Visible light and light are two different things?

[revv]

Main Question or Discussion Point

Is this correct? Visible light refers to the visible light section of the spectrum and light generally means the rest of the spectrum?

 

[rootone]

The electromagnetic spectrum runs from very low frequencies (radio) to very high frequencies (gamma rays).
Visible light is a narrow band of frequencies in the middle of the EM spectrum
EM outside of the visible range like radio for example, is not generally referred to as light.
UV is outside the visible range but sometimes is classified as light since it can cause objects to fluoresce.
That is the objects react to UV by emitting in the visible range, typically a blueish light.

 

[fresh_42]

This comes and goes with the word "usually". Usually, light is the visible part of the spectrum, perhaps extended to near IR and UV frequencies. Since they all are electromagnetic radiation, light and visible light are basically the same. EM waves with near-light frequencies are sometimes referred to as IR light or UV-A/B/C light, but this is hair splitting. In general light is visible and other parts of the spectrum have different names, like radiowaves, X-rays, gamma-rays and so on.

 

[revv]

Could you get away with saying that all the electromagnetic spectrum is light? Or would that be bad interpretation?

 

[rootone]

"All light is electromagnetism" makes more sense.

 

[russ_watters]

Note the term "speed of light"...

 

[revv]

Why do so many websites describe the whole electromagnetic spectrum as light then? Am I complicating things too much or am I interpreting it wrong? All the electromagnetic spectrum is also photons right? And photons are said to be light? :/

 

[revv]

When you say "This comes and goes with the word "usually". Do you mean it is correct to call the electromagnetic spectrum all light?

 

[fresh_42]

Why do so many websites describe the whole electromagnetic spectrum as light then? Am I complicating things too much or am I interpreting it wrong? All the electromagnetic spectrum is also photons right? And photons are said to be light? :/

This comes and goes with the word "usually".

As it's all electromagnetic radiation you can call it as such, our for the lazy ones: light. But this is unusual. You don't come home from the dentist and tell he has lightened you if he took an X-ray of your teeth, don't you?

 

[revv]

As it's all electromagnetic radiation you can call it as such, our for the lazy ones: light. But this is unusual. You don't come home from the dentist and tell he has lightened you if he took an X-ray of your teeth, don't you?

LOL! That made me laugh thank you.

Saying X-rays is just more specific to the kind of "light" you are referring to? I hope I make sense, I still need to do a lot more research but thank you all for trying to help.

 

[Nugatory]

Why do so many websites describe the whole electromagnetic spectrum as light then?

Because natural language is not a completely precise way of stating ideas. It may be usual to restrict the word "light" to the visible part of the electromagnetic spectrum, but not everyone is going to consistently do what's usual. It often doesn't matter, but when it does you may have to determine from the context what is intended.

All the electromagnetic spectrum is also photons right? And photons are said to be light? :/

The relationship between photons and electromagnetic radiation is much more complicated than any popular source would suggest. Generally it is unnecessary and even confusing to use the concept of photons in any discussion not involving quantum mechanical phenomena; but if you want to learn more you might try this thread and especially the links in the first two posts: https://www.physicsforums.com/threads/what-is-a-photon.879128/#post-5522356

 

[davenn]

Why do so many websites describe the whole electromagnetic spectrum as light then?

am I interpreting it wrong?

if they do, then they are wrong .... show some examples .... maybe you are misinterpreting

All the electromagnetic spectrum is also photons right?

not quite worded correctly and this is your misunderstanding. Photons are just the energy carriers in an electromagnetic wave
The EM wave/spectrum can easily be described in classic physics without referring to photons

And photons are said to be light? :/

other way around ( and with the basic definition I just gave above) ....
again visible or near visible light IR ---> visible ---> UV light is just names for a small section of the EM spectrum

 

[revv]

if they do, then they are wrong .... show some examples .... maybe you are misinterpreting

Paragraph
035.2
Here is just one of the websites mentioning that the "electromagnetic spectrum is all different forms of light radiation" https://uag-earthsci.blogspot.ca/2016/11/day-035-giftionary-electromagnetic_10.html

"The electromagnetic spectrum is all of the different forms of light radiation, put in order from lowest energy to highest energy. All of these forms of radiation travel at the speed of light, but only some of them are visible."

