Why pixel refresh times can be deceiving

The next five pages are taken verbatim from the last monitor review. If you haven’t read this before, please take the time to do so because it’ll explain how we evaluate monitors. If you read the last article, feel free to skip ahead.

The Myth of the 8 ms Panel

The techie in all of us wants a monitor with the fastest possible pixel refresh rate. After all, the faster the better, right? Well, it turns out it is not quite that simple. It’s obvious that if your pixel refresh is too slow, there’s too much blurring. It’ll interfere with your gaming. However, when the motion blur reaches a threshold point, it’s no longer a hindrance to your gaming performance and actually helps to smooth out the framerates. On the other hand, monitors that are too aggressive with the pixel refresh times don’t have anywhere near the same color or contrast.

The real problem is that rated pixel refresh times are rarely quoted as “averages.” They’re often quoting the best-case scenario. This is further complicated by the fact that there are different types of LCD panels on the market: S-IPS, TN-film, and PVA/MVA. Think of them as being differences CPU types (like a Pentium 4 vs. Athlon64). Depending on the type of LCD panel, there can be large differences in the pixels refresh depending on whether it’s going from black to white, or if the pixel is changing from gray to gray. It can actually be slower to transition from black to gray than it is to go from black to white for some panels. That can be a bit counter-intuitive.

What this means for you is that an 25 ms S-IPS LCD panel works as fast as a 16 ms “TN-film” based technology for the wide range of black to light gray. Only when a pixel is going from pure black to pure white is the TN-film is actually faster. So in nearly every real-world application including first person shooters, the difference in smearing will be minimal. On the other hand, a PVA or MVA monitor that may be advertised as doing 25 ms when going from black to white may very well need 80 ms to transition from black to dark gray!

Speed isn’t everything. IPS panels typically offer better viewing angles with more accurate color, however contrast is poorer. TN-Film technology (the 8, 12 and 16 ms) panels only display 18-bit color. PVA/MVA panels on the other hand are famed for deep black levels and superb contrast ratios that typically come the expense of speed.

So, while pixel refresh is important, the way it’s advertised, it’s about as useful as megahertz ratings for CPUs or watts for amplifiers. It’ll help you decide within a panel type only. That is, an 8 ms TN-film screen is better than a 12 ms TN-film screen, but a 20 ms MVA screen will have significantly worse ghosting than a 25 ms IPS panel. In addition, all things equal and the same advertised pixel refresh, 17-inch LCD panels tend to exhibit less smearing than 19-inch panels.

How fast?

With CRT monitors, it was important to have a high refresh rate to avoid flicker. This isn’t a problem with LCD panels anymore because instead of using an electron gun to energize phosphors, the LCD itself is a transparent film (like a 35mm slide) with a static light source behind the panel. The cold cathodes fluorescent tubes that light LCD panels operate at tens of thousands of hertz. Many LCD panels have a native display refresh of 60Hz, and if so, it’s actually better to run your LCD display at 60Hz rather than 75Hz. Both will be flicker free.

Does this mean that you only need a video card that does 60 fps? No, FiringSquad was one of the original proponents of the 100+ fps benchmarks when evaluating 3D graphics cards. The most common explanation for wanting this speed is that benchmarks reflect an average framerate, whereas it’s the minimum framerate under heavy load that matters for gaming. However, a more subtle distinction is the idea that games synchronize their display to user input as well. Having a higher framerate acts in the same way a higher mouse refresh rate works.

Even an 8 ms TN film panel is not immune to smearing. Fortunately at 12 ms or faster, we found the smearing associated with TN-film panels to be non-intrusive. You’ll be able to see the smearing when you’re looking for it, but it’s not at a point where it interferes with gaming, even at the professional competitive level. 16 ms TN-film is a good starting point as a minimum spec and most gamers will be happy with this level of blurring. We found the 12 ms PVA panels to perform similarly to the 16 ms TN-film panels. You will see smearing if you look for it, and for a skilled gamer, it’ll occasionally get in the way. By skilled gamer, that’s someone who consistently is in the top 2 spots for any given match. 25ms PVA panels were too slow for high-speed gaming and even casual gamers will notice the difference. That said, DVD movies will look fine. 25 ms IPS panels were on par, if not slightly better than 16 ms TN-film panels.