Cars with purple windscreens...

[Leopold]

I've seen quite a lot of them here in Europe, mainly relatively modern French mainstream cars like Citroen, Renault and such. Also other brands but not very common. Apparently they have windscreens that are supposed to attenuate IR radiation into the car and decrease AC needs.

I say "purple" because this is how it looks with my polarized driving glasses, also as seen by my dashcam equipped with CPL filter.

My question is: how does the polarizing CPL filters work in these cars? Does it work at all?

For some reason these kind of windshields cancel out the effect of ordinary polarized glasses - usually you can see right through a car with ordinary windshields, but here you have a purple shield that is very difficult to see through. If it is difficult to look into cars with these kind of windshields through polarized glasses, I would expect also difficulties for filters like CPL to work as intended when looking out via a dashcam.

How does it work for you in practice?

 

[Deleted member 37895]

I would expect them to be fine because chances are many drivers of those cars wear polarized sunglasses. BTW you don't need a CPL for a dashcam, you only need a linear polarizer

 

[Lola]

I would expect them to be fine because chances are many drivers of those cars wear polarized sunglasses. BTW you don't need a CPL for a dashcam, you only need a linear polarizer

Where do you get linear polarizer material ?

 

[Nigel]

I've seen quite a lot of them here in Europe, mainly relatively modern French mainstream cars like Citroen, Renault and such. Also other brands but not very common. Apparently they have windscreens that are supposed to attenuate IR radiation into the car and decrease AC needs.

I say "purple" because this is how it looks with my polarized driving glasses, also as seen by my dashcam equipped with CPL filter.

My question is: how does the polarizing CPL filters work in these cars? Does it work at all?

For some reason these kind of windshields cancel out the effect of ordinary polarized glasses - usually you can see right through a car with ordinary windshields, but here you have a purple shield that is very difficult to see through. If it is difficult to look into cars with these kind of windshields through polarized glasses, I would expect also difficulties for filters like CPL to work as intended when looking out via a dashcam.

How does it work for you in practice?

These windscreens contain a reflective layer in the laminated glass that allows green light and most of the red and blue either side through but reflects most of the IR, a lot of the UV and some of the red and blue. red+blue = purple so the reflection looks purple.

From the inside it has little effect other than to turn everything a stronger green than normal which your eyes soon get used to. If you look through polarised glasses or a CPL they will block the internal dashboard reflection as normal and you don't see the outside reflection so there is no issue from that.

Not sure what the issue from the outside is, but the purple reflection is being reflected off the lamination rather than the outside of the glass so is affected by traveling through the outer layer of glass, it may also have an additional coating that modifies the polarisation.