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I've just used "colored light" in the title to my History of Science and Mathematics SE question Did Newton every use filtered or prism-dispersed colored light to view “Newton's rings” or other thin-film interference effects? and I'm simply wondering if there available a different way to say it.

"Colored" is a valid and accurate term in this technical context but the word also has a substantial history when applied to people (discussion). I'm not saying it necessarily needs to be replaced in this particular case, I'm simply curious if an alternate exists.

Question: Is there a term for wavelength-restricted or filtered light having a fairly pure color besides "colored light"?


Thesaurus.com; colored provides terms that obviously won't work: dyed, flushed, glowing, hued, shaded, stained, tinged, tinted, washed

Merriam-Webster thesaurus/colored returns: chromatic, colorful, kaleidoscopic, motley, multicolored, multihued, polychromatic, polychrome, prismatic, rainbow, varicolored, varied, variegated, various

and if the wavelength range were very narrow one can use monochromatic but usually we don't use monochromatic to things like wide-band filter (e.g. stained glass, gel filters).

I then turned to Lennon's lyrics to Lucy in the Sky with Diamonds and there's "Cellophane flowers of yellow and green" and "With plasticine porters with looking glass ties" which invoke colorful images but offer no help here.

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  • @WeatherVane yes there are challenges when terms are used one way in technical contexts and another in common usage. We can say something weighs 10 kg and people will know what you mean, but weight and mass are fundamentally immiscible. In optics or physics proper there is no exact definition for monochromatic, but most folks would call a laser monochromatic and many would include a low pressure mercury or sodium light. Fewer still would include a single color LED as a monochromatic light source. Almost none would call a "band" monochromatic.
    – uhoh
    Jun 25, 2021 at 0:46
  • If there is no exact definition, does that not make a succinct title with its meaning expanded at greater length (five words replaced by one)? It seems open for you to define what you are exploring. Jun 25, 2021 at 0:52
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    Look up Broadening in laser systems; Wikipedia, which seems to imply that true monochromatism is a fiction, and that the only practical usage of 'monochromatic' is (Dictionary.com, my bolding) 'Having or appearing to have only one color'. This is the everyday English usage, appropriate on ELU. For more precision, you'll have to use 'covering the narrow range of wavelengths λ1 - λ2'. Jun 25, 2021 at 13:27
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    narrow-band is often used in wireless for a small range of frequencies. It may not fit exactly, but as others have said you'll struggle to find a better word. And if you're looking for a technical term, you should ask in a technical forum.
    – Stuart F
    Jun 25, 2021 at 14:07
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    @StuartF narrow-band is good; that might be something that most people can at least get some idea from in conjunction with "filtered" as it speaks to what kind of filtering we're talking about. If the question opens up again please consider posting that as an answer, thanks!
    – uhoh
    Jun 25, 2021 at 14:34

2 Answers 2

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Monochromatic really is likely to be the best word.

Cambridge has using only black, white, and grey, or using only one colour as the primary definition, with (Physics) (of light) having a single wavelength... as secondary.

I work in optical physics so use the 2nd definition all the time definition) or "of a single colour". It's never really true anyway, as linewidths never really reach zero, but for lasers and atomic lines is close enough.

The more general meaning does come into the optical field with thing like colour-separation filters (RGB or CMY filter sets for example). Each clearly has a broad bandwidth, but translates to one class of pixel or one ink in reproduction.

The downside is that "monochromatic" all too often refers to greyscale or black-and-white. But you mention gels, so here's an example of a tutorial on stage lighting that refers to "monochromatic lighting schemes"

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  • I note that in Synchrotrons used as a light source for experiments (for example) there are devices called "monochromators" which "transmit[s] a mechanically selectable narrow band of wavelengths of light or other radiation." Pretty strong evidence for the technical use of the term, and also speaks to the OP's concern that "Almost none would call a "band" monochromatic." Many years ago a friend of mine moved to Brasil to work with one of these particle accelerators in the study of Biology.
    – Yorik
    Jun 25, 2021 at 17:12
  • @Yorik I have a visible/near infra-red monochromator at work, and have used many before. As I said, I'm more familiar with this use. But the non-physics use is also valid, and my last link demonstrates that it's used just as the OP might like, for wide bands (I also have a selection of theatrical gels here, with their spectra, and most bands are indeed wide)
    – Chris H
    Jun 25, 2021 at 19:08
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The term is coherent light, or light that is frequency coherent.

Lasers do much of their magic because the light is generated in such a way that the light is made all at once and also of the same color. The waves are matched peak for peak and valley for valley. This can be done since all the waves are of the same frequency. The waves are temporally coherent, that is, matched peaks and valleys. They are also spatially coherent, that is, in frequency. I lood forward to being corrected on one of these.

from https://www.wordnik.com/words/coherent%20light coherent light n. Light in which the phases of all electromagnetic waves at each point on a line normal to the direction of the the beam are identical. Coherent light is usually monochromatic, and the most common source of such light for practical uses is from a laser. n. Light of a uniform wavelength and phase; as used in lasers

Also http://amasci.com/miscon/coherenc.html

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