Reducing dashboard reflections in the windscreen.

When I finally got a modern vehicle after 16 years with the Crown, almost the first problem I found was the reflection of the dash in the windscreen. I was in full sun and was attempting to drive into the shadow cast by a semi-trailer and I could hardly see anything.

I rushed out and bought a dash mat in a charcoal grey. It did not help all that much, jet black would have been better but I did not see one and I was concerned that it might overheat in the sun.

I was peeved at this feature of my new car and it was also a concern to others as the problem was noted in the Open Road magazine.

Then my wife said to give an old pair of polaroid sun glasses a go. The solution was found. As I wear bi-focals I thought there would be a problem and I would have to use clip-ons but I found that polarised bi-focals with a light neutral grey tint are available and things have never looked better.

The following photos were taken through my normal and then my polarised glasses. The bits of paper that I placed on the dashboard help to show the result. Without them I would have had to search for just the right location to show the effect. The wire mesh it is just my temporary driveway gate that I should have opened before taking the pictures.







I fished out my old physics book and found that when glass reflects light at an angle of about 32 Deg. it is polarised. This angle was given the name of the "Brewster Angle" and it is a piece of luck that just about this angle is used for the windscreen rake in modern cars. The polarised glasses cut this polarised light because they are set up to stop reflected light from similar surfaces for example sheets of water.




You can see from the above diagram the angles that the rays take. The red rays become polarised when they reflect off the windscreen and they can be blocked with polarised sun glasses or polarised prescription glasses.

Some of the pieces of paper are still faintly showing because their location results in reflection that is not quite at the magic "Brewster" angle.

Somebody mentioned that they could not see the car instruments when using polarized glasses. You should decide what is more important — the road or the instrument.



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