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The iPad's Polarizing Effect

I thought the universe, in the form of Apple products, was playing a nasty trick on me. A new MacBook Pro's hard drive had failed, and on my way to a Genius Bar appointment at the nearby Apple Store, I had to reboot my iPhone to get it to play over my car stereo. When I arrived outside the store, I tried to fire up my iPad, and the screen was blank. Nothing I tried could start or restart it.

I figured that the battery must have discharged. I went into the Apple Store to see if I could plug it in to a computer, and while a cast member - er, associate - went off to find a cable, I tried the iPad, and it woke up just fine.

I apologized, went back outside, and the iPad didn't work again. Then it struck me: my sunglasses. I removed them, and the iPad was, of course, just fine. The polarized sunglasses I was wearing had performed a neat trick.

This effect shouldn't have surprised me. I had noticed it in the past with my iPhone 3GS while testing over a dozen GPS apps for a Macworld review. If the iPhone was in portrait orientation, I could see it just fine with my sunglasses on; when I rotated to test the apps in landscape mode, the screen became nearly black.

Studying up on this, I found that LCDs rely on two perpendicular polarized filters with liquid crystal (and other things) in between the filters. The liquid crystal changes the light's polarization, essentially canceling the perpendicular effect that would block transmission.

I've never noticed this with other LCD monitors or screens, but that's likely because the vast majority of the time I'm using a device without sunglasses, or, if outdoors, using the device in a particular orientation.

The iPad's top polarizing filter is obviously rotated 90 degrees from the one used in the iPhone. In portrait mode, the screen is nearly black; in landscape mode, it appears normal. The photos were taken through the sunglasses I was wearing.


If this happens to you, don't fear for your sanity; just take off your sunglasses. The future's so bright, you gotta doff shades.


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Comments about The iPad's Polarizing Effect
(Comments are closed.)

I notice the same effect with my Oakleys - however, I think the designers realised this could be a problem and I think they've set the polarization at about 45. So in landscape or portrait mode you can see the screen OK, albeit dimmed. In-between though, it's totally black, but you never use it at that angle.

On the positive side, polarized shades can almost totally remove reflections from the screen
45 degrees, that sounds like a good idea. I wonder how the iPad looks like through those circular polarized lenses that they use in some 3D cinemas.
Glenn Fleishman  2010-04-28 10:15
I thought that most polarized glasses were set to block reflections parallel to the horzon because most of the reflected rays that would cause glare from water or pavement would be bouncing in that orientation.
tangobozo  2010-04-28 05:57
I wear prescription polarized glasses all the time and have "seen" this often. I would point out that it is not "all" LCD's that have this property. Next time you are in the Apple store try looking at the new Imacs also, you will probably have to turn your head 90 degrees to see the screen. But New Macbook Pros or Macbooks do not.
Glenn Fleishman  2010-04-28 10:15
All LCDs have this problem - but not in the same orientation. I suspect that the polarization is designed to prevent some reflected light in the preferred orientation. But why landscape is preferred in some cases and portrait in others, I don't know.

I suppose we'll see "computer sunglasses" that have some alternate technique at some point.
Vincent  2010-04-28 06:08
You know, I really misread the word 'polarising,' as in how divergent the opinions are of people about the iPad. Some consider it a toy, some love it, most are in the middle.
Jim C.  2010-04-28 06:18
Funny, I had just noticed this last week when trying read the iPad outside. I also happened to shoot a video (on my iPhone, through my sunglasses) to demonstrate the effect. Your article finally gave me the incentive to upload the film to YouTube:

Glad to know I'm not the only one who got fooled by this! (Oh, and I run into the polarization effect on the LCD readouts at gas station pumps all the time).
Fun article. First time I noticed the LCD polarizing effect was in a gas station. The LCD screen on the pump was black. But as I was twisting around to look for another pump, I caught a weak glimpse of the numbers and remembered I had polarizing sunglasses on and LCDs use polarized light. So it happens in other places.
Jeff Miller  2010-04-28 14:57
I found this out myself today. Kept clicking on the button on my iPad wondering why it wouldn't come one.
Jane Carter  2010-05-03 15:10
Always been this way with some LCD and polarized glasses, nothing new.
Its funny that its just been commented about.
You can do neat things with polarized glasses and camera lenses.
Fun stuff.
Ron Seybold  2010-05-03 15:50
I've seen the effect with my iMac 24-inch '08. If I lift my head a bit, even indoors, while wearing polarized sunglasses, the screen goes dark. Overall, I wouldn't give the iPad any better grade in the sunlight than I'd score the Kindle in dim light.
Alan Ullman  2010-05-03 17:04
The same thing happens with many digital cameras and even with LCD displays in my car.
larryy  2010-05-03 22:34
Heh. Too bad you didn't try to show it to the person in the store. "Look, it won't start." "But, umm, it looks perfectly normal to me." "No, look, it's completely black." "What? There's a picture right there. And icons. It looks fine." "Are you crazy? It's not responding at all." "Umm, security..."
Jennifer  2010-05-28 05:22
I had almost this same conversation with my husband after he handed me his ipad to look at. I asked "how do you wake it up?" He said "wake it up? It's on." I said, "the screen's black." He said, "no it's not." And so on until I thought to try taking my sunglasses off.
I never had this problem anywhere else.
I noticed this right after I received my first iPad (wifi, I'm not on a 3G). This is not a problem for me though, I just always use the iPad in the horizontal mode that works with my prescription lenses.