How Do Auto-Dimming Rearview Mirrors Work?

Auto-dimming mirrors are offered on many modern cars today, and they’ve actually been around for a while. It’s a subtle feature that doesn’t stand out, and you might not even notice it’s there. Self-dimming mirrors are more common than they used to be, but they’re still not standard on all models.

The technology that makes modern auto-dimming mirrors work hasn’t changed much in the past few years. But hey, if it ain’t broke—don’t fix it.

Mirror magic? Nope—electrochromism

If you never need to flip a switch on your rearview mirror to swap effortlessly from day driving to night, you likely have an electrochromatic rear-view mirror. It Still Runs explains that “electrochromism refers to a color change in a substance that results when an electric current is applied.” 

When light sensors on the mirror catch glare, a current is sent to the electrochromic gel that sits between two pieces of glass in the mirror. This current causes the gel to change color, which dims the appearance of the mirror. When there is no more glare to trigger the sensor, the current stops. Then, the color change is reversed and the mirror returns to normal.

There are a variety of auto-dimming mirror options. Some include a built-in HomeLink wireless control system to let you control garage doors, driveway gates, home security systems, and even lights and appliances.

Looking out through the windshield of a car at dusk. In the rearview mirror, you can see bright lights and activity. How do auto-dimming rearview mirrors work?
Lights and activity shown in a rearview mirror | Sinitta Leunen via Unsplash

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Are auto-dimming mirrors worth it?

It depends. If you’re not photophobic (sensitive to or intolerant of light) and you’re content to just flip the little tab on your standard rearview mirror, an auto-dimming mirror doesn’t need to be high on your list of must-haves.

But if your eyes are more sensitive to light at night than during the day, or you just don’t want to have to fiddle with the mirror while you’re doing 80 on the highway, an auto-dimmer could be worth it. These days, they come standard on many premium trim levels, so your next car may just arrive ready to protect your eyes from glare.

My last Outback came with an auto-dimming mirror, and I felt so pampered. Rogue high beams? Not a problem in this cabin. My latest ride does not have this feature, and I curse its absence almost daily.

Are there auto-dimming side mirrors?

Yes, some automakers offer full self-dimming mirror systems—rearview and side mirrors—but not all. Many of those companies only provide auto-dimming technology on the driver’s side mirror. This is puzzling since drivers need to be checking both mirrors for safety, and you can just as easily be blinded by other drivers on both sides when driving on the highway.

With more and more cars adopting hyper-bright headlights, it may be worth it to look for a car with auto-dimming mirrors everywhere.

A large grey van is shown in the side-view mirror of a car traveling on the highway
A grey van shown in a car’s side-view mirror | Patrick Pleul/picture alliance via Getty Images

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Can you install an auto-dimming mirror yourself?

Technically, you can DIY just about anything on a car, including new self-dimming mirrors. You can purchase OEM (original equipment manufacturer) auto-dimming mirrors or buy an aftermarket model that will work with your vehicle. The upside of doing it yourself is that you’ll save money and be able to get exactly what you want.

The downside? It’s time-consuming, you’ll need to be comfortable connecting power, and you could damage potentially damage your windshield if something does wrong. 

Unless you’re experienced in DIY auto work or you’ve done this before, I’d likely recommend just letting your local service department do it for you. You’ll need to pay for labor rates on top of the cost of the product, but it could be worth it if you don’t love doing car work.

Artistic, blurred shot of the dashboard of a car. You can see headlights and taillights out of the windshield, and there's a tag hanging from the rearview mirror
Rearview mirror with a hanging tag | A.L. via Unsplash

Don’t want to pay for a fancy new mirror? You can try anti-glare film

What if your current vehicle doesn’t have dimming mirrors, or the car you’re shopping for doesn’t have them installed? What if you don’t want to shell out for a new product? You can try anti-glare film.  

This film can be applied to the rearview mirror as well as the side mirrors. Bonus? You can install it yourself in minutes. It’s way cheaper than buying and installing auto-dimming mirrors, but results may vary. There are professional-grade films and basic films, and they may be able to do the trick if you want to reduce glare on a budget.

Me? I’m going to be saving up to just pay my Subaru dealer to install one for me. My peepers deserve to be coddled.

You can check out this short video showing the exact science of how most auto-dimming mirrors work. It’s an older video, but the technology has stayed roughly the same over the past few years, and the presenter does an excellent job explaining how electrochromatic mirrors reduce glare.

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