CMU-created headlights avoid rain, snow glare

Researchers hope mass production will reduce cost

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What driver hasn't experienced this danger? Nighttime in a downpour or snowstorm. The headlights, especially high beams, flicker, reflecting off of the raindrops and snowflakes, greatly reducing visibility. Clenching the steering wheel, the driver leans toward the windshield in an attempt to see the roadway through the blinding glare.

Soon there could be sight of the end of the struggle.

Researchers at Carnegie Mellon University's Robotics Institute are developing a "smart headlight system" that improves nighttime visibility during rainstorms or snowstorms by redirecting light between raindrops and snowflakes.

Srinivasa Narasimhan, a professor of robotics, is leading a research team that uses a computer, camera and projector to reduce the amount of light shined on particles of precipitation -- be it rain, snow or hail.

The camera takes continuous photographs of raindrop or snowflake positions a few yards ahead of the vehicle, where reflection is most severe. Based on the position, the computer calculates where the drop or flake will be milliseconds later so the light avoids the precipitation.

The prototype already works in a controlled setting. The goal is to shine light that avoids 70 to 80 percent of the precipitation, while losing only 5 or 6 percent of the luminosity of the head lamp. When light does hit a raindrop or snowflake, the driver sees a long streak of light. When the light bypasses it, the raindrop, if it can be seen at all, looks more like a thin black thread. The net effect is to provide the driver a better view of the roadway.

With the system in place, and with apologies to Gene Kelly, the driver is seeing in the rain.

"This will be useful for the driver but it could be more useful for the car approaching," Mr. Narasimhan said, noting that it works both ways. It shines light where the raindrops aren't. "Or you can say that it's shining light between the raindrops," he said. "It's the same thing."

During a demonstration last week at the Robotics Institute, the team used a standard projector, a camera and a computer, which eventually will be incorporated into a smaller headlight projection unit that will reduce the lag time, or latency period, required to process the photographs and shine light to the predicted spots between the raindrops. The shorter the lag time the better the results. Mr. Narasimhan said the goal is to reduce the latency period from 13 to 8 milliseconds.

Eventually, LED lighting combined with image sensors, all operated by a computer chip, could reduce the size and cost of the smart headlight system.

"The goal is being able to avoid enough drops to reduce the stress of the driver who's looking at the flickering of light," he said.

Another goal is a system that also can focus light on road signs or lines on the road. If the lines are too faint, the projector-style headlight could illuminate the entire lane to show the driver the way. It eventually could involve infrared radiation to detect pedestrians, deer or other animals moments before the driver typically would spot them.

Remaining challenges include gauging the path of raindrops and snowflakes when the vehicle is moving, especially at faster speeds, and how best to see through splashing water or snow, which has chaotic motions that are harder to predict. Blizzards and torrential rainfall could force the system to reduce light to a level that poses a danger for the driver. In those cases, the system could be programmed to revert to normal headlight function until conditions improve.

Beneficiaries of the technology would include older drivers with reduced vision and reflexes, Mr. Narasimhan said.

The technology's potential, like the view through the raindrops, is becoming more apparent. It could be available in a few years.

"The underlying science is there, but it's not yet in the form of a gadget that you can buy," he said. "By combining the technology and reducing the size of the headlights, I think we can think about this commercially."

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First Published July 18, 2012 4:00 AM


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