Talk:Refraction

Seems lacking
This seems lacking. Where're the history and mechanism? lysdexia 13:49, 27 Oct 2004 (UTC) Who Invented the idea of refraction?

Category
in what category would this article be placed in?

Physics. You need to put this in physics also because earthquake waves or seismic waves follow the same pattern using refraction. when an earthquake wave - either a P or S wave - travels through the earth, the mantel it flows through changes density as it gets closer to the epicenter the core because of gravity. The core it self has 2 layers - a liquid outer and a solid inner. Only P waves can travel through the core because they can travel through both liquids and soilds (mantel is solid - its a type of rock). Why this has anything to do with refraction is because as the waves move throught the earth is follows a curved path. why? because the change in densitys from gravity change the course of the wave. This is why the earthquake waves do just go straight through the earth from england to australia, instead an earthquake will be made everywhere in the earth but losing it 'shake' as it travels further along the earth. —Preceding unsigned comment added by 81.174.154.192 (talk) 14:33, 26 February 2011 (UTC)


 * Well I've put it in optics. it might need to go in other categories too though. Theresa Knott (Tart, knees hot) 21:51, 14 Nov 2004 (UTC)

Image Changes
Hi, this article looked weird on a wide monitor (1920 pixels). The "See Also" section appeared to the right of the eye image, and the whole thing looked cluttered and confusing.. It wasn't clear what image the "In this diagram..." text referred to. On Safari or Firefox, it looked completely broken; the "In this diagram..." text overlapped the eye image. So, I moved the "In this diagram..." text to the image caption, and moved the image to the right. I removed the ripple tank image because it didn't seem that helpful, and there are too many images for the amount of text. Before reverting anything, please look at the old page on a wide monitor on safari or firefox... Pfalstad 8 July 2005 03:41 (UTC) you need to put this in physics also because earthquake waves or seismic waves follow the same pattern using refraction. when an earthquake wave - either a P or S wave - travels through the earth, the mantel it flows through changes density as it gets closer to the epicenter the core because of gravity. The core it self has 2 layers - a liquid outer and a solid inner. Only P waves can travel through the core because they can travel through both liquids and soilds (mantel is solid - its a type of rock). Why this has anything to do with refraction is because as the waves move throught the earth is follows a curved path. why? because the change in densitys from gravity change the course of the wave. This is why the earthquake waves do just go straight through the earth from england to australia, instead an earthquake will be made everywhere in the earth but losing it 'shake' as it travels further along the earth. —Preceding unsigned comment added by 81.174.154.192 (talk) 14:30, 26 February 2011 (UTC)

improvement
I think this article needs more technical content. 203.98.102.12 19:22, 13 January 2006 (UTC)

the image provided also shows the aparent image rotated upwards from the object. this is incorect as it should be directly above the object. (ie rotated upwards and shortend). plz excuse spelling =) —Preceding unsigned comment added by 219.89.95.106 (talk) 08:28, 26 June 2008 (UTC)

I think that index for air should indicate the air pressure (e.g., one atmosphere) and the absolute humidity. I haven't checked it out but I would suppose that the provided index for air is at one atmosphere and zero percent humidity. Also, maybe some mention should be given that refraction tends to follow material density. I believe that there are a couple weird (i.e., laboratory) examples where refraction values didn't follow density. (But I could be wrong.) - WayneH 20:46, 19 August 2008 (UTC)

I'd love to see a derivation from maxwells equations and surface boundary conditions —Preceding unsigned comment added by 217.72.84.137 (talk) 19:18, 20 March 2009 (UTC)

Question About Content
how can the wavelength increase or decrease, yet the frequency remain the same, given that frequency has an inverse relationship to wavelength?


 * The wave's velocity is altered at the boundary between the two media. velocity of wave = frequency * wavelength.  Frequency remains the same, but wavelength and velocity are both different in the two media.  Pfalstad 17:27, 23 October 2006 (UTC)
 * Indeed, the wavelength has to change, because light travels slower in a medium than it does in vacuum (or a sparse medium like air). One can imagine the wavefronts "bunching up" as they move into the medium where light propagates slower—the wavelength becomes shorter in the denser medium.--Srleffler 22:30, 23 October 2006 (UTC)

"The waves (water waves) travel more slowly in the shallower water." Why?

Incorrect definition
According to the article

"Refraction is the change in direction of a wave due to a change in its speed. This is most commonly seen when a wave passes from one medium to another."

