In a huge city, lighting the streets is a necessary but pricey precaution. Pedestrians and motorists are no doubt safer when streetlamps, not just car headlights, illuminate roadways and sidewalks — but streetlamps are expensive and inefficient to run. A prototype system that turns the lights on and off depending on traffic could save money while preserving safety.

Researchers at the Institut Teknologi Bandung in Indonesia built a responsive streetlamp system that recognizes a toy car speeding past, and switches on automatically. Jakarta, the massive megacity at which this effort is aimed, has more than 200,000 street lights, which cost about $17 million to operate in 2007, according to their study.

Researchers Suprijadi, Thomas Muliawan and Sparisoma Viridi built a prototype automatic lighting system that consists of a video camera, a lamp, a PC and a toy car. The camera, shooting at 25 frames per second, captures a car and the computer processes the image to determine whether it’s really a car.