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Headlights Shine Between – Not Through – Raindrops

PITTSBURGH, July 10, 2012 — A new smart headlight system that can see around water droplets could help drivers navigate roadways during heavy rain- and snowstorms.

The system, developed by researchers at Carnegie Mellon University’s Robotics Institute, cannot eliminate all precipitation from the driver’s field of view, but it reduces the amount of reflection and distortion caused by water drops to substantially improve visibility and reduce driver distraction.

“If you’re driving in a thunderstorm, the smart headlights will make it seem like it’s a drizzle,” said Srinivasa Narasimhan, associate professor of robotics.

System at work: Naive illumination on left and fast reactive illumination on right during equivalent of heavy rainfall. Photos captured with long exposure time (2.5 s). (Images: professor Srinivasa Narasimhan)

The technology also could detect oncoming cars and direct headlight beams away from the eyes of those drivers, eliminating the need to shift from high to low beams.

The system uses a camera to track the motion of raindrops and snowflakes for a few milliseconds as a computer algorithm predicts their path and switches off light rays from a projection system that would normally hit the drops.

The headlight is a collocated imaging and illustration system consisting of a projector, camera and 50/50 beamsplitter. The camera images the precipitation at the top of the field of view, the processor determines the future locations of the particles, and the projector reacts to disilluminate the particles. The entire process, from capture to reaction, takes about 13 ms.

 “A human eye will not be able to see that flicker of the headlights,” Narasimhan said. “And because the precipitation particles aren’t being illuminated, the driver won’t see the rain or snow either.”

The entire process, from tracking to adjustment, takes 13 ms. At low speeds, the smart headlights could eliminate 70 to 80 percent of visible rain during a heavy storm, while losing only 5 to 6 percent of the light from the headlight.

Components of the prototype collocated imaging and illumination system.

For the device to operate at highway speeds and to work effectively in snow and hail, its response must be reduced to just a few milliseconds, Narashimhan said. Although lab tests have demonstrated the feasibility of the system, it will be a while before it could be installed in cars for road testing.

For road-worthy systems, the device would need to be based on arrays of LEDs that could be turned on or off individually, depending on the location of raindrops. The current test apparatus couples a camera with an off-the-shelf DLP (digital light processing) projector. New LED technology could make it possible to combine LED light sources with image sensors on a single chip, enabling high-speed operation at a fraction of the cost.

“One good thing is that the system will not fail in a catastrophic way,” Narasimhan said. “If it fails, it is just a normal headlight.”

Watch an Interview with Research Scientist Robert Tambor

Watch a demonstration by Carnegie Mellon associate professor of robotics Srinivasa Narasimhan

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