Re: Car Rearview Mirror

Hi Jean!
When you switch the mirror to nighttime driving, you *should* see the ceiling of the car. If you switch it in the daytime, you do see the ceiling. At night the ceiling is dark, so you see nothing in the mirror.

So, if the mirror is aimed upwards at night, why can you still use it to see out the back window of the car? Because the glass in the rearview mirror is not a flat plate. Instead, the back surface of the glass is manufactured at an angle to the front surface. The glass is a wedge shape. The aluminum mirror coating is on the back surface of the wedge, and this metal mirror surface is what we use in the daytime. At night, when we've aimed the mirror upwards, the *front* of the glass is now tilted correctly to act as a crude mirror for looking out the back window. The front of the glass is shiney and reflective, but only gives a dim image compared to the image we would see in a real mirror. But this is exactly what the inventor wanted; when the glass wedge is tilted to its night driving position, the image of the bright headlights coming from cars in back is greatly dimmed.