Now that you know what phosphors do, we can get back to the
refresh rate. Because phosphors only glow for a very short duration after being struck by
energy, they need to be constantly bombarded with it (refreshed). A CRT is refreshed in
what is called a "Raster" pattern. This means the electron beam starts at the
top left, scans to the right, drops down one line and repeats. There are two numbers
associated with this: horizontal and vertical scan rates. The numbers are how many times
the screen is updated per second. You'll typically find the horizontal scan rate to be
between 31KHz and 90KHz, and is generally ignored as the vertical scan rate is considered
to be much more important because it is so much slower.
As the vertical refresh rate drops, you'll notice an annoying flicker beginning around
60Hz (unless you are a little more sensitive like myself where 70Hz is the absolute
minimum.) Generally speaking, the lower your resolution, the
higher your vertical refresh rate. This is because it doesn't have to rasterize as many
vertical pixels. Take for example a screen resolution of 640x480. There are 480 vertical
pixels, and you could scan through this relatively quickly as compared to say a resolution
If you notice flicker, you might try to up your refresh rate, but remember this is
dependent upon your video card and monitor specifications. Consult your manuals first, as
setting an incorrectly matched refresh rate could possibly damage your monitor. Another
thing to check is to make sure that your monitor is not running in interlaced mode.
Interlacing is a means of refreshing the screen every other line and relying on the human
eye to combine two adjacent lines. Interlaced mode also rasterizes the screen, but it does
so in two passes. The first pass draws all of the odd lines, and the second, all the even.
This produces a much more apparent flicker.