How an Auto Dimming Rear View Mirror Works

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Here's a break down on how an auto-dimming electro-chromatic rear view mirror works.

Drivers often face glare from vehicles behind when driving at night. Traditional mirrors use a flip tab to deflect the glare up and away from the driver's sight-lines.

However most cars today come with auto-dimming rear view mirrors, which automatically dim the mirrors reducing glare as the conditions warrant.

Auto-dimming mirrors rely on the principal of electro-chromism. It consists of 5 materials sandwiched between a clear glass and a mirror. The two outer materials are conductors, followed by an ion storage layer, an electrolyte, and the electrochromic layer.

When a voltage is applied to the assembly a chemical reaction occurs whereby the ions migrate across the electrolyte into the electro-chromic layer causing it to darken. This significantly reduces the light that can pass through the electrochromic layer to be reflected by the mirror back to the driver.

Auto dimming mirrors have two light sensors, one in front to detect ambient light, and one in the back to detect glare. They feed into a control circuit which applies a low voltage to the electro-chromic glass accordingly.

Gentex was one of the first companies to pioneer and mass produce this technology to the automotive industry. Once a luxury item, auto-dimming rear view mirrors are common place on many cars today.

Mirror shown in the video was from a Toyota Solara but is universally applicable to many other vehicles.

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