Anti-glare filters on factory installed dashboard instrumentation

Question

I was reading about the reasons why pilots should not wear polarizing sunglasses when flying. Among the various reasons cited was that some cockpit instrumentation may be fitted with anti-glare filters, and may not be readable when viewed through polarizing sunglasses. This led me to wonder about the automotive situation, especially in newer cars equipped with digital dashboards, given that classic backlit or passively lit LCD displays incorporate polarizing filters as part of their normal function.

So, can the polarizing filters common in sunglasses cause problems with reading any type of automotive digital dashboard display (whatever display technology is used)?

Answer 1

Put your polarized sunglasses on, look at your LCD monitor, and tilt your head. (Or, for less neck stress, just hold the glasses in front of you and rotate them.) At certain angles, the display should be completely black. This is because most LCDs, without some sort of filter, emit polarized light. When the orientation relative to a filter - your sunglasses - is correct, the light just bounces off. All reflectance, no transmission. 3D TVs and movie theaters rely on this phenomenon to present different images to each eye.

I also notice this with ATMs, gas pump screens, and the like.

Not all displays have this issue - for instance, I can read my iPhone 6's display with my sunglasses on regardless of orientation.

So, to answer your question: whether or not this is a problem depends on the display technology and filters in play. These days, I expect the automotive designers to take into account that most "nicer" sunglasses are polarized, so they'd either orient the panel so that you'd have to be rotated 90* to have an issue - assuming, of course, that the glasses manufacturer consistently puts the "correct" side of the lens at the top of the frame, or that they would apply some sort of depolarizing coating to the display. If I were wearing my Ray-ban's while driving the wife's Caddy and I couldn't read that nav screen, I'd be nonplussed.

Answer 2

Yes, polarized glasses can be a problem. I haven't encountered a dashboard yet I can't read with my polarized glasses, but my iPhone 5 has to be installed in landscape mode to be readable. My Palm TX had to be in portrait mode, OTOH.

A quick check on my computer monitor shows it contains a polarized filter at an angle of 45°, so it's readable with my Polaroid in both landscape and portrait mode. So I've got a sample size of 3, with 3 different orientations.