Refresh rate
On CRT displays, higher refresh rates produce less flickering, thereby reducing eye strain.
[2] For computer programs or telemetry, the term is sometimes applied to how frequently a datum is updated with a new external value from another source (for example; a shared public spreadsheet or hardware feed).
In a CRT, the vertical scan rate is the number of times per second that the electron beam returns to the upper left corner of the screen to begin drawing a new frame.
[4] For instance, a monitor with a horizontal scanning frequency of 96 kHz at a resolution of 1280 × 1024 results in a refresh rate of 96,000 ÷ (1024 × 1.05) ≈ 89 Hz (rounded down).
In early videogame systems, the only time available for computation was during the vertical blanking interval, during which the beam is returning to the top right corner of the screen and no image is being drawn.
[5] Even in modern games, however, it is important to avoid altering the computer's video buffer except during the vertical retrace, to prevent flickering graphics or screen tearing.
Unlike CRTs, where the image will fade unless refreshed, the pixels of liquid-crystal displays retain their state for as long as power is provided.
However, the refresh rate still determines the highest frame rate that can be displayed, and despite there being no actual blanking of the screen, the vertical blanking interval is still a period in each refresh cycle when the screen is not being updated, during which the image data in the host system's frame buffer can be updated.
When LCD shutter glasses are used for stereo 3D displays, the effective refresh rate is halved, because each eye needs a separate picture.
Most low-end computer graphics cards and monitors cannot handle these high refresh rates, especially at higher resolutions.
The first reason was that the television's vacuum tube was susceptible to interference from the unit's power supply, including residual ripple.
This accident of chance gave European sets higher resolution, in exchange for lower frame rates.
These higher refresh rates are most effective from a 24p-source video output (e.g. Blu-ray Disc), and/or scenes of fast motion.
In the case of material shot on video, improvements in smoothness just from having a higher refresh rate may be barely noticeable.
[11] In the case of filmed material, as 120 is an even multiple of 24, it is possible to present a 24 fps sequence without judder on a well-designed 120 Hz display (i.e., so-called 5-5 pulldown).
