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The Secret Sauces of THG's LCD Tests

What About The Standards?

The ISO standard imposed on manufacturers is normally marked on the box as the latency of the panel, which is no bad thing. Unfortunately, they're only obligated to specify the most favorable situation. And that's something we're no longer in agreement with. While a TN+ film screen is perhaps specified at 8 ms, its actual latency in the worst case can climb to 23 ms - which is more than a 200% increase compared to the vendor's specification!

The illustration above shows the results of our latency tests. The x-axis lists the values of the transitions measured. On the y-axis, you can read the latency corresponding to these transitions, expressed in milliseconds (ms). So, to illustrate the point, the intersection on the abscissa (where X=130) corresponds to a transition black -> grey -> black (0 -> 130 -> 0). The point on the abscissa corresponding to an X value of 255 represents the ISO latency as specified by the manufacturer. It corresponds to a transition black -> white -> black (0 -> 255 -> 0).

With the aid of this graph, we can draw several conclusions concerning the performance in terms of latency. Firstly, the actual performance of the panel is definitely not 8 ms; the average is instead around 19 ms and in the worst case, 24 ms. Next, it's apparent that at the ISO value, latency isn't 8 ms either but closer to 11 ms. Why? Well, there are a few parameters that influence the latency of the panel, and contrast is one of them. If we push the contrast of the L90D+ to its maximum, then effectively we get the 8 ms ISO figure. On the other hand, although the average latency is satisfactory, the quality of the static image and color rendering deteriorates rapidly. As a consequence, we resolve to test the latency of LCD panels when the quality of the image is reasonable. The latency measured is therefore the most representative possible.