Talk:Visible spectrum

message: Is there any article on Audible spectrum?Anwar (talk) 19:35, 3 May 2008 (UTC)
thread_title:  Audible spectrum 

message: Isn't the exact range of the visible spectrum disputed?--Luke Elms 20:33, 17 May 2008 (UTC)
replies: text: Not that I know of.  It is widely accepted that there is no "exact range", since the sensivities curves fall gradually to zero at both ends. Dicklyon (talk) 21:33, 17 May 2008 (UTC)
thread_title:  The actual range of the spectrum 

message: Saw a short article a while ago in a science news magazine that Birds see more of the spectrum than we do.  They have additional cells in their retina that also have a tiny bubble of oil over them.
The speculation was that the non-bird animals or proto-mammals that survived the extinction of the dinosaurs (the great K-T Extinction) were almost exclusively nocturnal types and did not need the extra  part of the spectrum anyway.  I got the impression that this part of the extension was not at either end of our visible spectrum, but somewhere nearer the center.  I am not sure this makes sense, but maybe some can look into it. WonderWheeler (talk) 23:20, 20 August 2008 (UTC)
thread_title:  Visible spectrum by other Species 

message: Skoch3 (talk) 07:50, 3 November 2008 (UTC)
replies: text: Good. Dicklyon (talk) 20:54, 3 November 2008 (UTC)
thread_title: Spectral colors

message: Skoch3 (talk) 07:56, 3 November 2008 (UTC)
replies: text: Skoch3 (talk) 08:00, 3 November 2008 (UTC)
replies: text:  If you're wanting a good representation of the spectrum, a JPEG image is a bad idea, due to the type of image compression it carries out. A bitmap (e.g. PNG) file, at a minimum, would be acceptable, as long as it were derived from a RAW image, rather than a JPEG. The SVG files I've created keep getting replaced by other synthesised bitmap images, which would be better done as SVG files due to scaling, text compression, etc. -- I'd much rather have an actual photograph, but that requires a bit more effort. gringer (talk) 04:11, 17 November 2008 (UTC)

text: ... Generically: the colors and spectral range shown in a photo will be distorted by the response of the sensors.Eric Drexler (talk) 12:38, 17 March 2013 (UTC)
thread_title: New image needed

message: "In the illustration, the narrow red, green and blue bars show the relative mixture of these three colors used to produce the color directly above.
what illustration?
12.125.134.114 (talk) 16:22, 8 October 2008 (UTC)
replies: text: Long gone. Dicklyon (talk) 20:54, 3 November 2008 (UTC)
thread_title: Obsolete image reference

message: I changed the name from visble spectrum to visible light spectrum
--Chicagobears94 (talk) 21:21, 10 January 2009 (UTC)
replies: text: Why? --Old Moonraker (talk) 21:53, 10 January 2009 (UTC)
thread_title: Changed Name

message: Re: removal of indigo from the table. I approve. If I had noticed that the table was drawn from a source I would have removed it too.
The idea that there is a distinct colour "indigo" in the spectrum between blue and violet has no basis in objective fact nor even unbiased qualitative observation. It was added because of Newton's bias that the number of colours should be the same as the number of notes in the musical scale.--Srleffler (talk) 23:29, 4 December 2009 (UTC)
replies: text: I appreciate the feedback.  Dicklyon (talk) 04:13, 5 December 2009 (UTC)

text: Newton's "blue" probably referred to something like 488nm (close to cyan) whereas his "indigo" probably referred to something like 464nm (same as what's now called "blue" in sRGB). 142.119.100.34 (talk) 04:58, 11 May 2024 (UTC)
thread_title:  Indigo 

message: The image at the top of the page, showing a narrow beam of white light passing through a prism, is quite inaccurate and needs replacing. The problem is that the beam as it is shown inside the prism, after having passed through the left-side wall, is still a narrow beam of white light when it should be already diverging into color separations as it has been refracted once. Other images on the web get this part correct.
TimProof (talk) 20:51, 18 March 2010 (UTC)
replies: text: Britannica has a nice diagram here, and wikipedia has this diagram. It's pretty hard, I'd speculate, to take a good picture of a beam of light going through a prism – you'd need something like a broad-spectrum laser, with the whole set up in some kind of smoke or fog to scatter some of the beam towards the camera. Even doing a decent 3d render is probably pretty tricky. I'm not sure it's such a big deal, but if you want to try to make a better one, go for it! –jacobolus (t) 22:15, 18 March 2010 (UTC)
thread_title:  Refractive prism image, top of page 

