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Old 09-04-2008, 01:51 AM
Hirka T'Bawa Hirka T'Bawa is offline
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Location: Conyers, GA, USA
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Fogging up of Eyeglasses

As almost everyone who has to wear glasses knows, they have a tendency to fog up in areas that are humid. Especially in places like the bathroom, a sauna, Florida, and as I recently found out, Savannah.

What my question is, why do glasses fog up in some conditions but not others? Is it only due to the relative humidity in the area? The atmospheric pressure? The temperature? Altitude? Or what?

I guess my main question is: Why do my glasses fog up all the time in Savannah, Ga, but not in Atlanta, Ga?
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Old 09-04-2008, 03:55 AM
si_blakely si_blakely is offline
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Quote:
Originally Posted by Hirka T'Bawa View Post
What my question is, why do glasses fog up in some conditions but not others? Is it only due to the relative humidity in the area? The atmospheric pressure? The temperature? Altitude? Or what?
The major factors are relative humidity and temperature.

Basically, if your glasses are cold and the relative humidity is high, moisture will condense on the lenses. This usually happens when you move from a colder space (air-conditioned room) to a warmer one (outside).

Once your glasses have warmed up to ambient temp, the fogging disappears. Your glasses can also trap air between them and your face, which increases the humidity of that air if you are sweating. I get this sort of fogging while running on a treadmill with the fan blowing - the airflow cools the outside of the glasses and my face is hot and sweaty.

So your question about different locations should be :- what conditions in
Savannah, Ga lead to fogging that do not occur in Atlanta, Ga? I would suspect it is related to local humidity levels, prevalence of air conditioning, and rapidity of transition from indoors to outdoors. YMMV.

Si
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