Interior Rear View Mirror.?

Question

If I look at my rear view mirror (night position) during the day, I just see the back seats of my new car (Citroen C3) and not through the tailgate window. But at night, with the mirror in the same position, I do see througth the tailgate window, and the glare from the cars behind is reduced (as should happen I gather). Does anyone know of an online diagram that explains how this works? If not, could you please explain, in layman's language, how it works? Thanks.

Answer 1

Most mirrors are made of two components: a flat, highly polished, shiny metal surface, and a flat piece of glass. The shiny metal does the real
work, reflecting light rays back to the viewer. The glass simply serves to protect the metal; if it weren't there, the metal surface would tarnish,
accumulate dust and fingerprints, and quickly lose its reflectivity.

Ordinary mirrors use a flat piece of glass, mounted on top of the metal. Both the front and rear surfaces of glass are parallel to the shiny metal surface. A light ray which comes straight into the mirror, perpendicular to its surface, passes through the glass, bounces straight back off the metal, passes through the glass again, and comes out straight back towards its source.

Rear-view mirrors in cars are made slightly differently: the glass cover is thicker at the bottom of the mirror than at the top. This means that the
rear surface of the glass is parallel to the metal (since they touch each other), but the front surface of the glass is NOT.

To use the mirror in "normal", or daytime mode, you adjust it so that the metal surface acts as the reflector. Light rays from a car behind you pass
through the glass, strike the metal, bounce back, go through the glass again, and reach your eye. Like a regular mirror, the metal surface reflects most of the light which strikes it.

During the daytime, this is good. But at night, the bright headlights of the car behind you may be so bright that they blind you. That's bad. It would be nice to have a mirror which reflected only a small fraction of the light striking it -- so that the bright headlights would appear to be dim headlights: still obvious enough to catch your attention, but not so bright that they blind you.

To use the mirror in "dimmed", or nighttime mode, you adjust it so that the FRONT SURFACE of the glass acts as the reflector -- not the metal surface. Because glass is nearly transparent, only a small fraction of the light which strikes it will bounce back off it. You can detect this yourself
sometime: stand in a room at night with all the lights on, and look out a window. You will see reflections of the lights in the window.

Now, if you adjust the mirror so that light from the headlights of the car behind you bounce off the front of the glass at just the right angle to reach your eyes ... then the light rays which go through the glass and strike the metal surface will MISS your eyes. They will be reflected down farther, onto your mouth, or neck, or chest. That means most of the blindingly bright light rays won't enter your eyes, which is a good thing..

Answer 2

Probably following is the mirror you have.

From wikipedia: "A traditional rear-view mirror can be tilted to reduce the brightness and glare of lights, mostly for headlights shining directly on the eye level at night. This manual tilt mirror is made of a piece of glass that is wedge-shaped in cross section- its front side and back (silvered) side are not parallel, unlike normal mirror glass. In the default day view, the front side is tilted and the back side (which has a reflective coating, usually with silver like a mirror) is head-on and will give a strong reflection. When the mirror is tilted, its front side is head-on and the back is tilted. This view is actually a reflection off the clear, front piece of the glass rather than the back silver-coated part. Since the front part allows most of the light to go through, only a small amount of light is now reflected into your eyes."

That means you always have two mirrors, but only one of them is oriented towards the rear windov. In daily view the "night" mirror is oriented towards the ceiling of the car. In night view the "daily" mirror is oriented towards the back seat.
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Answer 3

If you want to see this effect in real time, adjust your mirror for daytime use, then at night, look at the overhead ceiling of your car...you'll see the mirror is reflecting both into your eyes and onto your ceiling...only the ceiling is fainter because it is the glass surface reflection, not the fully silvered surface. If you do it the other way around, you'll need to look down to your chin or chest to see a brighter reflection there. If you step out of the car, you'll probably be able to see both reflections, and the difference in their intensity at the same time.

Answer 4

During daytime the interior of the car has the same light as that of outside. more over the backseats are more closer than the rear view. At night , the interior of the car is less illuminated than the glare of the car coming behind.