I wear glasses. If you wear glasses then you can feel my pain and the pain of an estimated 164 million other Americans. Of course, I am speaking of the summertime tradition of stepping out of an air-conditioned building into the heat of the summer only to be blinded by a layer of fog covering my lenses.

While you might be tempted to think this phenomenon is caused by summertime temperatures, it's actually caused by a combination of that temperature and relative humidity. I don't have to explain humidity to residents of the Gulf South where I live. But, if you live in one of those "dry heat" places the humidity is the measure of moisture in the atmosphere.

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Here's Why the Weatherman Keeps Mentioning the Dew Point

Another term you'll want to know about is the dew point. You know what dew is, right? You probably see it on your lawn every morning. The dew point is the temperature that air needs to be cooled to in order to achieve a relative humidity of 100%. It as at that point the air can no longer hold moisture in the form of a gas. If the air is cooled below that point then the water vapor takes on a liquid form, usually as fog or rain.

What Does That Have to do With My Glasses Fogging Up?

Let's say you're in a building where the air temperature is 72 degrees. You step outside into a summer day where the dew point is 75 degrees. Because your eyeglasses have been cooled to 72 they are below the "dew point" temperature. Hence, the moisture in the air interacts with the relative coolness of your lenses and suddenly, you can't see squat.

So, What Temperature Will Fog My Glasses?

Again it's the combination of temperature and humidity. For example, at 0400 AM the dewpoint where I am in Lafayette Louisiana is 74 degrees. Inside my building, the temperature is 68 degrees. So, since my glasses are colder than the dewpoint I will get fog on my lenses if I step outside. By the way, that's the same basic reasoning that causes your windshield to fog up from the inside during the winter months.

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How Can I Prevent My Glasses from Fogging?

The easiest way is to simply adjust the temperature in your inside environment. But for most people during the summer that would mean an office or a car that's too warm for comfort. I suggest you just grin and bear it and maybe keep an eyeglass cloth handy to clear away the fog. Besides, it will all equalize in just a few minutes anyway.

So, now you know and you also know that in Louisiana, we love our air conditioners. Oh, here are few other things we love that you'll find in just about everybody's house.

Ten Things You'll Find in a Typical Louisiana Home