Understanding pixel defects in TFT flat panel monitors

ManualsBrandsHP ManualsMonitorHP L1908wm 19-inch Widescreen LCD Monitor

Understanding pixel

defects in LCD

monitors

Bob Myers

Displays Business Unit

Last revised: July 1, 2009

Introduction......................................................................................................... 2

Executive summary ............................................................................................. 2

Understanding TFT-LCD technology ...................................................................... 3

How LCDs work .............................................................................................. 3

Why TFTs? ...................................................................................................... 3

Understanding pixel defects ................................................................................. 4

How pixel defects occur................................................................................... 4

How to spot a sub-pixel defect ........................................................................ 5

HP pixel-defect standards .................................................................................... 5

HP specifications ............................................................................................. 5

International standards (ISO-9241) .................................................................. 6

Defect type definitions ..................................................................................... 8

The HP advantage ............................................................................................... 9

HP quality and reliability ................................................................................. 9

Designed with the environment in mind ........................................................... 9

HP service and support .................................................................................. 10

For more information ........................................................................................ 11

Summary of content (11 pages)

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Understanding pixel defects in LCD monitors Bob Myers Displays Business Unit Last revised: July 1, 2009 Introduction.........................................................................................................2 Executive summary .............................................................................................2 Understanding TFT-LCD technology ......................................................................3 How LCDs work .........................................................
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Introduction Liquid crystal display (LCD) technology was first invented decades ago and has been improving ever since—to the point that today’s high-quality flat panel displays deliver crisp, clear visual quality at a reasonable price. Even so, some LCD monitors may harbor tiny defects due to the extreme complexity of the manufacturing process.
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Understanding TFT-LCD technology Thin-film transistor (TFT) technology refers to a type of liquid crystal display (LCD), also known as an active-matrix LCD (AMLCD), used in all HP LCD monitors as well as HP iPAQ devices and HP notebook displays. To understand how pixel defects occur, it helps to understand the technology behind this type of LCD.
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The advent of thin-film transistor (TFT) technology allowed transistors to be placed at each picture element or sub-pixel. These can switch very quickly, and then hold the state of the sub-pixel while the panel drivers take care of the other rows and columns of the display. This results in a great improvement in the contrast and response time possible with LCD technology, and permits the manufacture of largesize, high-resolution displays which rival any other display technology in performance. Figure 1.
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How to spot a sub-pixel defect Due to their tiny size relative to the screen, defective sub-pixels can be extremely hard to see. A defect in a sub-pixel is, visually, a single, tiny spot that is so small, it may be visible only if you display it against a background that specifically contrasts with the defective sub-pixel hue. Because they appear brighter to the human eye, defective green sub-pixels may be easier to spot than defective red or blue ones.
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Table 2. This policy applies for HP monitors manufactured in May 2009 or later: Bright sub-pixel defects: 2 maximum Dark sub-pixel defects: 5 maximum Total sub-pixel defects: 5 maximum Full pixel defects: 0 allowed Note: the date of manufacture is on the label on the back of the HP monitor. As a result of these tight specifications, the majority of all HP monitors are shipping with no pixel defects at all (per HP’s internal audits), and a small percentage with only a single sub-pixel defect.
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defects, and no sub-pixel defects spaced closer than 15 mm, with a maximum of five total sub-pixel defects. Figure 2. Pixel fault definitions.
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Defect type definitions Bright/dark dot: A sub-pixel stuck on or off. Bright spots/lines: Spots or lines that appear light in the display. Defects do not vary in size or intensity (contrast) when contrast voltage is varied. Contrast variation can be achieved through the use of varying gray shade patterns. This defect may not completely block the light emitted by any pixels. Cluster: A group of defective sub-pixels which are in close proximity to each other.
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The HP advantage The HP pixel defect specifications are part of HP’s ongoing effort to provide high quality products. When it comes to LCD-TFT displays, fewer pixel defects mean better quality. HP quality and reliability HP prides itself on a reputation for industry-standard best-of-breed products—and our line of LCD monitors is a testament to that reputation.
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Development, the world's leading organization for quality and environmental certification.  Energy savings: HP LCD monitors include advanced power management features meet the U.S. Environmental Protection Agency's ENERGY STAR® requirements.  Recyclability: Commonly recycled materials are easily identified, making it easier to find a market for discarded components.  Packaging: Packaging consists of recyclable materials, no heavy metal inks, and minimal packaging material.
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For more information For the HP sales office nearest you, please refer to your local phone directory, or call the HP regional office listed below.