Recently, we received a brand new 47" LG LM670S LED-backlit LCD TV (Edge LED i.e. LED TV, as marketing brochures say) for a review. While this TV combines the factory default calibrated image with intuitive user interface, the built in operating system obviously requires serious work.
To be more precise, after using the Smart TV functionality such as web browsing, we have noticed the appearance of image retention or image persistance. In layman terms, we can describe this effect as a temporary "burn-in" effect
which is characteristic to plasma panels of yesteryear.
The appearance of ghosted image is typical for screens based on phosphorus, such as the old CRT (Cathode Ray Tube)
or plasma panels
. You can even notice the static content remaining unchanged after you change the content, or even after the complete shutdown of the TV. Given the time of curing the phosphorous, it takes some time for the cells to return to their normal position. Plasma panels are still subject to this effect, even though the cell cycles changed, manufacturers embedding different protection elements such as pixel shifting, or special image cleaning patterns.
As you can see for yourself, the LG LM670S TV shows residue of white-grey lines, such as ones from URL web address
Naturally, LCD panels are not based on phosphorous. However, they can show traces of previous image which remained on the screen for some time. LCD panels are consisted from tiny crystals positioned in a thin film, showing images by changing its rotating and letting more or less light. If the crystals are continuously exposed to the same amount of current, the crystals can develop a tendency to remain the same position even after the current changes. As a consequence, a new shade of gray will appear - if you change that image with a new one, it is possible to have a shadow of a former image, a problem known as image retention. The essential problem of these traces is the same in all technologies we mentioned above - phosphorous targets on CRT TV's, phosphorous cells on Plasma panels, or crystals on LCD panels.
In case of LG's LM670S TV set with an IPS panel, static image residue appears when a "Standard" preset which gives maximum LED backlit, increased sharpness, more dynamic colors as well as the dynamic contrast.
Given that you cannot change the "Standard" preset when using Smart TV platform, it's not odd that we've experienced lazy image on darker backgrounds. The very best (or worst) example is URL address bar. After you leave the browser, you can clearly see the address bar on top of the image. Test Signal Menu looks quite normal in out FPB Benchmark Blu-ray Test Disc.
We have tested this problem on the LM670S TV on our video materials, such as a 15-minute test in FPB Benchmark Blu-ray Test Disc using Standard, Vivid and ISF presets. Test was consisted out of leaving the Test Menu turned on for 15 minutes, after which we ran a gradient map going from completely black to completely white.But simply starting a test pattern reveals the "TEST SIGNAL Menu" and "TET SIGNAL" residue
Result of our tests shows that traces remain with all testing patterns, mostly with Standard and Vivid presets. As the internet browser test showed, you can see traces the best if you had a static white surface on a darker surface. After the image changed, you could read an outline of TEST SIGNAL at about one meter of distance or less (3 feet). Other static content was not visible in any of other test patterns.
The question that is probably tingling in your head is - how long does this effect last? Fear not, it is not a permanent issue as it was on CRT and Plasma panels. After 10 seconds or running dynamic content, the patterns would disappear, meaning it takes around 4,000 refresh cycles to return the crystals in their original pattern.
When using ISF patterns, the trace was very weak in its intensity. Thus, we can conclude that this is not something you should be worried about - but keep this information stored in your head when a discussion on "ghosting" or "burn in" rises in social circles. We did not notice the static image residue when running subtitled movies or TV station logos - as the test shows, this only lasts with specific gray/white patterns and doesn't last for long.
Having stated this, in all of our future reviews of Smart TV devices, we will pay special attention to the image retention / image persistance problem.About the Author
Darko HD Hlusicka is a founder and Editor-in-Chief of HDTelevizija.com, our sister publication. He is an experienced author with over 100 reviews of TV's. In his in-depth screen testing, Darko relies on industry-standard methods utilizing calibration equipment from SpectraCAL, Calman software, AV Foundry VideoForge. When he is not reviewing the latest in the world of TV's, the author spends his free time enjoying in technology, sport (codename: biathlon & zumba), photography (addicted to Canon) and movie music (an epic collection of movie soundtrack CDs and DVDs). Life motto: "Love many, trust a few, do evil to nobody."
© 2009 - 2014 Bright Side Of News*, All rights reserved.