Corporates and consumers in the market for liquid crystal display (LCDs) need to be aware of the questions being raised around the validity of LCD response times as quoted by  manufacturers. 

Tyrone Young of Philips says: “Response rates, measured in milliseconds (ms), are important since they indicate how quickly a pixel can change colours. The faster it changes, the less ghosting, blurring or streaking the user will see in a moving or changing image. However, there is a lot of confusion in the market around LCD response times at present, not least because there is more than one way of measuring response rates and no single standard that manufacturers are compelled to apply when doing so.”
The first method used is the on/off or rise and fall method which measures the total time it takes for an LCD to go from white to black and back to white again. A second method is to measure grey to grey (G2G) response times. The former is important for static, text-based business applications, while the latter measure is important where faster applications are used, such as for gaming.
Bruce Byrne, visual communications specialist at distributor Drive Control Corporation, explains: “For video, gaming or TV applications, 2ms to 15ms is suitable, while business applications can stand up to 8ms to 16ms response times. Striking a direct comparison between LCDS based on this measure is risky however. While advertised LCD response times have improved from about 25ms to 2ms over the last year, how that 2ms is measured is anyone’s guess.
“Few manufacturers explain how they reach their figures. G2G measures can start and end anywhere on a scale of 265 colours, while some manufacturers will only measure white to black responses, rather than the full white-black-white sequence. In addition, some figures represent averaged out response times that make use of only the top fastest 80% of measured responses, rather than 100% of all test responses.”
Consumers are better off testing the LCD visually by loading the application they will be using on the display and seeing for themselves, he says, adding that the fastest LCDs are not always the best. Business users should be aware that an LCD panel with a 2ms rating could degrade the performance of a static text application which requires a more stable display.
”There is more to monitor choice than the LCD response time,” says Young. “The type of panel used will play a large role. Twisted Nematic (TN) and In-Plane Switching (IPS) panels, for instance, will give different performance.”
TN displays contain liquid crystal elements which twist and untwist at varying degrees to allow light to pass through. These panels are the more common consumer display type due to lower pricing and sufficiently fast response times to avoid shadow-trail effects, but they suffer from limited viewing angles and some are unable to display the full 16,7-million colours.
IPS is an LCD technology that aligns the liquid crystal cells in a horizontal direction, consuming more power and making this type of display undesirable for notebook computers. IPS improves on poor viewing angles and colour reproduction of TN panels, but at a loss of response time.
The development of Super-IPS improves pixel refresh timing, while True Wide IPS has since been developed by LG Philips to improve the viewing angle of the current S-IPS.
”Both consumers and resellers should be wary of assessing LCDs on response times alone,” says Byrne. “Until standards can be applied to how manufacturers measure and advertise this functionality, thorough visual testing should be done. Users are welcome to call our offices at any time for advice on LCD performance and to check which LCDs would provide the best solution.”