Glasses get foggy or form condensation when you step out of an air-conditioned room due to a phenomenon called "thermal shock" or "dew point." Here's how it works:
Temperature and Humidity Difference: When you're inside an air-conditioned room, the air is cooler and drier due to the AC's cooling and dehumidifying action. As a result, the air inside the room has a lower temperature and lower humidity.
Warm and Humid Air Outside: When you step outside, you encounter warmer and often more humid air. Warm air can hold more moisture than cool air, so as the warm air comes into contact with your cooler glasses, the temperature of the glasses drops below the dew point of the outside air.
Condensation Formation: The dew point is the temperature at which the air becomes saturated, and moisture starts to condense into visible water droplets. When the warm and humid outside air meets the cool surface of your glasses (at a temperature below the dew point), the moisture in the air condenses on the glasses' surface, forming tiny water droplets. This is similar to how dew forms on grass in the early morning when the ground cools down.
The result is foggy glasses that obstruct your vision until the condensation evaporates or is wiped off.
To prevent your glasses from fogging up, you can try the following tips:
Warm Up Your Glasses: Before stepping outside, you can warm up your glasses slightly by breathing on them or using a hairdryer on a low setting. This helps raise the temperature of the lenses closer to the outdoor air temperature, reducing the temperature difference and the likelihood of fogging.
Anti-Fog Products: There are commercial anti-fog products available that can be applied to the lenses. These products create a thin layer that prevents condensation from forming on the glasses.
Proper Ventilation: If possible, slightly open your mask or find a mask with a nose wire that can be adjusted to allow warm breath to escape, reducing the amount of warm, moist air directed toward the glasses.
Properly Fitted Masks: Ensure your mask fits well, so exhaled air is directed downward rather than upward towards your glasses.
Remember, fogging of glasses is a natural phenomenon caused by the temperature and humidity difference, and while these tips can help minimize it, it may not be entirely avoidable, especially in extreme weather conditions.