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Light and Curved Windshields
Name: Ken M.
Status: educator
Age: 60s
Location: N/A
Country: N/A
Date: 12/16/2004
Question:
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.
Replies:
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
Hi
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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Update: June 2012
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