Refresh Rates of Plasmas and Projectors

Discussion in 'Projectors, Screens & Video Processors' started by brattle, Feb 22, 2002.

  1. brattle

    brattle
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    I wasn’t sure which forum to put this in, but I thought more people would know the answer here.

    Apologies for my lack of knowledge, but I was wondering about the refresh rates of plasmas and projectors. I know that larger screen CRTs and rear projections can be bought in 50hz and 100hz flavours, the argument being that as the screen size goes up, the amount of flicker becomes more noticeable (although this is a matter of some debate).

    I notice that I’ve never seen Plasmas or Projectors advertised as 100hz, even though they potentially have much larger viewing areas. Is this because they display the image in a different way and so the flicker can not be seen? Or are the refresh rates variable?
     
  2. Chris Frost

    Chris Frost
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    Various refresh rates are available with Plasma and DLP/LCD projectors, but they don't "scan" like a CRT TV so flicker isn't as much of an issue. Instead, they show a series of complete images.

    Regards
     
  3. brattle

    brattle
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    But isn't that progressive scan? I know Plasmas and Projectors can display prog scan, but what about interlaced material?
     
  4. LV426

    LV426
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    The two things aren't connected.

    Refresh rate is an issue pretty much exclusive to CRT devices, because of the way the image is "drawn" onto the screen using a single flying beam of electrons fired from a gun at the back of the tube. This makes the image intrinsically intermittent in nature, and it is the intermittent nature that causes visible flicker. The faster the refresh rate, the less visible the intermittent picture is.

    LCD and Plasmas do it, well, er differently. You can drive an LCD computer monitor at non-interlaced 50hz (totally unwatchable on a CRT) and see NO visible image flicker.
     
  5. brattle

    brattle
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    Thanks, that's just what I was after :).

    Just out of interest though, how come Rear Projections suffer from flicker, but projectors do not? At least I assume they suffer from flicker which is why you get 100hz versions.
     
  6. Chris Frost

    Chris Frost
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    Rear projection TVs based on (entry level) CRT projector technology will suffer from 50Hz flicker - they're working in the same way as an ordinary TV. Those based on LCD or DLP projector technology won't suffer as much (if at all) because they don't "scan" in the same way.

    The sort of Home Cinema CRT projectors you read about in this forum and the home cinema press generally have less of a problem with 50Hz flicker. Some of this is due to the types of picture tube.

    As with all things in life, there are compromises in the Rear Projection TV market. LCD/DLP based RPTVs sacrifice some black level and colour depth but have better convergence and geometry accuracy. CRT based RPTVs have better colour depth and black level, but poorer geometry unless they are set-up properly.

    Regards
     

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