Why are people ok with calling IR and UV "light" but not x-rays or radio waves

[Bohandas]

Since infrared and Ultraviolet are commonly acknowledged as "light" in day to day speech, why isn't the rest of the electromagnetic spectrum?

If it was simply a matter of distinguishing the rest of the electromagnetic spectrum from visible light I could understand it. But since infrared and ultraviolet are still acknowledged as light I don;t see why radio waves and x-rays aren't too

[gomipile]

Probably because they're close to visible. And because they're close to the visible spectrum, those wavelengths share a lot of optical properties with visible light.

For example, most 1cm thick barriers that are totally opaque to visible light are also totally opaque to UV and both near and deep IR.

Consider, say, a large sheet of black HDPE. It will block visible, UV, and all IR, but let hard X-rays, gamma, and everything with a wavelength longer than about a millimeter pass through.

Also, most optical equipment works fine with near IR, as long as it doesn't explicitly filter it out. It's possible to use familiar optical principles to make refractive camera lenses for everything between UVC and deep IR, as long as you're careful about the specific materials.

Go too far past UVC, and you can't make practical refractive optics anymore.

[Bohandas]

Go too far past UVC, and you can't make practical refractive optics anymore.

Aren't most high-end optics reflective anyway because of chromatic abberration?

[Khedrac]

Also, there are animals on earth that see into the near ir and uv (and arguable the no-so-near ir if you count the heat sensors on pit vipers) - we don't know of anything that "sees" with the more extreme wavelengths.

[DavidSh]

Aren't most high-end optics reflective anyway because of chromatic abberration?
That depends on the application, and what you mean by "high-end". Nikon makes some pretty pricey refractive camera lenses. A small sample of the thermal imaging cameras I see advertised on the internet all use lenses.

[Chronos]

And for that matter, reflective optics are very difficult for X-rays, too (and pretty much impossible for gamma).

That said, physicists do consider the entire electromagnetic spectrum "light".

[Manga Shoggoth]

It's entirely possible that back in the day the sources used for infra-red and ultra-violet also produced a lot of visible light as well, so they were lumped in with the visible spectrum. Microwaves and X-Rays were produced and detected by different methods.

[Rockphed]

Aren't most high-end optics reflective anyway because of chromatic abberration?

There are ways to have your primary focusing be both aberration free and refractive. At the same time, if you just care about a small frequency range and your lenses are aberration free enough over that range then refractive works just fine. Refractive also has the benefit of fitting everything in a line so you can easily just point your camera where you mean to look.

Edit: and in most scientific circles I have participated in, any electromagnetic radiation got called "light" just fine. I remember a class on EM propagation where we started by discussing Maxwell's equations as they related to radio waves and then moved into optics. We spent a fair bit of time discussing the assumptions that ray optics requires, but those assumptions apply just as much to a 30 meter radio dish as to a 3 meter panel for the JWST.

[CarpeGuitarrem]

Probably because they're close to visible. And because they're close to the visible spectrum, those wavelengths share a lot of optical properties with visible light.

Yeah; notice that both of them have colors associated with them: IR is close to red, UV is close to violet. From a layman's perspective, they're close enough to register as a special kind of light that's right on the edge and not quite visible to human perception.

[Murk]

I disagree with the premise of the question to begin with: that people are "not ok" with calling x-rays or radio waves light in day-to-day speech.

I don't think that's true. I think people are ok with whatever word for x-rays or radio waves, as long as that's the word the big smart scientists tell them to use. Big smart scientists communicate with the normal folk through things like school text books and wikipedia pages.
If school text books and wikipedia pages start calling x-rays "x-light" from now on, within a generation everyone would call it x-light, and people would absolutely "be ok" with that. I doubt most people would even notice.

It might be a good question why the big smart scientists do not call x-rays light (which others have answered), but that's very different from "people" and "day-to-day speech".

[Rockphed]

As a note, x-ray, uv-light, and gamma ray all have some overlap. I think, on some level, gamma rays are light emitted by nuclear decay while X-Rays are normally created by ramming high energy electrons into a metal plate, but if you have a detector in space, you have no idea what is causing the 3 high energy photons you detected in the last hour, just that they came from somewhere around cygnus.

[Bohandas]

I disagree with the premise of the question to begin with: that people are "not ok" with calling x-rays or radio waves light in day-to-day speech.

I don't think that's true. I think people are ok with whatever word for x-rays or radio waves, as long as that's the word the big smart scientists tell them to use. Big smart scientists communicate with the normal folk through things like school text books and wikipedia pages.
If school text books and wikipedia pages start calling x-rays "x-light" from now on, within a generation everyone would call it x-light, and people would absolutely "be ok" with that. I doubt most people would even notice.

It might be a good question why the big smart scientists do not call x-rays light (which others have answered), but that's very different from "people" and "day-to-day speech".

The issue came up for me because of a bunch of uninformative articles that talked about it this way which I came across while trying to verify my understanding of how wi-fi works

(on a related note, can anyone confirm my impression that the data is encoded in a pattern of flashes rather than in variation in the wavelength or intensity of a continuous beam?)

