This is as easy as it can get for you, if you're fogging up your anti-fog lenses, then you need a fan. Most people who buy fans wear glasses, so really, they're keeping their specs from fogging instead of their lenses. So, if you do need one, just listen to one hum at your local shop and see if it'll drive you insane or not. It's pretty fun though to watch everyone at the field look around trying to figure out, "what that blasted noise is."