MadSci Network: Chemistry
Query:

Re: Does window tinting block UVA and UVB radiation

Date: Sat Sep 12 21:50:01 1998
Posted By: Kenneth Mitton, Post-doc/Fellow, Molecular Development Retina, Cataract, Dept Ophthalmology / U. Mich
Area of science: Chemistry
ID: 905141449.Ch
Message:

Does window tinting block UVA and UVB radiation ?

I know sunglasses block UVA and UVB radiation. Are there plastics that can be tinted and still allow UV rays to pass through them?

Not to my knowledge, but you can get non-plastic quartz 
materials, here is why:

In the chemistry department at Carleton University, 
Ottawa, Canada, as an undergrad I learned to use UV, 
Vis, and IR spectroscopy for the determination of 
molecular structure. I also learned some very practical 
points. Wavelengths of about 340nm (often used to 
measure NADH levels) and above fall into the visible 
light region (ie. from a tungsten light bulb) and we 
could use glass or plastic cuvettes to measure 
absorbance spectra. However, not all plastics were 
transparent to light around 340 nm, just some. Once you 
move to lower wavelengths (ie. < 330 nm) we enter the 
UV regions. There are no plastics or glasses that are 
transparent to UV to my knowledge.

In this region of the spectrum, we have to use quartz 
cuvettes, very expensive little containers indeed. As a 
molecular biologist using site-directed mutagenesis and 
constucting DNA plasmids/vectors etc, I use absorbance 
at 260 nm (near UV-A) everyday to measure the 
concentration of DNA in my solutions. I have to use the 
quartz cuvettes to do this. 

In past colaborations with John Trevithick, 
Biochemistry, University of Western Ontario, I have 
studied the metabolism of tocopherols (vitamin E) in 
the skin during mild sunburn and recovery from sunburn. 
We made our own mouse-tanning bench with UV-A/B lights, 
and we use sensors to measure the UV A, B and C 
components of light in the lab and outside in sunlight. 
For fun we would take the light sensors outside and 
measure the UV blocking of expensive vs cheap 
sunglasses using students hanging on the "concrete 
beach" at the student centre. Many students, were kind 
of angry to find out that $5 plastic glasses blocked as 
much UV A/B as $300 designer glasses from those fancy 
shops in the upscale malls. 

The plain fact is that plastics are not very 
transparent to UV light. If someone has recently 
designed a unique plastic that is transparent, i have 
not heard of it myself. Some plastics will pass some 
near UV, ie. close to 330 nm, but UVA,B and C will not 
pass. Tinting may not affect the UV transparency, but 
clear plastic blocks UV just a good as green plastic. 
My clear prescription glasses, plastic, block UV light 
as good as dark sunglasses.

Ken Mitton, Ph.D.,  Kellogg Eye Center


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