From: SFPhysics@aol.com
Date: Fri Jul 27 2001 - 01:46:38 PDT
From: SFPhysics@aol.com Message-ID: <cd.9c81046.2892846e@aol.com> Date: Fri, 27 Jul 2001 04:46:38 EDT Subject: Re: UV through glass......
Dr. Paul, another person, and I posted at length about this last year so this
is just a quick synopsis:
UV is given three designations by wavelength (frequency). There is UVA, UVB,
and UVC. The higher frequencies of B and C are stopped by most common
glasses. The UVA does penetrate glass without great loss.
A good experiment is to take the UV "beads" that can be found to change color
when exposed to UV light. Put them outside and you will observe a change in
sunlight. Try the same with direct sunlight coming through a glass window.
The inexpensive beads will tell you if the glass stopped the UV.
Children's eyes are often damaged by plastic sunglasses that let the iris
open while the full UV comes through. Reflected UV from beach sand, etc.,
can even make the exposure worse. Sunglasses with true protection should
have a sticker on them that says blocks UVA and UVB. UVC does not transmit
far through air so it is not something sunglasses need to block. You can
test the sunglasses with the beads. I have had my students put sunglasses
over a hole in a light tight tube with the beads in it. Some fairly
expensive glasses were failures at blocking UV.
Glass that blocks UV is "doped" with several elements that absorb the UV
energy. The automotive industry uses a lot of this glass to protect the
plastic interiors.
Best of summer wishes to everyone on the Pinhole List,
Al Sefl
This archive was generated by hypermail 2b29 : Tue Oct 16 2001 - 12:22:26 PDT