message: Human beings are actually capable of distinguishing UV light that they cannot directly perceive due to fluorescence of material within the eye itself. Because human beings are intelligent enough to deduce the presence of UV, it can be said that people can see UV because when looking at a source of near-UV; it is distinguishable from other sources of light because of the fuzzy/blurry area that will appear to surround it. This is a direct indicator that one is seeing fluorescence in the eye itself, and thus, light that is capable of inducing this fluorescence. Additionally, it seems likely that many other mammals could eventually be trained to make this distinction as well, although other mammals would likely never have any idea of what was actually going on with the photons themselves, etc ... so why is it said that human beings are "blind" to this frequency of light, when we so clearly are not?
:Following this logic, we can "see" any radiation (focused to the eye) which is strong enough to affect it, through various processes (upconversion, local heating, mild damage, etc). As I understand, the idea is to separate frequencies which cause "direct" effect. Materialscientist (talk) 00:24, 29 April 2010 (UTC)
replies: text: "My God, It's Full Of Stars!" ... Yeah I suppose you are right, although a trip to Home Depot to get a special bulb is a whole lot cheaper and more common than a Moonshot. Zaphraud (talk) 01:44, 10 June 2010 (UTC)

text: Humans are quite capable of seeing UV light, out eyes simply block it out physically with a physical part of the eye; when people have the lens or something removed from their eyes (some types of cataract surgery or via accident) can lead to the UV light entering the back of the eye and the people clearly seeing UV light as an overly-intense, bright, glowing violet light; this is not the same as being able to sense other portions of the spectrum which humans eyes can not process at all. 24.84.31.39 (talk)  —Preceding undated comment added 13:48, 31 December 2015 (UTC)
thread_title: Human perception of UV spectra light

message: Violet needs some discussion as what is a tertiary colour, blue + blue + red
link
This is violet seen on our pictures, and article pictures.
The violet you see through a spectrometer has fluoresent background glow about it. To recreate this effect you could put some fluorent matterial in a camera. The reason you see it as violet, that is some mixing of red, arises from the lift in the spectral tail of the rho cone cell in the eye.
helpful diagram.
So to repeat: the colour violet shown is not the colour from a spectrometer even though they stimulate the eye in the same way firstly by two, secondly by one wavelength of light - a hue and a spectral colour.
The second issue arising from the problematic violet, is our ability to add an unrealistic amount of red to it making it purple and even magenta.  Rainbows have these colours, but this is due the addition of red by the underlying Airy Rings. I will try to find an excellent link for everyone from the US NavalLabs. Here is a picture for you. rainbow
What I would like to discuss is how to intelligently add this information into this page. I think it is important as links the colour wheel cycle with the linear spectra, and allows the decerning reader to identify unrealistically retouched photos.  I will ask how to include pictures and referencs, but in the meantime thanks in advance for any thoughts.
Drhillteach (talk) 13:02, 9 May 2010 (UTC)
replies: text: Everything said here makes perfect sense to me in a clear way except for the part about how it would allow one to discern less than perfect photo-editing. While I can see how the information would be useful in specific cases, like where spectra are visible in the photo, in the absence of lens-flare how often does that happen? Also, what assurances does this detection make against legitimate corrections that most cameras probably make as the signal from the CCD is processed into an actual image? It would be harsh to label such a photo as being "edited"; even when there is no implication of fraud, at the very least human involvement in the process is implied - so is there any way to clarify the use of this technique, to distinguish badly edited or forged photographs from those that are simply automatically color-corrected in the usual way? Zaphraud (talk) 01:54, 10 June 2010 (UTC)
thread_title:  How to handle Violet? 

