Projection or flat panels for videowalls? - Christie Digital Systems

Considerations for video wall product selection FPDs CubesViewability • •Brightness • •Brightness uniformity•Contrast • •Auto brightness and color balancing•Gaps/seams between screens•Image retention•Image degradation•Video wall footprint•Initial system price•Total cost of ownership – 24/7•• = Best/typicallybest optionDisplay technologyConsiderations for videowall product selectionViewabilityHow easy is it to see display information from different anglesand room locations? Both FPDs and cubes are designed tomaximize the viewability of information when the user is notdirectly in front of the display screen. However, as you movefurther off-angle from the display, brightness, and possiblycolor, may be affected, thus it is important to verify the productperformance specifications in advance. For cubes, opticalscreens are typically used and each type has its own uniqueviewability characteristics. For FPDs, viewability characteristicscan vary based on the LCD panel manufacturer. Both solutions(cubes and FPDs) can provide very good viewability characteristics,but during product selection it is important to ensure theactual characteristics for a selected product meets the designrequirements set for the application.BrightnessBrightness requirements for video wall applications varydepending on the actual application. For instance, if the videowall is to be used in a signage application, brighter is usuallybetter as it attracts more attention and interest. Also, higherbrightness may be necessary to improve overall contrast inenvironments where ambient light is very high – such as theoutdoors. However, for control room applications, too brightcan be considered a negative. Many control rooms have peoplethat work and operate in front of the display wall for a fullworking shift. If the wall is very bright, those people may sufferfrom headaches or eye strain over time. On the other hand,if the wall is not bright enough, contrast will likely be too low,making it difficult to quickly and accurately discern informationas required. For typical control room applications, a nominalbrightness of 250 cd/m 2 is quite adequate and reasonable.Above 500 cd/m 2 may be too bright whereby brightness mustbe lowered and managed. FPDs and cubes vary in brightnessand size but can usually accommodate most requirements.If cubes are preferred for high brightness applications, thenMicroTiles ® might be the best solution to consider.2

Display technologyIf brightness is not uniform within eachscreen, the overall video wall may exhibit a“checkerboard” type appearance which maybe more noticeable if content is mostly staticand includes a full white background.Brightness uniformityThis section covers brightness uniformity within each displayscreen, not just across the entire video wall display. If brightnessis not uniform within each screen, the overall video wall mayexhibit a “checkerboard” type appearance which is veryundesirable. The impact of this effect will be more noticeabledepending on the content displayed. For instance, if thecontent is mostly static and includes a full white background,non-uniform displays will likely be quite noticeable. On theother hand, if the displays have lots of video or static contentwith dark backgrounds, non-uniform displays may be of muchless concern. Most cubes offer a uniformity of 95% or better– which is quite good, while FPDs are typically not as high.Additionally, because uniformity is not typically measured rightto the edge of the bezel on FPDs, it is recommended to actuallytest/view the product solution in advance with the contentbeing used to ensure that the uniformity meets the expectationsfor the application.Auto brightness and color balancingWhen multiple displays are used together in a tiled displayarray or video wall, it becomes very critical that brightnessand color from display to display be well matched and remainthat way over time. Our eyes are very sensitive to even subtledifferences in color across multiple displays, therefore videowall display products include capabilities to finely adjust thecolor for best matching performance. However, over time,color or brightness may slightly change or drift, requiringre-adjustment. A major benefit of cubes and MicroTiles ®versus FPDs is that projection technology allows color sensorsand monitoring to be embedded within the design so thatcolor and brightness can be constantly monitored andautomatically re-adjusted without human intervention.This occurs continuously and is transparent to the user.For FPDs, color and brightness must be manually re-measuredwith an external meter and re-adjusted on a regular interval.This creates disruption to the display wall, additional expenseand cyclical performance variations.ContrastHigher contrast enables easier and faster recognition of theinformation displayed and reduces eye strain. For controlroom design, the overall system contrast ratio is quite critical.This takes into account ambient lighting within the room aswell as the imaging from the video wall display. Typically,a system contrast ratio of >100:1 is what is required. Displayproducts themselves have their own contrast ratio which isused to help determine the overall system contrast ratio.Fortunately for both FPDs and cubes, the display contrastratio is usually at least 1500:1, which is acceptable in mostenvironments and applications.3