The causal relationship stated is incorrect. The change in velocity (direction AND speed) is caused by passing from one medium to another. Also, by definition, refraction is the change in the direction of a wave passing from one medium to another with a different refractive index. So this is incorrect:

"This is most commonly seen when a wave passes from one medium to another." —Preceding unsigned comment added by 119.94.125.10 (talk) 15:17, 17 September 2008 (UTC)

I have only one question, why? There isn't a sensible explaination to the phenomena of refraction here. I remember vaguely there was a quantum mechanic explaination for this in the article some years back. —Preceding unsigned comment added by 218.186.12.204 (talk) 14:12, 1 February 2009 (UTC) I have added "easier explanation". It might help. 84.16.123.194 (talk) 12:45, 18 May 2009 (UTC) Consider the "first atom" concept related to the refraction of a beam of light. It is evident that there has to be an immediate stress/strain relationship in the reaction of the atom to the stress of the passage of the light wave/energy material. It would also have to be the sum of the stress over an integrated time interval. But since all the different light wave frequencies arrive with the same speed of propagation, it is doubtful that the speed of the passing of the wave/particle material is the guiding factor resulting the angular deflection of the beam.WFPM (talk) 17:34, 31 August 2010 (UTC)

Incorrect use of the term Velocity in the first line
The first line says:

"Refraction is the change in direction of a wave due to a change in its velocity."

BUT velocity is a vector quantity, meaning it has a magnitude and a direction. Therefore, the use of velocity is incorrect. To my understanding the sentence should either:

1. "Refraction is the change in direction of a wave due to a change in its speed."

or

2. "Refraction is the change in direction component of a wave's velocity due to a change in its speed component." (or words to that effect, as that is poorly worded).

may be wrong just though I'd point it out. —The preceding unsigned comment was added by Annannienann (talk • contribs) 14:00, November 6, 2006.
 * It's not outright wrong, but isn't good wording.--Srleffler 20:08, 6 November 2006 (UTC)
 * But different color frequencies of light waves arrive at a point of refraction at the same speed, and are nevertheless refracted by different amounts, So the light's frequency has to be a significant factor.WFPM (talk) 23:36, 1 September 2010 (UTC)


 * If the magnitude of a velocity, so |v|, is changed but the direction stays the same, the velocity (vector) has also changed. For a vector to change it is not required that both its direction and magnitude change - it can be either of them or both. --Felix Tritschler (talk) 15:37, 10 January 2021 (UTC)

Shouldn't wave refraction in the sea (water waves) get a look in?
we have nothing on the refraction of water waves. When I work out what it is, i'll write up on it (included in this article or seperate?)TDN 22:26, 23 November 2006 (UTC)
 * It's already in there. There is a paragraph on it, and two pictures.--Srleffler 05:46, 24 November 2006 (UTC)

Is it? I'll have a lookTDN 12:09, 10 December 2006 (UTC) Oh, it is. I wasn't looking carefully enough, but anyway, should there be a separate article about it? It is a different subject, coastal erosion, headlands, bays, beaches, etc. TDN 12:13, 10 December 2006 (UTC)
 * I'm not sure that wave refraction in water waves needs its own article. Look around carefully, you may find that there is already a lot of information on the behavior of water waves. Check out Ocean surface wave, Surface wave, and Gravity wave for various approaches to the subject. Coastal erosion may also be of interest.--Srleffler 20:08, 10 December 2006 (UTC)

sorry I can't make anything out of the water wave refraction diagram, maybe my poor sight, could anyone provide a more explicit image128.79.5.188 (talk) 18:37, 5 February 2015 (UTC)

Way too many vague images
At the moment, the images actually make the article appear more sporadic -- there's no real need to have the whole gamete of refraction if there's not that much expansive information. Also, the soda straw thing DOES demonstrate refraction, but it's definately a more finite example of virtual imagery. James S 19:50, 12 December 2006 (UTC)

Change in the speed of light
I got really puzzled trying to understand how could the speed of light be altered while reading this article, as I had long thought of it as the only universal measure. And took an hour thinking and searching to get the answer. Maybe linking this topic http://en.wikipedia.org/wiki/Speed_of_light#Interaction_with_transparent_materials somewhere could make it easier for people to understand it.

edit: Also, pure light would never undergo refraction or alteration of its speed? Sorry for not signing and editing this maybe not the way I should, I'm used to only reading wikipedia. thanks.

