# Infrared light and auto windshields.



## Alin10123 (Sep 18, 2005)

Ok... now i recall hearing about it but i'm not sure what it is. 
The reason why i'm asking is because i recently attained a cruise card for the tolls in my state. The instructions say "place 2 inches below top of windshield behind rear view mirror." But then it goes on to talk about "higher end cars" where some of the windshields like the BMW 745 will block out "infrared light". The instructions them go on to say which spots on that particular model will block out infrared light. 

I dont drive a bmw. But i do drive an Acura. 2 inches from the top of the windshield is sort of this blue strip that helps keep the car cool. It's pretty much the same as the Honda's have at the top of the windshield. 

Will that block out infrared light? The instructions didn't say anything about that. I dont want to start racking up tickets without even knowing it when i'm cruising through the CC lane at the tolls.

thanks in advance. Sorry if this is in the wrong forum, but i tried actually posting this in a car forum and nobody knew what infrared light was. I figured here... it'd be a no brainer for some of you guys.

Is infrared light like the signal that the TV remotes give out? 
I'm guessing that since this cruise card has a small 3 volt battey in it... at the cruise card lane, there's a beam of infrared light constantly shinning down through the lane, then when the card picks it up, it will shoot back the cruise card #. Is that why if infrared light is blocked it wont work?

thanks again.


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## wasBlinded (Sep 18, 2005)

*Re: Infrared light.*

I think they are referring to a metallic film on the windshield that is used to block infrared light and reduce heating of the contents of the car. The problem is that this extremely thin metallic film can also block radio signals, hence the warning with your card.


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## Alin10123 (Sep 18, 2005)

*Re: Infrared light.*



wasBlinded said:


> I think they are referring to a metallic film on the windshield that is used to block infrared light and reduce heating of the contents of the car. The problem is that this extremely thin metallic film can also block radio signals, hence the warning with your card.




ok...
So... does anyone here know if Acuras/Hondas have it? or are ok to use with this particular cruise card?


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## Zelandeth (Sep 19, 2005)

*Re: Infrared light.*

Over here the only cars I've actually had a chance to look at it on have been Peugeots and Renaults.

Generally speaking it's a semiconductor film they apply to the glass (exactly the same as is applied to the inside of the outer envelope of an SOX lamp incidentally - just that it's keeping heat in there, rather than out of your car).

This can usually be detected by looking at the reflections in the windscreen (on the outside) - as coated screens firstly are usually visibly more "shiny", and secondly these films will usually impart a slight colour tint to the reflections, with the colour depending on the type used - as I remember the following are common:

Stannic Oxide: Yellow/orange.
Indium Oxide: Greenish - Blueish.
Tin Oxide: Pale Red.

These tints will be quite slight generally - but should be pretty easy to see when compared to a non-coated screen. 

The blue strip at the top is just tinted to reduce glare - isn't really anything to do with thermal management. It'll just be a simple paint/laquer most likely (or even just a transfer in some cases), rather than a hyper-expensive semiconductor film. Though some higher end cars to actually use coloured glass for it too.

Hope that helps!


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## Alin10123 (Sep 20, 2005)

*Re: Infrared light.*

THanks for the replies... i actually went ahead and applied the cruise card 2 inches from the top of the windshield behind the rearview mirror. I crossed my fingers this morning as i commuted to work and the green "thank you" light came on. Which means that everything was cool.

thanks for your guys' help.


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