Is all EM radiation light?

[paulb203]

TL;DR

Is all EM radiation light, or just the visible light part of the spectrum?

Are gamma rays, x-rays, microwaves, and radio waves considered as light?

What about UV and infrared radiation?

I'm getting conflicting definitions.

They all travel at c (in a vacuum), yes?

But does that mean they are all actually light?

 

[Baluncore]

All light is EM radiation.

 

[pines-demon]

TL;DR Summary: Is all EM radiation light, or just the visible light part of the spectrum?

Are gamma rays, x-rays, microwaves, and radio waves considered as light?

What about UV and infrared radiation?

I'm getting conflicting definitions.

They all travel at c (in a vacuum), yes?

But does that mean they are all actually light?

I do not know if there is a unique definition for light but I have never heard somebody refer to radio waves as light. Light usually is about the human-visible part of the electromagnetic spectrum.

All EM waves travel at the speed of light $c$.

 

[Ibix]

All light is EM radiation, not all EM radiation is light.

However, the study of light predates the knowledge of the existence of other wavelengths of radiation by quite some time. Terminology may reflect that. And you may also find different jargon that is specific to particular fields.

As a general rule, try not to get too hung up on terminology in any part of science. It's often not entirely consistent. If you find specific references that appear to contradict each other and you can't make sense of them, citing those and asking about them is more likely to be helpful than a general question.

 

[Ibix]

They all travel at c (in a vacuum), yes?

Yes, but so does anything massless, including gravitational waves.

 

[kuruman]

However, the study of light predates the knowledge of the existence of other wavelengths of radiation by quite some time.

It all started with "Let there be light . . . ", according to some.

 

[DaveC426913]

Light usually is about the human-visible part of the electromagnetic spectrum.

.. and UV and IR.

 

[gyorgiy]

I'll limit myself to physics:
It depends on the context and on who is talking. In astronomy, EM radiation can leave its source as viviable light and arrive on Earth as infra-red or even radio waves. Simlarly, radiation can start as x-rays and arrive here as visible light. This makes the distinction somewhat arificial (in this context), and many astronomers refer to all ofthis as light.

On the other hand, light can refer to visible human-radiation only when looking at the physics of the human eye.
Or to include IR and UV when considering sunight
Or to include just specific parts of the spectrum when considering animal vision.

The contaxt will usually make the meaning clear.

 

[pines-demon]

I'll limit myself to physics:
It depends on the context and on who is talking. In astronomy, EM radiation can leave its source as viviable light and arrive on Earth as infra-red or even radio waves. Simlarly, radiation can start as x-rays and arrive here as visible light. This makes the distinction somewhat arificial (in this context), and many astronomers refer to all ofthis as light.

On the other hand, light can refer to visible human-radiation only when looking at the physics of the human eye.
Or to include IR and UV when considering sunight
Or to include just specific parts of the spectrum when considering animal vision.

The contaxt will usually make the meaning clear.

True and sometimes "light-matter interactions" include gamma rays. So I guess the definition of light depends on the field. However the set of light phenomena is generally smaller than the set of all electromagnetic wave phenomena.

 

[kuruman]

Is all EM radiation light, or just the visible light part of the spectrum?

In my mind, this question is analogous to asking "Is an automobile a 4-door sedan or something that rolls on wheels using a self-contained power source?"

 

[DaveC426913]

It would be an interesting experiment to think of it in terms of what kind of detectors are required for each frequency band. There's a smooth transition from light to microwaves to radio waves but they use very different detectors.

• How long does a wavelength of light need to be before it can't be detected using a photo-cell?
• How short does a radio wave need to be before an antenna won't pick it up?
• How much overlap is there?

 

[DaveC426913]

.. and UV and IR.

*although technically, my son can see into the IR spectrum. Either that, or what I consider IR is not what he considers IR.

The light on a TV remote is theoretically infra-red, but he can see it plain-as-day (we did a controlled experiment. He passed with 100%). I suspect it might be more accurate to say "the remote control's LED is mostly IR but bleeds into the far visible red", but six-a-one-half-dozen-a-the-other.