 

[davenn]

"The electromagnetic spectrum is all of the different forms of light radiation, put in order from lowest energy to highest energy. All of these forms of radiation travel at the speed of light, but only some of them are visible."

yeah ... very bad wording and probably not what would be called a reputable source of info
be careful when you source your information from. Here at PF we go for information in peer reviewed, published papers as being the most accurate

There is a lot of "pop-science out there, in print and on various TV doco's that overall can be generally good, but unfortunately can have inaccurate statements and ideas in the mix. And for the general non-science public, they have no idea if what they are hearing or reading is really correct.

this would be a much more accurate wording .......

"The electromagnetic spectrum is all of the different forms of electromagnetic radiation, put in order from lowest energy to highest energy. Electromagnetic radiation travel at the speed of light ( in a vacuum), but only some of them are visible."

It's no wonder people get confused and then come onto forums like PF and get their physics sorted out


Dave

 

[sophiecentaur]

Why do so many websites describe the whole electromagnetic spectrum as light then?

You could also ask why so many websites offer perpetual motion machines, health tonics and faster then light travel. The www needs to be approached with care and you need peer review and common sense before accepting anything you read.

 

[revv]

Even a nasa websites says all electromagnetic radiation is light. https://science.nasa.gov/ems/09_visiblelight

I just don't know what to believe anymore

 

[fresh_42]

I just don't know what to believe anymore.

Perfect! This is number two on the list of properties needed to improve knowledge: skepticism! (Number one is curiosity.)

One can call it light because it is shorter and in the end the same thing, only different by wavelength, resp. frequency. As in the case of NASA

"All electromagnetic radiation is light, but we can only see a small portion of this radiation—the portion we call visible light."

We may not forget their goal. Here common people are addressed and it's probably the shortest way to explain what EM radiation really is: visible and invisible light. It's not meant to be scientifically rigorous. How would you explain microwaves, X-rays, radio signals, IR radiation and so on and so on if it has to be brief, understandable to everyone and a side note, because the purpose of the webpage is a different one, in this case astronomical observations and conclusions. The alternative would be either a large detour or not easy to understand and in any case: longer. It is as wrong as saying an ultrasound examination is by sound or elephants' communication is by sound (infrasound), dog whistles uses sound (although neither can be heard by us) and similar. They all are a kind of sound, although they don't make a sound. That's the same with light. All the same electromagnetic radiation: some is visible to us, why we usually call it light, some is visible to bees, although we don't, with some we heat our meals, open car doors and switch tvs and others we use for medical purposes. It's up to everybody to make that distinction (visible=light - invisible=rest of the spectrum) or not. If you don't, chances are high to be misunderstood. But it can abbreviate a longer course which is done on the NASA page, just because they do not want to hold a lecture on EM radiation there. They even start by telling it's the same but eventually invisible!

 

[revv]

Thank you!

I deleted my post but I will re-post what I posted for later or if anyone wanted to know.

My post was about Nasa saying that all electromagnetic radiation was light on there webpage https://science.nasa.gov/ems/09_visiblelight

Anyways I think I get it now thank you all very much I really appreciate all the great people on this site helping out.

 

[Nugatory]

I deleted my post but I will re-post what I posted for later or if anyone wanted to know.

It's back now.

 

[revv]

It's back now.

Thank you.

 

[sophiecentaur]

Nasa saying that all electromagnetic radiation was light on there webpage

You really shouldn't worry about stuff like this. You have to remember Nasa is addressing a broad range of people and many of them would switch off at the term Electromagnetic Radiation. "Radiation" means "BAD" to many people.
If you spend too much time about the words people use on popular Science sites you will miss out on the really worth while things that Physics has to offer.

Exmple: We say that light from fast receding objects gets "red-shifted". That doesn't mean that microwaves get shifted in the red direction, does it?

 

[bob012345]

Could you get away with saying that all the electromagnetic spectrum is light? Or would that be bad interpretation?

All of the electromagnetic spectrum consists of photons. The word photon suggests light because of its historical origins involving the photo-electric effect. That leads to some confusion regarding the whole spectrum. But loosely, I think one can talk about UV light, IR light but I wouldn't talk about X-ray light or gamma-ray light or even microwave light. I'd use the word radiation in those cases.

 

[Drakkith]

As with most words, context is important. Light will mean visible light, IR light, UV light, or even most or all of the EM spectrum depending on how it's used. All of these uses are perfectly legitimate in most cases.