US 5,285,060 · Granted 1994-02-08
The Automatic Dimming Mirror That Reads the Road's Light
Imagine a rearview mirror that automatically gets darker when bright sunlight hits it and brighter when it's dark outside — all without you touching anything. This patent describes how a mirror can sense light conditions around your car and adjust itself in real time, while also adjusting any display info shown on the mirror so you can always read it clearly.
The plain-English version
What it protects
The claim covers a rearview mirror system that combines three key features: a reflective surface that can change how much light passes through it, a light sensor that continuously measures brightness around the vehicle, and a control circuit that automatically adjusts the mirror's darkness based on those light readings. What's also protected is the intelligence behind it — the system that adjusts any digital display shown on the mirror so it stays readable whether the mirror is dark or clear, and compensates for reduced light transmission by boosting display brightness accordingly.
Why it matters
Automatic dimming mirrors solve a real driver safety problem: glare from headlights behind you at night can cause temporary blindness and accidents. By automatically darkening in response to brightness, the mirror protects driver vision without requiring manual adjustment. The patent's innovation — especially the simultaneous adjustment of both mirror darkness and display intensity — creates a seamless user experience that didn't exist before. This became a standard feature in higher-end vehicles because it genuinely improves nighttime driving safety.
Real-world use
Every time a car with an automatic rearview mirror drives into bright sunlight or gets hit by headlights from behind at night, the mirror darkens itself to protect the driver's eyes without any button press or hand movement needed.
Original USPTO abstract
A rearview mirror system for a vehicle having a reflective element with a reflective surface and a variable light transmission element includes an optical display device behind the reflective element in order to produce a visual display to the driver. A control is provided having a light sensor that senses light conditions in the vicinity of the vehicle and produces a continuously variable light signal indicative of such sensed light conditions. The control further includes a drive circuit that is responsive to the light signal in order to supply a drive signal to the reflective element and thereby establish the light transmission level of the light transmission element. The control further includes an intensity control circuit that varies the intensity of the optical display as a function of the value of the sensed light in the vicinity of the vehicle in order to accommodate physiological changes in the driver's eyes. The intensity control circuit further varies the intensity of the optical display device as a function of the drive signal supplied to the reflective element in order to compensate for reduced light transmission levels of the light transmission element. The intensity control circuit sums values of the light signal and the drive signal and processes the sum to a pulse-width modulated signal using a non-linear processor. The intensity control also provides a substantially constant high intensity of the optical display device for all values of sensed light above a predetermined high light.
Patent details
- Publication number
- US 5,285,060
- Filing date
- 1992-12-15
- Grant date
- 1994-02-08
- Assignee
- Donnelly Corporation
- Inventor(s)
- LARSON; MARK L., LYNAM; NIALL R., SCHIERBEEK; KENNETH L.
- CPC class
- B60R1/088
Want to file your own patent?
If you're designing an automotive gadget that reacts to light or motion, explore our free patent scanner to see what's already locked down in your space before you build a prototype.
Free patentability scan