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Panels a la carte: Mura, components, dead pixels...
by Vincent Alzieu
Published on September 29, 2005

Introducing the Mura effect
->Consider the following correlation: the price of LCD monitors drops at the same speed as buyers´ interest increases. Starting at $800 for a 19” monitor two years ago (Summer 2003), its price has now fallen to $300 for a brand name monitor and $280 for a generic.

->So taking this into account, what are the factors behind very low priced monitors? How can Fujitsu-Siemens sell a Premium C19-4 MVA 8 ms panel for half the cost of a ViewSonic VP191b equipped with the same panel? Where do the 19” MVAs and 8 ms TNs sold for under $300 come from? What are the real dead pixel risks with these products? And finally, why do some manufacturers have a “zero dead pixel” warranty while others say we are killing them when we suggest following Philips´ example?

We´ve been asking these questions for years now. Sometimes we went straight to manufacturers, but as you may know, sometimes it´s difficult to obtain clear information in such sensitive areas. So we asked the question to a lesser known new manufacturer, Atlantis Land. They are nowhere near giants such as Samsung, LG or the others, but have a “O pixel” product line, meaning “zero dead pixels” whether they are white, black or color. Monitor prices aren’t extreme and the next 19AM-C08 (of the "O pixel" line) will be available in October for 399€. Their representative, Frank Demouth, was very willing to respond to our questions. With these answers we added the confirmation of several manufacturers (which weren’t necessarily eager to see their names in an article entitled “hidden LCD monitor defects”) and new information on today´s topic, the “Mura Effect” and variations in panel component quality. We thank all manufacturers who more or less participated, giving us the possibility to show a defect (another some will say) not covered in the warranty.

The Mura, a defect not covered in the warranty
To begin with, we already know that panels belong to several classes, ISO 13406-2 Class I, II, III and IV, in reference to their tolerance to dead pixels (see this article on the subject). The most common is the second (ISO 13406-2 Class II). We remind you that it considers a 17” or 19” monitor with 2 black or white or even 6 colored dead pixels in the norm. Class one is the strictest with zero dead pixels tolerated. And then there is the III, used by BenQ for the T series. With this norm the number of dead pixels tolerated increases to 5 black, 18 white and 64 colored!

But did you know that there are 6 subcategories within these classes? Panel manufacturers test their products at the end of the production line. They attribute a class AND rank. The best is A+ followed by A, A-, B+, B and B-. Each rank is based on only one criteria, the importance of a defect called the “mura effect”. This term actually refers to several types of problems.

Mura Effect type 1 corresponds to a lack of homogeneity in control circuit adjustments. From one cell to another color control can change and it will lead to permanent defects in intensity in displayed images.

Mura Effect type 2, or Cell Gap Mura comes in two forms. If liquid crystal cell sizes are superior to the normal size in an area of the panel, the images produced in this area will be brighter. This is a White Mura. In the opposite way, if the cell size is too small, it will be darker. This is a Black Mura. Cell distortions sometimes come from a « normal » defect in manufacturing, but most of the times are due to an impurity in the panel such as dust, a drop of some chemical or an accidental ionisation of liquid crystals, which then misalign. For the first two cases, it is possible to move the defect by gently pressing the panel with your fingers to move the Mura to the side from a useful area in the screen. In the case of ionisation, the defect can fade or even disappear with time. For us it was the opposite with the appearance of a Mura on two monitors after a few years of use (three and five years, respectively). It looks as if you were pushing on the screen with your fingers except now it´s permanent.

Mura Effect type 3 is related to distance or defects between the panel and liquid crystals. This occurs when the panel is sealed and side pressure is imperfect. If it´s too strong, cells are crushed and there is a bright halo in a corner along the panel.

These are the three types of Mura effects detected in the factory. Two others exist:
  • One Murat effect can appear when color filters (red, green and blue) placed on cells are made of different materials, which react differently to heat and light,
  • the next one can be included as a manufacturing Mura, even if it isn’t one. The “spot” is a mark on the backlighting itself. It doesn’t properly light up an area of the monitor and causes a small spot of 1 to 5 mm in diameter.

    Panel and processor manufacturing are similar. The best possible panel is produced and there is a sorting at the end of the production line resulting in a full classing. A product line´s can vary in price from 5 to 7% from class to class. The gap between an A+ and B- panel can be up to 30% within the same line.

    For example, a 19” MVA 25ms panel will be sold $200 if it´s a B- and $260 if it´s an A+.

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