Low Refresh Rates for CRT Monitors
While the majority of new computer monitors being sold are now flat-panel LCD monitors, some CRT monitors are still in use. Low refresh rates (under 60Hz) can be perceived as a screen flicker. A refresh rate of 60Hz means that the screen is redrawn 60 times a second, and this may be too slow for many people. Increasing the refresh rate to 70-85Hz will eliminate the noticeable flicker.
Flat-panel LCD monitors use different technology, and will not have a noticeable flicker. The pixels of an LCD monitor do not need to redraw in the same way. And, while the backlight of an LCD monitor does need to refresh, it generally operates near 200Hz, well above any perceptible flickering threshold.
To change your monitor's refresh rate, open your computer's display control panel. On Microsoft Windows 7, right click the desktop and choose "Screen Resolution," then click "Advanced Settings" and open the "Monitor" tab. Here you will be able to increase your screen refresh rate above 60Hz.
For more information about types of computer monitors, including CRTs and LCDs, see this guide.