The light and rain sensor automatically controls the windscreen wipers and the headlights.
It independently activates the appropriate lights in poor weather, deteriorating light, tunnels or darkness. The rain sensor adjusts the wipe interval to match the strength of the rain.
LEDs inside the sensor emit invisible infrared light which is reflected at the outer surface of the windscreen only where it's free of raindrops. The reflected light is continuously measured by photodiodes.
As the quantity of water hitting the windscreen increases, less infrared light is reflected back, thus allowing an exact regulation of the wipe interval – from wiping with long pauses to continuous wiping at high speed.
In addition, the automatic headlight activation controls the headlights depending on the ambient light conditions. The light sensor measures the light conditions and controls the coming home/leaving home function.
When the driver leaves the vehicle or unlocks it via remote control, the lights illuminate the way to or from the vehicle. A handy feature, as the driver does not need to switch on the lights when getting into the car or switch them off when leaving it.
Article source: www.audi.co.uk