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Black vs white vs red with relation to UV rays

  1. Sep 3, 2009 #1
    which color is better at blocking UV rays?

    my take on it is this analogy:
    you have a room with one window, cover it with a fabric curtain that is black the room becomes very dark. cover it with that same curtain except white and the room is somewhat brighter. less light = less UV rays

    a better question to ask would be if black absorbs UV rays as well as light. UV is a part of the invisible spectrum which is a part of light if im correct. also the inverse, does white reflect UV rays as well as light?

    Which color would protect your skin better in an extremely sunny day? (please do not not use rhetoric like "white is cooler therefore it is better". black is hotter because of the light transforming into infrared which is less damaging than UV. scientific logic, please

    my take:
    a fabric tee shirt
    black - absorbs light and UV rays lets less light through than white (less UV), is hotter to wear
    white - reflects light and UV rays, although lets light through (which lets UV through), is cooler to wear
    red - absorbs light and UV rays and lets less light through *to the extent that black does. somewhat cooler to wear than black because red reflects infrared

    *confirmation needed on whether red has those properties of black

    another analogy is that darker peoples are more suited to sunny environments than lighter peoples, so therefore darker is better for UV than lighter colors e.g. a caucasian gets sun burned easier whilst an african is more resistant to sun burn.
     
  2. jcsd
  3. Sep 3, 2009 #2

    Born2bwire

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    None really without actually testing the dyes and fabrics. We are only able to perceive within the visible light region. We cannot take the absorption and reflection properties of objects within the visible region as an indication of what occurs in the ultraviolet region. You could place a true infrared light source or ultraviolet light source in a room and you would not be able to see (ok, technically you could probably see with the UV light since most of our clothes are purposely dyed with UV sensitive dyes to bring out that whiter whites and brighter brights look). It might be reasonable to assume that the absorption of black dyes extends beyond the visible region but we cannot make such an assumption without any testing in my opinion.

    If you ask me, search for pictures of the Bedouin and take a cue from the colors they wear. Most of the ones I have seen wear lighter colors but it they also seem to be wearing dark colors too. But, I would expect their pigmentation allows better protection against UV and they are mainly dressing for cooling and shielding from direct sunlight.
     
  4. Sep 4, 2009 #3
    so uv isn't part of visible light? on the em spectrum it shows infrared as red and ultraviolet as violet(or is it blue?). are those colors just for reference, or are they really representative of the actual color of radiation (if radiation has a color)?

    as for a test, what do you think about have two cloths that are exactly the same, black and white. ill have an ultraviolet light, and an infrared source to test each color's transmission capabilities. first ill use some sort of ultraviolet sensitive object behind the cloth and see how much it fluoresces when i shine the uv light on it. ill use an infrared source (something hot i guess since there isn't an infrared light(or is there?)) put it next to the cloth and measure the infrared being transmitted to the other side with a nightvision scope
     
    Last edited: Sep 4, 2009
  5. Sep 4, 2009 #4

    f95toli

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    The colours are just a way to remember that UV is closer to the blue than to the red part of the visible spectrum; but humans can see neither UV nor IR.

    Note that what we refer to as UV and IR covers a very large range of frequencies whereas the visible spectrum is quite narrow. The infrared part of the spectrum actually overlaps with the microwave band (there are microwave components that work all the way up to deep-infrared frequencies).

    Also, as Born2Wire has already pointed out, there is in general no reason whatsoever why there would be any relation between an objects colour in the visible range and its properties in the IR or UV bands.
     
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