—The preceding unsigned comment was added by Japaa (talk • contribs) 23:09, 10 February 2007 (UTC).


 * "Pure light"? Photons, as opposed to electromagnetic waves?

The universal-measure part is only light in a total vacuum--I don't have a definite reason why light slows down in a medium (since it doesn't seem to lose energy), but...yeah. 24.16.140.208 (talk) 04:44, 15 February 2008 (UTC)


 * If you're going to believe that light slows down when passing through denser media, shouldn't you then have an explanation of how it manages to speed back up after it exits the media.WFPM —Preceding unsigned comment added by WFPM (talk • contribs) 11:16, 28 August 2009 (UTC) Oh yes, now I see it in the Dispersion section about the Speed of light.WFPM (talk) 11:35, 28 August 2009 (UTC)

I can't find an explanation of why it slows down (I might be missing it). Is it related to the presence of atoms and the influence of mass (gravity) on the passage of time?Ninahexan (talk) 04:10, 9 February 2011 (UTC)


 * It is true that it is not light that slows down. It is the interactions within the medium that slows it down. At least a partial explanation, contained within this article is here. I think I use to have access to a more complete explanation, but the speed of light article appears to be different in some parts (since the last time I looked). So, I recommend reading that article - it should be in there somewhere.


 * This article also contains this explanation, which is probably helpful:


 * "At the microscale, an electromagnetic wave's phase speed is slowed in a material because the electric field creates a disturbance in the charges of each atom (primarily the electrons) proportional to the permittivity of the medium. The charges will, in general, oscillate slightly out of phase with respect to the driving electric field. The charges thus radiate their own electromagnetic wave that is at the same frequency but with a phase delay. The macroscopic sum of all such contributions in the material is a wave with the same frequency but shorter wavelength than the original, leading to a slowing of the wave's phase speed. Most of the radiation from oscillating material charges will modify the incoming wave, changing its velocity. However, some net energy will be radiated in other directions (see scattering)."


 * Well, good luck. Steve Quinn (talk) 07:04, 9 February 2011 (UTC)


 * Also, I am talking about ordinary materials - not cold atoms and lasers. --- Steve Quinn (talk) 07:26, 9 February 2011 (UTC)
 * Visting the above italisiczed explanation once again, I see that this gives a good explanation of why light slows down in a material. I think I misunderstood the question (or something) (or I was tired?). Steve Quinn (talk) 07:21, 1 March 2011 (UTC)

I think this article misses the important point of why the speed of light is lower in a medium, its direction changes, or, how light travels in a medium. —Preceding unsigned comment added by 84.120.147.185 (talk) 07:56, 23 May 2011 (UTC)

Only when it hits the boundary at an angle
Assuming that refraction is only observed when the wave changes direction (rays change velocity) why does it not mention that it is only observed when it reaches a boundary (at which a speed change is observed) at an angle? anybody? —Preceding unsigned comment added by 89.218.46.165 (talk) 14:58, 22 October 2007 (UTC)

Blue Jays/Indigo Buntings are black
Someone should add that somewhere. I don't see that anywhere! ;) --HoopoeBaijiKite 18:29, 26 June 2007 (UTC)

Momentum of a refracted ray
Apparently there is a paradox here some say could be p= nE/c (Hermann Minkowski 1908) Or p= E/(nc) (Max Abraham 1909) where n= refractive index, E energy of light quantum, c= speed of light in vacuo.

Rudolf Peierls raises this in his "More Surprises in Theoretical Physics" Princeton (1991). Discussed in Nature vol 444 14 December 2006 p823-824 including experiments to resolve.

It's rare for physics to fall clearly and absolutely flat on its face and a discussion of this problem by an expert should be included in the main article.--Nick Green 19:55, 9 October 2007 (UTC)

No equation?
This article needs some equations. —Ben FrantzDale 02:30, 4 November 2007 (UTC)

Geometrical Optics
Do we need a more scientific explanation of this? Saying light changes direction due to a change in speed doesn't really explain the processes involved (and is effectively incorrect as the velocity only appears to change). I'm not suggesting an in depth essay with reference to quantum electrodynamics, but the oscillating dipole model could feasibly be included. Doctorp9999 (talk) 23:12, 23 November 2007 (UTC)

