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Should i be worried? (UV lamp wavelength)

  1. Sep 15, 2013 #1
    (not exactly sure where i'm supposed to post this)

    i was looking at my UV lamp that i got from walmart. i was looking for a wavelength on there but i only saw "color temperature" i immediately thought Wien's law; so then i calculated the peak wavelength and got 96nm which is on the far side of the UV spectrum (close to X-ray). it's a 118V with a 20W power rating so i don't exactly imagine the intensity being tiny either. should i be worried?
     
  2. jcsd
  3. Sep 15, 2013 #2

    Drakkith

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    Color temperature does not tell you the wavelengths emitted, it merely tells you how hot a blackbody would have to be to emit radiation over a broad spectrum that would look that color. Your UV lamp is NOT emitting 96 nm radiation. Your lamp probably emits radiation in the 200-300 nm range.

    Is this UV lamp like a blacklight, or something else?

    Edit: Actually, if you could link the lamp you bought or tell us the brand it would help.
     
  4. Sep 15, 2013 #3
    by giving the color temperature aren't they essentially giving me the distribution with the peak wavelength? if not, what was the point of giving the color temperature?

    this was the best link i could find: http://www.sc-liquidations.com/product_info.php?products_id=33551 [Broken]
     
    Last edited by a moderator: May 6, 2017
  5. Sep 15, 2013 #4
    although, now that i think about it, unless the lamp has just all the right elements/compounds in it to produce that exact distribution, it cannot produce that distribution of colors because simply it is not that hot. So that still begs the question what was the purpose of writing the color temperature?
     
  6. Sep 15, 2013 #5

    UltrafastPED

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    The inexpensive ones are usually mercury vapor lamps (http://en.wikipedia.org/wiki/Mercury-vapor_lamp).

    Depending on the envelope it will emit 254 nm (UV-C) or 365 nm (UV-A).

    The 254 nm is germicidal, while the 365 nm is the usual blacklight; the 180 nm line is blocked unless you have a quartz envelope - this would be a lamp intended for some special purpose.

    You don't want to look at or expose your skin to the 254 nm light; the Wikipedia article lists some of the hazards. When I work with this wavelength I always were safety goggles which block everything below 400 nm, and use the lamp in a dark box. I use the lamp for modification of material surface conditions.
     
  7. Sep 15, 2013 #6

    UltrafastPED

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    The color temperature doesn't tell you the peak wavelength unless it is a blackbody. However it is useful in the lighting industry to describe how "natural" a light source is ...
     
  8. Sep 15, 2013 #7

    Drakkith

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    Take a fluorescent light bulb, one of those new kinds we have everywhere. If you look at it through a spectrograph you'll see that it emits light in only a few frequencies. These mix together and we see the light as being "white" or some other color. This color that the light looks, is what color temp is. (Well, technically it's their "spectral power distribution") If you calculate what the temperature of a blackbody needs to be to give you that same color, you could end up with a peak wavelength that the bulb doesn't even emit. It's just the way the energy is split between the different wavelengths.

    As a simple example, let's say I have a light that emits ONLY 400 nm and 500 nm light. Depending on the ratio of the two wavelengths, my color temp could be almost anything. Adding a near equal mix gives me around 5,000 k, give or take some. If the 400 nm light is twice as strong as the 500, then my color temp is much higher, say 10,000 k or something.

    Does that make sense?
     
  9. Sep 15, 2013 #8

    Drakkith

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    The purpose is to let people know what color the light will be when they turn it on. That way if I go to the store and buy a 5500 k bulb, I know it will be "white", or if I buy a 2700 k bulb I know it will be "orangeish".

    See below:

    Incand-3500-5500-color-temp-comparison.png
     
  10. Sep 15, 2013 #9

    UltrafastPED

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    Hopefully the fluorescent tube does not emit any of the UV mercury lines - the light that you see should all be from the phosphor coatings; the UV lines are the activators.

    See http://home.howstuffworks.com/fluorescent-lamp2.htm
     
  11. Sep 15, 2013 #10

    Drakkith

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    Okay, it appears to be a normal blacklight. See the following article for a list of peak wavelengths emitted by various blacklight bulbs.

    http://en.wikipedia.org/wiki/Blacklight
     
    Last edited by a moderator: May 6, 2017
  12. Sep 15, 2013 #11

    Drakkith

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    I'm sure they don't.
     
  13. Sep 15, 2013 #12
    okay, so i calculated the corresponding wavelength for the 5500K, and it was near the green meaning all the colors would be mixed almost evenly giving a white color. however, i calculated the corresponding wavelength for the 2700K, and i got 1074 nm which is definitely in the infrared spectrum, and the graph of the color distribution falls off pretty rapidly as you move to the left from the peak wavelength, which seems like the color should be alot redder than the color of the 2700K in the picture. 3500K corresponds to 828nm which is still on the IR side! hmm.. everything seems to be shifted to the right of where the peak wavelengths are....
     
  14. Sep 15, 2013 #13

    Drakkith

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    Not true. A 5500 k object has a spectrum with a significant difference in radiation towards the blue and red ends. But our eyes are "calibrated" to see this as white still. (We actually see "white" over a wide range of conditions)

    Consider that metal glows cherry red at around 1,000 k and distinctly orange at around 1500 k. By 2,000 k objects are yellowish-white.

    Play around with this calculator: http://www.spectralcalc.com/blackbody_calculator/blackbody.php
     
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