Talk:Prism (optics)

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[edit] Bit Rot

This page is in serious need of work. Some mystical rubbish has crept in here about refraction of Dark.

I don't like to flag work needing attention, but I'm battling on other fronts right now. — Xiong熊talk* 23:29, 2005 August 7 (UTC)


The caption to the first image doesn't make sense to me — what does such that the colored edges meet mean? I will change this unless someone can explain. Michael Fourman 07:18, 6 March 2007 (UTC)

I don't have time to think about it right now, but it sounds similar to some of the things discussed in the Theory of Colours article. The gist of that is that the familiar spectrum we think of coming out of a prism only appears if the beam of white light is narrow. If the beam is wider, one sees a white beam with coloured edges come out of the prism, not a traditional spectrum. Goethe (the author of Theory of Colours) developed a theory of colour based on this. While Newton's work best addresses the physical properties of light, Goethe's model perhaps better deals with the peculiarities of colour perception in human beings.--Srleffler 08:11, March 6, 2007 (EST)

[edit] Shape of Prism

Note: "Traditionally, these prisms are built with a triangular base and rectangular sides." Shouldn't this be rectangular base with triangular sides? -- 217.129.246.156

Sorry, no. The object you describe is a pyramid.
In geometry, a prism is any solid generated by extrusion of a polyhedron. The classic optical prism is generated by extruding a triangle, which is its base. It is a right prism, so its sides are rectangles. — Xiong熊talk* 02:05, 2005 August 26 (UTC)

What are the shortest and longest spectrum wavelengths capable of being dispersed by a prism?

Any wavelengths that can be transmitted through the material of the prism can be dispersed. Typical optical glass transmits from somewhere in the near ultra-violet up to a few microns wavelength (near infra-red). Other optical materials may transmit a wider range of wavelengths.--Srleffler 12:17, 23 February 2006 (UTC)

[edit] DSOM

I removed the following from the article, but perhaps we should have a discussion about it:

Prisms in popular culture

This keeps popping up in the article. The fact that someone used a prism on an album cover once is just not that important a fact about prisms, even if the album does happen to be especially famous. It is barely justifiable to even link to DSOM from here. Since the person who added the above felt it was confusing having a link in the See also section, I removed the DSOM reference from the article altogether.--Srleffler 02:33, 27 September 2006 (UTC)

[edit] what are prisms made from?

I came here to find out what prisms are made from, and I still don't know. glass? crystals? —Preceding unsigned comment added by Raw melk (talk • contribs)

It says "the glass of the prism" in the 2nd paragraph. But any transparent material will do. Han-Kwang 22:14, 23 November 2006 (UTC)
Yes, typically glass, but sometimes prisms can be made out of plastic instead. Prisms made out of crystals are also pretty common; especially for polarizing prisms.--Srleffler 05:41, 24 November 2006 (UTC)

[edit] Confusion

In the beginning of the article, it is said that "In optics, a prism is a device used to refract light, reflect it or break it up (to disperse it) into its constituent spectral colours". From this I would suppose that there are refractive, reflective and dispersive prisms. But later in the article, prisms are classifed as reflective, dispersive or polarizing. Could we make this more clear? Jorge Peixoto 10:58, 29 November 2006 (UTC)

Fixed. Han-Kwang 11:20, 29 November 2006 (UTC)

[edit] Prism definition

Srleffler reverted two changes that I made:

  • with flat polished surfaces that are not parallel to each other. - What is wrong with this? Anything that classifies as an optical prism should have at least one pair of flat optical surfaces that are nonparallel. Otherwise it is simply called a substrate, optical window, or rod. From the Melles Griot catalog: "...blocks of optical material with flat, polished sides arranged at precisely controlled angles..."
  • If not indicated otherwise, the term prism usually refers to a triangular prism - My main argument is that about half of the articles that linked to prism (optics) use wordings similar to "the light was sent through a prism" and were actually referring to triangular prisms to disperse light. (I changed most of them to direct to triangular prism (optics)). Although in optics catalogs such as those from Melles Griot, Newport, and Thorlabs, prisms are always specified as "right-angle prism", "equilateral dispersing prism", "penta prism", it seems that in colloquial usage the word "prism" most often refers to a triangular dispersing prism. A google search on "prism light" confirms this. I think the article should respect this common usage. Maybe the wording "usually refers to" was too strong; how about "in colloquial usage, the term 'prism' most often refers to a triangular dispersing prism"?—Preceding unsigned comment added by Hankwang (talk • contribs) Nov. 30 2006
  • My main reason for the change to the first sentence was that it failed to specify that a prism is an optical device, and failed to give any indication of its purpose. Instead, it said that a prism is a "transparent object...with flat polished surfaces that are not parallel to each other". Function is more important than form: A prism is an optical device that refracts light at flat optical surfaces. Also, in general some of the surfaces can be parallel to other surfaces. Your version implied that this was not the case. I understand your concern though with distinguishing it from a window or flat. We can probably come up with wording that addresses both of our concerns.
  • Yes, "usually refers to" was too strong, and isn't true within the field of optics. I'm fine with a statement about common colloquial or historical usage.--Srleffler 15:31, 30 November 2006 (UTC)

[edit] Newton

There have been several attempts to rephrase the paragraph on Newton, which I believe change the intended meaning of the paragraph. If I am right, there are a couple of sentences that are poorly phrased, which are leading to confusion. I would rephrase them, but need confirmation that my interpretation is correct. The section in question reads:

Isaac Newton first thought that prisms split colors out of colorless light. Newton placed a second prism such that a separated color would pass through it and found the color unchanged.[citation needed] He concluded that prisms separate colors.

I believe what is intended here, is that Newton at first thought that prisms produce colors in some fashion from light that is intrinsically colorless (white). By performing the experiment described, he convinced himself that prisms separate preexisting colors, and therefore that white light is not colorless, but rather is composed of a mixture of colors. If I am right, the paragraph needs to be rephrased, because other editors seem to routinely miss the fact that a change in Newton's point of view is seen here. What is needed is a confirmation of this statement from an external source, so we can verify what meaning was intended.--Srleffler 00:31, 15 March 2007 (UTC)

Sorry, but this is my fault. Quite some time back, it was I that added the word 'colourless' in the place of 'white' light. I did this because today it is often assumed that colourless light is white. Someone subsequently didn't see the sense of it, and rewrote the sentence by adding the phrase, 'first thought' -- and this changed the meaning enough that it devolved into the subtle shift you noted above. There is no change in Newton's thought here from colourless to white. He assumed it was white all along, and used the experiment crucis to prove his point. Johnrpenner 16:43, 7 July 2007 (UTC)

[edit] Explanation first, then history

I have moved the "history" section back after the "how prisms work" section. It is often better in science articles to explain the substance of a topic before the history of the subject. How things work is fundamental in a science article. The history of how something was discovered is of secondary importance. Additionally, the text in the "history" section is not really a history of prisms, but a much narrower bit of history about how the spectrum came to be understood using prisms. --Srleffler (talk) 05:27, 26 April 2008 (UTC)

nice edit. now we're two steps closer to the great overhaul this article needs. Johnrpenner (talk) 15:17, 26 April 2008 (UTC)