Strolling around your local appliance store, you might have noticed that while LCD and LED televisions are labelled with refresh rates of 60Hz or 120Hz (or 50Hz and 100Hz if you're in a PAL region), newer model Plasma televisions are labelled with a 600Hz sub-field motion rate. With this in mind it seem as thought Plasma televisions are 5-10 times better then the equivalent LCD television. But this isn't necessarily the case.
The first thing to note when comparing these specifications is that 120Hz on an LCD and 600Hz on a plasma aren't even comparable terms. A plasma probably still has a refresh rate of 60Hz or 120Hz, exactly the same as a LED. The 600Hz number refers to something completely different, called sub-field drive.
What is sub-field drive?
Sub-field drive is a marketing term coined by plasma manufacturers to clear up some misconceptions perpetrated by LED/LCD manufacturers. It was a part of plasma television technology long before it began to be quoted in marketing, and is indeed essential to allowing a plasma to work properly.
At the time that sub-field drive first became an important part of plasma packaging and marketing, LCD manufacturers were making direct comparisons between plasma televisions' "poor" 60Hz refresh rate when compared to those of LCDs, which could be as high as 480Hz. The manufacturers knew this was a silly and inaccurate comparison, but they still used it in an attempt to gain an edge over the plasma manufacturers.
While an LED is broken down into pixels, plasma televisions take this even further, breaking each pixel down in to 8-12 "sub-fields". Essentially this is a smaller pixel within the main pixel. While a tv might have a refresh rate of 60Hz (that is, the image is updated 60 times every second), this image pulses through the sub-pixels to keep the image constantly showing brightly and crisply. Therefore multiplying the panel's refresh rate of 60Hz by the 10 sub-fields (for example), 600Hz comes out. This is where the sub-field drive term comes from.
Does sub-field motion help for high-speed motion in film and sport?
The simple fact is that the sub-field motion doesn't actually affect fast motion. While plasma TVs are better than their LCD counterparts are at displaying fast motion and quick transitions, this isn't because of the sub-field motion. It's because of the response time of the panel.
Plasma panels update at fractions of a millisecond, meaning that while most of the extra images produced by the sub-fields aren't used, when the image in a video does change, it is updated on the screen far more quickly, and gets back to the viewer far quicker than an LCD's would.
Sub-field motion roundup
When looking for a new television, the sub-field drive numbers on a plasma's product card shouldn't be used to sway a purchase decision. Instead, the intended usage of the TV should be the deciding factor.
Check out our article on the differences between an LCD and Plasma for more information on making an informed purchase decision
References
Pendlebury, T. (2009, June 15).Please explain: 600hz sub-field drive. Retrieved from http://www.cnet.com.au/videos/please-explain-600hz-sub-field-drive-22479973.htm
Stevens, C. (2009, August 07). 120hz vs. 600hz - which is better?. Retrieved from http://www.tvlampsnbulbs.com/2009/08/120hz-vs-600hz-which-is-better/
Lachlan Stevens - Lachlan Stevens is a Journalism student. The Entertainment Editor at Newcastle's Yak Magazine, Lachlan has written for numerous ...
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