message: No doubt this was discussed and settled ages ago, but what is the reason why the article use the word "cyan" (which to me is a subtractive, printer's color, not a spectral color) and not the time-honored, hallowed, Newton-approved "indigo?" Is there a citation, in the "citation required" sense, to some authority that has decided it is better or more accurate or a recommended practice to use the name "cyan" for the spectral color between "blue" and "violet?" IMHO the article explains the traditional use of the name "indigo" adequately, but does not explain the article's own use of the word "cyan;" I think it should, if only in a footnote. Dpbsmith (talk) 22:31, 28 August 2010 (UTC)
replies: text: You’re right. There is no reason cyan should be here. The word implies the printer’s subtractive primary (a light greenish blue), and should not be used to stand for blue-green generally. There’s really no authority behind the use of cyan as this article uses it, as far as I know, though in general categorizing the spectrum is somewhat arbitrary and observer-specific. As for indigo: it’s not really a generally recognized “basic” color category (at least in English), and was made up mainly so that Newton could break things into 7 categories for musical/etc. analogy. –jacobolus (t) 10:37, 29 August 2010 (UTC)

text: A better source of the color names of various wavelengths might be this JOSA paper from 1943, which has a diagram which has been widely copied and used as a basis for other diagrams. (e.g. the lines in this image). Then again, that diagram is trying to fit colors to ISCC–NBS names, which means that there’s also no “violet” but only “bluish purple” and “purplish blue”. –jacobolus (t) 10:45, 29 August 2010 (UTC)
replies: text: Well, if other editors don't remember a good reason for naming "cyan" as a color of the spectrum, and agree that it's really a name for a subtractive color, then I'm thinking that a) maybe cyan should not be used.  I'm also thinking that b) maybe whatever set of names  is used needs a footnote, and that c) a color between blue and violet should be named and cited. It doesn't need to be a really heavy-duty citation IMHO, even a modern textbook would do, but the choice of name shouldn't be an arbitrary editor's decision and it should be explained. The footnote should mention what other names might be used. A native-Russian-speaking correspondent of mine says, by the way, "In Russian, the light-blue color is called 'goluboy,' and it is used much more frequently than cyan or indigo in English.  In fact, I now recall being surprised that there was no color in English corresponding to goluboy.  Baby-blue, sky-blue -- these were derivative names, not clean ones like goluboy.  And so, at least in Russian, Newton's seven colors have fairly equal representation." Dpbsmith (talk) 15:51, 29 August 2010 (UTC)

text: I'm not familiar with the ISCC–NBS but our article on it does include "violet" as an "intermediate" category. In fact the names used source Jacobolus cites do not accord with the article, i.e. perhaps the authors of the image were not trying to fit it to ISCC-NBS names. I notice that our article gives a name "purplish blue" but does not mention any "bluish purple." I'm thinking I like the idea of using the name "purplish blue" for the color between blue and violet, with a footnote explaining it traditionally called "indigo," because the name "purplish blue" is easily understood by readers who may be vague about indigo--if you were shown a swatch and asked whether it was "indigo," "cobalt blue," or "royal blue" would you be confident in answering? And the name "purplish blue" conveys uncertainty about its psychological primacy. Dpbsmith (talk) 16:25, 29 August 2010 (UTC)
replies: text:  If you’re interested, shoot me an email and I’ll send you a copy of the Kelly paper. I believe that “royal blue” is typically more blue/less purple than “cobalt blue” which is less purple than “indigo” (sometimes called “blue-violet” or “purplish blue”), which is less purple than “violet” (this Kelly paper uses the term “bluish purple” for what the ISCC–NBS system calls “violet”; the two can be considered synonyms in this context) which is less purple than “purple”. Anyway, the main point is that our current set of categories is pretty arbitrary, and I can’t tell what its source is. Any set of categories is in some sense arbitrary (though I believe there have been some studies measuring a typical viewer’s boundaries between color categories), so it might be worth showing a couple of different historical categorizations, but we should have sources for whatever we do say, and “cyan” probably doesn’t belong. (Oh, also, that’s my (woefully incomplete) ISCC–NBS article. I’ll happily send you PDFs of various papers/books about that too, if you want.) –jacobolus (t) 19:26, 31 August 2010 (UTC)

