Talk:List of refractive indices

8 Dec 2003

This list is meaningless and misleading and, I suspect, wrong in many cases. For one thing, you have to specify a wavelength in order to give the index, since all realistic materials are dispersive (i.e., index varies with wavelength). Second, you must cite your sources, especially since measurements of indices aren't always the same to three decimal places between experiments. Third, some of the materials are just plain wrong. For example, copper (a metal, which will have a complex index with very large magnitudes in both the real and imaginary parts, at least for visible wavelengths) is listed with an index of 1.675, the same as copper oxide! Ditto for aluminum (perhaps alumina was intended?). Steven G. Johnson 22:52, 8 Dec 2003 (UTC)

Note that these criticisms applied to the list of indices in the original version of this article. Steven G. Johnson 23:06, 17 Mar 2004 (UTC)

I agree with your criticism of the lack of citations 100%. Gfutia 22:34, 6 October 2007 (UTC)

PS. A good reference for this sort of thing would be the Handbook of Optical Constants of Solids by Palik.

A very large table of simple values is avaliable at http://www.robinwood.com/Catalog/Technical/Gen3DTuts/Gen3DPages/RefractionIndexList.html . Could some expert comment or post a link to it on the article? Thank you.

Unfortunately, this list is meaningless because it doesn't give the wavelength(s). Since it is for 3d modelers, I'm guessing it is intended to be at optical wavelengths, but in this case its metallic indices seem questionable to me. Since the page gives no reference, it is impossible to know where he got them and how accurate they are (or, indeed, if they are just fudges to get good-looking results in ray-tracing tools). —Steven G. Johnson 22:52, Nov 5, 2004 (UTC)

It is standard practice to quote the index at nD²⁰, that is the sodium 'D' doublet is used at 20 C. You will see such values tabulated as nD²⁰. Askewmind | (Talk) 01:40, 24 Mar 2005 (UTC)

That may be common practice, but that doesn't mean you can assume any random indices someone posts on the Internet, without citing sources, are at that wavelength. —Steven G. Johnson 18:07, Mar 24, 2005 (UTC)

Very true, Steven, I was not trying to say we don't need references, wikipedia has no credibility since we all can write whatever we want. I was mainly considering the fact that we need some sort of consensus whe we point the refractive index of substances. References are always required. I recommend Sigma-Aldrich for most of the common chemicals. Askewmind | (Talk) 18:23, 24 Mar 2005 (UTC)

The entries for HgS, GaAs, and Si do not make a lot of sense because they are either poorly transparent in the visible range, or not at all. So, yes, they have high indeces of refraction, but no lens for the visible range would be made from them. The values can be used to estimate surface reflectance off the air-material interface, but the imiginary component becomes important if it's not pretty small. Could a new column with the imiginary index value be added to the table? Metals are very complicated, the two index components can change a lot over the visible range, and are best shown with a plot, not just one data point. 131.252.124.185 22:05, 29 September 2006 (UTC) David

This list would be more useful if every value listed had some citation that gave a link to relevant and trustworthy external material. These numbers have little meaning taken out of context. Each value needs additional information about both the material and the wavelength. Selain03 20:51, 2 February 2007 (UTC)

Complex Number?

How does a pair of two different physical properties--refractive index and absorptivity--constitute a complex number? Was this concept taken from scientific literature, or from the mind of a creative contributor? It reminds me of Hawking's "complex time". I would rewrite this myself, but I see the person who added it is a professor of Applied Math and has a background in Physics, so I'll leave it up to him.

It is completely standard; look in any textbook. Because Maxwell's equations are linear (for linear materials), it is correct and convenient to write oscillatory fields with a time-dependence exp(-iωt) instead of with cos or sin (with the understanding that the "physical" solution is the real part of this). Then, in a uniform medium, the spatial dependence becomes exp(iωx * n/c), where n is the index. Thus, the real part of n gives an oscillatory term, and the imaginary part gives an exponential decay. Equivalently, if you look at how the conductivity σ of a material enters Maxwell's equations, it can be equated with an imaginary dielectric constant ε=iσ/ω for time-harmonic exp(-iωt) fields. —Steven G. Johnson 17:22, Apr 7, 2005 (UTC)

Stevnj is correct. I'm more familiar with the complex representation manifesting itself as complex permittivity or a complex impedance, but not of free space, here is the reference article. Impedance of free space. Gfutia 22:39, 6 October 2007 (UTC)

neuron?

