Why in the dark does it seem LCD screens move.?

This also happens with some screens on appliances such as digital clocks or ovens and microwaves with clocks, and sometimes happens in the light, when you move rapidly, it seems the numbers shake outside where they belong. You can replicate this by laying down in bed in the dark and looking at big text on your phone screen and bouncing.

3 Answers

  • 1 month ago
    Favorite Answer

    It's a combination of "persistence of vision" and the display update or multiplex frequency.

    Any time your eyes (or rather retinas) are exposed to a bright image, it takes a fraction f a second before it fades, even if the light is off - like looking at a lamp then closing your eyes, you see an "afterimage".

    That's persistence of vision.

    If images are repeated at around 50 times a second or higher, your eyes never register the gaps between them. That's what cinema film systems, TVs and computer video etc. rely on.

    The display or screen it updated at a regular rate which is too fast for your eyes to notice when you are looking at it normally.

    However if you move the display or screen while looking at a fixed place, or glance from one side of the screen to the other, you see each update as a separate image with small distances between them.

    It used to be extremely obvious with some LED type clocks and calculators, as they display each digit one at a time, sequencing through the entire display so fast it seems continuous..

    Wave one of those about and you can see the individual digits separately.

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  • Dixon
    Lv 7
    1 month ago

    I think it happens with small lights that have mains frequency flashing and it is something related to the "aliasing effect" that happens when sampling signals at a rate near to their own frequency. Ie the sampling is effectively when the light is bright and then it goes dull but the light is moving with respect to your gaze as well, so the apparent position changes between flashes. I think that when the light is continuous our brain tracks this motion and filters out head movement but when the light isn't continuous we see the dislocation.

    Try looking at the lights and blow a loose lipped raspberry, kind of like when you go "Brrrrrr" to show it is cold. The vibration of your head makes the lights jiggle like crazy.

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  • 1 month ago

    Lay off the wacky baccy.

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