Sunday, April 1

Refresh Rate of monitor

I joined a local IT consultant company, and visited some clients, then I realized that there were still so many CRT monitors being used, and most of them are running in default (60 Hz) refresh rate.

Refresh rate shows how many times the computer refreshes monitor in one second. When the electronic gun hit one spot of the CRT screen, the spot will show white (or color) spot, then it will dim off immediately. That's why the electronic gun has to come back to hit this spot, after scanning the whole screen. If the refresh rate is high enough, you feel that the spot is always white; but if the electronic gun is running slow, the refresh rate is low, you can feel the spot is white , dims off, then becomes white again. This is how flicker being introduced.
The refresh rate doesn't apply to LCD monitor, because for the LCD monitor, each spot is white (or color) if the voltage of this spot is high. The spots are controlled by vertical and horizontal voltage unit, and we don't need to "refresh" them.

So, now we now that low refresh rate can introduce flicker, or monitor flashing. How low is low? Our TV sets are running under NTSC (US, 60Hz) standard or PAL(Europe, 50Hz) standard, and these standards are developed in 1930s. So I would say that 50Hz is the lowest refresh rate human can stand of. Remember, when you are watching TV, you sit 2 meters away from the TV set, but when you are using computer, you are sitting 0.3 meters away from your monitor. You have to consider higher refresh rate for computer use. If it is too low, you can't stare to it for too long.
Dizzy, nausea, or even vomit are the normal feelings if the refresh rate is not suitable for you.

Different people feel different to the same refresh rate. I am more sensitive than others. Most people can't feel anything with 60Hz refresh rate, but I can actually see the monitor flashing. When I see a new computer, I can instantly tell if this computer is using 60Hz refresh rate without check the settings. The fact is: No matter you can feel the flashing or not, it is. It is hurting your eyes.

If you want to check the refresh rate of your computer, go to Control Panel->Display:

Then in the tab Settings you click "Advanced" and open a new window. The Monitor tab will show the refresh rate. 60Hz is Windows' default value. 10 years ago, setting a refresh rate higher than the hardware's specification can harm the monitor. Now the monitor can intelligently shut down the cable, if the refresh rate is too high. So Microsoft decides to adopt the lowest rate to fit into all monitors.