Index of refraction for neuron. A nerve cell, is this correct?

wavelength or frequency ?

Someone said that through refraction, it is the speed (so the wavelength) which modifies, not the frequency. If that's so, I think it would be more accurate to give the frequency of the wave as related value, not the wavelength.

When people give a wavelength associated with an index of refraction, they normally mean the frequency associated with that wavelength in vacuum. (You're right that the wavelength changes inside a material, whereas the frequency is preserved. However, the vacuum wavelength is much more conventional to give at infrared and higher frequencies. A note about this in the article would be nice, or perhaps just a link to vacuum wavelength.) —Steven G. Johnson 21:50, Jun 10, 2005 (UTC)

Are you sure about this statement. "The wavelength changes in side of the material, where as the frequency is preserved?" I agree that wavelengths should also be given for each measurements since due to dispersion (optics) the index of refraction is dependent of the frequency/wavelength of the light. Gfutia 22:34, 6 October 2007 (UTC)

Yea. Wavelength means wavelength in vacuum. It does change in media but in terms of light wavelength(in vacuum) is what everyone uses this to discuss light frequencies. Everyone knows 500 (nm) light is green light, no one coverts this to frequency, f = c/lambda and calls it 600,000,000,000,000 Hz = 600 PHz light. Gfutia (talk) 06:33, 20 February 2013 (UTC)

Crystal

Could someone add information to this page and to lead crystal about the index of leaded glass? —Ben FrantzDale 20:31, 5 June 2006 (UTC)

If your think the information belongs on this page, you should find a source for the information and add it. Gfutia 22:34, 6 October 2007 (UTC)

Anon - nonsense ?

Just think about ether as no cristal or water, but as lead travelling...just as our core Earth Heart swingles bellow us like a pendulum...

http://en.wikipedia.org/wiki/Pendulum http://www.paradox-paradigm.nl/The%20electron.htm

A better source of information?

After reading the discussion page for this article, I searched for a better source of information regarding refractive indices. I found a site that gave a few formulas to calculate the index of refraction. I recommend including the formulas in the article or listing the site under 'external links'

http://emtoolbox.nist.gov/Wavelength/Documentation.asp

Smithg86 19:25, 22 September 2007 (UTC)

If you think this is of value, you should include it in the article. Gfutia 22:34, 6 October 2007 (UTC)

Feel free to include it in #External links, but don't use the numbers that come out in the table. Empirical data should always be used in preference to a model that only works (say) around 20°C, or even a decent model (one exception is heat capacities near 0 K, where the current model is probably more accurate than any data we can get). ⇌Elektron 15:38, 23 September 2007 (UTC)

External links are not references. Gfutia 22:34, 6 October 2007 (UTC)

Column Additions

Addition of the wavelength columns

The refractive index of materials is dependent on the wavelength used for measurement due to dispersion. A claim was made that the Sodium D light at 589 nm is the standard used for measurement. Although this is likely true, I still feel that the wavelength column should be added to the table. The column would force the adder to confirm that measurement was made at the standard wavelength, and if it was not, the material could be specified for an alternative wavelength. The column would also reinforce to the reader the dependence between wavelength and refractive index.Gfutia 23:04, 6 October 2007 (UTC)

Addition of the reference column

It is not the job of the reader to verify the information source. I think all people on the talk page agree that each item in the table needs to have a verifiable source. Source citation is essential to the credibility of the information. Since each item needs a source, a good way to do this would be to add a reference column to the table. Also, External links are not references, they are just place for the reader to turn to for additional information. External webpages are fine sources, but just adding it as a link is lazy, a well known referencing standard such as one from IEEE or Harvard referencing should be used. I recommend just going the simple route and using the Wikipedia:Citation templates.Gfutia 23:04, 6 October 2007 (UTC)

