Jakarta is one of the biggest cities in the world. With 10 million inhabitants, it is the most populous in south east Asia and the 10th biggest on the planet.

Lighting such a city at night is an expensive business. Jakarta has over 200,000 street lights, which cost the equivalent of about $17 million dollars to run in 2007. The city has plans to double the number of street lights but would obviously like to minimise costs.

So Suprijadi, Thomas Muliawan and Sparisoma Viridi at the Institut Teknologi Bandung in Indonesia have come up with a novel plan. Their idea is to switch on street lights only when passing vehicles need them. And they've set up a model to test the idea.

The prototype is very simple. It consists of a toy car track monitored from above by a video camera. When the camera spots a toy car, it switches on lights by the side of the track.