CRT Versus LCD

First published September 24th, 2012

This video, from a high-speed camera, compares an LCD and a CRT display slow-motion.

  • The LCD display is continuously illuminated even during refreshes.
  • The CRT display is only illuminated for a short period during refreshes.

On this specific CRT, the phosphor decays within 1-2 milliseconds, so the remainder of the CRT is dark for most of a refresh cycle. The CRT phosphor is many times brighter than the LCD backlight, but for a very short period. The scanning is cycled every refresh very rapidly, 60 times a second on most CRT displays (60 Hertz), so it appears as a continuous image to the human eye.

An LCD monitor with a properly-designed scanning backlight, under a high speed camera, can be made to look similar to a CRT display being scanned. Most commercially available displays with scanning backlights use a longer illumination duration than CRT phosphor due to insufficient brightness, and thus do not reduce motion blur as much as a typical CRT display.

Newer strobe backlights (e.g. LightBoost) are now available in certain models of 120 Hz computer monitors. This is accomplished by turning off the backlight between refreshes, while waiting for pixel transitions. The backlight is strobed only on fully-refreshed frames, bypassing pixel persistence as the motion blur limiting factor! There is no backlight diffusion, unlike a scanning backlight. In this case, strobe backlights can be superior to scanning backlights, and allow LCD displays that have the motion clarity of a CRT.

Both CRT and a scanning/strobed backlight, can share the same disadvantage of flicker. This can be solved for most people when using a computer running at a native 120 Hz refresh rate, on a 120 Hz LCD. At 120 Hz, backlight flicker is invisible for most people, unlike a CRT flickering at 60Hz or 85Hz refresh. In addition, a scanning/strobed backlight can be made fully adjustable (flicker can be disabled when motion-blur reduction is not needed).

For more information, see Eliminating LCD Motion Blur and Scanning Backlight FAQ.

2 Responses to CRT Versus LCD

  1. Pingback: Ordered LED ribbons | The LCD BlurBusters!

  2. hehe2 says:

    Just to make it clear, CRT can have high refresh rates too.

    I used to play with a Iiyama CRT using 640×480@144Hz, 800×600@120Hz or 1024×768@100Hz resolutions… 85Hz was really for top “high resolutions” (1600×1200 at this time) which weren’t playable with old computers… (we had to cap the FPS to its max to have better physics and be able to compete with no disadvantage with other players, so low details and low res was our way to get that :).

    Kudos !

    (what about input lag on LCD with lightboost compared to CRT ?)

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