[Rockphed]

The issue came up for me because of a bunch of uninformative articles that talked about it this way which I came across while trying to verify my understanding of how wi-fi works

(on a related note, can anyone confirm my impression that the data is encoded in a pattern of flashes rather than in variation in the wavelength or intensity of a continuous beam?)

I am not an expert and a quick look at Wikipedia does not give me any information to be certain, but I think the answer to your last question is "it does both". WiFi uses a series of short bursts to communicate, but that is largely because that is how ethernet works. I think it encodes data as changes in wavelength and intensity (based on seeing QAM and BPSK, which both mean "change the intensity and wavelength of a carrier to encode data"). It also jumps around in frequency to reduce interference from microwave ovens.

One thing that may be confusing is that we can detect and perfectly reproduce the phase of radio waves, which we cannot do with visible light (or most things termed "infrared"). So while technically we encode data as a change in frequency, what we actually look at is "how do the peaks of these waves align".

[hamishspence]

As a note, x-ray, uv-light, and gamma ray all have some overlap. I think, on some level, gamma rays are light emitted by nuclear decay while X-Rays are normally created by ramming high energy electrons into a metal plate, but if you have a detector in space, you have no idea what is causing the 3 high energy photons you detected in the last hour, just that they came from somewhere around cygnus.

Astrophysicists tend to go with "any photon with an energy of over 100 KeV is a gamma ray, anything with an energy of less than 100 KeV, but more than is typical for ultraviolet, is an X-ray"

https://en.wikipedia.org/wiki/Gamma_ray

X-ray energies typically go from 145 eV to 124 KeV - so there's going to be an overlap at the high end of the scale - something between 100 KeV and 124 KeV might be called an X-ray by some, and a gamma ray by others.

https://en.wikipedia.org/wiki/X-ray

Extreme ultraviolet goes up to around 124.24 eV - so there's a gap between high energy ultraviolet and low energy x-rays - no overlap in this case.

https://en.wikipedia.org/wiki/Extreme_ultraviolet

[DavidSh]

X-ray energies typically go from 145 eV to 124 KeV - so there's going to be an overlap at the high end of the scale - something between 100 KeV and 124 KeV might be called an X-ray by some, and a gamma ray by others.

https://en.wikipedia.org/wiki/X-ray

Extreme ultraviolet goes up to around 124.24 eV - so there's a gap between high energy ultraviolet and low energy x-rays - no overlap in this case.

https://en.wikipedia.org/wiki/Extreme_ultraviolet

The lower limit on X-ray energy should be 124 eV -- the Wikipedia value of 145 seems to be an error introduced on an edit on February 5th of 2022 that claimed to be only editing the date of discovery. The range of wavelengths given is a power of 10, so the range of energies should also be a power of 10. So there's no gap, and any overlap is probably rounding error.

[HeraldOfExius]

(on a related note, can anyone confirm my impression that the data is encoded in a pattern of flashes rather than in variation in the wavelength or intensity of a continuous beam?)


I am not an expert and a quick look at Wikipedia does not give me any information to be certain, but I think the answer to your last question is "it does both". WiFi uses a series of short bursts to communicate, but that is largely because that is how ethernet works. I think it encodes data as changes in wavelength and intensity (based on seeing QAM and BPSK, which both mean "change the intensity and wavelength of a carrier to encode data"). It also jumps around in frequency to reduce interference from microwave ovens.

One thing that may be confusing is that we can detect and perfectly reproduce the phase of radio waves, which we cannot do with visible light (or most things termed "infrared"). So while technically we encode data as a change in frequency, what we actually look at is "how do the peaks of these waves align".

My main issue with the question is that "a pattern of flashes" is going to be a result of (certain) "variation[s] in the wavelength or intensity of a continuous beam." While I'm more experienced with the technical aspects of satellite internet as opposed to WiFi, they both use variants of PSK, so I feel that I can safely say that its closer to "variations of a continuous beam" than "flashes." So while I agree with most of what Rockphed said, I don't like the use of "frequency" to describe what we look at when using PSK. While a PSK wave is going to have peaks occurring at variable time intervals, the frequency (and amplitude) of the wave remains constant. This matters a lot when it comes to satellites, but I honestly have no idea how important it is for WiFi. PSK also tends to have a higher data rate than other forms of keying, which is an easy sell when it comes to internet.

[Bohandas]

Well what got me onto the wi-fi question was an earlier question I was pondering , which was the question of weather a single photosensor, that couldn't distinguish between the frequencies in a narrow band that it's sensitive to, would be sufficient to receive it (in the absence of counfounding factors that would cause the transmitter to switch bands).

(Which was in turn meant to hopefully answer the rhetorical question "what use is half an eye" in a way that is illustrative due to not having to reference situations the average human is unlikely to have encountered)

[DavidSh]

Well what got me onto the wi-fi question was an earlier question I was pondering , which was the question of weather a single photosensor, that couldn't distinguish between the frequencies in a narrow band that it's sensitive to, would be sufficient to receive it (in the absence of counfounding factors that would cause the transmitter to switch bands).

