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  • The rear view mirror tab lets you switch the mirror between day and night driving modes, protecting you from glare in the latter.
  • The rear view mirror provides a good view of the road and objects at the car’s back and sides, and it often has a double-swivel mount.
  • Prismatic rear view mirrors can change between day and night driving modes.
  • Older prismatic rear view mirrors have a mechanical control tab that lets you switch between driving modes by hand.
  • When you press the rear view mirror button, the prism rotates into its night driving mode, dimming the image in the reflective device.
  • Automatic rear view mirrors dim the reflected image by changing the reflective material’s color to a darker shade.
  • A new rear view mirror can cost between $10 and $400.

Despite the increasing prevalence of rear view cameras, the old-fashioned rear view mirror remains the best way to keep track of what’s going on behind your vehicle. Unfortunately, you can’t always avoid cars with irritatingly bright headlights or fog lights coming up behind you. When you look at the mirror, the reflected glare can briefly blind you, putting you in a potentially unsafe position on the road.

Thanks to the rear view mirror tab, you can switch the mirror between its daytime and nighttime modes of operation. In the latest vehicle models, the power button on the rear view mirror does more than prevent glare. Read on to find out more about rear view mirror tabs and buttons.

What Is a Rear View Mirror?

The rear view mirror is a reflective device that provides a good view of the road and objects behind and to the sides of the vehicle. You can usually find this mirror attached to the top of the front windshield.

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Most rear view mirrors use a double-swivel mount. This mount type lets you tweak the mirror’s height and viewing angle to match your preference.

Furthermore, the double-swivel mount contributes to the safety of the people inside the car during an accident. If the driver or a passenger somehow strikes the rear view mirror, the device will swing away from them. By giving way to the occupant hitting it, the mirror reduces the risk of injuring that unfortunate person.

automotive rear view mirror with tab
The rear view mirror tab is a button or switch that can change the prismatic rear view mirror to daytime and nighttime driving modes.

Prismatic Rear View Mirrors

Mirrors that can change between day and night mode are called prismatic rear view mirrors because of their shape, which we’ll cover in detail shortly. They’re also sometimes called day/night mirrors.

What Does the Rear View Mirror Tab Do?

The rear view mirror tab is a button or switch that can change the prismatic rear view mirror’s mode of operation. Moving the switch lets you change between daytime and nighttime driving modes.

In daytime driving mode, the rear view mirror operates like usual. You see everything crisp and clear. Driving with this mode engaged during night will lead to plenty of glare from the overly bright headlights and even more powerful fog lights of the cars behind yours.

When it gets dark enough to turn on the headlights, push the rear view mirror tab. Moving the tab will shift the mirror to its nighttime driving mode.

In this mode, the rear view mirror reduces the brightness of the reflection on its surface. The image looks darker and less vibrant, rather like an old movie might appear on a modern TV screen.

More importantly, nighttime driving mode dims the glare from light sources, including headlights and fog lights. By bringing the brightness down to a more comfortable level, the rear view mirror helps protect you against potentially blinding glare.

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It isn’t a perfect system. Driving can become more difficult if you accidentally engage the rear view mirror’s nighttime driving mode during broad daylight. Since the mirror will dim everything and the other drivers usually keep their lights off during the day, you might find it harder to spot vehicles coming up behind you.

The nighttime driving mode doesn’t discriminate between artificial and natural light. It dims both types equally. Daytime will look darker than it should, making it harder to notice vehicles that don’t have running headlights or fog lights.

Manual Button on Rear View Mirror

Older prismatic rear view mirrors require adjustment by hand to switch between driving modes. You can find the mechanical control tab on the mirror’s bottom.

Pushing the manual button in a certain way will engage nighttime driving mode, making everything in the mirror look darker. Moving the control switch the other way will return the mirror to its daytime driving mode.

Once you’ve set the driving mode, the rear view mirror will stick to that mode until you change it by adjusting the tab.

What Happens When You Push the Rear View Mirror Button?

At first glance, the rear view mirror appears like a flat sheet. Looks are deceiving, though. The mirror is a prism, a wedge-shaped piece of reflective glass with one end thicker than the other.

A mirror creates an image by bouncing light off its surfaces. The resulting image is called a reflection.

In daytime driving mode, light reflects off the mirror’s front side. Since light doesn’t travel far or change direction multiple times before bouncing off the glass, it produces a bright reflection.

When you push the button at the bottom of the rear view mirror, the wedge orients into its nighttime driving mode. The light must now take a different, longer path through the glass.

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In the rear view mirror’s new orientation, the light goes through the glass’ rear side first before reflecting off the front side. The resulting image looks dimmer than its actual brightness.

adjusting manual rear view mirror tab
Older prismatic rear view mirrors have a mechanical control tab on the mirror’s buttom, which you need to adjust by hand to switch between driving modes.

Power Button on Rear View Mirror

Automatic rear view mirrors handle the job of switching the prismatic rear view mirror between driving modes according to the current lighting condition. By taking over the task, they reduce the risk of distraction and let you concentrate on keeping an eye on the road.

The typical automatic mirror system features photo sensors that measure light levels. When the sensors notice it’s getting dark, they’ll dim the mirror’s surface to reduce the amount of light that reflects off their surface.

Instead of tilting a prism-shaped glass, many automatic rear view mirror systems dim the material through electrochromism. Electrodes apply voltage to the mirror, changing the color to a darker shade.

In some vehicles, the side mirrors are also automated to darken or lighten alongside the rear view mirror. The combination further reduces the risk of glare.

In some vehicles, the power button on the automatic rear view mirror resembles the manual tab that controls the older mirror. You activate the computer-controlled system by pressing the button and shut it down the same way.

How Much Does a Replacement Rear View Mirror Cost?

A new rear view mirror can cost anywhere between $10 and $400. The exact price can vary according to factors like the product’s manufacturer and your vehicle’s year, make, and model.

About The Author
Written By Automotive and Tech Writers

The Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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