numbers 4, 5, 6, 7 and 8. I suppose one multiplies by 100 to get the frequency. I got it as an aid for less scientifically inclined project members to see that light sources have a spectrum, independent of my verbal opinion. And these light sources, even if looking 'white,' can have distinctly different color spectrum. Also, I got each member a grating mounted in a picture slide, so they had it at home to use as well with any light source ... again independent of me.

Seems physics is near uncomprehensible to grown adults, who just do not believe 'words,' until seen with their own eyes. Which is the basis of PhysicsForums.com and other physics forums.

I since took considerable time to author the world's first Fusion Primer Poster, which will be online at the end of summer, along with a smaller Fusion Basic Poster. This outreach effort has been well received by members, and after review by a few professors, will be published.

In addition, I made a color slide presentation of the project's fusion device operation, a 23 slide version, then a 9 slide version. The 23 slides has many details (which I found were best left out for the lay person). The most frequently asked question about fusion is "Where does the power come from?" The complexity of that answer amazed me, so I needed a short, simple version, thus only 9 slides. It eliminated most of the fuel preparation, down from 10 slides to 1.

The light from the fusion device is 'white' light to the eyeball. And too much velocity spread in the many lines, for any initial spectrum snapshots to be of even qualitative use. So, not monochromatic, but perhaps at the initial ignition it might have several dozen lines appear in the sub microsecond sampling rate. Most spectrometers are not that fast, so a fast 'shutter' is in my future (spinning disk with slits is best I read).

Due to the plasma there is high RFI across all bands, including IR and UV. I hope the Gamma Ray spectrum has less noise than other photon bands. I just found out yesterday about Radiacode low cost analyzer, but there are no published stats on the resolution, so may be too low a resolution to resolve individual lines that are spread wide due to velocity angles.

 

[renormalize]

The light from the fusion device is 'white' light to the eyeball.

I'm guessing that you are describing a "fusor" device: https://en.wikipedia.org/wiki/Fusor
If that's true, these involve high-voltage, as well as possible x-ray & neutron emissions, all of which raise significant concerns of safety for a personal experimenter. These issues may well require review by the appropriate authority-having-jurisdiction. What is your background in identifying and mitigating safety concerns in your experiment and complying with required safety regulations?
Note also that Physics Forums rules specifically prohibit discussion of personal projects that are potentially dangerous or illegal.

 

[BVirtual]

Safety is my number ONE goal, which is if you walked in on your feet, then at the end of the day you will walk out. I have Zero Tolerance for unsafe behavior. There will be no discussion of the device, just the rare diagnostic needs. It is not a personal project, nor illegal and ionizing radiation shielding will be in place upon first operation.

 

[sophiecentaur]

Even humans disagree on what frequencies are in each "color NAME BAND." Most 'city' people see 5 greens or so, while native tribes living in the forest will name more than 20 green colors by different names, even over 30 different greens. And each member of the same tribe will have agreement between them.

Which is a very good reason not to use colour as experimental data (except in [Edit: colourimetric ] applications). However would the vital relationship E = hf have been found if the experimenters (physicists) had tried it with rainbow colours? The title of this forum has the word Physics in it so we are aiming to promote Physics and not easy alternatives. The colours are, of course relevant and useful for descriptions but not for theory. If you don't find theory important then stick with colours and avoid trying to 'educate' other people about Physics. It really doesn't help them.

 

[BVirtual]

Given the name of this forum "Atomic and Condensed Matter" I agree inside this context.

 

[sophiecentaur]

Given the name of this forum "Atomic and Condensed Matter" I agree inside this context.

Can you explain?

 

[BVirtual]

Yes. PF is a website with policies for each of each of its Forums to match the target audience that is desired by the Moderators. Some PF Forums are homework help where adherence is demanded to textbook and citation references in specialty fields of physics. Other Forums are for professionals within the specialty field. These Forums must promote posts with insight to the proper conceptual understanding within that specialty field. Thus, your desire to promote quantitative analysis using frequency over color. A good thing for professionals.

I never thought that someone might use "color names" for quantitative analysis. Never occurred to me, until this thread. I was glad when you mentioned your context of quantitative analysis. That was the turning point in this dialogue.

For me it is a given that analysis with mathematical precision is done with numbers, not conceptual words.

Where qualitative analysis is mostly word based. Color names can be accepted, but only roughly.

It has been a real pleasure for me SophieCentaur to dialogue with you in this thread, as you are able to have a productive dialogue that includes correcting both objective and subjective misunderstandings. A rare skill.

 

[sophiecentaur]

Thus, your desire to promote quantitative analysis using frequency over color. A good thing for professionals.

This suggests to me that you just don't want to get your hands dirty with 'actual maths'. I can safely say that no advance in Physics has ever ben achieved with arm waving, non-quantitive thinking. If you want to be listened to seriously in these matters or to have understanding you will need to be prepared for calculations and formulae. Your "professionals" are just genuine (or aspiring) Scientists.
The very least you can do is to use terms that are appropriate for any message you want to get across. Do not confuse the result (observed colour, for instance) with any 'explanation' in terms of Physics you may feel you have.

 

[ketoenol]

Which is a very good reason not to use colour as experimental data (except in [Edit: colourimetric ] applications). However would the vital relationship E = hf have been found if the experimenters (physicists) had tried it with rainbow colours? The title of this forum has the word Physics in it so we are aiming to promote Physics and not easy alternatives. The colours are, of course relevant and useful for descriptions but not for theory. If you don't find theory important then stick with colours and avoid trying to 'educate' other people about Physics. It really doesn't help them.

I hate to break it to you, but color (even by eye) is routinely used in pretty sensitive analytical chemistry techniques. Color can change a lot over pretty narrow concentration ranges. Theory can be important to tell you why the iodine-starch complex looks blue, but at the end of the day if you're doing a redox titration to figure out the concentration of something you're looking for that blue color to show up.

 

[weirdoguy]

I hate to break it to you, but color (even by eye) is routinely used in pretty sensitive analytical chemistry techniques.

I hate to break it to you, but...

(...) (physicists) (...) Physics (...) Physics (...) Physics (...)

 

[sophiecentaur]

I hate to break it to you, but color (even by eye) is routinely used in pretty sensitive analytical chemistry techniques. Color can change a lot over pretty narrow concentration ranges. Theory can be important to tell you why the iodine-starch complex looks blue, but at the end of the day if you're doing a redox titration to figure out the concentration of something you're looking for that blue color to show up.

Just what is your point here? Can you show me just one formula in which 'colour' is used in any other study but colour analysis / synthesis? What are you trying to defend?

What number is associated with the blue colour which indicates the presence of starch. I could expect the numbers out of a colorimeter might be used but we're not dealing with Physics in that case.

Of course we all use the terms "Red Shift" and "Blue Shift" in astronomy but could you possibly say how those two observable effects could be used to find the distance or speed of a departing (or approaching) galaxy can be used. Your photons, in this case, tell us nothing more than a perceived colour. ("by eye", as you say).