Re: Sunscreen and UV

[RuthWeiner@AOL.COM]

In a message dated 8/5/02 10:49:18 AM Mountain Daylight Time, neildm@id.doe.gov writes:



> For the white, reflection of UV may not be a valid assumption.  
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>  
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> In order to get a nice bright white, a fluorescent dye is often used, which absorbs the UV and emits a blue-white color (probably several phosphors, mixed).  Laundry detergent uses it, too, for the same purpose.
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>  


I am not talking about anything with a fluorescent additive, but simply light-colored paint. Pure zinc oxide suspended in vaseline (when my four were babies I bought it in one-pound jars) is indeed bright white, because that is the color of zinc oxide powder.


Basic optics tells us that white is a total reflector of the visible spectrum and black is a total absorber.. My white bike helmet reflects the sunlight and is (albeit marginally) cooler than my black bike helmet.  I hgave never measured to see how transparent something like zinc oxide paste is to UV, but my experience tells me that it's not very transparent.



Ruth Weiner, Ph. D.

ruthweiner@aol.com