Here’s how Tesla’s auto-dimming mirrors work

The auto-dimming side and rear-view mirrors on Tesla vehicles is something that generates polarizing opinions. Some owners love them because of how safe they can make night driving. Others hate them because of how unsafe Tesla’s auto-dimming mirrors make night driving.

Auto-dimming mirrors were added to help combat what’s known as the Troxler Effect. This is when a car with bright lights behind you turns off on to another street, and you’re left with a blind spot in your eyes and temporarily have impaired vision.

This can impact your reaction time by up to 1.4 seconds when travelling at 60mph (96km/h). At that speed, you car covers 123 feet in those 1.4 seconds, a distance that could be the difference between life and death.

When it comes to Tesla’s auto-dimming mirrors, those who hate them say the mirrors become too dark at night, to the point where they are unusable.

These same owners claim the mirrors become this dark even when there are no trailing cars with bright lights behind them.

It looks like those owners may be right, based on information provided to an owner by a Tesla Service Center. The information details how and when the mirrors adjust to 50% darkness (via Reddit).

“The Model3 will dim the mirrors to half their brightness when the following are present: * The sun is down(UI_solarElevationAngle <-5 degrees, calculated using GPS and time of day) * The headlights are on (DAS_headlightRequest = DAS_HEADLIGHT_REQUEST_ON or DAS_HEADLIGHT_REQUEST_INVALID) * Whether it is in gear (DI_gear) is D or N”

Don’t let all the tech talk confuse you, there are just three things considered. The first is where the sun is, which is calculated using the car’s GPS location and time of day. If the sun has set, condition #1 has been met.

Condition #2 is if the headlights are on. Most people have the auto-headlights turned on, so once it gets dark enough, this condition is met.

The final condition is if the car is in gear. If the car is in Park or Reverse, and #1 and #2 are met, the mirrors will not dim. If the car is in Drive or Neutral, and the conditions above are met, the mirrors will dim to half their brightness.

In an interview with Drive Tesla, hacker @greentheonly said there is actually a sensor that could be used for the mirrors, but due to its poor placement it rarely detects headlights from behind. As a result, Tesla had to come up with another solution to dim the mirrors, and this was it.

Hopefully all of this will become a moot point when Tesla releases the ability to adjust the level of brightness, or turn off the feature entirely. CEO Elon Musk agreed to add this back in May 2020, which will come via an over-the-air (OTA) software update.

Not all Tesla Model 3’s come equipped with the special mirrors. The automaker quietly stopped producing them in about February this year, removing them from the description of the car on the Design Studio. Then just a few weeks ago we had several reports of the mirrors returning on newly built cars. The re-introduction was confirmed when Tesla added them back to the Design Studio earlier this month.

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