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Very short infrared remote control question

  1. Nov 2, 2013 #1

    I asked a question about infrared and UV a while back for which I got some very informative responses:


    This is in a sense a very short follow up question: Is the reason that we don't feel 'heat' from an infrared remote control because the intensity of the signal is very weak or because it is at a frequency of infrared that is not sensed by humans as 'heat'?

    Additionally, I came across a comment under the article at:


    The comment was:

    I don't believe that this is correct - because although the intensity of visible + UV light from the sun is greater than the intensity of infrared, the important point is that it is the amount that these wavelengths are absorved that is important.
    It does however raise some questions for me: If the intensity of visible light were high enough, would we feel the same kind of 'heat' as when there is infrared light shone on our skin? (I know that we can get optical lasers that are able to cut through objects due to the amount of energy they deposit in them but could we for example builld an optical laser that deposits just enough energy in the skin that it would feel warm?).
    And a related question: UV light in fact does get absorbed by our skin - causing sun tans and (much less desirable!) skin cancer. If we are out on a sunny day, do we feel this UV light as 'heat' on our skin or again is it only the IR in the sun light that causes this sensation?

  2. jcsd
  3. Nov 2, 2013 #2


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    You don't feel any heat because it is very low intensity.

    For the solar spectrum, see: http://en.wikipedia.org/wiki/File:Solar_Spectrum.png
    You can see from the chart, which is in watts/m^2 per nm of wavelength, that most of the energy is in the visible. Anything that is not reflected from your skin is absorbed ... so from a "visual integration" it looks like about 50% would be from visible and UV.

    And yes, if there is enough energy being absorbed, you will feel it as heat.
  4. Nov 2, 2013 #3
    thanks for the information. The only thing I would question about the solar spectrum image you have linked is that this in itself is not enough - as I understand that the amount the skin absorbs is highly wavelength dependent - so to be sure that 50% is due to UV and IR we would also need to know the absorbtion vs wavelength function for the skin.... then multiply by the solar spectrum ... and only then is it meaningful to integrate.
  5. Nov 2, 2013 #4


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    I will let you do that research ... you should note that not all IR is absorbed either.

    Please report back with your findings!
  6. Nov 2, 2013 #5
    Oh if only I had the time! Thanks for your help.
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