text:  From the intro to that paper: “The development of the ISCC-NBS system of color names [...] suggested to the author the possibility of adapting the same system of names to the description of colors of other than drugs and medicines. In this paper the possibility of applying this system to the colors of self-luminous sources is explored in the hope of offering a basis for the resolution of the conflicting terminology now used for flares, fluorescent and phosphorescent materials, and signal lights. This system could not displace precise specifications in terms of either chromaticity coordinates or standard filters such as are used for railway signal lights (3), but it is expected to provide color names recognized by the general public as appropriate. The spacing of the color-name boundaries is based on that of the ISCC-NBS system (1), but the shape of the boundaries is based on the extensive data collected by the O.S.A. subcommittee (4) on the spacing of the Munsell colors. Both spacing and shape have been modified in accordance with observations by two observers.” I’m not quite sure what the reason is for Kelly’s use of “yellowish orange” instead of “orange yellow”, addition of new categories “red purple” (between “reddish purple” and “purplish red”) and “blue green” (between “bluish green” and “greenish blue”), and use of the name “bluish purple” instead of “violet”. Maybe just his personal aesthetic preferences? Otherwise the categories are the same. –jacobolus (t) 19:30, 31 August 2010 (UTC)

text:  Actually, Table I from that paper is especially useful: here's a link. Here’s a link to Kelly’s diagram. (These are under copyright, and since Wikipedia’s image policy only supports hosting fair-use images if they’ll be used directly in articles, I put them at imgur instead). –jacobolus (t) 19:38, 31 August 2010 (UTC)
replies: text:  Dick, did you see the Table I linked just above? Any thoughts? Also, do you know of any good more recent sources for partitions of the visible spectrum? –jacobolus (t) 22:17, 2 September 2010 (UTC)

text: Here is a paper that talks about a "cyan laser", even in the title. Given that lasers are monochromatic light, it seems reasonable to suggest that this paper at least demonstrates that cyan is a spectral colour. gringer (talk) 23:01, 1 September 2010 (UTC)
replies: text: It suggests that the term is sometimes used that way, but I'd argue that it's rare and that no authority explicitly supports it.  Dicklyon (talk) 05:26, 2 September 2010 (UTC)

text:  Sure, the word cyan is used by various people for greenish blue and blue-green. But the term is very strongly associated with the subtractive primary, used for instance for one of the inks used in process printing, or one of the dyes of a dye-transfer photographic process. Many computer graphics type sources, especially sources without much grounding in color science, refer to the additive mixture of blue and green additive primaries as “cyan” for lack of a better term (sometimes it is even suggested that RGB images could be reproduced in CMY inks by inverting each of the RGB image components), and this usage has spread somewhat, but I think the term cyan is closely enough associated with the subtractive primary that it’s misleading to use it in partition of the visible spectrum, especially since nearly all reliable sources for such partition use some term other than cyan for this range (e.g. “greenish blue”) –jacobolus (t) 22:08, 2 September 2010 (UTC)

text:  I put an image over to the right that shows the difference between the hue/lightness (in Munsell space) of subtractive cyan in process printing, versus the additive combination of RGB B and G primaries. –jacobolus (t) 22:20, 2 September 2010 (UTC)

text: As WP's own article on Cyan explains, cyan is both the name of a subtractive primary and of an additive secondary color (equal amounts of blue and green). It comes up so often in computer graphics, and so many people these days have computers, that there might be some question about how badly a reference is needed.Zyxwv99 (talk) 03:28, 12 September 2013 (UTC)
replies: text:  By "there might be some question about how badly a reference is needed", did you mean "It should be obvious, so we don't need a reference"? I've been a (home) computer user since at least the mid-80s (Apple IIe), and I've only ever thought of "cyan" as referring to the subtractive color. That's certainly what it means in the most common usage in my experience, which is computer-related: printer inks, which come in the subtractive primaries cyan, magenta, and yellow (CMYK). That's what I thought the Newton reference (which I just now tagged "citation needed") was about. Clarification is definitely needed here! --Thnidu (talk) 04:15, 22 January 2014 (UTC)
replies: text: You've convinced me. Just because something seems obvious to me doesn't mean it's obvious to everyone else. Zyxwv99 (talk) 00:59, 23 January 2014 (UTC)
thread_title: Cyan vs. Indigo

message: The introductory paragraph of this article currently remarks: "The spectrum does not, however, contain all the colors that the human eyes and brain can distinguish. Unsaturated colors such as pink, or purple variations such as magenta, are absent, for example, because they can be made only by a mix of multiple wavelengths."
Although the general idea is correct, I think the wording should be revised to avoid misinformation. Magenta (50% blue, 50% red, 0% green) is a fully saturated color; see http://en.wikipedia.org/wiki/Magenta. Pink can also be a fully saturated color depending what type of pink it is. White might be a better color choice here, although even white/gray could be said to be within the spectrum, namely manifested as black, depending on what kind of spectrum is being referred to. To avoid any kind of confusion, it might be best to reference a color such as 40% blue, 40% red, 20% green. 67.53.36.194 (talk) 22:46, 16 March 2012 (UTC)
replies: text: I would suggest the word "purity" instead of "saturation". See also Colorfulness#Excitation_purity.--SiriusB (talk) 08:52, 1 February 2013 (UTC)
thread_title: Definition of saturation

