US 4,902,108 · Granted 1990-02-20
The Smart Mirror Patent That Killed Blinding Headlights
Imagine a car mirror that automatically dims when a bright headlight hits it from behind—that's what this patent does. It uses special chemicals that change how much light they let through when you apply electricity, so the mirror can go from clear to dark in seconds without any moving parts.
The plain-English version
What it protects
The claim covers a device with a single container holding a solution of electrochromic compounds that change their light-blocking properties when electric current is applied. What's protected here is the specific chemical formulation and the way these compounds let light transmittance vary continuously—shifting from clear to dark or vice versa by more than tenfold—all without the solution needing to be replaced or having separate compartments for different states.
Why it matters
This patent became the foundation for auto-dimming rearview mirrors, a feature that's now standard in millions of vehicles. By replacing mechanical dimmers and rotating mirrors with an electronic solution, Gentex created a category that's been licensed across the automotive industry. The ability to respond instantly and adjust smoothly to changing light conditions made driving safer and more comfortable, turning what was a convenience feature into a necessity.
Real-world use
When a car behind you flashes its high beams at night, your car's rearview mirror automatically darkens to protect your eyes from the glare—that's this patent technology at work.
Original USPTO abstract
Single-compartment, self-erasing, solution-phase electrochromic devices, solutions of electrochromic compounds for use as media of variable transmittance in such devices, and electrochromic compounds for such solutions are provided. The devices of the invention are surprisingly stable to cycling between light and dark states, have continuously variable transmittance to light as a function of electrical potential applied across the solution in a device, and have transmittance that can be varied over more than a factor of 10, from clear to dark or from dark to clear, in several seconds. Thus, the devices are especially suitable as variable transmittance components of variable transmission light filters, including windows, and variable reflectance mirrors, including anti-glare rearview mirrors in automobiles. Also provided are improved variable reflectance mirrors, wherein transmittance of reflected light is varied by thermochromic, photochromic or electro-optic means and wherein the reduction in transmittance which is required to eliminate perceptible reflection of an object to the eyes of an observer is reduced by disposing the plane of the highly reflective surface of the mirror at an angle with respect to the plane of the surface through which light from the object enters the mirror.
Patent details
- Publication number
- US 4,902,108
- Filing date
- 1986-03-31
- Grant date
- 1990-02-20
- Assignee
- Gentex Corporation
- Inventor(s)
- BYKER; HARLAN J.
- CPC class
- C07D498/04
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