Flicker Makes a Comeback?

About 20 years ago, when CRT computer monitors started to get bigger than about 14″ diagonal, people started to notice an annoying flicker on their screens. It appears that history may be repeating itself, and researchers are looking for ways to eliminate flicker from large HDTVscreens.

A paper in the Journal of the Society for Information Display from the School of Electronic Engineering at Southeast University in Nanjing, China and Philips Consumer Electronics, discusses some research into the problem of flicker and how to prevent it. The problem comes from trying to reduce the amount of motion blur in an LCD HDTV. Many techniques are used, but one of the methods is to flash the backlight rapidly as the image on the screen is refreshed. The effect is somewhat like a strobe light in a dance club; it freezes the motion so you get a sharp image. The problem is that if you flash the light too slowly, the average person may see a flickering image like an old movie.

The reason for this is that the human vision system is designed to detect motion. We are especially sensitive to motion in the periphery of our vision. So as HDTVs get larger and people sit closer to them for to get the full, cinematic effect, more of the image falls in the range of their peripheral vision (just as happened when people started using larger CRTs on their personal computers).

The research paper indicates that if the LCD panel and backlight are strobed at 60 Hz — 60 times a second — which is the standard rate for many sets, subjects are more likely to notice the flicker effect. If the rate is increased to 75 Hz, the flicker becomes less noticeable.

The take-away from this research is that scanning backlights can help reduce motion blur, but you want a fast refresh rate to go with it. As a result, scanning backlights are likely to be most effective when paired with the new 120 Hz refresh rate panels, to eliminate any flicker.