External link suggestion

I would like to suggest to add an external link to RefractiveIndex.INFO. This website contains dispersion formulas for many materials and has a simple interface for finding a refractive index value for a specified wavelength. Wikipedia's policy does not allow me to add the link myself as I am the author of this site. Please, add a link if you find this site appropriate. Thanks! Mpolyanskiy (talk) 00:32, 1 September 2008 (UTC)

Radio frequencies

I added a sourced mention to refractive index formulation for radio frequencies [1]. User Materialscientist reverted it, on the grounds that it's "irrelevant (low frequency)". I referred him to the motivating application (namely, GPS), and undid his reversion. Materialscientist reverted it again, arguing at this time that "for low-frequency applications see Relative static permittivity". But permittivity is obviously distinct from refractivity or index of refraction; their relationship, however obvious, is non-trivial, requiring a third concept (permeabilitty). I undid the reversion once again.

Materialscientist, please let other people contribute! Let me remind you that "Reversion throws away proposed changes by the other editor (even those made in good faith and for well intentioned reasons), rather than improving upon them or working with the editor to resolve any differences of opinion. Therefore reverting is not to be undertaken without good reason." -- "Try to avoid deleting things as a matter of principle."

There really should be some penalty for editors that revert bona fide sourced contributions, like you are doing. I hope you understand how frustrating and time-wasting unnecessary reverts can be, and realize that these repel potential contributors to Wikipedia. You might not see the need for the proposed edit, but please realize that you are not aware of all the possible nuances of the subject, so if another editor think the edit is necessary, don't revert it unless the edit harms the article. Otherwise people will start scraping from the Wikipedia claims that they find unnecessary, however true and informative they might be, simply because they are unaware of the facts mentioned. See Wikipedia:Revert only when necessary. —Preceding unsigned comment added by 128.138.43.254 (talk) 04:46, 30 August 2009 (UTC)

1. You are more than welcome to contribute, if the contribution is constructive.
2. Please sign your posts with four tildas.
3. You could come to this talk before reverting me, not after. Please discuss the article content, rather than what I might or night not possibly see.
4. The added sentence "At radio frequencies (as needed in, e.g., GPS), see [7] for a recent, thorough, review" has several problems:(i) Incomplete; (ii) The refractive index is defined in the lead for visible range (589 nm) rather than radiowaves, (iii) A common convention in physics is to refer to refractive index as high frequency value and to "static dielectric constant" for low-frequency values; this is not about underlying science but just a matter of terminology (iv) The added reference advertises itself as "thorough", though it is a conference proceedings and as such would not qualify for reliable source in an encyclopedia; (v) The added link is dead; (vi) As I can not verify the content, I can only guess that it is about air, which would be much too narrow for this article. Materialscientist (talk) 05:27, 30 August 2009 (UTC)

1) Thanks. 2) Why bother if unsigned posts are automatically signed by a bot?

Because it is a basic WP rule of politeness. Because there are tons of unsigned post on WP. Bots fail every now and then. Materialscientist (talk) 23:20, 30 August 2009 (UTC)

3) (i) "You could come to this talk before reverting me, not after." I use your own words. (ii) I was referring to your behavior because it is typical of "revert trolls", defined as editors with an excessive rate of type I errors (i.e., the error of undue skepticism, e.g., a court finding a person guilty of a crime that they did not actually commit). Such behavior should be discouraged at Wikipedia.

You're ignoring my comment on being impersonal.