 

[gyorgiy]

True and sometimes "light-matter interactions" include gamma rays. So I guess the definition of light depends on the field. However the set of light phenomena is generally smaller than the set of all electromagnetic wave phenomena.

Agreed - albeit it does depends on the field of work.
Neverthelss, the only EM waves I personally have not seen referrenced as "light" are coherent radio frequency emissions below 100-MHz - presumably because there is no known significant source* of these that originally arose from electronic transitions. But maybe I should just get out more...
*A gigamaser in a sufficiently distant galaxy would potentially change this situation...

 

[Nugatory]

Natural language can be sloppy and imprecise.

Sometimes when people say "light" they mean "all EM radiation"; when someone says "the speed of light is $c$" they really mean "the speed of all EM radiation is $c$"

Sometimes they mean just visible light, as in "it doesn't look very bright because mostly it's radiating at infrared instead of light frequencies"

And sometimes they mean some other sort of electromagnetic radiation, as in "ultraviolet light", "black light", "infrared light", "sunlight is mostly ultraviolet light"....

We're expected to work out exactly what is meant from the context. And if we don' want to be sloppy and imprecise and expect our listeners to figure what we mean from the context...
Then we do like the pros and say exactly what we mean: "electromagnetic radiation at wavelength X" or "electromagnetic radiation from this part of the spectrum".

 

[martinbn]

It all started with "Let there be light . . . ", according to some.

"Nature and nature's laws lay hid in night; God said 'Let Newton be' and all was light." - A. Pope

 

[paulb203]

I do not know if there is a unique definition for light but I have never heard somebody refer to radio waves as light. Light usually is about the human-visible part of the electromagnetic spectrum.

All EM waves travel at the speed of light $c$.

Thanks, pines-demon.
Yes, there doesn't seem to be a definition of light that everyone is agreed upon. As for radio waves being referred to as light; this from Nasa Hubblesite;
“Other types of light include radio waves, microwaves, infrared radiation, ultraviolet rays, X-rays and gamma rays — all of which are imperceptible to human eyes.”

 

[paulb203]

All light is EM radiation, not all EM radiation is light.

However, the study of light predates the knowledge of the existence of other wavelengths of radiation by quite some time. Terminology may reflect that. And you may also find different jargon that is specific to particular fields.

As a general rule, try not to get too hung up on terminology in any part of science. It's often not entirely consistent. If you find specific references that appear to contradict each other and you can't make sense of them, citing those and asking about them is more likely to be helpful than a general question.

Thanks, Ibix.
Here are just a few references (definitions) I've come across.

The Oxford Dictionary of Physics;
“The form of EM radiation to which the human eye is sensitive and on which our visual awareness of the universe and its contents relies (see colour).”

Brittanica;
“Light is electromagnetic radiation that can be detected by the human eye.”

Nasa;
“When we talk about light, we usually mean any radiation that we can see.”

But then Nasa also says;
“All EM radiation is light, but we can only see a small portion of this radiation, the portion we call visible light.”

Also, Nasa, Hubblesite;
“Other types of light include radio waves, microwaves, infrared radiation, ultraviolet rays, X-rays and gamma rays — all of which are imperceptible to human eyes.”

And, finally, Google AI Overview;
“Yes, the electromagnetic spectrum is made up of all types of light, including visible light and light that humans can't see.

 

[pinball1970]

TL;DR Summary: Is all EM radiation light, or just the visible light part of the spectrum?

Are gamma rays, x-rays, microwaves, and radio waves considered as light?

What about UV and infrared radiation?

I'm getting conflicting definitions.

They all travel at c (in a vacuum), yes?

But does that mean they are all actually light?

The coloured bit

“Yes, the electromagnetic spectrum is made up of all types of light, including visible light and light that humans can't see.

A bit messy, if we cannot see it it is not light.

“Other types of light include radio waves, microwaves, infrared radiation, ultraviolet rays, X-rays and gamma rays — all of which are imperceptible to human eyes.”

