My new sunglasses’ lenses include a filter for polarised light. While this has certain advantages, such as giving you a better view on the roads because the irritating reflections of the sun in car windows are removed (meaning that even on sunny days you can quite clearly see people in their cars) or generally making the world look a little crisper (think Truman show), there are disadvantages as well which may make this a somewhat bad feature.
The first problem is of course photography. Filters for polarised light are a cool tool in photography. For removing those annoying reflections or just giving you cool skies. And thus, these sunglasses are particularly bad for taking photos with (any sunglasses are, but the filter makes things worse) because the image is changed between the camera and your eye.
But as I walked around I noticed that there are many other occurrences of polarised light as well. One thing is normal light that is reflected from the sidewalk, say. While this isn’t of a single polarisation, it still seems to have a pre-dominant direction of polarisation. And thus – wearing those sunglasses – will give you a varying brightness of the sidewalk if you happen to lean your head sidewards, thus changing the angle between the light and the filter. Not that I great I think. Another, slightly irritating thing is that tensions in glass seem to change the polarisation of the light they reflect. And with the glasses you can easily see patterns in seemingly straight car windows, say.
Another issue are flat panel displays. These seem to emit polarised light as well. And the problem comes in different severities there. Using my MacBook this isn’t a big deal. The polarisation is such that I have a fairly normal view of the screen. Just when leaning my head over to the left or right, the brightness will be reduced. As I normally look at a screen straight on without tilting my head, I hardly notice the problem. Well, I hardly notice the problem anyway as I usually don’t wear sunglasses when using a computer…
When visiting the local Mac dealer recently [my brother’s MacBook’s top case cracked in the same way mine did on his way here and they managed to fix this for him within a few hours despite the Saturday shopping rush, thus saving the trouble of having to use some other and potentially unreliable shop] I noticed something odd, though. It appears that the polarisation on their 24″ iMac is of a different orientation. Which made that machine’s screen simply look black to me. Very irritating.
I wonder whether having such a filter in sunglasses may actually be a real problem for some. If modern displays emit polarised light and the polarisation can be of any angle, people with such a filter in their glasses may face quite a bit of inconvenience when trying to use their mobile phone, say (for which the right polarisation filter could actually be great if it filters out the reflections). And it seems that cars are switching to more and more fancy displays as well. It’d be a bit of a bummer if you couldn’t read off your current speed just because the light coming from its displays is polarised in an unfortunate way.
A bit light inverted X-Ray glasses, I think. At a 0° and 90° angle, the screen’ content is visible:
But at a 45° angle, the screen goes black:
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