Here's the main reason why the automatic dimming mirror needs to see both forward and backward:

It needs to know if it's day or night (dark) outside! If the sensor was only rear-facing, the mirror would dim out all day long.

Try it for yourself. During the day, put your finger over the forward facing sensor (to trick it into thinking it's nighttime). The mirror will dim based on the ambient daylight hitting the rear-facing sensor.

It's not sensitive enough to pick-up street lights at night, etc. It simply needs to know if it should be active or not based on the current level of daylight.

 

Thanks, Rudy.

skidster,
it works, doesn't it ???

 

i'll try it.
i'll let you know.

didn't say that i wasn't thick - just that normally am not!

 

Thanks, Ice!

 

I tried it on the way home this evening.

You need to cover the forward hole tightly so no light gets to it. Once you've done that, wait about ten seconds and you'll see the mirror dim.

(BTW: I helped the process by retracting the rear sunshade.)

 

I understand how the rear view mirror dims with the 2 sensors front and back. However in a similar query. How do the side mirrors dim??? I have the folding mirror option which includes dimming side mirrors but you don't see the sensor at the back of the side mirror housing. So how does it work?
Is it using the rear view mirror sensor?

 

Yes.

 

We've got a winner !

 

Thanks. I'm must be a genius or great at guessing.