I think the answer to this question is "no". It wouldn't be able to interpret any of the modulation techniques that depend on the phase of the signal. Probably also the spread-spectrum features of WiFi would also be a problem.

[Lord Torath]

Since infrared and Ultraviolet are commonly acknowledged as "light" in day to day speech, why isn't the rest of the electromagnetic spectrum?

If it was simply a matter of distinguishing the rest of the electromagnetic spectrum from visible light I could understand it. But since infrared and ultraviolet are still acknowledged as light I don;t see why radio waves and x-rays aren't tooWho are these "people"? And are they actively denying that X-rays, radiowaves, etc are light? Or is it just that they generally call them X-rays and Radiowaves instead of X-light and Radiolight?

I'll never pass up an opportunity to post to my favorite video on the subject, though: NOTGLaDOS: Electromagnetic Spectrum The Musical (https://www.youtube.com/watch?v=OYK7G6r0Pec)

Feel free to direct these "people" to it! :smallbiggrin:

[hamishspence]

The lower limit on X-ray energy should be 124 eV -- the Wikipedia value of 145 seems to be an error introduced on an edit on February 5th of 2022 that claimed to be only editing the date of discovery.

Apparently "supersoft x-ray sources" can get into the 90 eV range (0.09 keV):


https://en.wikipedia.org/wiki/Super_soft_X-ray_source


A luminous supersoft X-ray source (SSXS, or SSS) is an astronomical source that emits only low energy (i.e., soft) X-rays. Soft X-rays have energies in the 0.09 to 2.5 keV range, whereas hard X-rays are in the 1–20 keV range.




Possibly it's the wavelength that makes the difference between soft X-rays and extreme ultraviolet, if energies overlap.

[Chronos]

Quoth hamishspence:

Possibly it's the wavelength that makes the difference between soft X-rays and extreme ultraviolet, if energies overlap.
Not possibly. Wavelength and energy have a 1:1 relationship, so if you can't distinguish the two by energy, then you can't by wavelength, either.

Quoth Rockphed:

We spent a fair bit of time discussing the assumptions that ray optics requires, but those assumptions apply just as much to a 30 meter radio dish as to a 3 meter panel for the JWST.
Well, the assumptions are the same, but the assumptions for ray optics include things like "the instrument must be much larger than the wavelength of the light", which is a criterion which, in practice, is much easier to achieve for visible light than for radio, and so, in practice, ray optics applies to visible light more often than to radio.

[Bohandas]

I think the answer to this question is "no". It wouldn't be able to interpret any of the modulation techniques that depend on the phase of the signal. Probably also the spread-spectrum features of WiFi would also be a problem.

So it doesn't work sort of like a super-sped-up aldis lamp (albeit with different encoding)?

[Rockphed]

So while I agree with most of what Rockphed said, I don't like the use of "frequency" to describe what we look at when using PSK. While a PSK wave is going to have peaks occurring at variable time intervals, the frequency (and amplitude) of the wave remains constant. This matters a lot when it comes to satellites, but I honestly have no idea how important it is for WiFi. PSK also tends to have a higher data rate than other forms of keying, which is an easy sell when it comes to internet.

We might not look at the frequency change in PSK, but we theoretically could since it totally exists. It is just much easier to check the phase because the phase shift part of the waveform is going to be relatively short compared to the constant phase part of the waveform. Also, while the constant phase waveform is going to need to meet certain specifications, the only requirements on the phase change are going to be that it happens quickly enough and doesn't generate too much out of band radiation. I suppose you could make a PSK system that shuts off transmission while changing the phase, which would make it impossible to detect the frequency change associated with changing the phase.

And I would imagine that for many SNR levels you are better off with both phase and amplitude modulation than phase alone in terms of data-rates. If I have 16 points around the unit circle, the closest are 0.39 apart. For 16 QAM I can get at least 0.4 between any two points by having 4 levels (at -0.6, -0.2, 0.2, and 0.6) in each of 2 orthogonal directions. Assuming the highest I can do is full power in the phase shift keying, I can get sqrt(2) / 3 separation, which is about 20% higher than with phase shift keying. I might even be able to eke out a little more separation by not having my positions be independent in the 2 directions. Now I am a radar not a communication engineer, so I am just rambling off the things I picked up when my classmates were proofing their theses about communications. Feel free to scoff at my relative ignorance or to point out how PSK is going to use simpler encoding and decoding circuits than full QAM or is going to have a lower noise figure for the same incoming power or whatever other details I have missed.


Well what got me onto the wi-fi question was an earlier question I was pondering , which was the question of weather a single photosensor, that couldn't distinguish between the frequencies in a narrow band that it's sensitive to, would be sufficient to receive it (in the absence of counfounding factors that would cause the transmitter to switch bands).

If you have a photo-detector that cannot distinguish between frequencies you are pretty much limited to amplitude modulation. Back in school I built a laser-tag system that used amplitude modulation on an LED and a solar cell to tell who got the hit.