Does the rear view mirror automatically dim?

Yes, many modern vehicles are equipped with an automatically dimming rear view mirror. This feature helps reduce glare from the headlights of vehicles behind the driver, improving visibility and safety.

How Automatic Dimming Rear View Mirrors Work

Automatic dimming rear view mirrors use a sensor to detect the brightness of the light behind the vehicle. When the sensor detects bright headlights, the mirror automatically adjusts its reflectivity to reduce the glare. This is typically done using an electrochromic gel or liquid crystal display (LCD) technology that can change the mirror's tint or opacity.

The sensor in the mirror monitors the light levels and continuously adjusts the mirror's reflectivity to maintain an optimal brightness level for the driver. This helps prevent the driver's eyes from being dazzled by bright lights, which can temporarily impair vision and increase the risk of an accident.

Benefits of Automatic Dimming Rear View Mirrors

• Improved visibility and safety: Reduces glare from headlights behind the vehicle, allowing the driver to see more clearly and reducing eye strain.


• Convenience: The automatic dimming feature means the driver doesn't have to manually adjust the mirror, keeping their focus on the road.


• Enhanced driving experience: Helps create a more comfortable and less stressful driving environment, especially during nighttime or low-light conditions.

Automatic dimming rear view mirrors are a common feature in many modern vehicles, providing drivers with an added level of safety and convenience on the road.

How to test auto dimming rear view mirror?

To test an auto-dimming rearview mirror, simulate a glare by covering the front sensor with your hand while shining a bright light (like a flashlight) on the back sensor. The mirror should dim within a few seconds. If it doesn't, check that the feature is enabled on your mirror and that the sensors are clean and unobstructed. 
Step-by-step test

1. Enable the mirror's power: Turn on your car's ignition and make sure the auto-dimming feature is activated. There may be a button with a light on the mirror itself to ensure it is "on". 
2. Locate the sensors: Find the sensors on your mirror. One is usually on the front (often a small, dark square) and the other is on the back. 
3. Cover the front sensor: Use your hand to cover the sensor on the front of the mirror. This simulates nighttime, as the mirror will think it's dark and needs to dim. 
4. Shine a light on the back sensor: While keeping the front sensor covered, shine a bright light (like a phone flashlight) directly on the sensor on the back of the mirror. 
5. Observe the result: The mirror should dim within a few seconds. If the light is removed, the mirror should become clear again. 

Troubleshooting

• Clean the sensors: Make sure both sensors are clean and free of any dust or grime that could block the light. 
• Check for aftermarket tint: Too much aftermarket tint on the rear window can interfere with the sensor's ability to work correctly. 
• Check the fuse and wiring: If the mirror still doesn't work, the problem could be a blown fuse or a loose connection. You may need to check your car's fuse box or consult a professional, says this Inside EVs Forum post. 
• Consult a dealer: If the above steps don't resolve the issue, it may indicate a faulty sensor or a problem with the mirror itself. A dealer or specialist can diagnose and fix the issue. 

How does rear view mirror night mode work?

Rearview mirror "night mode" works in two main ways: manually with a wedge-shaped mirror or automatically with an electronic system. Manual mirrors use a lever to tilt the reflective surface from a highly reflective back layer to a much less reflective front glass surface, which dims the reflection. Auto-dimming mirrors use electrochromic gel between two glass layers; sensors detect bright headlights and send an electric current to the gel, which darkens to reduce glare automatically.
 
This video explains the difference between manual and automatic rearview mirrors: 58sHistory of Simple ThingsYouTube · Oct 22, 2024
Manual "Day/Night" mirrors

• How they work: These mirrors have a wedge-shaped piece of glass, meaning the front and back surfaces are not parallel. 
• Daytime: The mirror is positioned so you look through the glass to the highly reflective, silvered back surface, which provides a strong, bright reflection. 
• Nighttime: Flipping the small tab at the bottom of the mirror tilts it so you are now looking at the much less reflective front glass surface. 
• Result: The front surface reflects only a small amount of light, significantly reducing the glare from headlights behind you while still allowing you to see the vehicle. 
• What you are actually seeing: You see a dimmer reflection off the front surface of the glass instead of the main, bright reflection off the back silver coating. 

