SUN GLASSES

At 00:11 14 June 2013, Ramy wrote:
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

Polarised sunglasses should genarally be expected to have
vertical polarization because the whole point about reducing
glare from water surfaces etc is that the light reflected of the
surface to the eye tends to be polarised horizontally.

On another topic - genuine question - do polarised lenses made
without a UV absorbing tint, and without a UV absorbing lens
material such as polycarbonate, reduce UV transmission more
than in proportion to the reduction in general light
transmission?

John Galloway