Refraction effect
There is a very popular effect called Refraction, by the magician David Penn. In case someone is looking for it, I thought I should add it to the the article as a disambig link. It is a commercial effect, so I will understand if someone wishes to remove it, as potential spam. However, I understand it is the fourth best selling magic DVD in the world at the moment (though I have yet to find a valid source to confirm it). I should add that I am not benefiting from the sale of these DVDs, nor do I advertise these. I am just trying to help Wikipedia expand. StephenBuxton (talk) 18:27, 6 December 2007 (UTC)

KY3R4N —Preceding unsigned comment added by 78.149.111.200 (talk) 21:45, 27 January 2008 (UTC)
 * My opinion is that is is too far removed from the subject of the article to be potentially confused. Most people know about the optical effect, and someone searching for the magic effect would certainly not be confused by arriving at the optical article. Am I right? Feel free to discuss further if needed; in the mean time, I am being bold and removing the link. TWCarlson (talk) 13:07, 14 September 2011 (UTC)

The 'Refraction in a Perspex (acrylic) block.' picture
It might be just me, but I think this picture is too vague, I can barely see what's the light source (I guess it's coming from the left side). I think we should get another picture like this (http://www.phys.ufl.edu/demo/6_Optics/A_GeometricOptics/HalfCircleRefraction.jpg sorry can't get a nice linkey) picture 131.155.108.56 (talk) 11:18, 9 May 2008 (UTC)

Near perfect sphere
File:Einstein gyro gravity probe b.jpg claims to be caused by refraction, but I see nothing in this article that would account for this effect. --Pascal666 18:33, 15 May 2009 (UTC)

Easier explanation
Look at image, or animation, of refraction and split velocity into horizontal (x) and vertical (y) component. Notice how horizontal (x) velocity changes.

It is smaller when ray travels into more dense space and vice versa. (There are more particles to slow down movement ...)

That way it is easier to grasp. 84.16.123.194 (talk) 12:33, 18 May 2009 (UTC)

Light Physics RE Refraction
Alright now my mind is having trouble grasping the photophysical events happening during refraction: Consider light, in the form of particulate photons, pouring down their projected path (lets say, emitting from a flashlight) in a cylindrical shape. As it hits a transparent glass surface at, say, a 40o-from-horizontal angle, it becomes bent. (This is just an inquiry, I will not do the calculations) We know this is true.

However let's say it were a stream of physical particles, passing through a "transparent" liquid media from a vacuum. It would not bend--it would keep it's physical path through the liquid if no gravity or other forces enacted upon it.

So...what property of light conditions it to bend around a corner as the photon particles hit a transparent glass medium?

In my (visual-working) brain, this seems to be a property of a force of attraction, due to the fact that stream of photons on the acute-angle side hit first, and as the photons hit the medium on the opposite side of the cylinder later, they become more attracted to the more numerous photons that have concentrated on the acute-angle side (light slows down as it hits the glass, which might cause an "accumulation" of sorts of photons). This attraction can cause the entire cone of light to shift IMO.

Is this plausible, nonsense, or something else? What photophysical properties am I missing in my hypothesis or misunderstanding?

I apologize if this entry is inappropriate to Wikipedia talk pages, please contact me if it is. Bullercruz1 (talk) 16:45, 25 December 2009 (UTC)


 * Better to ask on the Reference desk/Science. As the Talk Page is meant for discussing ways to improve the artilce it relates to.:-) Anyway, I think you have to consider light as waves not as photons in order for refraction to be easily understood. Perhaps Prism_(optics) may help. Then again, consider that as the 'photons' enter a denser medium they will slow down (as will EM waves) and this is the cause of the bending and refraction. --220.101.28.25 (talk) 11:49, 10 January 2010 (UTC)

Hubble red shift hypothesis
How about that the light interacts with the matter in some way that is proportional to the frequency of the light particles, being more in relation to the greater number of particles, but not reducing it's velocity of propogation. So the photon size is also related to the number of particles per reaction. And I'll give you a wild one where you suppose that the space of the universe is curved such that the farther away a source of light is the more it's light is refracted and the redder it gets. So how's that re the Hubble red shift?WFPM (talk) 22:50, 28 April 2010 (UTC).WFPM (talk) 22:53, 28 April 2010 (UTC)

recovered from revert
I reverted an edit but the editor added some material that might be useful for someone else--Profitoftruth85 (talk) 17:46, 25 May 2010 (UTC)

