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Are blacklights hazardous?

  1. Sep 23, 2005 #1
    My roommate and I have set up a couple fairly strong black lights in our dorm room. They're forty watt fluorescent tubes about three feet tall, and look quite cool.

    However, we are both wondering whether there's any health risk associated with being exposed to the black lights for an extended period of time. They're the sort of light you purchase at a novelty store like Spencer's Gifts. I would expect that nothing sold under those circumstances would emit any significant radiation at potentially harmful wavelengths, but perhaps I'm too trusting.

    So, is there a health risk here?
  2. jcsd
  3. Sep 23, 2005 #2

    Doc Al

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    Interesting question. I think most "blacklight" is longer wavelength ultraviolet, which is less dangerous than the shorter UVB or UVC radiation. You probably won't get a sunburn!

    Maybe someone in the biology forum can give a more authoritative answer.
  4. Sep 23, 2005 #3


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    Blacklight like ones you see over in clubs are UVA. Those arent as dangerous as germicidal light - UVC. My UVC light burned down plants in a few hours. I wont recommend sitting under blacklight for extended periods of time though.. you may get a malignant melanoma so why risk it?
  5. Sep 23, 2005 #4
    "It all depends on the dose and wavelength of the radiation. UVA (315 - 400 nm) is pretty harmles. This is what you get from those black-light disco tubes. It is not dangerous if you don't stare to the tubes for long periods. The dose remains so low that you don't even get suntan."

  6. Sep 23, 2005 #5


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    I'm not sure what to think. UV-a, being non-ionizing, was intially thought to be safe. Apparently, however, it has recently been linked to melanoma (skin cancer)

    For hard figures, we have some exposure limits at


    The wikipedia puts the wavelength of the typical mercury vapor fluorscent lamp at 254 nm, which is fairly near the peak of the weighting curve.


    There is some additional radiation at 185 nm, but this is lower in magnitude and off the peak of the weighting curve.

    The limit at that freqency is 60 joules/meter^2 in an 8 hour period, which really isn't a lot. A 40 watt UV bulb would generate 40 joules/second at 100% efficiency. Without a meter, I guess you could (over)-estimate the radiation flux by assuming 100% efficiency on the part of the UV bulb, and divide the power (joules/sec) by the total area of the walls and ceiling (in m^2) to get (joules/m^2) / sec.

    If we had 100m^2 of area that would reach the above limit in a couple of minutes, unless I'm making a major calculational error (?!).

    For less technical sources, we have


    which I thought intially was over-conservative, but having looked up their referred technical sources and run the numbers above, perhaps it is not as over-conservative as I thought.

    On the other hand, I would still expect that walking outside with sun-screen for a few minutes would generate much more UV exposure than your UV lamps would.

    Anyway, that's about the best I can do - look up some of the sources and make up your own mind.
  7. Sep 24, 2005 #6
    UV-A will damage your eyes: look up "snow blindness".
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