‘Smart’ headlights see through rain

CARNEGIE MELLON (US) — Driving at night in a rain or snowstorm can make it difficult to see, but a smart headlight system improves visibility by constantly redirecting light to shine between particles of precipitation.

The system, demonstrated in laboratory tests, prevents the distracting and sometimes dangerous glare that occurs when headlight beams are reflected by precipitation back toward the driver.

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

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The system uses a camera to track the motion of raindrops and snowflakes and then applies a computer algorithm to predict where those particles will be just a few milliseconds later. The light projection system then adjusts to deactivate light beams that would otherwise illuminate the particles in their predicted positions.

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

To the human eye, rain can appear as elongated streaks that seem to fill the air. But to high-speed cameras, rain consists of sparsely spaced, discrete drops. That leaves plenty of space between the drops where light can be effectively distributed if the system can respond rapidly.

In their lab tests, Narasimhan and his research team demonstrated that their system could detect raindrops, predict their movement and adjust a light projector accordingly in 13 milliseconds. At low speeds, such a system 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 headlamp.

To operate at highway speeds and to work effectively in snow and hail, the system’s response will need to be reduced to just a few milliseconds, Narasimhan says. The lab tests have demonstrated the feasibility of the system, however, and the researchers are confident that the speed of the system can be boosted.

The test apparatus, for instance, couples a camera with an off-the-shelf DLP projector. Road-worthy systems likely would be based on arrays of light-emitting diode (LED) light sources in which 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.

Narasimhan’s team is now engineering a more compact version of the smart headlight that in coming years could be installed in a car for road testing.

Though a smart headlight system will never be able to eliminate all precipitation from the driver’s field of view, simply reducing the amount of reflection and distortion caused by precipitation can substantially improve visibility and reduce driver distraction. The system also can 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.

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

The research was sponsored by the Office of Naval Research, the National Science Foundation, the Samsung Advanced Institute of Technology, and Intel Corp.

More news from Carnegie Mellon University: www.cmu.edu/news/