HP L1535 Reference Guide
Contents
1. UNDERSTANDING PIXEL DEFECTS IN LCD MONITORS Bob Myers Displays Business Unit Last revised July 1 2009 Introd ON accusam AE 2 Executive SUMIMOLY scccscsincniscncvcvcncecedavesecstscedecsdecscvansecstccsevendecetavessusdesedsecesusesuntvte 2 Understanding TFT LCD technology sssssssssesesseeseeseesecececeeceeceececeeceeees 3 How LCDs rascals occ eee es 3 a ee ee re 3 Understanding pixel defects sccssssssssssssssessesscssssecccsececsecsececsecseeseeeeees 4 How pixel defects occur seesssesesesesessesesesessesesesessesesesessesesesesseseseseseesesesese 4 How to spot a sub pixel defect nies nnnnennsnnensnnaenndenwdaananane 5 HP pixel defect standards sssssssssisiscsisesisossvesivesivescsosivessvssivosesesisessscsivesevisisosssi v s 5 HP specifications occ occ ys essed eee dee 5 International standards ISO 9241 ssccssccsssesssecssscsssessecessceseessscesscesseees 6 Defect type definihons iiss cssccsctis cc taticccassccinsiccestescssivaccsivatuseceuscesacssccaunscnauneacoees 8 The FAP cre cai ge ood 05 cud asak i siesahanasansianabsudeassbesabananabsbonabsndesnsensbanananauacabanse 9 HP quality and reliability ic ssecscccicciscodesscecesccvcecalideceveidiedicesdvudevedtiecocndviedsceddeness 9 Designed with the environment in Mind sssessesesesesesesesesesesesesesssseseseseseseses 9 HP service and SUpmitl cca canis whan dn dnninnnnndnndneinnn 10 For more information gasp tog ccheacocs2. s how HP builds quality into every product e Customer feedback HP products are a result of extensive customer feedback including focus groups trade shows customer visits support calls human factors studies and surveys of thousands of desktop users e Testing HP internal product teams help ensure reliability and long life by testing every model with hundreds of third party devices in a variety of networked environments to simulate years of real world stress HP systematically pushes its products to make sure they will perform in the toughest workplace conditions e Factory audits Before leaving the factory each unit passes a rigorous examination to help minimize defects and increase likelihood of operation out of the box e Engineering excellence HP quality does not stop at the factory door Our service and engineering teams continue to support each unit throughout its lifecycle The award winning HP call center quickly resolves most issues on the first call Designed with the environment in mind HP environmental policies are designed to help integrate sound environmental practices into every aspect of product design including the following features e EPEAT The Electronic Product Environmental Assessment Tool EPEAT is a set of voluntary environmental performance criteria established by the IEEE 1680 American National Standard for the Environmental Assessment of Personal Computer Products that identifies 23 required and
3. Kong Ltd 19 F Cityplaza One 1111 King s Road Taikoo Shing Hong Kong 2005 2009 Hewlett Packard Development Company L P The information contained herein is subject to change without notice and is provided as is without warranty of any kind The warranties for HP products and services are set forth in the express warranty statements accompanying such products and services Nothing herein should be construed as constituting an additional warranty HP shall not be liable for technical or editorial errors or omissions contained herein ENERGY STAR is a U S registered ark of the United States Environmental Protection Agency Intel and Pentium are trademarks of Intel Corporation in the U S and other countries 5981 6351EN July 2009 ii
4. be clustered in groups Nevertheless special practices and policies have been devised to reject any complete pixel defects and minimize sub pixel defects e What is HP doing about it HP has conducted a detailed study of its standards for sub pixel defect specifications and as a result has adopted a more stringent unified standard for all models which is discussed in greater detail later in this paper e Why is this important to me Doing business with HP gives you the advantage of dealing with a company that strives to consistently deliver a higher standard of quality to its customers In this case no full or complete pixel defects and fewer sub pixel defects than most competitors This means better quality for the customer and ultimately greater satisfaction for the end user because the user is viewing a cleaner image without the distraction of pixel defects 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 How LCDs work A liquid crystal is exactly what it sounds like a fluid substance which also exhibits some properties such as an ordered arrangement of its molecules similar to a solid crystal In 1963 an RCA researcher discovered tha
5. the light emitted by any pixels Polarizer scratch Physical damage to the polarizer that does not damage the glass When the unit lights lines appear light white with display patterns dark and do not vary in size This defect may not completely block the light emitted by any pixels Rubbing line defects Horizontal or diagonal lines that appear gray with the display patterns dark and may have resulted from an out of control rubbing process on the polyimide or waves on the BEFs or prism sheets Sub pixel A single point of light representing a primary color red green or blue which combines with the other two primary color sub pixels to form a complete pixel Vertical line A line of pixels that crosses the display vertically in portrait mode 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 HP quality and reliability helps reduce maintenance repair and support costs throughout the monitor lifecycle and result in a high residual value for HP products The HP strong market share reflects a global awareness and strong customer loyalty to the HP full line of innovative and competitively priced products Here
6. translucent plastic diffuser layer which spreads the light evenly across the screen Why TFTs In the simplest LCD technology the voltage applied across the LC material is delivered by transparent row and column electrodes lines of conductive material which cross at 90 degrees one set on the top glass and the other on the bottom The intersection of rows and columns define the pixels and subpixels of the display and applying a voltage to a given row and column switches the pixel at that particular intersection If the panel is driven such that the pixels are switched in order across the display very rapidly the appearance of a complete image is produced Unfortunately when the drive voltage is removed from a given pixel and we move on to the next that first pixel starts to switch back to its off state This limits the contrast resolution and the response time that can be achieved with such a simple passive matrix drive system 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 large size high resolution displays which rival any other display technology in performance F
