US 5,530,240 · Granted 1996-06-25
The Smart Rearview Mirror That Dims Itself at Night
Imagine a rearview mirror that automatically gets darker when bright headlights hit it at night, protecting your eyes from glare. This patent covers a mirror system with a built-in display screen and smart light sensor that adjusts both the mirror's darkness and the screen's brightness based on what's happening around your car.
The plain-English version
What it protects
The claim covers a rearview mirror assembly that combines a reflective surface with a variable light transmission element (basically a layer that can get darker or lighter), plus an optical display screen hidden behind it. What's protected is the specific control system that uses a light sensor to measure ambient brightness, then automatically adjusts the mirror's tint level and simultaneously controls the brightness of any display on that mirror to keep the driver comfortable. The system uses a special processor that blends the light sensor signal with the mirror's drive signal to create the right intensity balance.
Why it matters
Glare from oncoming headlights is a real road safety hazard, especially at night. Before automatic rearview mirrors, drivers had a manual lever they'd flip to reduce glare — but it was crude and easy to forget. This patent represents the electronics that made auto-dimming mirrors practical for mass production, detecting light in real time and adjusting seamlessly. Donnelly Corporation, a major automotive supplier, locked down this technology early, giving them a competitive edge in a feature that became standard on mid-range and luxury vehicles.
Real-world use
When you're driving at night and a car behind you flashes its bright headlights, your rearview mirror automatically darkens to protect your eyes — that's this patent in action.
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 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 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 level and below a predetermined low light level.
Patent details
- Publication number
- US 5,530,240
- Filing date
- 1995-04-21
- Grant date
- 1996-06-25
- Assignee
- Donnelly Corporation
- Inventor(s)
- LARSON; MARK L., LYNAM; NIALL R., SCHIERBEEK; KENNETH L.
- CPC class
- B60R1/088
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