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Smart Headlights Help Drivers See Better in the Rain

Srinivasa Narasimhan (Carnegie Mellon University)

Srinivasa Narasimhan (Carnegie Mellon University)

Researchers at Carnegie Mellon University’s Robotics Institute in Pittsburgh have devised a new type of car headlight that is better able to illuminate the road ahead in rain or snow. The team led by computer scientist Srinivasa Narasimhan (pictured left) says lab tests have demonstrated the feasiblity of the new headlight.

The system works by directing beams of light away from falling rain or snow that can reflect back into the eyes of the driver, causing distracting and sometimes dangerous glare. Narasimhan notes that to human eyes, rain can appear as elongated streaks that fill the air. High-speed cameras, however, can capture rain as sparsely spaced, discrete drops, which leaves plenty of space between the drops where light can be effectively distributed if the system can respond rapidly.

The prototype system uses this principle with a camera to track the motion of raindrops and snowflakes, and then applies an algorithm to predict where those particles will be just a few milliseconds later. A separate digital light processing (DLP) projection device then deactivates light beams that would otherwise illuminate the particles in their predicted positions.

In lab tests, Narasimhan’s team demonstrated that their system could detect raindrops, predict their movement, and adjust a DLP projector accordingly in 13 milliseconds. At low speeds, a system with this capability could eliminate 70 to 80 percent of visible rain during a heavy storm, while losing only 5 or 6 percent of the light from the headlight.

A road-ready headlight would likely need to replace the DLP projector with arrays of light-emitting diode (LED) lights where individual elements could be turned on or off, depending on the location of raindrops. New LED technology could make it possible to combine LED light sources with image sensors on a single chip, enabling high-speed operation at low cost.

A smart headlight system would probably not be able to eliminate all precipitation from the driver’s field of view, but reducing the amount of reflection and distortion caused by precipitation can substantially improve visibility and reduce driver distraction. “If you’re driving in a thunderstorm,” says Narasimhan, “the smart headlights will make it seem like it’s a drizzle.”

Another benefit of the system is the ability to detect oncoming cars and direct the headlight beams away from the eyes of those drivers, eliminating the need to shift from high to low beams. The Carnegie Mellon team is now building a more compact version of the smart headlight that could be installed in a car for road testing.

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