Final answer:
To guard against glare from vehicle headlights at night, you should use and adjust your rearview mirror's night setting or anti-glare feature before you start driving. Polarized sunglasses can reduce glare in daylight from reflected surfaces but are not advisable for night driving. The rearview mirror's anti-glare setting is the correct tool for this situation.
Step-by-step explanation:
To guard against glare from the headlights of a vehicle behind you, you must use the rearview mirror and adjust it before you drive. Although devices like sunshades and sunglasses can help protect against direct sunlight, the rearview mirror has a specific feature designed to reduce the glare of headlights during nighttime driving. This feature is known as the night setting or anti-glare setting, which can be activated typically by flipping a tab or rotating the mirror to reduce the reflection of the bright lights coming from vehicles behind you, thus preventing the glare from interfering with your vision.
While sunglasses, specifically polarized sunglasses, can help reduce glare during daytime, they aren't the proper tool for addressing glare from headlights at night. Polarized sunglasses are designed to cut glare from reflections on horizontal surfaces like water or roads during the day by filtering out polarized light, making them ineffective in blocking glare from headlights at night.
On the other hand, understanding how polarization by reflection works can be important when choosing sunglasses. For instance, you can test if sunglasses are polarized by looking through them at a reflective surface and rotating the glasses; if the light intensity changes, this indicates that the reflected light is partially polarized. However, this is unrelated to the use of the rearview mirror's night setting to guard against glare from a vehicle's headlights at night.