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What does the term 120 hz mean on a tv?


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December 07, 2011 4:39PM

Normally in the US voltage for TVs is 120 volts at 60 Hz (hertz). Many countries use 220, 230 or 240 volts at 50 Hz. To understand hertz, you need to understand AC voltage. AC voltage cycles between a positive voltage and a negative voltage. It basically goes up to the peak voltage, then comes down to a negative voltage. It does not do this instantaneously, but instead, does it over time. If you were to graph this pattern, it would form a sin wave, which would slope up, then slope back down. It looks like the tilde on a keyboard "~". Each time this full cycle happens within 1 second, we call it a hertz. So our 60 Hz system would cycle from positive to negative 60 times a second. When you see Hz, it means cycles per second.

I am not a TV expert, but I think some manufacturers double the cycles per second to 120 Hz so that they can refresh the picture twice as fast in order to try to get rid of flicker and show a cleaner looking picture.