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I am doing a project where I would like to do some UV exposure to some concrete and stone samples. Therefore I have bought a couple of 400 watt UV bulbs, the product specification says it has an irradiance of 82 watt UV-A and 12 watt UV-B. I am not sure if they mean W/m2 and at what distance, but I will have that tested in a lab.

I am bit concerned about the amount of UV-B light, therefore I would like to know if I can block the UV-light with some sort of improvised filter. Would tinfoil work? Or does anybody have a better idea?

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    $\begingroup$ What are you trying to protect from the UVB? yourself? Could you just leave the room when doing the experiment? $\endgroup$ – George G Oct 16 '14 at 19:22
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    $\begingroup$ UV-A isn't good for you either. $\endgroup$ – Brandon Enright Oct 16 '14 at 19:22
  • $\begingroup$ UV-B is blocked by usual glass (but not by transparent plastic, like polycarbonate). You should be, however, more concerned about UV-A: UV-B will just burn your skin, but UV-A penetrates deeper and damages DNA. Look for brown- or orange-colored glass. $\endgroup$ – gigacyan Oct 16 '14 at 19:42
  • $\begingroup$ Aluminum foil would work great, so would any kind of sheet metal. 400W UV bulbs produce A LOT of UV radiation if you are close to them. Make sure you don't get exposed much. I would definitely wear sunscreen and dark sunglasses (with guaranteed UV protection) while working with these. And the power rating is absolute, so in this case you are getting pretty close to $82(12)W/4\pi$, if it's an open lamp without reflector. $\endgroup$ – CuriousOne Oct 16 '14 at 19:52
  • $\begingroup$ Yes I want to protect myself from the UV, of course i will not stay in front of it but i have to monitor the experiment once in a while. Thanks for the tip on brown/orange glass and sheet metal. $\endgroup$ – Kim Petersen Oct 16 '14 at 20:17
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I have been recently performing experiments using UVB (and UVA light) light.

The personal protection I have been using have been a welder's mask (to protect the face) and sun glass like material for the eyes and sun protective clothing that did not leave any skin exposed (e.g. hands, arms etc).

As mentioned in the comments, surround the experiment in a glass shield, or standing behind a glass shield could be an option. According to the article Photoprotection by window glass, automobile glass and sunglasses (Tuchinda et al. 2005), states that the main factors for broad UV (UVB and UVA) protection are:

The degree to which glass products provide UV protection depends on the glass type, glass color, the presence of an interleave between pieces of glass, or the presence of a coating on the glass.

They also state that the dark tinted glass sometimes used on office buildings provides broad UV protection.

As UVA is also potentially dangerous (depending on dose), Tuchinda et al. (2005) also conclude that

Recent developments in the glass industry have resulted in the introduction of additional filters for UVA and infrared radiation. This UVA filtering technology can now be incorporated into a glass coating, providing more comprehensive photoprotection.

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