FPDs - between screensCubes - between screens1st STREETStatic image displayedfor long durationWEBERSTATIONHESPLERFREECAROLINE ST. JACOB1st STREETImage remaining afterstatic image removedWEBERSTATIONCAROLINEDisplay technology1 2 3 4 5 61 2 3BezelsGapsCubes have the ability to minimize this transition by offering a gap betweenscreens of only 1mm. FPDs on the other hand, have a disadvantage in thatthey require a bezel which supports the liquid crystal glass.Image retention is a reality for all LCD panels and its severity will varydepending on the content displayed and the duration the panels areoperated. DLP technology does not have this same issue.Gaps/seams between screensIdeally, a video wall display should be completely seamless.That is to say, viewers should not notice or a see a transitionfrom one display screen to the next. But in reality, this is notpossible with the emissive display products and technologiescurrently available. However, cubes have the ability to minimizethis transition by offering a gap between screens of only 1mm.This 1mm space is typically required to allow for expansion/contraction of the screen materials during temperature orhumidity fluctuations. Fortunately, for large display walls whereoperators and users are typically at least 3 meters (10 feet) away,1mm is considered negligible. FPDs on the other hand, havea disadvantage in that they require a bezel which supports theliquid crystal glass. Most “narrow bezel” FPDs offer an “imageto image” transition of approximately 6mm, or slightly less. Forapplications where there is lots of data displayed versus motionvideo, the bezels may be too large, causing too much distortionof the information being displayed.Image retentionAn effect that can occur with LCD based technology is whatis typically referred to as “image retention.” This occurswhen a static image is displayed for a period of time, causingelectrically charged particles to collect at the electrodes ofthe LCD panel, which in turn affects the future behavior of theLCD crystals. The outcome is that when the image is eventuallychanged, a “phantom” image of what was previously displayedmay be still visible, disrupting the new information beingdisplayed. Depending on the situation, this “phantom” imagecould remain permanently on the display. It is for this reasonthat LCD panel suppliers rate their LCD panels for only 20/7operation. Also, image retention is typically not coveredunder warranty. For best practice, it is recommended to leavethe panel turned off for at least 4 hours per day to allow theLCD crystals to “stabilize,” reducing the impact of retentionissues. It is also recommended to operate the panels at loweroperating temperatures within the rated specifications to helpminimize this effect.Image retention is a reality for all LCD panels and its severitywill vary depending on the content displayed and the durationthe panels are operated. DLP ® technology does not havethis same issue. However, if the installation is not 24/7 or thedisplays are typically showing fast moving images such as videorather than static images such as data, maps, schematics, etc.,image retention may be less of a concern. Although displayperformance may degrade over time, it may be acceptable forthe understood usable life of the FPDs.4

Long term costsOwnership cost ($)FPD replacementInitial video wall purchaseFPD systemCube systemGenerally, for FPDs running 24/7 or 20/7,plan for a useful life of about three years.For cubes and tiles, expect a useful life ofapproximately 6 years or more.Display technology0 12 3 4 5 6YearsTotal cost of ownership – 24/7This takes into account the initial equipment investment as wellas the ongoing operational costs such as power consumption,HVAC and maintenance. Generally, for FPDs running 24/7 or20/7, plan for a useful life of about three years. Although FPDscan usually survive beyond three years, the image degradationand imaging quality will likely require that the wall be replacedwithin that time. For cubes and tiles, expect a useful life ofapproximately 6 years or more. These products are designed forhigh reliability, very low maintenance and minimal performancedegradation over time. In considering operational costs, alsonote the power consumption required for the entire videowall display. This can vary greatly from design to design. Forexample, for a medium size video wall using 55" FPDs, thepower consumption and heat dissipation might be over doublethat of the same size wall using 80" cubes.Final Comments…This paper covers, in simplified terms, many of the key factorsfor consideration when selecting the appropriate productand technologies for a video wall display. This informationprovides insight for consideration of any new video walldesign. However, aside from what is covered here, thereare many other design-related factors, requirements orconstraints within the physical environment that can alsohave a big impact on setting directions and decisions forsolution design and product selection. With more knowledgeand understanding by all the people involved with the process,there is a higher probability of success while utilizing the bestsolution available for the given application.Jim Gavloski, CTSDirector, Product ManagementControl Room and Video Wall Display SolutionsChristie ®(Jim Gavloski has been with Christie for over 17 years developing and providing video wall displaysolutions for the global Control Room display market).6

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