FYI iPad screen polarized

Discussion in 'iPad' started by mrgoat, May 4, 2010.

  1. mrgoat macrumors newbie

    Joined:
    Jul 23, 2008
    #1
    I just about freaked out a sec ago. I have my bolle polarized sunglasses on when I pulled out the ipad the screen was black and unresponsive. After several minutes of panic, I took off my glasses and miraculously the screen appeared. So it would appear that when in portrait mode the ipads screen is polarized almost perpendicular to the polarizing of glasses.
     
  2. ClemTiger0408 macrumors 6502

    Joined:
    Jun 30, 2007
    #2
    Apple has used these screen types for some time. I remember using an OLD OLD iPod (I think it might have been the first video one) and I get black streaks when wearing my polarized glasses.
     
  3. Stealthipad macrumors 68040

    Stealthipad

    Joined:
    Apr 30, 2010
  4. Bodhi395 macrumors 6502a

    Joined:
    Jul 23, 2008
    #4
    Don't have any idea about the science behind polarization, but anyone know if this could be reversed somehow so the screen would appear blank, and then if you put on the glasses you'd suddenly be able to see it?

    That would be a really cool feature if it were possible.
     
  5. kenmarable macrumors member

    Joined:
    Jun 11, 2007
    #5
    I'm no expert, but I think you could almost do that by having the screen be nothing but noise and then the glasses filter out the noise and display only the signal. Would probably need at least 2 displays on top of each other with one shining through the other (since you would need both a polarized "signal" and an unpolarized "noise" display).
     
  6. phpmaven macrumors 68040

    phpmaven

    Joined:
    Jun 12, 2009
    Location:
    San Clemente, CA USA
    #6
    LOL, I had the same thing happen to me in the car a couple of days ago. I was using it as my GPS and I looked down and the screen was black and I started hitting the button trying to figure out what was going on.
     
  7. Alkiera macrumors regular

    Joined:
    Mar 11, 2008
    #7
    Not with polarization, no.

    Polarized materials act as a filter; they alter light that passes through them so only waves aligned with the filter can pass through. Most sunglasses are polarized at a 45 degree angle(/), which helps a lot with reflections of the sun from glass, water and shiny metal, as reflection tends to organize light into a vertical(|) or horizontal(-) wave, this preventing you from being blinded by glare, as you only see a small percentage of the total light from the reflection.

    However, if you have one filter going (/) and one going (\), all the light is blocked, and you can't see anything. You can see this on a normal computer LCD by putting on polarized glasses and tilting your head 45 deg left and right. In one direction your view of the screen gets brighter(it's aligned with the polarization of the LCD) and the other it turns black(it's perpendicular to the LCD polarization).

    I have this problem with fuel pumps all the time, I have to tilt my head to one side in order to read them with my sunglasses on.
     
  8. err404 macrumors 68020

    Joined:
    Mar 4, 2007
    #8
    It not possible with polarized screens. It's just a filter to reduces glare by blocking light waves emitting from the screen that are not aligned at a certain angle. The effect that you get with your glasses is that you have a second filter performing the same task, but since the light from the screen is already uniformly aligned, it acts like an all or noting gate. That's why when you rotate you iPad while wearing your sun glasses, you will see the screen fine at some angles but others are black.

    However there is a variation on polarizing that is used in "privacy screens". It will reduce the viewing angle so that screen looks black unless you are directly in front of it.
     
  9. err404 macrumors 68020

    Joined:
    Mar 4, 2007
    #9
    Interesting Idea. This would require two sandwiched OLED panels with a polarized filter in the middle. Unfortunately this would be very expensive and not very reliable, since anybody with polarized sun glasses will be able to read your screen
     
  10. Bierp macrumors member

    Bierp

    Joined:
    Apr 19, 2010
    #10
    Peril Sensitive Sunglasses?

    I believe this is a feature:

    Peril Sensitive Sunglasses

    Joo Janta 200 Super-Chromatic Peril Sensitive Sunglasses have been specially designed to help people develop a relaxed attitude to danger. At the first hint of trouble, they turn totally black and thus prevent you from seeing anything that might alarm you.