7. 0 lux average room lighting can vary from 60 to 600 lux typical museum lighting is 50 lux e Viewing angle of 70 to 110 degrees horizontal and 80 to 100 degrees vertical HP pixel defect standards Since some degree of sub pixel defects are inevitable all manufacturers find it necessary to tolerate a minimal number of sub pixel defects in their products Replacing a panel with just a few minor sub pixel defects is not recommended since the replacement unit may also have a similar number of defects Historically HP has maintained stringent manufacturing specifications for pixel defects and it has been tightening those specifications over time HP specifications HP pixel defect specifications continue to be refined but will always represent the best panel quality standards which can reasonably be achieved consistent with expected panel yields the need to deliver products at competitive costs and most importantly the goal of producing high quality images on our displays In a simplified format the pixel defect specifications are as follows Table 1 This policy applies for HP monitors manufactured before May 2009 Bright sub pixel defects 3 maximum Dark sub pixel defects 5 maximum Total sub pixel defects 5 maximum Full pixel defects O allowed 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 maxim
8. 0 single or double sub pixels stuck on or off The HP specification ensures that all of our products exceed the ISO Class 2 requirements as no full pixel defects are ever permitted in most cases HP displays will meet the more stringent Class 1 specification As mentioned earlier the HP specifications dictate no full pixel defects further we require no double sub pixel 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 The pixel faults are defined in the following way A pixel is a group of 3 assigned subpixels red green blue Each subpixel corresponds to a transistor Pixel fault Typ 1 constantly bright pixel Pixel fault Typ 2 constantly dark pixe Pixel fault Typ 2 defect subpixel either constantly bright red green blue or constantly dark For example SubPixel Typ 2 A cluster is an area of 5 x 5 pixe Cluster pixel fault Typ 1 and Typ 2 constantly bright or dark pixels within the clusters Cluster pixel fault Typ 3 defect subpixel either constantly bright red green blue or constantly dark within the cluster i ny P i I 3 Typ2 Typ 3 Types 274 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 achi
9. 28 optional criteria Select HP business monitors are designated EPEAT Silver indicating that they meet all of the required criteria and at least 14 of the optional criteria The HP L1950g and HP L2245wg are designated EPEAT Gold which indicates they meets all 23 required criteria plus at least 21 of the optional criteria e Low emissions HP monitor products meet the demanding emissions environmental and ecological guidelines known as TCO 99 and TCO 03 TCO approved products meet a number of strict new requirements set by TCO Development the world s leading organization for quality and environmental certification e Energy savings HP LCD monitors include advanced power management features meet the U S Environmental Protection Agency s ENERGY STAR requirements e Recyclability Commonly recycled materials are easily identified making it easier to find a market for discarded components e Packaging Packaging consists of recyclable materials no heavy metal inks and minimal packaging material e Disassembly Products are easily disassembled at the end of the product life to aid in recovery of recyclable components e CFC free Both HP and its suppliers use only CFC free processes to protect the ozone layer from further damage HP service and support HP LCD monitors are protected under the industry leading HP support umbrella which includes 65 000 sales and service professionals in 160 countries around the world who pro
10. cssececcceaaseeceucaieesdecetensdcsssesdeesseasseesssacsseseuisesss 11 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 To deal with these inevitable minor flaws HP has developed a set of policies and detection methods to help ensure that each customer receives the highest quality product available Executive summary Flat panel LCD technology is a complex subject To help you understand how pixel and sub pixel defects occur and what HP does about them this white paper explains e What are sub pixels and how do they work A detailed look will show that millions of tiny sub pixels cover the typical flat panel screen producing the mixture of color and detail that forms the sharp vibrant images flat panel users have come to expect e How do pixel and sub pixel defects occur The HP specification does not allow for any full or complete pixel defects It does however allow for some minimal sub pixel defects This is because the current state of the art in manufacturing processes still may produce a few sub pixel defects per screen These defects can be extremely hard to see unless they are viewed under special conditions or unless they happen to
11. epresents a failure rate of only 25 millionths of one percent To look at it another way having 10 sub pixel defects on a 1280 x 1024 color panel means that the panel is still 99 9999 defect free 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 Sub pixel defects are also easier to spot when they are clustered together in a single area If all three sub pixels in the same pixel fail simultaneously you are more likely to detect the resulting light or dark pixel However since HP specifications require that TFT panels not have any complete pixel defects i e all three sub pixels defective HP customers are not likely to encounter this situation To locate defective sub pixels the monitor should be viewed under normal operating conditions in normal operating mode at a supported resolution and refresh rate from a distance of approximately 20 inches 51 cm The following standards show the typical conditions under which HP scans for pixel defects e Viewing distance of approximately 14 inches 36 cm e Ambient illumination of 300 to 50
