AUTOMATIC RAIN SENSORS:

In 1958, the cadillac car motor company of general motors experimented with a water-sensitive switch that triggered various electric motors to close the convertible top and raise the open windows of a specially-built eldorado biarritz model, in case of rain. The first such device appears to have been used for that same purpose in a concept vehicle designated le sabre and built around 1950–51. For Model Year 1996, Cadillac once again equipped cars with an automatic rain sensor; this time to automatically trigger the windshield wipers and adjust their speed to conditions as necessary.

The most common modern rain sensors are based on the principle of total internal reflection: an infrared light is beamed at a 45-degree angle into the windshield from the interior — if the glass is wet, less light makes it back to the sensor, and the wipers turn on. Most vehicles with this feature have an "AUTO" position on the stalk.

sources:vw

The rain sensors automatically regulate the frequency of your windscreen wipers, according to how heavily it is raining.

Our rain sensors mean you won't have to keep switching your wipers on and off, or adjusting their speed, according to how hard it is raining. This clever system uses an LED sensor, fitted behind your internal mirror, to detect the amount of rain falling on your windscreen and adjusts the wiper accordingly.

You can also choose different settings, depending on how sensitive you want the rain sensor to be. If you choose the most sensitive setting the wipers will clean off just a few spots of rain, whilst the least sensitive setting will wait a little longer before starting to work. And you don't even have to worry about reversing. When the sensor is on and you select reverse gear, the rear wipers will automatically wipe away any rain.

The sensor system consists of a number of infrared light-emitting diodes (LEDs) and a central photodiode. The light emitted by the LEDs is reflected by the windscreen onto the photo sensor. The more drops of water there are on the windscreen, the less light the sensor receives. This information is passed to an electronic control unit, which adapts the wipe intervals of the windscreen wiper accordingly.

And the design means that dirt, minor defects and ageing of the windscreen do not impair its efficiency. You'll find driving in wet conditions safer and more comfortable because the rain sensor does the hard work, leaving you to concentrate fully on the road. It's especially useful in situations when your visibility is suddenly impaired - while overtaking lorries on a wet road....