US 5,193,029 · Granted 1993-03-09
The Single-Sensor Mirror That Knows When to Dim
Imagine a rearview mirror that automatically darkens when a car behind you flashes its headlights at night, but stays clear during normal driving. This patent describes how one tiny light sensor can tell the difference between blinding glare and regular light by processing the speed of brightness changes—like your pupils adjusting to sudden brightness.
The plain-English version
What it protects
The claim covers an automatic rearview mirror system controlled by a single light sensor that can distinguish between glare-causing light (like oncoming headlights) and normal light by analyzing how quickly the light changes. What's protected is the processor logic that responds differently to decreasing brightness versus increasing brightness, allowing the mirror's reflective surface to automatically tint in response to glare without needing separate sensors for different types of light.
Why it matters
This patent solved a real problem: how to make an anti-glare mirror without expensive multi-sensor systems. By using one sensor and smart processing logic, Donnelly Corporation created a practical way to improve driver safety and comfort at night without significantly raising manufacturing costs. The innovation made adaptive mirrors accessible to mainstream vehicles rather than just luxury cars.
Real-world use
Every time you drive at night and a tailgater's headlights suddenly wash your rearview mirror in light, an automatic mirror like this one dims within a second to protect your vision and let you focus on the road ahead.
Original USPTO abstract
An automatic rearview mirror system having a reflective element that is actuatable between at least two different reflective conditions by a control that discriminates between glare-causing and nonglare-causing light simultaneously sensed by a single light sensor. The control includes a processor that is more responsive to decreasing levels of light than to increasing levels of light to produce a signal that is indicative of the slow-transient characteristic of the light sensed by the single light sensor. The processor may include a very slow signal processor that is always operative and a somewhat faster-slow signal processor, which may be selectively inhibited when the mirror is fully colored, or when a differential circuit indicates that the difference between the glare and the non-glare light sensed by the light sensor exceeds a predetermined level. The differential circuit may additionally limit the differential between the glare and the nonglare lights sensed by the light sensor.
Patent details
- Publication number
- US 5,193,029
- Filing date
- 1991-11-19
- Grant date
- 1993-03-09
- Assignee
- Donnelly Corporation
- Inventor(s)
- SCHOFIELD; KENNETH, GAHAN; RICHARD J., SCHIERBEEK; KENNETH L., LARSON; MARK L.
- CPC class
- B60R1/087
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