UV Rays

[person]

Earlier this week i went on a school tour and i was sitting in direct sunlight for 3 hours on the school bus yet i wasnt sunburnt at all ??

 

I was wondering if UV radiation can pass through glass ???

 

If not then why??

 

Does it pass through water(i have been burnt wile swimming)??

 

Does infra red radiation pass through water or does it just get absorbed ??

 

P.S I live in south africa 3 hours of light is more than enough to get seriously burnt even now during winter!!!

 

P.P.S thnx in advance

[ecoli]

UV light can't pass through polarized glass: http://en.wikipedia.org/wiki/Polarization

 

edit: excuse me, I was thinking about polarized plastic. Window glass does naturaly absorb UV radiation: http://en.wikipedia.org/wiki/Ultraviolet#Natural_sources_of_UV

[Klaynos]

Most glass absorbs UV light. It's REALLY annoying if you are trying to do UV and visible experiments, need to spend lots of money on special lenses.

 

Some examples of transmission graphs from the people we buy most of our lenses:

 

Normal "BK7" glass, which is pretty close to what you find in most windows:

 

http://63.161.211.69/BK7_TransmissionGraph.jpg

 

Fused silica:

 

http://63.161.211.69/UV-FusedSilicaTransGraph.jpg

 

Fused silica is normally about 5 times more expensive...

[swansont]

Sapphire for me (but I'm working in the near-IR)

 

http://www.mellesgriot.com/products/optics/mp_3_5.htm

 

 

Cheap plastic generally does not absorb UV, which is why they make crappy, possibly dangerous, sunglasses. Your iris opens up and lets all that UV in to do damage. Most kids' sunglasses are of the cheap variety.

 

———

 

The absorption coefficient for water is a minimum near the transition from visible to UV, so "soft" UV is certainly transmitted by water, while IR is absorbed much more readily.

 

http://www.lsbu.ac.uk/water/vibrat.html (scroll down most of the way)

[Thushara]

Wow interesting site.

..................

Thushara

srilanka latest news

[SkepticLance]

UV is not a single wavelength but a band. For medical pruposes, the band is often divided into two parts, called UVA and UVB. The UVA part of the UV spectrum causes sunburn, and will not pass through glass to any great extent. The UVB part does not cause sunburn but does cause melanoma, and should also be avoided. It has no problem at all passing through glass. For this reason, exposing unprotected skin to sunlight, even through glass, is not a good idea.

[person]

Well that clear it up a bit thnx for all info and links!!

[igosaur]

I used to work in a nursrey (the greenhouse kind) and would spend all day in the blistering sunlight and come out just a pasty and white as when I went in.

[swansont]

UV is not a single wavelength but a band. For medical pruposes, the band is often divided into two parts, called UVA and UVB. The UVA part of the UV spectrum causes sunburn, and will not pass through glass to any great extent. The UVB part does not cause sunburn but does cause melanoma, and should also be avoided. It has no problem at all passing through glass. For this reason, exposing unprotected skin to sunlight, even through glass, is not a good idea.

 

There's also UVC, which gets absorbed by the atmosphere, and VUV (vacuum UV) and a few others.

 

UVB is more energetic than UVA and definitely causes sunburn, and is why sunscreens protect against it. It's the UVA that can cause some cancers but not sunburn.

 

http://healthlink.mcw.edu/article/964647970.html

http://wwwn.cdc.gov/travel/yellowBookCh6-Sunburn.aspx

[SkepticLance]

My apologies. Got my A's and B's round the wrong way. Whoops!