Purple windscreen?

[ElSupreme]

Ok, I did a couple of searches on this and am still not satisfied.

I have polarized sunglasses. When I look at some GM (think Pontiac minivans) vehicles, and some MB vehicles (less pronounced effect) with my sunglasses the windscreens look purple. After you see it you can sometimes see (although much less obvious) the purple color without any polarization.

Doing a quick search online gave me no credible reason this happens. I think it has something to do with a UV filter, and some partial polarization but I have no idea really. The only thing I found was people asking the questions. I am sure it has something to do with the glass prep.

My question is does the Model S have a purple windshield (when viewed with polarized glasses)? Does the pano roof, or back glass have this effect (possibly due to a UV/IR filter)?

 

[TEG]

Why do some car windshields look purple when Im wearing my polarized sunglasses? - Yahoo! Answers

Somewhat related:
Wikipedia: Annealing_Glass
How to Test for Tempered Glass | eHow.com

Put a pair of polarized sunglasses on and hold the glass up to a light. The polarized lenses of your sunglasses will reveal a pattern of hardening on the surface of the glass. This pattern is distinctive to tempered glass. You'll clearly be able to see that the pattern does not go all the way through to the core of the glass.

(Not sure about Model S...)

 

[ElSupreme]

Why do some car windshields look purple when Im wearing my polarized sunglasses? - Yahoo! Answers

Somewhat related:
http://en.wikipedia.org/wiki/Annealing_(glass)
How to Test for Tempered Glass | eHow.com

I am aware of this effect. And I grasp the concept why you get the 'checkerboard' with polarized lenses.

But I am talking about a very noticeable purple tint. And I found that Yahoo answers also. But the windshield will remain transparent while rotating the glasses. And (I left them at home today) I believe you get the purple no matter what the rotation. If you have seen this you would know it. Pontiac Montana/Trans-Sports seem to be the worst offenders. Although some other GM vehicles do this also. Some MB vehicles do this although it seems much less obvious.

I think it may be a UV/IR laminate in the glass that is partially polarizing certain wavelengths. But I don't even know if that is possible.

EDIT: And once you see the purple, you can see it without the polarized glasses. It is very subtle without it though.

 

[doug]

Why do some car windshields look purple when Im wearing my polarized sunglasses? - Yahoo! Answers

View attachment 7875

No one in that Yahoo answers seems to know what they're talking about.

Just look up stress induced birefringence.

 

[spatterso911]

No one in that Yahoo answers seems to know what they're talking about.

Just look up stress induced birefringence.

Sounds like something you need to consult a gastroenterologist for...:tongue:

 

[ElSupreme]

No one in that Yahoo answers seems to know what they're talking about.

Just look up stress induced birefringence.

Thank you. That is the knowledge I wanted.

Now is the Model S windshield purple?

I orginanally had the line "I saw that Yahoo answers, but I don't buy it." I ended up toning it down a little.

 

[doug]

I should clarify, if it depends on polarization (and the color changes when you rotate a linear polarizer) then it's likely stress induced birefringence. If you can see it without a polarizer, then it's likely just optical interference between some layers on the glass.

 

[brianman]

Now is the Model S windshield purple?

Anecdotal ...

I've been looking at every picture that came in on this forum (my "New Posts" list is empty) of the Model S, and I don't recall seeing any pictures that showed a purple or green tinge to the Model S windshield.

 

[ElSupreme]

I should clarify, if it depends on polarization (and the color changes when you rotate a linear polarizer) then it's likely stress induced birefringence. If you can see it without a polarizer, then it's likely just optical interference between some layers on the glass.

I think there is a slight purple tint to the window of the Pontiac minivans. And thinking about it harder I don't think I can see purple in MB windscreens without polarized glasses. I am going to do some tests in the parking lot tomorrow.

 

[ElSupreme]

Anecdotal ...

I've been looking at every picture that came in on this forum (my "New Posts" list is empty) of the Model S, and I don't recall seeing any pictures that showed a purple or green tinge to the Model S windshield.

Yeah but without a polarized filter on a lens I don't know if it would show up.

 

[TEG]

I think the "stress induced birefringence" and "annealing" are not what ElSupreme is noticing.

Some cars do have coatings to reduce UV passage that can cause colored reflections.
Roadster offered the "Solar Guard" option.
http://webarchive.teslamotors.com/display_data/teslaroadster_specsheet.pdf

...FACTORY OPTIONS ...
• Solar Guard Windshield $400
...

Other somewhat related threads:
Effect of Polarized Sunglasses on Model S's Touchscreen Dashboard
Car Windshields are not polarized!!

 

[TEG]

This looks like it has a slight purple tint:

What vehicles require license plate TAGs instead of regular TAGs? Harris County Toll Road Authority

What vehicles require license plate TAGs instead of regular TAGs?

Usually vehicles that feature a solar coated windshield will need to display the EZ TAG on the license plate.

Vehicles known to require license plate mounted tags instead of regular sticker (or windshield) EZ TAGs are:

Audi A6 (2005-2006)

Chevrolet Lumina APV (1991-1996)

Chevrolet Venture (2005-2005)

Oldsmobile Silhouette (2002-2004)

Pontiac Montana (2002-2005)

Pontiac Transport (1995-1996)
...

 

[baltobrewer]

Hey all, long time lurker, first time poster here. Love the forum, by the way. The reason that that NSX in the above picture looks like it has a rainbowed windshield is that it has aftermarket tinting on it. Yes, I know that's illegal in most states, (but so is speeding, just don't get yourself caught). A very light tint on the front window (and tinting on any other window, for that matter) will cause the rainbow effects when viewed through polarized glasses. For some reason, this seems to be endemic only to aftermarket films, not factory glass that's either darkened or UV-d. So, long story short, if Tesla doesnt tint their glass (and they've said that they can't - thanks New York...) then you won't notice a thing. Slap some aftermarket tint on the windows, and I guarantee that you will. I have tint on both of my current cars, a Honda Civic Hybrid and Accord Hybrid, and the effect is noticeable. Oddly enough, it depends more on the sunglasses. Maui Jim's are very noticeable, Ray-Ban's not so much, etc. Your mileage may vary on that one. Hope this helps!

Jay

 

[TEG]

Based on that list I included in the last post, I searched "2006 Audi A6", and sure enough:

 

[ElSupreme]

Ok TEG I think you may be onto something.

Right now I am assuming the Model S does NOT exhibit this behavior.