Why your spectacles fog up the second you step into an AC car in June — physics in 30 seconds
• The sudden fogging of spectacles upon entering an air-conditioned car during hot, humid months is a common occurrence, particularly in India, explained by the scientific principle of condensation.
• As you transition from a warm, moist outdoor environment into a cooler, drier interior, the temperature difference causes water vapor in the air to condense on the cooler surface of your lenses.
The speed at which this happens is remarkable. The moment the lenses, which are at a lower temperature than the surrounding air, encounter air with a high dew point (the temperature at which air becomes saturated with water vapor), condensation begins. This rapid transition from clear to foggy vision can be startling and inconvenient, especially when you need clear sight immediately upon entering the vehicle, such as when driving.
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