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Panels that are produced too economically?
by Vincent Alzieu
Published on September 28, 2007

Panels that are produced too economically?
We are still reaping the results from the tests and unveiling of the various Samsung SyncMaster 226BW versions. At first, it enabled us to see the number of different panels used for the same reference number as well as the variation in settings. This especially resulted in random color fidelity despite rather similar components.
Another point that has now come up is that for same family of panels from the same manufacturer (Samsung, in this case), colors may appear homogenous to the eye but there are darker zones as soon as we move our eyes from the center of the panel. From what we’ve gathered, this has nothing to do with a potential Mura effect and is more a problem related to the filter applied to panels and viewing angles that are much too small.

Once again the alarm was sounded on the Forum and this brought our attention to the problem. Readers started complaining of darker zones on their screens and imperfect color homogeneity. More specifically, unified images were darker in the upper area of the screen than on the lower area. We didn’t really understand (or notice) this before because none of the monitors that passed through our lab displayed this characteristic.

Then we received the Iiyama ProLite E2201W, a 2 ms TN equipped with a Samsung panel. Reactivity, input lag, and homogeneity measured by our sensor – all matched up perfectly to characteristics of the Samsung SyncMaster 226BW “S” series that we obtained. However it even if you sit directly in front of the screen, it is possible to see tint variations in the corners.

Here is a graph displaying homogeneity measured with our sensor:

More specifically, the maximum brightness difference between two points is 25 % with an average of 8.6%. This is completely within the norm and even better than average. A classic screen can easily go as high as 30 % between two points while the more homogenous ones are at 15 %.

And yet when we look at the center of the panel and simply move our eyes to a corner, the image immediately turns darker:

This is a photo of the panel superimposed on a shot taken directly in front of the screen.
We could start to suspect a defect related to the Mura effect, in other words, poor brightness homogeneity due to a problem with the light reflectors. However, the difference measured between the center point below and the one above was only 4%. Another troubling fact, and which definitively ruled out the Mura effect, was that if we then looked up at the upper right hand corner of the screen, here is what we obtained (the two images are the closest reconstructions we could manage with Photoshop) :

Another possible variation was that if we barely change our gaze the dark zone moved:

We noticed this defect on the first Iiyama ProLite E2201W and then in the company of their representative with a second one that they brought us for verification. We expressed our surprise to them and then to our even greater surprise (and to their credit, we suppose) they admitted to be aware this problem. They didn’t see that the defect wasn’t homogenous and thought it to be associated to a Mura effect. For them, this was already noticed on a more basic product also equipped with a TN panel, that time an AU Optronics.

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