The highway stretches dark ahead, and your headlights carve a tunnel through the night. A car pulls up behind with LED beams so bright they flood your rearview mirror with white light.
The glare burns into your peripheral vision and makes the road ahead harder to see. Most drivers don’t know their rearview mirror has a built-in fix for headlight glare. Plenty of driving advice covers headlights and windshields, but the best tips for night visibility start right above your dashboard.
Man’s hand presses adjusting rearview mirror dimming. Selective focus.
Flip the small tab under your rearview mirror to instantly dim glare from bright headlights.
Image credit: Shutterstock
Your rearview mirror has a small tab that dims glare instantly. The tab sits at the bottom center of the mirror, usually about an inch wide and sticking out half an inch from the housing. Flip it forward when bright LED beams flood your view, and the blinding light drops to something manageable.
How The Dimming Works
The tab changes the angle of your mirror when you flip it. Some tabs push and pull while others flip up and down, but all make a subtle click when moved. That click tells you the mirror has tilted to its night position. The change looks subtle if no bright lights are hitting the mirror, so test it with headlights behind you to see the difference clearly.
The view behind you should stay visible, but it looks much darker. This happens because rearview mirrors use wedge-shaped glass with a reflective coating on the back surface. In the day position, light bounces off that back surface to give you a bright, clear reflection. Flip to night position, and the mirror tilts so the reflection comes from the weaker front surface instead.
The mirror’s geometry controls which reflection reaches your eyes. The front surface reflects only 4% of incoming light, while the back surface reflects around 80%. This difference creates the dimming effect without batteries or sensors, which explains why the design has barely changed since manual day/night mirrors first appeared in the 1930s and became standard equipment by the early 1970s.
Simple wedge shape and mechanical lever prove more reliable than many electronic alternatives because there are no batteries to die and no sensors to fail.
The dimmed view takes some getting used to because cars appear farther away than they actually are, but this tip makes sense for night driving when bright headlights can wipe out your vision for several seconds.