message: In the lede it says:
:"The visible spectrum is the portion of the electromagnetic spectrum that is visible to (can be detected by) the human eye."
I don't think we should define the word "visible" here. Even though the definition provided is a perfectly valid definition, it is not the only possible definition of "visible." Many people who are legally blind have eyes that can detect light. Since "visible" is a common word, it should not require a definition. Also, "Visible spectrum" is a noun phrase that cannot be analyzed entirely in terms of its constituent parts. The temperate zone of the Earth, for example, is actually defined astronomically, and only coincides very roughly with the region in which temperate climate occurs.
Next, the range 390nm - 700nm seems odd. Even though it's referenced (to a textbook) I don't think it's one of the five most commonly cited ranges, or even in the top ten. The 390 at one end suggests a degree of precision that is not matched by the 700 at the other end. I suggest we go back to 400nm - 700nm, but qualify it with words such as "conventional," "nominal," or "customary." For example: "The conventional range of the visible spectrum is 400nm - 700nm. This range is, of course, purely nominal."
After that we could mention a few alternative ranges. For example, the CIE range for photopic (color) vision, 360nm - 830nm, and the CIE range for scotopic (night) vision, 380nm - 780nm. There's also a much narrower range, 420nm - 680nm, that comes up occasionally in technical literature, especially biochemistry. Even though that may seem exceedingly narrow, most people rarely see anything below 420nm or above 680nm, not because we are not capable of seeing it, but because our sensitivity at those wavelengths is so weak that they are drowned out by more visible wavelengths.
And finally, two subjects near and dear to my heart.
1) Nowadays many people have access to exotic light sources such as ultraviolet and infrared lasers, diodes, etc. As a result, many people are seeing light at wavelengths far beyond the more widely published ranges. For example, many people who work with uv lasers in the 320s and 330s can see the Rayleigh scattering. At the opposite end, a $15 5mW 980nm laser pointer shined directly into the eye (reasonably safe for up to 0.25 sec.) is clearly visible. In other words, people are "seeing the impossible."
2) Over the years there has been quite a bit of fundamental research into the extremes of human vision. The upshot is that the actual of range of human vision is about 300nm - 1100nm, but with qualifications. For example, children can usually see down to about 300nm, teens and young adults to 315nm, the elderly usually not below 400nm, the middle aged highly variable. In the low 300s color perception and visual acuity are seriously compromised. The more extreme the wavelength (both in uv and ir) the brighter the light needs to be in order to be visible. Eye damage is a serious concern for wavelengths below 320nm (because of the inherent dangers of uv at those wavelengths) and for brightness reasons above 950nm. Zyxwv99 (talk) 02:33, 22 September 2013 (UTC)
replies: text: This all seems excellent stuff.  Why not make some changes to the article? Martin Hogbin (talk) 13:56, 12 February 2014 (UTC)
thread_title:  Suggestions for further improvement 

message: Color	Wavelength	Frequency	Photon energy
violet	380–450 nm	668–789 THz	2.75–3.26 eV
blue	450–495 nm	606–668 THz	2.50–2.75 eV
green	495–570 nm	526–606 THz	2.17–2.50 eV
yellow	570–590 nm	508–526 THz	2.10–2.17 eV
orange	590–620 nm	484–508 THz	2.00–2.10 eV
red	620–750 nm	400–484 THz	1.65–2.00 eV
should be changed to 
Color	Wavelength	Frequency	Photon energy
violet	380–450 nm	789-668 THz	2.75–3.26 eV
blue	450–495 nm	668-606 THz	2.50–2.75 eV
green	495–570 nm	606-526 THz	2.17–2.50 eV
yellow	570–590 nm	526-508 THz	2.10–2.17 eV
orange	590–620 nm	508-484 THz	2.00–2.10 eV
red	620–750 nm	484-400 THz	1.65–2.00 eV  — Preceding unsigned comment added by Tempedi (talk • contribs) 15:57, 31 May 2017 (UTC)
thread_title:  Frequency Chart 