This video shows how to manually dim the rearview mirror: 47sMake It Easy MechanicYouTube · Aug 6, 2021
Automatic (Auto-Dimming) mirrors

• How they work: These mirrors are made of two layers of glass with a special electrochromic gel in between. 
• Sensors: They have light sensors on both the front and back to detect the difference between ambient light and bright light from behind. 
• Nighttime: When the rear sensor detects bright headlights, it signals a microprocessor to send a small electric current to the gel. 
• Result: The current causes the gel to darken, absorbing excess light and dimming the reflection so you are not blinded by glare. 
• Daytime: When the bright headlights move away, the sensors note the change and turn off the electric current, allowing the gel to return to its clear state and the mirror to function normally. 

You can watch this video to learn how auto-dimming mirrors work: 56sspeedkar99YouTube · Jul 8, 2015

Why is my auto dimming rear view mirror not dimming?

If your auto-dimming rearview mirror isn't working, first check the light sensors for obstructions and clean them. If that doesn't fix it, check the fuse for the mirror, look for loose or damaged wiring connections, or ensure no aftermarket window tint is blocking the sensors. If these simple checks fail, the internal components may be faulty and the mirror may need professional repair or replacement.
 
This video demonstrates how to check if your auto-dimming mirror is working correctly: 32shybrid32494YouTube · Oct 3, 2018
Simple checks

• Clean the sensors: Locate the small sensors on the front and back of the mirror (typically a little square on the front and a larger one on the back) and clean them to remove any dirt or debris that might be blocking the light. 
• Test with a flashlight: Shine a flashlight directly onto the rear-facing sensor. The mirror should dim. If it does, the sensors and power are likely working, and the issue might be related to external light. 
• Check for aftermarket tint: Make sure no aftermarket tint has been applied to the rear window, as this can block the light sensors and prevent the mirror from dimming. 
• Confirm the auto-dimming is enabled: Check your vehicle's settings, often through the infotainment system, to ensure the "auto dimming" feature has not been accidentally turned off. 

You can also watch this video to learn how to check if the auto-dimming feature is enabled in your car's settings: 1mEdBwoyYouTube · Aug 15, 2022
Electrical checks

• Inspect the fuse: Look for a blown fuse labeled "Rearview Mirror," "Auto-Dim," or similar in your car's fuse box. Consult your owner's manual to find its exact location. 
• Examine the wiring harness: Check the wiring harness connecting the mirror to the car, especially where it enters the windshield. Make sure connections are secure and that wires are not loose, corroded, or damaged, which can happen after a windshield replacement. 

Potential hardware issues

• Faulty sensor: If the mirror doesn't dim after cleaning the sensors and shining a light on them, a sensor may be faulty. 
• Internal damage: The liquid inside the mirror can leak, causing distortions and rendering the auto-dimming function useless. In this case, the mirror itself is likely damaged and will need professional repair or replacement. 
• Loose connection: A short in the wiring harness or a loose connection can cause the mirror to work intermittently or not at all. 

Next steps

• If the simple fixes don't work, consider replacing the fuse or securing the wiring as described in the electrical checks. 
• If the problem persists, it's likely a more complex issue. You can look for a specialized auto glass repair shop or a dealer to either replace the faulty glass or the entire mirror assembly. 

How does auto dimming rearview mirror work?

An auto-dimming rearview mirror uses electrochromism to reduce glare, employing sensors to detect bright light and an electric current to darken a special gel sandwiched between two glass layers. When headlights are detected, a sensor triggers an electric current that passes through the gel, causing it to darken and reduce glare automatically. When the light source is gone, the current stops, and the gel returns to its clear state.
 
This video demonstrates how an auto-dimming mirror works: 28sspeedkar99YouTube · Jul 8, 2015
Key components and process

• Glass and gel sandwich: The mirror has two layers of glass with an electrochromic gel in between. 
• Sensors: Photo sensors, usually on the front and back of the mirror, detect light levels. 
• Control unit: A control unit processes the information from the sensors. 
• Electric current: When the sensors detect bright light, the control unit sends a low-voltage current through the gel. 
• Dimming: The electric current causes the gel to change color and darken, reducing the amount of light reflected. 
• Clearing: When the sensors no longer detect bright light, the current is cut off, and the gel becomes clear again. 

You can watch this video to see a real-time test of an auto-dimming mirror: 27shybrid32494YouTube · Oct 3, 2018