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A Curious Question about LCD Display

  1. May 9, 2013 #1

    I have observed that if by chance a hair strand manages to cling to LCD Screen like TV or laptop screen, a small region near the hairline shows chromatic abberation. Is it due to some diffraction or Interference? Please explain..

    Thanks in advance
  2. jcsd
  3. May 9, 2013 #2


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    Would that happen to be noticeable only when you remove the hair? Since Lucy sheds so much, my screen is constantly plastered with cat hair. It doesn't cause any distortion. Mechanical pressure from my fingers, however, while removing that hair does induce a sort of "rainbow" effect. I always figured that it was just a matter of distorting the crystal matrix, but I'm not sure. I try to avoid it for fear of damaging the display.
  4. May 9, 2013 #3


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    The material in a liquid crystal display is (doh!!) a liquid. If you distort the display to make it flow, the liquid carries the "image" with it for a short time.

    It's easier to see what is happening with a simple calculator that has a 7-segment type of LCD display, rather than a display with small dots. And if you break a $5 calculator, you haven't lost much.

    I don't know about the OP's question. Maybe the hair is about the same width as the individual dots on the display, so it is selectively covering up the red green and blue dots forming the image?
  5. May 9, 2013 #4
    True that. The LCD screen is made up of pixels and contains fluid crystal matrix filled in it. Application of mechanical pressure to the screen tends to displace the pixels from that area and also causes color providing matrix to drift away. Press it too hard or for long time and then you'll find that that portion is locally damaged. But that doesn't answer my question exactly.
    Last edited: May 9, 2013
  6. May 9, 2013 #5


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    No ****?! I never would have guessed. :grumpy:
    I meant that I'm worried about damaging the addressing components, not the liquid.
  7. May 9, 2013 #6
    The pixels can be quite small, so you can get a hair significantly blocking some pixels. Each pixel is either red, green or blue. Blocking a green pixel will result in a magenta 'fringe' at the side of the hair. Often, depending on orientation, you will see a cycling of colour 'fringing' along the length of the hair.
  8. May 10, 2013 #7
    That could be possible. But one question- suppose the green pixel is blocked, why would I see magenta color, shouldn't i see a mix of red and blue- purple?
  9. May 10, 2013 #8
    Magenta is mix of blue and red light; add green and you get white. Purple is mix of blue and red pigments; add yellow and you get a muddy dark colour. First is additive colours, second is pigment (subtractive) colours. Red green and blue are additive primary colours, red yellow and blue are subtractive primary colours.
  10. May 10, 2013 #9


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    I suspect (as mentioned above) that it's not a diffraction, interference, or LCD-specific effect, but rather simply due to the arrangement of pixels on a modern color display. The hair edge is probably only partially blocking some pixels, causing visible color fringing. The easiest way to visualize this is probably by imagining a pure white screen. If you look closely, it'll be made up of red, green, and blue subpixels. If the edge of the hair is blocking the red and green subpixel, but the blue is left uncovered, you'll get a blue fringe around the object. This can even be seen with something as simple as a piece of paper - the blocking object doesn't need to be small, it merely needs to have a fairly sharp edge (so as to be able to block individual subpixels).
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