Smart Headlight System Removes Raindrop Glare

You're driving down a twisting mountain road at night and all of a sudden the storm clouds open. Whatever you do with your headlights you can barely see more than a couple of metres in front of you. Fortunately, that's all set to change thanks to a team of scientists who can make the reflections from the rain disappear.

Researchers from Carnegie Mellon University have developed a system that can detect the distinctive streaks left by raindrops and remove them by changing the way the headlights illuminate the path ahead of the vehicle.

The system uses a digital projector to illuminate the raindrops for a couple of milliseconds, then works out what their likely path is within the drivers field of view. Armed with that information, it's possible to selectively switch off beams of light from the headlights that would illuminate the drops as they fall -- achievable when you have a matrix of lights which can be switched on and off rapidly to steer beams.

While that means that there is less light projected from the headlights, it also means that there is far less glare as the drops don't reflect back any of the light. Combined, the result is much improved visibility. Outside of the lab, the system has also been tested in a Toyota Prius where it effectively removed rain streaks up to 4m in front of the car -- the so called "critical range" at which glare is most distracting.

The only snag is that the system doesn't currently cope too well at high speeds. While it can remove 70 per cent of streaks at 30km/h, that drops to 15 to 20 per cent at 100km/h -- and it's not clear how that can be improved without some serious expense. [Technology Review, Carnegie Mellon]

Image: Chrisbkes/Flickr, Carnegie Mellon

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