    A double-pair is frequently worn by Zaphod Beeblebrox.

    :D
     
  11. mcdj macrumors G3

    mcdj

    Joined:
    Jul 10, 2007
    Location:
    NYC
    #11
    I noted the polarizing effect on the wifi only iPad in the Apple store a few weeks ago. I was wearing polarized sunglasses and could only see the screen in landscape.

    Yesterday I bought a 64GB 3G, and fitted it with a Speck anti glare screen protector before turning it on. Upon turning it on, the screen is not polarized in any direction.

    Dunno if that's because of the screen protector or if the 3G glass is somehow different. Wouldn't be the first time. The 24" iMac screen and the 27" screen have different polarization.
     
  12. Krevnik macrumors 68040

    Krevnik

    Joined:
    Sep 8, 2003
    #12
    Light polarization is very sensitive. If you pass it through certain materials, the effects of polarizing the light are lost, as it becomes unpolarized again. This is why 3D movies in theaters require specific materials to be used for the screen itself, to preserve the polarity of light reflecting off of it.

    All LCDs use polarizing filters (both the old style used in digital watches, and what you see on your LCD TV or computer display). It's part of the core design of the LCD. The light from the backlight goes through one filter, then the crystal matrix, and then another filter at a right angle to the first. The electrical signals to the sub-pixels control how much the light 'rotates' to match the front filter. Done this way, you turn a pixel off by just making it so that the light doesn't rotate, and is instead blocked by the front filter. (Wiki has a more in-depth explanation on this)

    Interestingly enough, this is the same reason you don't get real deep blacks without also controlling the backlight like current LED TVs now do. Two polarizing filters at right angles won't block 100% of the light passing through, just the vast, vast majority of it.

    What's likely happening is that the anti-glare film has a property to it that will scramble the rotation of the light coming out, unpolarizing it. It might be a side effect of the design (it is meant to provide a matte surface to light, which has lots of small imperfections at specific angles), or intentional. Not sure.
     
  13. MobiusStrip, Nov 25, 2011
    Last edited: Nov 25, 2011

    MobiusStrip macrumors regular

    Joined:
    Dec 11, 2009
    #13
    The problem here is that Apple polarized the screen in the wrong direction for mobile applications, which is where most people will be wearing sunglasses.

    For example, pilots keep the iPad on a kneeboard, which is where they'd keep their paper notebook and checklists if they weren't using an iPad for those things. A kneeboard orients the iPad vertically (portrait orientation) on top of your thigh so you can look down at it while flying. I don't think I've ever seen a pilot fly in the daytime without sunglasses, and a great many good sunglasses are polarized. So Apple has crippled the iPad for aviation use.

    Portrait is also the most space-efficient orientation for a vehicle (where horizontal space is at a premium). It also makes the most sense for navigation and map usage in a vehicle, since portrait orientation can show you more of what's ahead (if you keep the map in "forward is up" mode instead of "north is up").

    So there's no advantage to making the screen visible in landscape orientation, but there are advantages to making it visible in portrait. Apple knows about the problem and has had the costs of this error pointed out. Unfortunately they don't have the greatest track record when it comes to acting on design defects when customers report them. Witness their continued production of laptops that have no real Delete key (but inexplicably have a dedicated Eject key for that all-but-dead optical media).

    [​IMG]
     
  14. goosnarrggh macrumors 68000

    Joined:
    May 16, 2006
    #14
    Most sources I've read -- including FAA recommendations -- universally pan polarized sunglasses as unsuitable for use in aviation. It may be more difficult -- and possibly expensive -- to find nonpolarized sunglasses with quality that's equivalent to some of their higher-end poalrized cousins, but they are more highly recommended for aviators.

    So Apple's decision hasn't necessarily done anything to cripple the iPad for aviation use, provided the pilots are following best practice guidelines for eye protection.
     
  15. MobiusStrip macrumors regular

    Joined:
    Dec 11, 2009
    #15
    I've never heard or seen such a recommendation. Why are they supposedly unsuitable?

    And I don't think Apple's design had anything to do with best practices. There are plenty of other situations where the current orientation doesn't make sense.
     
