On Thursday, June 13, 2013 3:12:14 PM UTC-7, noel.wade wrote:
P7 has the best answer...



But Let's step back to facts, shall we?



Polarized lenses literally block light, unless the light-waves are

oriented at a specific angle to the lens.



Almost all LCDs (including PDAs, cell-phones, iPads, and even simple

displays like Cambridge *-NAV devices or digial variometers) have 1 or

2 polarized screens, as part of how they work. See he

http://en.wikipedia.org/wiki/Liquid-crystal_display



Stacking multiple polarizing filters in the proper orientation lets

light pass through. But stacking them in the wrong orientation causes

the light passing through the first filter to be BLOCKED by the

second.



Your polarized sunglasses _are_ a "second filter", sitting between

your eyeballs and the LCD screens in your cockpit. Ergo, if the

orientation of your sunglasses' polarized surface is not near the same

angle of your electronic displays, the visibility of your instruments

will be negatively impacted. Here are two video demonstrations of

this:

http://www.youtube.com/watch?v=GkLBMAY406Q

http://www.youtube.com/watch?v=HcQWAqL2JUw



Polarized sunglasses are not all manufactured the same; and even

different batches of the same sunglasses may not always have the

orientation to the polarized lenses - don't assume that because your

glasses work for you, that you can recommend them to others or that

you can simply buy another pair of the same, and have them work

identically. Additionally, just because you find glasses that may work

with _your_ cockpit instruments and canopy, do _not_ assume that it

will work with _all_ instruments or canopies. Finally, don't assume

that all of your instrument displays have the same polarization on

their screens. I have polarized lenses that work fine when viewing

some of my instruments, but not with others (unless you rotate the

glasses 90-degrees). Also, these polarized sunglasses worked fine

with my DG-300 canopy, but created horrible moire & checkerboard

patterns on a couple of Diamond DA-20 rental aircraft canopies.



If you're going to fly with a lot of cockpit electronics, I strongly

recommend against polarized lenses because you don't want to be

distracted or fumbling with your instruments because of this effect.

There are plenty of effective non-polarized sunglasses out there that

give you good visibility and protection.



Lastly, if you're going to be flying in a club or rental environment,

where you switch ships with any regularity, do NOT assume that

polarized sunglasses which work in one cockpit will work in another.



--Noel

Good points.
I guess it all boils down to "it depends". Polarized glasses always worked for me in the gliders I flew, but I agree this is not always going to be the case.
So the solution is to have a spare non polarized glasses with you in case there is an issue.

Ramy