4) (i) if it's incomplete, complete it or tag it as such -- only revert if it is detrimental or unsourced, none of which applies to my edit. (ii) your clam is plain wrong! See, e.g., ray tracing (physics). I can cite as many articles as you want defining refractive index for radio waves! To convince yourself, just search for "radio refractivity" at google scholar [2]. It's really frustrating that you don't hesitate to waste one's time before trying something as easy as that. (iii) again, this might be the terminology in your field, not in everyone's else! Please recognize that you are acting as if you are trying to impose your view! (iv) again, please do you homework before wasting one's time: Wikipedia:Reliable_sources#Scholarship says that "The scholarly acceptance of a source can be verified ... by checking the number of scholarly citations it has received": the source given has been cited several times by academic peers, see [3]; furthermore, Wikipedia:Verifiability#Sources says that "academic ... publications are highly valued and usually the most reliable sources in areas where they are available", and the cited article is an abridged version of a 90+ page university report; I preferred to cite the article rather than the report because it is available online; both could be cited, though. Finally, the author has credentials, because he was the convener of the "Working party on refractive indices of light, infrared and radio waves in the atmosphere" of the "International Association of Geodesy" . (v) the whole website (www.fig.net) is down, presumably only temporarily, because it belongs to an international federation; you can see a cache available at [4]; deadlink is not a reason for removing a citation to a publication available elsewhere (e.g., your library)! (vi) please explain what you mean by "too narrow"; if you don't see the need for the modification, please respect and trust other contributors that do see the need for it! It's a sourced statement, for heaven's sake! 5)There really should be some penalty for "revert trolls" that discard legitimate, well-sourced statements. It's a pity that such editors keep wasting the time of other contributors. Your behavior illustrates very well this issue. 128.138.43.254 (talk) 18:36, 30 August 2009 (UTC)

(i) I did follow your advice and reverted your edit because it was unsourced. (ii) Refer to the lead of this article, which defined its scope. It is impossible to cover refractive index for all frequency ranges in one article (iii) Refer to Lide, D. R., ed. (2005). CRC Handbook of Chemistry and Physics (86th ed.). Boca Raton, Florida: CRC Press. ISBN 0-8493-0486-5. and please do not try to assume scopes of my field (iv) You're missing a magic word "peer-reviewed" and focus on atmosphere. Please understand that "air" is only one entry in this list, and its refractive index should be discussed in atmopsheric or GPS articles. (v) Deadlink is a valid reason for removal if the source has never been assessed before. (vi) Thank you for providing the cache link. The document is useful, but technical and dedicated to atmospheric sciences. I am fine to include it somewhere, but only when the server is up, and I can't think of a good place for this link. Definitely not in this article, as it merely discusses technical aspects of empirical fitting of the refractive index variations vs. some parameter, it does not provide clear values for the "List of refractive indices". Materialscientist (talk) 23:41, 30 August 2009 (UTC)

Since I know almost nothing about this subject, I am not sure that either of you will welcome my comments, but here they are. The information in the added link, which worked fine just now, seems encyclopedic to me--a summary would seem to be a good addition to the project. OTOH, it does not seem to fit in the body of this article, since it does seem to be off-topic, as the topic is defined in its lead. I suggest that you consider including it in the end material, perhaps as a "See also" link to a new article or a to new section in Refractive index (and wouldn't Feynman have wanted some QED in there, even if just a "See also"?), perhaps as an "Additional reading" link to the external source with just enough text to explain the subject. I would also suggest that your mutual sniping was ill-considered.--Hjal (talk) 06:25, 1 September 2009 (UTC)

Thanks for your constructive comments, Hjal. Now past one week I must admit that my comments were unnecessarily personal; please accept my appologies, Materialscientist. Moving on with the issue, it seems to me that the title of the article does not match the scope set in the lead of the article -- do you agree that the former is much broader than the latter? If so, we need to rectify either one. We could rename the article to "List of optical refractive indices", but my preference is to keep the title as it is and enlarge the scope in the lead. That way we could include the citation originally proposed. What do you think? 128.138.43.211 (talk) 07:10, 5 September 2009 (UTC)

No problem. In my experience, most physicists see "refractive index" pertinent to optical frequencies (I understand atmospheric sciences are different), and your link does not seem to fit into "list of values" - it is rather on variation of n for air with temperature, etc. Thus, even if we squeeze it in here, no-one would read it. Why not placing it into the GPS or Atmospheric diffraction article. There, they would be more visible too - I guess nobody reads this abandoned article. Materialscientist (talk) 07:26, 5 September 2009 (UTC)

References

Table sort sequence error

The refractive index column seems to sort Silicon carbide and diamond the wrong side of each other. - Rod57 (talk) 12:59, 1 December 2020 (UTC)

Many of the Other materials should be under Solids at room temp

eg Cinnabar, Sapphire, cubic zirconia. - Rod57 (talk) 13:29, 1 December 2020 (UTC)