What Is Refresh Rate on a Computer?

by Heather Lindsay

The refresh rate on a computer is used to describe how often a monitor draws the current data to the screen. Refresh rate effects visual quality for CRT, LCD and even HD TVs as they are commonly connected to computers for high definition playback. Refresh rate is not to be confused with frame rate. Refresh rate is a measure of how often a frame is written to the screen repeated or not, and frame rate refers to how often a new frame is sent from the graphics source. Refresh rates can degrade data presentation quality and even cause discomfort in viewers if set too low.

Cathode Ray Tubes

Cathode ray tube or CRT monitors use an electron beam directed at the screen. The number of times a monitor is painting a frame of data to the screen per second is its refresh rate. Increasing resolution size on a CRT display reduces the maximum refresh rate--it takes longer to paint a frame to the screen because of the extra lines added by the increased resolution. The refresh rate of a CRT monitor can be calculated by dividing its horizontal scan rate by the display's current horizontal resolution multiplied by 1.05. For example, 96 KHz horizontal scan rate at 1280 x 1024 resolution would be expressed as 96,000 / (1280 x 1.05).

LCD Monitors

Much of the mechanics of refresh rate do not directly apply to LCD monitors, as they use a different display system. Unlike CRT monitors, which repaint their screen so many times a second, LCD monitors paint a picture and hold it there, only changing it as needed using the LCD monitor's back lighting system. However, they do have a similar measure, known as response time, which is how often the monitor can flicker its back lighting system on and off. This response time is normally measured at near 200 Hz a second. Further they have a limit on how often a new image can be received for the display. This is usually 60Hz maximum.

Refresh Rate vs Frame Rate

The frame rate of a computer is how often a video processing device can send a new image to be received by the monitor. As opposed to how often the monitor can actually present the image, which is the monitor's refresh rate. A common misconception by video and gaming enthusiasts is to use frame rate as a measure of how good their display is. This technique only works to a point, however, as any frames sent to the monitor above the monitor's refresh rate are not rendered and simply lost. Thus it is important to have a monitor capable of high refresh rates at high resolutions lest your frame rate be a useless calculation of system performance.

Warning

Refresh rates also serve another purpose outside of video presentation quality. Viewing computer monitors with low refresh rates can lead to headache and eye discomfort. This discomfort is due to the computer monitor refreshing slower than your eyes can update the image. The slower refresh produces a flickering effect to the human eye at lower refresh rates which causes headaches and eye pain as it is like looking at a flashing light for extended periods of time. This flickering is of special concern to those susceptible to seizure.

Refresh Rate Constraints

Although it is possible for the monitor to bottle-neck the graphics card's ability to render images to the screen, that is not always the case. Setting your refresh rate high will allow for a higher frame rate to be utilized by the monitor and thus allow for a more streamlined user experience, especially when playing demanding video games. Conversely, if a particular computing solution does not posses the power to properly send frames at or above the set refresh rate there will be noticeable lag and unresponsiveness from the system as the monitor will simply repeat already sent frames to take the place of the frames not sent by the graphics solution.

About the Author

Heather Lindsay is a stained glass artist who holds a master's degree in library science, a bachelor's degree in anthropology with a minor in art, and has enjoyed working in special libraries with photograph collections.