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How rain-sensing wipers detect a downpour

Dec 18, 2017

toyota rain sensing wipers image
You’re heading down the highway and Mother Nature is being miserable and unpredictable. It’s nearly freezing outside. Patchy rain, sleet and even flurries come and go, making roadways slick, impeding visibility and wearing away at your peace of mind.

The inconsistency of the precipitation means you’re continually fiddling with the windshield wiper stalk, in the sort of driving conditions where you should be focusing entirely on the road ahead.

That is, unless you have rain-sensing wipers. These automatically detect precipitation from mist to downpours to blizzards, and automatically adjust, activate and deactivate the wipers accordingly – leaving you to focus on the drive.

But how do they work? Turns out, all you need is a little bit of the right sort of light.

How do rain-sensing wipers work?

Rain-sensing wipers are powered by a circuit board, mounted inside the windshield glass near the rearview mirror. The circuit board houses a small infrared lightbulb that is the key to everything.

The concept is simple: the bulb emits a stream of low-energy infrared light that is invisible to the naked eye, similar to the light projected from your TV remote. The light from the bulb reflects back off the inside of the windshield and is detected by an optical sensor on the circuit board.

When the windshield is dry, most of the infrared light emitted by the bulb is reflected by the glass, and picked up by the optical sensor. When the windshield is wet, the droplets of water mean the infrared light is scattered, not reflected. This means less of the infrared light winds up being reflected back into the optical sensor. It is this change that then triggers the wipers.

In a nutshell, rain-sensing wipers constantly measure the amount of infrared light returning to the optical sensor, to determine how wet the windshield is. That information is used to operate the wipers accordingly, with no driver action required.

Enhanced visibility, no effort

With rain-sensing wipers on board, drivers only need to flick the wiper stalk into the auto position. When there’s no rain or snow, the windshield stays dry, and the wipers stay off. At the first sign of precipitation, the wipers are activated instantly – and their speed is adjusted automatically, with millisecond precision, to keep your windshield clear. Drivers can adjust the sensitivity of the system’s response to precipitation to their own preferences with a small adjustment ring on the wiper stalk.

One less worry

This is all part of the confident driving experience that comes with vehicles like the Toyota RAV4 and the Toyota Highlander. Combined with other automatic or self-regulating Toyota features such as Automatic High Beams, Dynamic Radar Cruise Control and automatic all-wheel drive (AWD), rain-sensing wipers are a key part of a suite of technologies that give drivers more assurance on the road.

Other benefits

The ability of Toyota’s rain-sensing wipers to react faster than a human driver to spray from other vehicles, and to eliminate any second-guessing about when to activate the wipers or what speed setting to use, provides  peace of mind. Further, by running the wipers at the appropriate speed at all times, the system prevents over-use of the wipers on a dry windshield.

Of course, Toyota’s rain-sensing wipers can be operated manually, and can be turned off when appropriate, such as when going through a car wash. Best of all, if your Toyota is also equipped with Dynamic Radar Cruise Control, the system is deactivated for safety’s sake when the rain-sensing wipers detect heavy precipitation.

Try for yourself

For more information on rain-sensing wipers, or to try the system for yourself, visit your local Toyota dealer. If it’s not raining, set the rain-sensing wipers to ‘auto’, and pour or spray some water on the windshield, just outside of the rearview mirror, to see the system in action. rain-sensing wipers are available on numerous Toyota models, including the RAV4 Hybrid, Sienna Limited and Highlander Limited AWD.

The features and functions in might not be applicable to your Toyota model. See your Owner’s Manual for details.