In the rain, or in thick snow, visibility sometimes gets worse when the headlights are on. But imagine if headlight beams could bend around the raindrops so that the driver can see what's ahead of them.
At Carnegie Mellon University a team led by Srinivasa G. Narasimhan has found a way to do just that. By not illuminating the raindrops the headlights would avoid a common problem: in heavy rain, headlights make it harder to see, not easier. Headlight beams reflect off the rain (or snow, or fog). The reflected light heads back to the driver's eyes, not to the obstacles on the road.
The prototype system consists of a camera, projector and beam splitter, linked to a computer processor. The camera takes a picture of the raindrops at the top of the field of view. The processor can tell where the drops are headed and sends a signal to the headlights, which adjust the beams of light they send out so that there isn't any light where the raindrop is.
The whole system is fast -- the time from capture to when the light adjusts is about 13 milliseconds. A raindrop moves falls at anywhere from nine to 13 meters per second, so the drops will only fall about 9 to 13 millimeters, or about a third to half an inch.