What is a Refresh Rate?

The refresh rate of a monitor or TV is the maximum number of times the image on the screen can be drawn, or refreshed, per second. The refresh rate is measured in hertz.

Refresh rate may also be referred to by terms like scan rate, horizontal scan rate, frequency, or vertical frequency.

The image on a TV or computer monitor screen, at least the CRT kind, is not a static image even though it appears that way.

Instead, the image is "redrawn" over and over on the screen so quickly (anywhere from 60, 75, or 85 to 100 times or more per second) that the human eye perceives it as a static image, or a smooth video, etc.

This means that the difference between a 60 Hz and 120 Hz monitor, for example, is that the 120 Hz one can create the image twice as fast as the 60 Hz monitor.

An electron gun sits behind the glass of the monitor and shoots light to produce an image. The gun starts at the very top left corner of the screen and then quickly fills it with the image, line by line across the face and then downward until it reaches the bottom, after which the electron gun moves back to the top left and starts the whole process over again.

While the electron gun is in one place, another portion of the screen may be blank as it waits for the new image. However, due to how fast the screen is refreshed with the light of the new image, you don't see this.

That is, of course, unless the refresh rate is too low.

If the refresh rate of a monitor is set too low, you may be able to notice the "redrawing" of the image, which we perceive as a flicker. Monitor flickering is unpleasant to look at and can quickly lead to eye strain and headaches.

Screen flickering normally happens if the refresh rate is set below 60 Hz, but may also occur with higher refresh rates for some people.

The refresh rate setting can be changed to reduce this flickering effect. See How to Change a Monitor's Refresh Rate Setting in Windows for instructions on doing this in all versions of Windows.

All LCD monitors support a refresh rate that is typically over the threshold that normally causes flicker (usually 60 Hz) and they don't go blank between refreshes like CRT monitors do.

Because of this design capability, LCD monitors do not require refresh-rate adjustments to prevent the flickering.

The highest possible refresh rate isn't necessarily better, either. Setting the refresh rate over 120 Hz, which some video cards support, may have an adverse effect on your eyes as well. Keeping a monitor's refresh rate set at 60 Hz to 90 Hz is best for most.

Attempting to adjust a CRT monitor's refresh rate to one that's higher than the specifications of the monitor may result in an "Out of Frequency" error and leave you with a blank screen. Try starting Windows in Safe Mode and then changing the monitor refresh rate setting to something more appropriate.

Three factors determine the maximum refresh rate: The monitor's resolution (lower resolutions typically support higher refresh rates), the video card's maximum refresh rate, and the monitor's maximum refresh rate.