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Are there any display/monitor technologies available or in the works that do not constantly refresh the screen? Ie, the individual pixels only change when there is a change to be made, rather than redrawing the entire image signal at once?

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2 Answers 2

Sure. Various e-paper technologies only change when needed; they retain the charge during redraws.

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On a CRT, the entire image is redrawn on every possible refresh, since it is drawn by illuminating pixels by an electron cannon. The pixels glow for just a short while (which is wanted to keep latency low), and need to be re-illuminated many times per second (refresh rate).

On an LCD (there are different technologies here as well, so this is well general) there is an always-on backlight that throws light towards a panel of pixels that are individually controlled to let through a specific amount of light depending on what the screen wants to show. This is controlled by (using TN technology to demonstrate) "twisting" a pixel corresponding filter to different degrees by applying a voltage. If twisted so it blocks all incoming light, the pixel is dark. If twisted perpendicularly, the pixel is maximally light (= back-light color = white).

The twisting is not reset during every screen update if no image change is wanted (a few years ago, this would have rendered these displays unusable since they were so slow to update, hence ghosting), so LCD displays should fall under your wanted category, depending on what you mean by "redrawing".

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You're partly right, but LCD backlights do flicker, so technically they're not on constantly; it's just not anything to do with the refresh rate but rather how LCDs control overall screen brightness. Also, CFLs (at around 5-6 kHz, I think) and LEDs (at the AC power frequency) flicker naturally. –  Lèse majesté Apr 22 '12 at 16:34
    
@Lèsemajesté: true about the backlights (though the kHz range is for most purposes (e.g. human eyes) equivalent to always on), but the question was if there was a display where "the individual pixels only change when there is a change to be made" (emph mine), and this is the case for LCD:s. But the question is a bit unclear on what is meant by "redrawing". –  Daniel Andersson Apr 23 '12 at 7:57
    
Right, that's why I upvoted your answer. For all intents and purposes, anything in the kHz range can be treated as continuously on. It's completely undetectable by the human eye, and it won't show up in regular video recordings of the screen either (unlike CRT refresh rates). –  Lèse majesté Apr 24 '12 at 21:50

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