[AlanHo]

being an ex-engineer I have always had a natural curiosity about how things work. It has cost me some embarrassment and trouble over the years when I have been unable to re-assemble something I took apart in my quest for knowledge.

So yesterday I was driving the car and it started to spit with rain - causing the wipers to start and then stop when the screen was dry. Having nothing better to do I started speculating how the rain is noticed by the car.

Rather than dismantle the car - I Googled when I got home.

A beam of infra red light from within the car is angled at 45^o to the screen. Some of it is reflected back to the sensor. If the screen is wet, the light is deflected and it reduces the amount received by the sensor - at a certain level it causes the wipers to start up and remain working until the screen is dry.

So now we know.

[Cookie Thumper]

Yeah its pretty cool how they work, even with a 42mm multilayer laminate windscreen they still work !

[Dazzler]

Thanks Alan, so the next question to answer is why are some better than others. My SR is much better than my Calais at sensing light rain but the system is probably not quite as slick as my first (2010) Hybrid Camry (the only other car I've had with the feature)

[AlanHo]

Thanks Alan, so the next question to answer is why are some better than others. My SR is much better than my Calais at sensing light rain but the system is probably not quite as slick as my first (2010) Hybrid Camry (the only other car I've had with the feature)

Dunno - perhaps it's a sub-conscious measure of your psychological attachment to inanimate objects - like a car. You are currently in love with the i30 but the Calais was just a passing fancy.

[Dazzler]

Nah... Don't think it was that. 

[mickd]

My rain sensor always made the my hand move to turn them off or on. 
Santa has this function, now all we need is some RAIN.