US 5,451,822 · Granted 1995-09-19
The Smart Mirror That Dims Itself When Headlights Blind You
Imagine a rearview mirror that automatically darkens when bright headlights hit it from behind—that's what this patent does. Sensors detect glare and ambient light, then signal the mirror to adjust its reflectivity electronically. The system even turns on your headlamps automatically when it gets dark or when you use your windshield wipers.
The plain-English version
What it protects
The claim covers an electronic control system that combines an electrochromic mirror (one that changes reflectivity via electrical signals), ambient light sensors, glare sensors, and sky light sensors all wired to a microprocessor. What's protected here is the specific method of using these sensors to automatically dim the mirror based on detected light levels, and to automatically activate vehicle headlamps based on sky light detection or wiper activation. Anyone making a similar auto-dimming mirror system using these sensor-and-microprocessor logic would infringe on this patent's core mechanics.
Why it matters
This patent represents a foundational piece of automotive safety technology. Glare from following vehicles is a documented cause of accidents and driver fatigue. By automating the dimming response—rather than requiring manual adjustment—the system removes a distraction and improves nighttime driving safety. Gentex Corporation built a major business around electrochromic mirror technology, and this patent helped establish their foothold in the auto-safety market, eventually becoming standard equipment on millions of vehicles.
Real-world use
Every time you're driving at night and a car with bright headlights tailgates you, a mirror governed by this patent automatically darkens to protect your eyes without you lifting a finger.
Original USPTO abstract
An electronic control system for controlling automotive vehicle vision related equipment including an electrochromic rearview mirror comprising an electrochromic variable reflectance member the reflectivity of which varies as a function of electrical signal levels applied thereto, and an electrically energizable vehicle headlamp, the system including ambient light sensing means, glare causing light sensing means and sky light sensing means, each of said light sensing means being effective to generate an electrical signal indicative of the sensed light level, the system also including microprocessor means operable to apply electrical control signal levels to the electrochromic variable reflectance member to change the reflectivity thereof as a function of sensed ambient and glare causing light levels, the system also including means to effect energization of the vehicle headlamp as a function of the sensed sky light level. The system may also include means to effect energization of the vehicle headlamp as a function of the actuation of the vehicle windshield wiper.
Patent details
- Publication number
- US 5,451,822
- Filing date
- 1991-03-15
- Grant date
- 1995-09-19
- Assignee
- Gentex Corporation
- Inventor(s)
- BECHTEL; JON H., SCHMIDT; DAVID J.
- CPC class
- B60Q1/143
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