Light shining through clouds is not refraction
Concerning the caption: Sorry, but that is patently false (says me, a stranger on the internet). But seriously: the different angles observed in the photo are merely a geometrical effect of perspective. All rays can be followed back to the position of the sun in the photograph. This has nothing at all to do with refraction. — Preceding unsigned comment added by 192.12.184.7 (talk) 19:15, 24 August 2011 (UTC)
 * I agree with you. The image with the laser was replaced by the clouds picture, which is really beautiful, but not caused by refraction.
 * I'm going to revert the image. The one before was a clear example of refraction. (A source that proves me wrong would open the debate back up.) Nice catch - just one day after the image was changed! TWCarlson (talk) 12:31, 14 September 2011 (UTC)

Concerning the current caption: it's a bit poorly-worded and confusing ("air-plexi", etc). I'd like to change it to: "Light passing from air into acrylic undergoes refraction (lower ray) and relfection (upper ray)." Any objection/correction? Chconnor (talk) 03:11, 23 June 2016 (UTC)

Rearranged images
I went ahead and put some images in a gallery at the bottom. I also put clear space below sections to leave room for the image so the alignment with between the image and text didn't get messed up. I still think the article is disorganized and could use some work, but it is better than before, in my opinion. TWCarlson (talk) 13:10, 14 September 2011 (UTC)

Image
In the third image the angle of incidence is in fact π/2-θ, that is very confusing. --Chricho ∀ (talk) 00:00, 2 November 2011 (UTC)

History
Some is given at Snell's law and History of optics, but this could be greatly expanded. -- Beland (talk) 21:20, 10 June 2012 (UTC)

Incorrect use of the word waves at many places
This article is about the refraction of light and light is in the form of rays and not waves. So I think 'waves' should be replaced with 'rays' wherever necessary.Mangal.anukriti (talk) 17:31, 1 December 2012 (UTC)
 * Light rays are streams of photons. Photons are wave packets. --Felix Tritschler (talk) 16:01, 10 January 2021 (UTC)

Where's the Background of the theory
This article really needs some history about the idea of refraction. Like the inventor and his origin. I am not convinced this is a good article. :( — Preceding unsigned comment added by 76.18.163.201 (talk) 22:14, 1 May 2014 (UTC)


 * Refraction, like gravity and magnetism, was not invented. They have always existed since the universe was created.  Man was just unaware of them until they were discovered.  DieSwartzPunkt (talk) 16:13, 10 May 2014 (UTC)

Permanent vandalism?
"ashisbiswas" is in the top section, which I can't edit. Can any of you? 2604:6000:6BC2:9D00:919D:67B7:D577:F5F3 (talk) 16:41, 19 August 2014 (UTC)
 * Fixed. You should be able to edit it, too. There's no direct link for editing only the top section, but you can use the "Edit" tab at the top right to edit the whole page. &mdash;&thinsp; H HHIPPO  19:30, 19 August 2014 (UTC)

From vacuum to air
I don't see any mention in the article at present of what happens when light passes from the (near) vacuum of space into the earth's atmosphere. I presume that there is always some refraction if the light enters the atmosphere obliquely, and that this would be an important consideration in astronomical observations.109.150.6.192 (talk) 20:24, 27 February 2016 (UTC)

Since the light is entering a denser medium (air) than vacuum it will definitely undergo refraction while passing through each layer of the atmosphere. The same concept is used for the explaination of the twinkling of star and why sunrise is early and there is delayed sunset on viewing from earth. So there will always be refraction when light enters the earth due to different refractive indices. Alison Kennedy (talk) 17:10, 3 October 2017 (UTC)

Refraction of sound from highways has meteorological effects? :-\
To me, that would be the plain reading of "...the designing of urban highways and noise barriers to address the meteorological effects of bending of sound rays in the lower atmosphere.[7]". It's the current last sentence in the Acoustics section near the bottom of the article. The given source abstract mentions meteorological effects on sound propagation, but not vice versa. Unfortunately, I don't know enough on the subject to be certain whether "sound has meteorological effects" is true. If it is true, it's very interesting and should be explained - but if it's poor wording it badly needs to be rephrased. 2001:558:600A:4B:78C0:A7BD:D471:9409 (talk) 01:22, 5 March 2016 (UTC)