12. eved 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 Cross lines off When the unit lights lines in both the minor and major axis do not appear Dark spots lines Spots or lines that appear dark in the display patterns and are usually the result of contamination 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 Dim line When the unit lights line s in the minor vertical or major horizontal axis appear dim but not completely on or off Horizontal line A line of pixels that crosses the display horizontally in portrait mode Mottling When the unit lights variation non uniformity splotchiness appears light white with the display and might vary in size Newton ring A rainbow effect caused by non uniform cell thickness Pixel A picture element made up of three primary color sub pixels red green and blue which combine to represent a single color dot on the display Polarizer dent Physical damage to the polarizer that does not damage the glass When the unit lights spots appear light white with display patterns dark and do not vary in size This defect may not completely block
13. igure 1 How thin film transistors are placed in the LCD array Column Electrodes TFT _ TFT Electrodes across mm LC material Row Electrodes Understanding pixel defects Active matrix TFT LCDs require at least one transistor to be created at each subpixel on the panel This makes the average AMLCD an enormously complex device For example producing one of today s high resolution WUXGA displays with a 1920 x 1200 pixel native format requires embedding nearly seven million transistors in the screen 1920 x 1200 x 3 6 91 million This is more than double the number of transistors found in the original Intel Pentium processor How pixel defects occur Damage to any one of the millions of transistors within the LCD panel may leave a sub pixel permanently on or off creating a tiny dark spot or bright spot on the display This is fairly common even for small TFT displays on handheld computers Minute specks of dust on the panel slight errors in the panel processing and other problems encountered during manufacturing of the TFT array on the glass substrate cause these defects When we look at the total number of pixels and subpixels on a 1920 x 1200 display we see that the failure of one sub pixel out of the 6 91 million is a very low failure rate indeed only about 14 millionths of one percent 0 000014 For lower resolution SXGA displays a single sub pixel defect still r
14. t liquid crystals can be used to control light by switching a voltage across the material on and off Before long the technology was being applied to everything from calculators to computer monitors Because of their long rod like shape and electrical properties liquid crystal molecules tend to line up in parallel rows in their natural state When used in computer displays this material is enclosed between two pieces of glass in a flat panel display and an image is generated by controlling the alignment of the LC molecules electrically causing them to effectively act as light valves letting light either pass through the panel or be blocked depending on the voltage applied across the material Color filters are placed on one side of the glass panels with three different colors red green and blue for each pixel Combining red green and blue light in different amounts controlled by the voltage applied across the LC material at each of these individual areas called subpixels lets each pixel appear as any color and any brightness and the combination of all the pixels on the panel creates the complete image Fluorescent lights very similar to the fluorescent tubes used in standard office lighting but much smaller or light emitting diodes LEDs provide the backlighting for the LCD display the light that will pass through the panel from the rear and so create the image The light from the backlight unit passes through a
15. um 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 Most remaining units are shipping with only a few pixel defects that fall within the above listed range of acceptable pixel defects International standards ISO 9241 The International Standards Organization ISO has published its own set of specifications for pixel defects contained within the ISO 9241 set of standards These identify three classes for measuring pixel defects in flat panel monitors e Class O panels are completely defect free including no full pixel or sub pixel defects e Class 1 panels permit any or all of the following 1 full bright stuck on pixel 1 full dark stuck off pixel 2 single or double bright or dark sub pixels 3to 5 stuck on or stuck off sub pixels depending on the number of each e Class 2 panels permit any or all of the following 2 full bright pixels 2 full dark pixels 5 10 single or double bright or dark sub pixels again depending on the number of each no more than 5 bright stuck on subpixels are permitted e Class 3 panels permit any or all of the following 5 full bright pixels 15 full dark pixels _ 5
16. vide an impressive depth of service and support at the local level All HP LCD monitors come with a three year limited global warranty on parts and labor including the backlight You can purchase a monitor in one country move it to another country and receive warranty service if the unit is still in warranty In the United States HP offers toll free round the clock telephone hotline support terms and conditions may vary by region Additional support is available 24 hours a day on the Web at www hp com HP Care Pack Services are also available A part of the HP Total Care portfolio these extended service contracts go beyond standard warranties and help maximize the initial return on investment and reduce the loss of productivity For more details visit www hp com hps support 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 Corporate and North American headquarters Hewlett Packard 3000 Hanover Street Palo Alto CA 94304 1185 Phone 650 857 1501 Fax 650 857 5518 Regional headquarters Latin America Hewlett Packard Waterford Building 9th Floor 5200 Blue Lagoon Drive Miami Florida 33126 USA Phone 305 267 4220 Europe Africa Middle East Hewlett Packard Route du Nant d Avril 150 CH 1217 Meyrin 2 Geneva Switzerland Phone 41 22 780 8111 Asia Pacific Hewlett Packard Asia Pacific Ltd Hewlett Packard Hong
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