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B Visible light and light are two different things?

  1. Jul 13, 2017 #1
    Is this correct? Visible light refers to the visible light section of the spectrum and light generally means the rest of the spectrum?
     
  2. jcsd
  3. Jul 13, 2017 #2
    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.
     
    Last edited: Jul 13, 2017
  4. Jul 13, 2017 #3

    fresh_42

    Staff: Mentor

    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.
     
  5. Jul 13, 2017 #4
    Could you get away with saying that all the electromagnetic spectrum is light? Or would that be bad interpretation?
     
  6. Jul 13, 2017 #5
    "All light is electromagnetism" makes more sense.
     
  7. Jul 13, 2017 #6

    russ_watters

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    Note the term "speed of light"...
     
  8. Jul 13, 2017 #7
    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? :/
     
  9. Jul 13, 2017 #8
    When you say "This comes and goes with the word "usually". Do you mean it is correct to call the electromagnetic spectrum all light?
     
  10. Jul 13, 2017 #9

    fresh_42

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    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?
     
  11. Jul 13, 2017 #10
    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.
     
  12. Jul 13, 2017 #11

    Nugatory

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    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.
    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
     
  13. Jul 13, 2017 #12

    davenn

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

    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

    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
     
  14. Jul 14, 2017 #13
    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."
     
  15. Jul 14, 2017 #14

    davenn

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    yeah ... very bad wording and probably not what would be called a reputable source of info :smile:
    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 :smile:


    Dave
     
  16. Jul 14, 2017 #15

    sophiecentaur

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    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.
     
  17. Jul 14, 2017 #16
  18. Jul 14, 2017 #17

    fresh_42

    Staff: Mentor

    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
    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!
     
  19. Jul 14, 2017 #18
    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.
     
    Last edited: Jul 14, 2017
  20. Jul 14, 2017 #19

    Nugatory

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    It's back now.
     
  21. Jul 14, 2017 #20
    Thank you.
     
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