No Mention of Relationship with Temperature and Density
I have checked the wiki pages on Snell's Law, Temperature, and Density. Though I can see the mention of density in passing in relation to Descartes/Snell, there is no actual discussion of the direct relationship of refraction to density and its variation with temperature, thereby of refractive index to the temperature of a solid, liquid or gas, and specific example. Everyone is familiar with the phenomenon, if they have ever seen a tarmac road on a hot day, of course. I was seeking clarification and info on the potential extremities of the effect, such as how typical atmospheric gases alter with regard to refractive index given extreme variations in temperature. The page on temperature also omits any mention in its summary of effects of temperature on refraction et al. This seems a major oversight. 86.187.50.34 (talk) 18:18, 28 September 2016 (UTC)

Theory before Practice
From the "Explanation" section: "A ray traveling along the normal (perpendicular to the boundary) will suffer change in speed, but not direction. Refraction still occurs in this case (by Snell's Law as angle of incidence will be 0°). Understanding of this concept led to the invention of lenses and the refracting telescope."

This is quite untrue - lenses and telescopes were devised empirically long before a coherent theory of geometric optics was established; in fact it might be said they inspired the development of the theory. The wiki article on lenses says this about 13th century lensmakers: "Spectacle makers created improved types of lenses for the correction of vision based more on empirical knowledge gained from observing the effects of the lenses (probably without the knowledge of the rudimentary optical theory of the day)"172.103.138.179 (talk) 17:46, 3 October 2018 (UTC)-just a wiki reader, occasional (mostly grammar) editor.


 * Agree. I have now removed that sentence. Ulflund (talk) 05:25, 4 October 2018 (UTC)

Focus article on optical refraction
The subject of this article is now the general concept of refraction for any wave. When someone talks about refraction, though, it will 99% of the time (my estimate) be about optical refraction. A google search for refraction also only shows hits about optical refraction in the first few pages except for the pure definition of the word.

Would it be ok to change the subject of this article to that of optical refraction by starting the article with
 * In optics refraction is ...

still mentioning refraction for other types of waves briefly in the lead and give it a section in the article?

I think most readers would then find earlier what they are looking for. It would also be easier for newcomers to the subject to understand the concrete example of light rays compared to the concept of a general wave. Refraction (sound) has its own article but that for refraction for light which is a >100x bigger field of study (my guess) does not. Would this change be acceptable? Ulflund (talk) 04:38, 15 October 2018 (UTC)


 * I have started to rewrite the article and I think it works well keeping it general and have the optics case as the primary example. Thus, please disregard the above suggestion. Ulflund (talk) 21:14, 18 October 2018 (UTC)

General Explanation Section is Insufficient
The General Explanation section is insufficient. Refraction is observed in various forms of wave phenomena - to my knowledge all - but the section only explains light. 31173x (talk) 12:11, 20 February 2020 (UTC)
 * I agree. The very first two sentences of the lead explain "In physics, refraction is the change in direction of a wave passing from one medium to another or from a gradual change in the medium. Refraction of light is the most commonly observed phenomenon, but other waves such as sound waves and water waves also experience refraction." Then there's a "general" explanation section that covers only light. Then a section on light with a number of subsections. Then a section on water waves. Then a Clinical Significance section covering light, and then a section on acoustic waves, and then a gallery focusing only on light.
 * I've taken the liberty of organizing the article so that all the parts related to light are in the Light section. If someone comes up with a higher level explanation that's "general" to all types of refraction, then that will belong above the Light section Largoplazo (talk) 02:24, 1 March 2020 (UTC)

Oscillation of the free electrons inside an antenna is known. Oscillation of the orbital electrons inside a material is known as the fluorescent effect. Both have different results. — Preceding unsigned comment added by 84.205.231.44 (talk) 08:47, 5 January 2022 (UTC)

Question
If speed of light is constant then why it is said to have decrease due to refraction? — Preceding unsigned comment added by 2601:2c3:4201:d70:cc1a:c3c1:6db3:367b (talk • contribs) 23:10, 28 February 2020 (UTC)
 * It's constant in a given medium, or in a vacuum. The fact that it's different in different mediums and in a vacuum is what causes refraction. Largoplazo (talk) 01:55, 1 March 2020 (UTC)

