US 5,253,109 · Granted 1993-10-12
The Smart Window Patent That Lets Car Glass Change Tint on Demand
Imagine glass that gets darker or lighter with the flip of a switch—that's what this patent describes. It sandwiches a special liquid between two clear layers; when you apply electrical current, the liquid changes how much light it lets through, so your car window can dim itself without a motorized shade.
The plain-English version
What it protects
The claim covers an electro-optic sandwich: two transparent panes with a special liquid or gel between them whose light-blocking ability changes when electricity is applied. What's protected is the specific arrangement where a transparent interlayer bonds the two outer panes, and the back pane can have a reflective coating with windows cut into it. The innovation is keeping a constant viewing area while the liquid's opacity shifts electrically.
Why it matters
This patent addresses a real problem in automotive design: how to dim sunlight without blocking the driver's view or adding mechanical parts that break. Donnelly Corporation, a major supplier of automotive glass and mirrors, filed this to protect an early version of electrochromic glass technology. Smart windows reduce glare and heat inside vehicles, which improves comfort and fuel efficiency by reducing air-conditioning load.
Real-world use
When you're sitting in a parked car on a sunny day and the windshield gradually darkens to keep the interior cool, or when a rearview mirror automatically dims when headlights hit it from behind, you're experiencing technology pioneered by patents like this one.
Original USPTO abstract
An electro-optic device including first and second optically transparent elements mounted in spaced relationship to each other to define a gap and each having a front and rear surface. At least one optically transparent interlayer element is sandwiched between the first and second elements and joining a predetermined area of the rear surface of the first element and the front surface of the second element. A liquid, semi-liquid, gel, or semi-solid electro-optic medium, whose light transmittance is variable, is added to the gap between the first and second element. One surface of the second element may include a reflective coating except in those areas aligned with the transparent interlayer element sandwiched between the first and second element. A photoelectric cell/sensor or display is disposed behind the rear surface of the second element and may be aligned with the window formed in the reflective coating so as to receive or transmit light through the first element, the transparent interlayer, and the transparent second element.
Patent details
- Publication number
- US 5,253,109
- Filing date
- 1992-04-27
- Grant date
- 1993-10-12
- Assignee
- Donnelly Corporation
- Inventor(s)
- O'FARRELL; DESMOND J., GAHAN; RICHARD J.
- CPC class
- B60R1/088
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