Many drivers rely on the rearview mirror constantly, yet few realize that it often has a built-in feature designed specifically for nighttime driving. This small lever or button—usually located at the bottom or back of a manual rearview mirror—is there to reduce glare from headlights behind you. When flipped, it activates a “night” or anti-glare mode that makes driving in the dark much more comfortable and safer. Despite its simplicity, this feature is incredibly effective, though it frequently goes unused simply because people don’t know what it does.

When a mirror is switched into night mode, it tilts slightly using a special prism inside. In normal daytime mode, the mirror reflects light directly, creating a bright, clear image. But when the night lever is activated, the angle changes so that the most intense reflection is deflected away. This softer, less direct light makes bright headlights from cars behind less blinding. You’re still able to see, but without the harsh glare — the mirror gives you a dimmer, gentler view that doesn’t overwhelm your eyes.

This adjustment brings major benefits for eye comfort, especially during long or dark drives. At night, your eyes must constantly shift between the dim road ahead and the bright lights behind. Sudden glare forces your pupils to adjust rapidly, which can be tiring and distracting. By reducing that glare, the night mode helps your eyes stay relaxed and better adapted to low light. That improved visual balance makes it easier to notice lane markings, brake lights, or road hazards, and can help you stay more alert and less strained over time.

While this manual version is common, more modern vehicles often come with automatic (electrochromic) rearview mirrors that handle glare reduction without any action from the driver. These mirrors use light sensors—typically one facing forward and one facing backward—to measure ambient light and glare. When the rear sensor detects bright lights, it sends a small electrical current through a gel layer inside the mirror, causing the gel to darken and reduce reflection. When glare decreases, the current drops and the mirror clears again.

This auto-dimming technology is based on electrochromism — the mirror contains a gel between two glass layers that changes its opacity in response to voltage. When the system detects glare, the gel darkens, reducing the amount of light you see in the mirror. Once the glare source goes away, the current stops, and the gel lightens back up.  The result is a mirror that continuously adapts to light conditions, keeping glare under control without requiring the driver to adjust anything manually.

The benefits of using either the manual or automatic anti-glare function are substantial. By limiting bright reflections, these mirrors reduce eye strain, help maintain your night vision, and decrease driver fatigue. That in turn enhances reaction times and improves safety — especially on long nighttime drives when glare from trailing cars can be distracting or dangerous. Auto-dimming mirrors also make the driving experience more comfortable without requiring constant manual intervention.

To make the most of these features, a few simple practices help. Keeping your mirrors and windows clean is key — dirt, smudges, and fingerprints can scatter light and reduce the effectiveness of the anti-glare system. Also, make sure the sensors on auto-dimming mirrors are not blocked; for example, tinting rear windows too dark can block light reaching the sensors, interfering with the dimming function. (Some Reddit users report needing to adjust sensor coverage after window tinting to restore proper dimming.  In manual mirrors, just make sure you flip the lever when you’re dealing with bright headlights, then switch it back when it’s no longer needed.

Ultimately, the night-mode feature on rearview mirrors is a small but powerful tool for safer nighttime driving. Whether it’s a manual lever or a high-tech electrochromic system, using it helps protect your eyes, preserve your focus, and reduce glare-related distractions. It’s a reminder that many vehicles include thoughtful design features that often go underutilized — and something as simple as flipping a mirror lever or letting a sensor do the work can make a real difference when driving in the dark.