Explanation for change of speed of light directly uses diffraction, plus, is not plausible
It is said that "Common explanations ... based upon the idea of light scattering ... are ... incorrect. Yet, it continues that the correct explanation is that light as EM-wave causes electrons to oscillate, which in turn emit EM-waves of their own. But that exactly describes Rayleigh scattering! Then, the slowing down is said to be caused by constructive interference of these re-emitted (so: scattered) waves with the original waves. Why would that be? - I watched the Youtube video given as (the only!) reference, and there they show that the superposition of two waves moving at different speeds moves at a lower speed than either of them. Great, but why would the re-emitted waves move at a different speed than the primary wave? --Felix Tritschler (talk) 17:17, 10 January 2021 (UTC) "may have wave packets that pass an observer at a slower rate" This is an arbitrary assumption. Is this observed elsewhere, in a TV antenna for example? — Preceding unsigned comment added by 84.205.231.44 (talk) 08:53, 5 January 2022 (UTC)

Semi-protected edit request on 27 January 2022
The second figure (showing angles etc.) is inconsistent with the text: in the text the angles are those of incidence and refraction, whereas in the figure they are the complementary angles. Under "More details" related to the figure, the first alternative figure listed is correct and should be used in its place. Philip G. Ratcliffe (talk) 17:57, 27 January 2022 (UTC)

Not done: - According to Jenkins & White the figure is correct. PianoDan (talk) 23:04, 27 January 2022 (UTC)

Question about Image in "General Explanation"
The first image in the "General Explanation" section (the second image in the "light" section) says light waves change direction in a slower medium because the wavefronts need to stay connected at the boundary as they get compressed in the slower medium.



A video by Fermilab describes how this explanation involves faster-than-light travel.

Are the two explanations exactly analogous? The image discusses compressed wavefronts while the video discusses compressed rows of "marching soldiers", but I feel like they're addressing essentially the same thing. Tamedu quaternion (talk) 19:00, 7 May 2022 (UTC).

"vacuum" vs "a vacuum"
, that was my bad for redoing my edit after a revert; I was not tracking history and I'd forgotten that this one I'd chosen to leave reverted. But now I feel compelled, due to my faux pas, to engage in a discussion. In response to your point: a simple Google ngram frequency is not the basis for any argument about what to use, except possibly demonstrating the complete absence of a phrase. There are just too many confounding factors, such as the phrase occurring in incomparable contexts (e.g., "in a vacuum tank"). I presume that was what the "_NOUN" suffix was meant to avoid (I'm not familiar with Google ngrams' syntax), but then, what about this: "light in vacuum" vs "light in a vacuum"? However a major omission in this approach is that there are contexts in which something is countable and others where it is not. We do not speak of "the speed of light in a water", when referring to a propagation medium. You could argue that "a vacuum" is shorthand for "an evacuated region" ("a vacuum" does get used in this sense), but I think this is too weaselly. My point so far: you need to distinguish uncountable versus countable use, and you have not done so in the ngram, making it completely valueless (not even accounting for Google's inaccuracies as illustrated here). Next: When we write in WP on technical subjects, it is appropriate to use more precise language as it is used by technical people, as long as this does not confuse or lose the average reader who can otherwise largely understand the passage. That is, if there is a strong trend among experts, we should use their phrasing in preference to that of journalists, science writers, and nonexpert authors. Don't get me wrong: I'm not saying "speed of light in a vacuum" is incorrect English, only that WP should give low weight to layperson usage in technical areas; otherwise we would end up with a worse mishmash of language use than we already have, based on which editor groups get involved in a type of article. Trying to filter more precisely, but still without differentiating by expertness we get a predominance omitting the "a": "light in vacuum" vs "light in a vacuum". But as I said, ngrams is not an argument: it just a tool to help direct an investigation. It would make more sense to take a sample of the expert literature, and see what the usage is. If we use Google Scholar: "speed of light in vacuum" (61800 hit) vs. "speed of light in a vacuum" (19900 hits), we can see that there is a strong bias in technical literature versus the average. It is again not definitive because we have not weighted this by reputability. Going to ones that I know, the SI Brochure uses the word "vacuum" many times (40?), not once preceded by "a". BIPM has a super-strong bias (492 hits vs 2 hits. NIST shows a less pronounced bias: 5070 hits vs 360 hits. Without an individual analysis of reputability of sources, if you buy the idea that in WP "what is appropriate" is not the same as "what is correct language", do you still feel as strongly that "speed of light in a vacuum" in a technical article is really not just a reflection of what would seem to be a minority use?  —Quondum 15:31, 25 January 2023 (UTC)
 * All in all, I have to conclude that you're correct. I'm not convinced by the particular Ngram you provided because it isn't clear that the corpus even had much of a sample of the version (with the final word being a noun) that it did report having. I say that because ordinarily Google Ngrams provides links under the chart to discover actual works containing the phrases being sought, and there are no links in this case!
 * However, I conducted additional examination, following you lead, leaving out the _NOUN specifier, and running the comparison of the two alternatives on Google Scholar. I see from that that I was mistaken. I've restored your version. Largoplazo (talk) 23:29, 28 January 2023 (UTC)
 * Thank you – I appreciate the thoughtful approach, especially as this one has plenty of room for different opinions and neither is "wrong". It has helped me dig into this more, and hopefully will make my life easier when I discuss this with others.  —Quondum 01:14, 29 January 2023 (UTC)

