How Do Rain-Sensing Wipers Work?

Many new cars these days, especially those belonging to top-end trims, come equipped with rain-sensing windshield wipers. It's amazing how these devices spring into action when it detects rain falling on your windshield glass. But how exactly do they work?

It starts with an electronic module

In cars with rain-sensing wipers, you'll observe an electronic module attached to the windshield. This module--usually found at the top middle portion of the windshield--is generally made up of three main components: light emitting diodes (LEDs), photo sensor, and processor. The LEDs emit infrared light that's invisible to the naked eye onto the windscreen, which is reflected to the photo sensor. The information is then processed by the processor so it can send out signals on whether to turn on the wipers or not. Check out the illustration below.

On a clear day, the light coming from the LEDs will reflect back to the sensor with ease. But when the windshield starts to get wet, the light passes through the water droplets and are no longer reflected. And so the amount of light that the sensor receives is very low. When the processor detects this drop, it then activates the wiper motor, and so the windshield wiper turns on.

Various rain-sensing wiper features

The speed and frequency at which the wipers activate depend greatly on the level of wetness of the windshield. The stronger the rain, the faster the wipers work to ensure you have a clear view in front of you. Advanced rain-sensing systems are even able to measure the amount of moisture on the windshield glass.

Different wipers have different sensitivity settings. Some will wait until the droplets get large, while some activate immediately the moment moisture is detected. In some vehicles, the rain sensor is connected to both front and rear windshield wipers. Some have additional light sensors that also detect changing light conditions, such as when the car enters a tunnel or day turns into night, to turn on the headlight along with the wipers.

Thanks to automotive advancements such as rain-sensing wipers, drivers can enjoy safer and more comfortable driving in various wet conditions, allowing their hands to remain on the steering wheel and their eyes affixed on the road ahead.