"how fast light travels" vs "how slowly light travels"

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In the introduction, I noticed the refractive index is explained to be "how fast light travels" through a material. And yet, as the refractive index of a material increases, the speed of light in the corresponding material decreases.

Is it then clearer to explain that refractive index is "how slowly light travels" through a material? Put another way, the more refractive index a material has, the slower light passes through it - so can it be interpreted that refractive index measures slowness?

2601:80:C97F:EFD0:C901:84BE:3D6A:D71D (talk) 06:54, 23 December 2021 (UTC)Reply

Yes I would say so. But it doesn't really matter if we say "it measures slowness" or "it measures fastness", because if we look at it this way, "how fast light travels" is nothing but the quality or state of light being fast or slow. It would consider both the slowness and fastness of the speed of light. It has probably become a convention of saying that Refractive index is "how fast light travels". Arnav Raj Singh91 (talk) 02:57, 7 June 2023 (UTC)Reply

Inconsistency in complex refractive index

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We have defined $$\overbar{n} = n - i\kappa$$ but then in the formulae below we substitute $$\overbar{n} = n + i\kappa$$. Is it true that it only makes sense to define $$\overbar{n} = n - i\kappa$$ when we adopt the other convention, that $$E = exp(i(\omega t - k x))$$?

Optical extinction coefficient is not absorption coefficient?

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In the complex refractive index section, it states: "the imaginary part κ is called the optical extinction coefficient or absorption coefficient." But I don't think those can be the same because the extinction coefficient is unitless but the absorption coefficient has units of 1/length. Quicknick5k (talk) 00:08, 4 September 2024 (UTC)Reply

@Quicknick5k I applied a fix, please review. Sadly Attenuation coefficient is complete bogus.
I don't have Hecht with me, so I can't verify what it says on the subject. Johnjbarton (talk) 01:05, 4 September 2024 (UTC)Reply
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Independent of density changes caused by temperature, the refractive index is also directly affected by temperature. Although it's currently alluded to in in the article, this topic is not explicitly discussed. Linking to the page for the effect fills in this knowledge gap.

https://en.wikipedia.org/wiki/Thermo-optic_coefficient Zamicol (talk) 22:52, 6 August 2025 (UTC)Reply