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Name: Ken M.
Status: educator
Age: 60s
Location: N/A 
Country: N/A
Date: 12/16/2004

Hi (This may be a re-send, I lost my text) What effect does direct sunlight (say at a perceived angle of 25 degrees in the sky on an early Fall evening), in terms of driver/passenger visibility, have when it enters the windshield of a motor vehicle? I would be interested in the refractive effect as the sunlight transitions along the curved surface (at one side) to the comparatively flat center part of the windshield, and on the differences between the visibility of the driver and passenger that the sun's rays produces.

The curvature of the windshield has little effect on the view out of (or into) the windshield. As physics textbooks show, light is refracted (bends) when passing into the glass from the air. However, when the light comes out through the other surface of the glass, it bends the "other way" an equal amount. Thus the view out the windshield is hardly distorted at all, even as the window is curved.

If the thickness of the windshield is not uniform, however, then distortion is noticeable because the variations in thickness act like a lens and produce non-uniform bending.

Bob Erck


Here is all I know, or can think of. First, architectural standards show plots of the sun angle. You may want the morning sun in the kitchen. I would think a Google search for sun path , or AIA ( arch. ) could get the angle.

By asking about difference between driver and passenger, the other factors, assume same head/ eye position, and direction of focus ( passenger does not look as low as the driver). The complicating aspect is glare. Glare can be from hood, or many other points.

Because you mention the flat part in the center, I think you may be injecting the angle. Meaning the sun more from the side. If then can you separate the driver is next to the door window?

What I am trying to get at is the complications. There are refractive indexes, in physics text. Another point which is involved. You may get some results, but cars have safety glass, so the question, "How does the layers of glass affect the index angle?"

Last, back to glare, as I think back to driving against a bright sun, the view is more explosive, by that I mean, you lose total view, it may be wrong to look at single rays of light ( there was a pun there, but I skipped it).

I expect a return message, hope some of this helps.

James Przewoznik

As you explained "the whole can be greater than the sum of its parts".

That is why they do crash tests with cars. You've explained the parts, but how far can you go with just numbers?

When I mentioned glare, and the explosion of light that blinds you, it may be that trying to identify that event is a key. At what point, or what set of conditions create the blinding glare.

Just to throw the thought out, sometimes complex problems can be solved "working backwards". Start with glare and when does vision return?

James Przewoznik

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