  16. psonice macrumors 6502a

    Joined:
    Jul 22, 2005
    #16
    We've just discovered that LCD screens and polarised glasses don't mix. The average airline cockpit is full of LCD displays. Somehow, I suspect that the pilots just might be ahead of us here. :rolleyes:
     
  17. IllIllIll, Nov 26, 2011
    Last edited: Nov 26, 2011

    IllIllIll macrumors 65816

    Joined:
    Oct 2, 2011
    #17
    Ever use a circular polarizer in photography? It "scrambles" the alignment of the light waves after polarization so people wearing polarized sunglasses (and camera autofocus sensors) can still see the image. This is why most modern autofocus cameras cannot use linear polarizers on their lenses. So this is not an insurmountable problem, it's one of practicality and cost/benefit.
     
  18. TLewis macrumors 65816

    Joined:
    Sep 19, 2007
    Location:
    left coast, US
    #18
    A google search gives a fine FAA PDF document as the first result.
     
  19. MobiusStrip macrumors regular

    Joined:
    Dec 11, 2009
    #19
    Well, I'm a pilot, and I can tell you that this isn't a problem in any competent cockpit. Garmin systems, for example, are polarized properly. Even their consumer-grade systems don't exhibit this problem.

    I encountered an Avidyne system a few years ago that was defective in this regard, but that's their problem. A total failure of testing.

    Don't expect the customer to abandon his best practices to work around defective design. There's nothing stopping manufacturers from making LCDs that work just fine with polarized glasses. Anyone who doesn't should exit the business immediately, since their attention to detail is obviously lacking and they shouldn't be trusted.
     
  20. borisiii macrumors 6502

    Joined:
    Jul 4, 2010
    #20
    Light from an LCD is collimated in a particular plane. Cheaper polarised sunglasses tend to use linear polarisation, displaying the effect in Mobius' picture when the plane of polarisation is perpendicular to that of the display.

    More expensive sunglasses use circular polarisation. That way they still serve their purpose of reducing reflections and glare, but the display is visible from any angle.

    3D glasses that you get in cinemas also use circular polarisation - in this case one lens is clockwise polarised and the other is anticlockwise polarised. That way each eye sees a distinct image, but you can still see the film even if your head isn't horizontal, e.g. you are leaning on someone's shoulder.
     
  21. kdarling macrumors P6

    kdarling

    Joined:
    Jun 9, 2007
    Location:
    First university coding class = 47 years ago
    #21
    Pilots already are trained by most flight instructors to use a similar defense mechanism:

    During an emergency engine-out landing (what the FAA calls a "forced landing", and the press usually calls a "crash landing") at night, you are trained to wait until the last second and then turn on your landing light.

    If you like what you see, keep the light on. If what you see terrifies you, turn it back off !

    :)
     
  22. MobiusStrip macrumors regular

    Joined:
    Dec 11, 2009
    #22
    Where do you get that idea? The glasses in the picture are Oliver Peoples, and my other pair are Oakleys. Neither of which would be considered cheap. Movie-theater glasses, on the other hand, are cheap as hell.
     
  23. stordoff macrumors regular

    Joined:
    Aug 24, 2009
    #23
    You can just about do this if you remove the filter from the LCD, and use that in a pair of sunglasses instead.

    Instructions here: http://www.instructables.com/id/Privacy-monitor-made-from-an-old-LCD-Monitor/
     
  24. goosnarrggh macrumors 68000

    Joined:
    May 16, 2006
    #24
    The points I've read included warnings about enhancing striations in laminated windscreens leading to optical dead spots in the window, and incompatibility with certain avionics equipment which incorporate anti-glare coatings.

    The FAA recommendation is here:
    http://www.faa.gov/pilots/safety/pilotsafetybrochures/media/sunglasses.pdf

    An American Optometric Association link is here:
    http://www.aoa.org/x5349.xml
     
  25. borisiii macrumors 6502

    Joined:
    Jul 4, 2010
    #25
    Would you prefer if I replaced the word 'cheap' with 'less advanced'? Your sunglasses may be from a designer brand - they were probably expensive - but that doesn't mean they incorporate the best in anti-glare technology.
     

Share This Page