How Automatic Windshield Wipers Work

by Whitney Arana


There is no doubt that windshield wipers are vital on any car. Without wipers, driving in the rain would be extremely dangerous. Previously, drivers were responsible for adjusting their windshield wipers using manual controls on or near the steering column. Constant attention to the wipers, though, can be distracting, especially when precipitation is falling at an inconsistent rate.

Automatic Wipers

Now widely available is a solution to this type of driver distraction: windshield wipers that sense accumulating water on the windshield and automatically adjust themselves accordingly. These wipers turn on at the first sign of impaired visibility and constantly adjust their rate as rainfall, acceleration and traffic varies.


Imperative to these wipers' function is an optical sensor that monitors the front windshield glass. The optical sensor casts infrared light into the windshield at a 45-degree angle, then monitors how much light is reflected back. If the windshield is completely clear, nearly all of the light will be reflected back at the sensor (total internal reflection). If the windshield is clouded with water or dirt, less light is reflected back at the sensor, triggering the wipers. The wipers' speed, then, is constantly adjusted according to how much light makes it back to the sensor between each wipe.


The sensor is always mounted on the front windshield, usually just behind the rearview mirror.


Rain sensing wipers aren't completely outside of the driver's control. They must be activated at the start of each use (turning off the car shuts them off, as does a manual override). This prevents the wipers from becoming worn or damaged by trying to wipe a dry-but-dirty windshield or being activated in a car wash.


Automatic windshield wipers come either standard or as a factory option in the majority of new cars. Aftermarket installation is quite simple, as well. Any car can easily be fitted with this technology.

About the Author

An American living in Prague, Whitney Arana holds a Bachelor of Arts in English language and literature from Davidson College. Currently, she works as a teacher of advanced business and exam-prep English plus conversational Spanish. She contributes regularly to both Czech and American publications on topics including health, literature, food, and travel.

More Articles

Photo Credits

  • photo_camera jtravism