Redundant explanation
Remove redundant explanation: In the Light/General explanation section the phenomenon is explained the same way 2 times, the second one is just slightly more in depth. I suggest removing the first explanation.

REMOVE: Light slows as it travels through a medium other than vacuum (such as air, glass or water). This is not because of scattering or absorption. Rather it is because, as an electromagnetic oscillation, light itself causes other electrically charged particles such as electrons, to oscillate. The oscillating electrons emit their own electromagnetic waves which interact with the original light. The resulting "combined" wave has wave packets that pass an observer at a slower rate. The light has effectively been slowed. When light returns to a vacuum and there are no electrons nearby, this slowing effect ends and its speed returns to c. When light enters a slower medium at an angle, one side of the wavefront is slowed before the other. This asymmetrical slowing of the light causes it to change the angle of its travel. Once light is within the new medium with constant properties, it travels in a straight line again.

E440QF (talk) 09:02, 27 March 2023 (UTC)

Not done for now: please establish a consensus for this alteration before using the template. I don't think the two bullet points in that section ARE redundant - the first one explains why light slows in a medium other than vacuum, and the second explains why that slowing alters the direction of a beam of light in that medium. PianoDan (talk) 18:54, 27 March 2023 (UTC)


 * The two bullet points are not redundant with each other, the point is, just after the bullet points there are more in depth explanations for the same phenomena:

1. Light slows as it travels through ....

2. When light enters a slower medium at an angle ....

are redundant with

Explanation for slowing of light in a medium ....

Explanation for bending of light as it enters and exits a medium .... E440QF (talk) 21:34, 27 March 2023 (UTC)


 * OK, I understand the point you're making now. However, I still don't necessarily have an issue with the page as it stands.  There's the bulleted list that gives the basic points, and then detailed explanations of each bullet. If anything, I might SHORTEN the bullets a little but, but I don't think having the summary at the top of the section is a problem.
 * Fundamentally, I don't think this is an uncontroversial change, per WP:EDITXY, so it needs further discussion here, after which either an editor with permission to modify the page, or you, if you've made enough edits for permission, can do so. PianoDan (talk) 14:29, 28 March 2023 (UTC)

Redundant explanations
I totally agree with a former critic. It is unnecessary repetition. 2A02:A463:2848:1:E4B9:E90B:2C57:CB34 (talk) 13:26, 15 August 2023 (UTC)

Additional image for gallery section
Hi, I think it would be great to add this image to the gallery section of this article. The distorted square tilling shows the effect of a change in the refraction index quite well.

WorldWideWalrus (talk) 18:45, 28 November 2023 (UTC)


 * It's unclear what the image shows. It seems more likely that bright lines are caused by reflection, not refration. I've no idea why there's a distorted white grid. Maproom (talk) 20:55, 5 December 2023 (UTC)
 * Red information icon with gradient background.svg Not done: Please make your request for a new image to be uploaded to Files For Upload. Once the file has been properly uploaded, feel free to reactivate this request to have the new image used. Additionally, please find consensus for this image's use on this page. -- Pinchme123 (talk) 00:03, 8 December 2023 (UTC)

Semi-protected edit request on 22 February 2024
In the last paragraph of the "On Water" section, replace superscript lowercase o with actual symbol for degrees (90o → 90°) 67.42.15.205 (talk) 19:42, 22 February 2024 (UTC)
 * ✅ Largoplazo (talk) 22:49, 22 February 2024 (UTC)