message: The section "Animal color vision" makes this statement about snakes: "other snakes with the organ may detect warm bodies from a meter away." However, no "organ" is mentioned in this section, so it is unclear what is meant here by "the organ." Presumably there was something here previously about which organ allows a snake to perceive radiant heat, but no such reference is present now. This statement needs to be made clearer.  — Preceding unsigned comment added by 2601:602:8480:3343:2145:CFCE:C4CA:A507 (talk) 05:03, 4 February 2019 (UTC)
thread_title:  Ambiguous statement about snakes in section "Animal color vision" 

message: I don't know if it is already mentioned in this quite large page, but... I want to say that when the spectrum from a sunlit prism (corners 60°) is observed at a large distance (the distance prism - projection screen) then one shall notice the absence of the colors orange, yellow, yellowish green, cyan (greenish blue), and indigo. There's only the three colors red, green, and ultramarine blue (the same colors from the RGB color model). So... Sir Isaac Newton's color system (red, orange, yellow, green, blue, indigo, violet) is a bit childish or schoolish. Johann Wolfgang von Goethe also knew about this rather childish approach of Newton and noticed Newton's wrong observations after he (Goethe) performed his own experiments with sunlit prism. Moreover, there's no violet in the spectrum of white light! Sir Isaac Newton observed the Primary Rainbow but he didn't knew about the existence of the Supernumerary Arcs on the "inside" (on the blue part) of the bow. He noticed a color that he called violet, but... what he really observed was the "overlap" of the ultramarine blue from the Primary Rainbow with the red from the first Supernumerary Arc. This "overlap" is the color Magenta (deep pink). Newton must have been unaware of the existence of the "overlap-color" Magenta, thus... he thought he observed the color violet. DannyJ.Caes (talk) 07:25, 5 August 2019 (UTC)
replies: text: Perhaps a case of anomalous color vision (indeed, deuteranomaly can be found in 6% men). Or crankery. Incnis Mrsi (talk) 09:59, 5 August 2019 (UTC)

text: Anyway it’s the spectral color article where color perception is to be addressed. “Visible spectrum” mostly stresses the fact that certain part of the EM spectrum is visible. Incnis Mrsi (talk) 10:15, 5 August 2019 (UTC)

text: Goethe's work is covered at Theory of Colours. Fundamentally, Newton and Goethe explored two different aspects of light. Newton's work correctly addresses the spectral composition of light, and identifies the apparent colors of monochromatic radiation. Goethe's work addresses aspects of human color vision that are ignored in Newton's work. From a physics perspective, Newton's work is fundamental—physics cares about the nature of light itself, not how colors appear to the eye. The Newtonian model cannot easily tell you where pink or brown come from, however. (NB: You cannot make a brown spotlight.)--Srleffler (talk) 18:09, 29 August 2019 (UTC)
thread_title:  Only three colors in the projected spectrum at a large distance from the sunlit prism 

message: The chart is incorrect at the end of spectrum: the atmosphere is quite transparent to the long waves.  — Preceding unsigned comment added by 2003:DF:2812:FF05:EEF4:BBFF:FE36:3F5C (talk) 07:42, 25 September 2020 (UTC)
replies: text: According to NASA the ionosphere is opaque to wavelengths longer than about 10 m.--Srleffler (talk) 16:16, 27 September 2020 (UTC)
thread_title:  Spectroscopy - atmospheric opacity chart 

message: While reorganising the article Optical window, I noticed that although this atmospheric window is characterised as optical, its range also covers the UV and infrared spectra. After some research I found that many valid sources differentiate between the visible and optical spectra, defining the visible spectrum as the one the human eye can detect and the optical spectrum as the one including the UV, the visible and the infrared spectra (see for example Frank L. Pedrotti's "Introduction to optics", Cambridge University Press, 2017, pp. 7-8). It seems that at some point in scientific history the terms optical and visible coincided, something that might hold true for many contemporary scientific fields as well. However, the matter should be looked into and this article should probably not present the terms visible spectrum and optical spectrum as synonymous.--L'OrfeoGreco (talk) 04:07, 28 December 2021 (UTC)
thread_title:  Differentiation between the visible and the optical spectra