What if your car had roof panels that let you see the sky during the day, but that lit the interior of the vehicle at night? This is now a distinct possibility, thanks to work being done by BASF and Philips. As members of a consortium assembled by Germany's Federal Ministry of Education and Research, the two companies have created OLED panels and installed them in the roof of a car. When switched on, the panels glow, lighting the cabin of the car - when switched off, they simply go transparent.

OLEDs are a type of light-emitting diode, which produce light by applying an electrical current to an electroluminescent film of organic compounds. Due to the fact that the light comes from all of this film, as opposed to a single focused point, the illumination provided by the new panels is said to be very soft and even.

Because the film is just 1.8 mm thick, it can also be combined with transparent solar cells. This would allow the roof panels not only to provide illumination at night, but to generate electricity during the day.

While the Philips/BASF panels may be a new innovation, panels that are at least able to switch between clear and tinted states aren't. Mercedes-Benz's MAGIC SKY CONTROL system utilizes particles in the glass that block sunlight in their "off" state, but align themselves to let it through when voltage is applied.