Re: Can Ultra Violet Waves Pass Through Glass?

Yes, UV waves can pass through glass.  But remember that glass can bend
and focus the rays, and you are in danger of getting burned instead of
dark.

I do not recommend trying to make your skin dark by exposure to the sun.
It is well-known that damage to the skin from ultraviolet exposure can 
lead to skin cancer (melanoma).  

Additional Comments:

.......................
We have to go into some detail to properly answer the question
"Can UV rays go through the [car] glass and make my skin dark?"

The people who work in the field of UV radiation usually talk
about 3 "bands", or groups, of UV wavelengths.  UV A is from
320 to 400 nm wavelength, UV B is from 280 to 320 nm, and
UV C is from 200 to 280 nm.  When we talk about UV light and
tanning we are usually talking about the UV B band.  The more
energetic photons are in the UV C band, but fortunately most
UV C light is absorbed by ozone in the atmosphere.  Let's
assume that we are, then, talking about UV B.

Most glass types absorb UV light to some degree.  The table
below shows the external transmittance (the transmittance
taking into account not only the absorption by the glass but
also the reflections off the surfaces) of a 5 mm thickness of
an everyday type of glass that would be used in car windows.

Wavelength    Ext. Trans.   Designation
----------    ----------    -----------
280           0.016         UV B/C
300           0.38          UV B
320           0.71          UV A/B
340           0.85          UV A
360           0.89          UV A
380           0.90          UV A
400           0.91          UV A

Notice that at 320 nm wavelength, the top of the UV B band,
the transmittance is 71%, but at 280 nm wavelength, the
bottom of the UV B band, the transmittance is only 1.6%.  So
through glass we get more of the longer wavelengths.  If we
take the middle wavelength of the UV B band, 300 nm, the
transmittance is 38%, so the answer to your question is YES,
we CAN be tanned by UV light inside a car, but it will take
a longer time to do so.  This assumes, by the way, that the
car windows do not have a UV-blocking film!!

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



John Link
Durham, NC
madlink@mindspring.com