I would not say light but this is NASA, what do I know?

The first four definitions I think are better.

 

[DaveC426913]

A bit messy, if we cannot see it it is not light.

The rainbow from red to violet is called visible light, implying the existence of light that is not visible.

Such as infrared light and ultraviolet light.

 

[Steve4Physics]

The ‘Diamond Light Source’ is a source of X-rays*. And, to add to any confusion, it contains no diamonds.

*EDIT. To be more accurate, EM radiation in the range X-rays to IR.

 

[trainman2001]

Isn't all EM exactly the same… Simply higher or lower frequency/shorter wavelength of exactly the same phenomenon? Some animal species see UV others "see" IR (eg. snakes). Calling it electromagnetic radiation or light seems like semantics to me. There may be living things out there that can "see" deeper into the spectrum than we can imagine.

 

[pinball1970]

The ‘Diamond Light Source’ is a source of X-rays. And, to add to any confusion, it contains no diamonds.

Yeah.

Physicists know what they mean, even technologists most of the time.

 

[DaveC426913]

Isn't all EM exactly the same… Simply higher or lower frequency/shorter wavelength of exactly the same phenomenon? Some animal species see UV others "see" IR (eg. snakes). Calling it electromagnetic radiation or light seems like semantics to me. There may be living things out there that can "see" deeper into the spectrum than we can imagine.

There is a limit to the wavelegnths that can be detected by a given sensory organ.

Small organs, such as eyes cannot detect long wavelengths - organic tissues cannot refract longer wavelengths and the molecules that actually get stimulated only respond to certain wavelengths.

Animals that can sense far infrared usually are unable to focus it, and get less an image than a "warm thing thataway" sense.

 

[Herman Trivilino]

The phrase "visible light" is used because the term "light" is ambiguous. The term "light" may indeed mean only the visible part of the electromagnetic spectrum or it may refer to the entire electromagnetic spectrum. The meaning is often, but not always, clear from the context.

Note: Edited for clarity.

 

[DaveC426913]

The phrase "visible light" ... may refer to the entire electromagnetic spectrum.

I think that's bit of a stretch. Radio waves in the hundred metre range can't really be described as light by any but perhaps the most cloistered of radio astronomers, no?

 

[jtbell]

Some animal species see UV others "see" IR (eg. snakes)

And surely different people perceive different ranges of frequency or wavelength with their eyes, at both the red and violet ends of the "visible" spectrum. Just like different people can hear sounds in different frequency ranges.

 

[pinball1970]

Such as infrared light and ultraviolet light.

I have mentioned I use light boxes and that in includes UV, a UV "lamp" looking at samples under UV "light."
A "black light." A little bit oxymoronic.
The diagram says "rays" for a wavelength shorter than 400nm.

Common use and technical use gets a bit fast and loose.

We would probably not name them this way if we started from scratch.

 

[Herman Trivilino]

I think that's bit of a stretch. Radio waves in the hundred metre range can't really be described as light by any but perhaps the most cloistered of radio astronomers, no?

I wasn't clear. The pronoun "It" that began the 2nd sentence was meant to refer to the noun "light". I edited the post for clarity.

 

[DaveC426913]

I wasn't clear. The pronoun "It" that began the 2nd sentence was meant to refer to the noun "light". I edited the post for clarity.

Sorry, I don't see how that's changed the meaning.

I re-iterate: I think that's bit of a stretch. Radio waves in the hundred metre range can't really be described as light by any but perhaps the most cloistered of radio astronomers, no?

 

[Herman Trivilino]

Sorry, I don't see how that's changed the meaning.

I re-iterate: I think that's bit of a stretch. Radio waves in the hundred metre range can't really be described as light by any but perhaps the most cloistered of radio astronomers, no?

It's all semantics. There is nothing uncommon about the statement "All light travels at speed $c$ in a vacuum, regardless of its frequency".

That statement could just as easily refer to the spectrum of visible light as it could the entire electromagnetic spectrum.