Why are there dots around the edges of some car windshields? --- Jim, Annandale, Va.
Marshall Brain Answers:
If you watch this video, you can see how a new windshield is installed on a car:
The basic process is pretty simple:
As they install the new glass, you can see that there is a black edge around the windshield. And you can understand why the black edge is there. If it were not there, the glass would be clear around the edge and you would be able to see the urethane glue through the glass. It would look ugly.
When they apply that black edge to the glass, manufacturers sometimes get creative. For example, when I look at the windshield on my car, there is one place where the black edge is not applied – it allows people to read the Vehicle Identification Number (VIN). And then, up around the rear view mirror, there is an array of dots. These dots are put there to cut the amount of light coming through the glass in half around the rear view mirror. It's done to cut glare and backlighting around the mirror, and also because the little drop-down windshield shades can't shade the area around the rear-view mirror.
On other cars, there may be a dot pattern all the way around the edge of the windshield. This is a way of breaking up the straight edge – it's cosmetic, in other words. Some cars have it, some don't.