iMac LCD panel vertically polarized?

Discussion in 'Buying Tips and Advice' started by tweakers_suck, Jan 7, 2007.

  1. tweakers_suck macrumors regular

    Feb 7, 2005
    Los Angeles, CA
    I put on my new sunglasses today and noticed that the light from my new iMac mostly disappears. My sunglasses are polarized -- verically polarized light is blocked and horizontally polarized light passes through.

    Why would LCD panels be polarized? And why would Apple choose to make the display output vertically polarized light?
  2. mkrishnan Moderator emeritus


    Jan 9, 2004
    Grand Rapids, MI, USA
    I think the polarization is fundamental to the way they work. The optical activity of the liquid crystals is what makes the display able to change opacity in the first place. And by optical activity I mean absorption of light in one polarization....
  3. fivetoadsloth macrumors 65816


    Aug 15, 2006
    I think this is correct, I know that polarization is necassary for them to work.
  4. greg555 macrumors 6502a

    Mar 24, 2005
    I've walked into a store (London Drugs) with my polarized sunglasses on and noticed that the 17" iMac is still visible, but the 20" is blacked out. So I guess different LCD manufacturers polarized different ways.

  5. bdemers macrumors newbie

    Jan 7, 2007
    Correct, polarization is key

    Hi, first post here, not the most exciting... but:

    You are correct. LCD's have two polarizing filters in them, one on each side of the liquid crystals. Light from the backlight is polarized in one direction, "spun" by the crystals depending on their charged state, and re-filtered by a second filter in front. Somewhere in this sandwich, there's also a color filter involved, but I fail to remember in which layer it lies (I'm not sure it's important).

    The amount that the polarized light is "spun" determines its final intensity as it passes through the second filter. One of the reasons LCD's are so inefficient is that the primary color filter immediately cuts intensity to 33% (dividing into R,G,B) and then each polarizing filter (even when the light is perfectly aligned for both) cuts another significant chunk, something like 5-10% each. The resulting light is a mere fraction of the original source backlight.

    I suppose different manufacturers might put their polarizing filters in different directions. I'm not sure if one orientation or another would pose any benefits.

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