The reactivity test Initially, we wanted to physically measure afterglow with an oscilloscope. We approached an electronics specialist, Tektronics, and they were nice enough to supply us with a sensor + oscilloscope combo of their making. This was to be used to measure the transition from white to light gray, white to a darker gray, gray to black, etc. We came up with some great 3D graphs but the problem was that practical tests (based on a visual evaluation) didn’t always match these results. A screen that was judged more reactive with the oscilloscope sometimes appeared to our eyes as being slower than other products. We therefore abandoned this method to come back to more practical, concrete, and in our opinion, realistic tests.
Our other method put into place since 2005 and based on photos, has proven to be more reliable.
Here’s the concept in this test: A car moves from right to left at high speed. The movement isn’t perfectly fluid and depending on its speed, the car is shown in several successive positions. When this process is sped up, the car goes very fast, positions are very close and the eye perceives a fluid movement. The perfect screen monitor with two afterglow images
A monitor without ghosting effects would have previous images completely fading away when a new one appears. This is ideal, however in practice, it's often not the case as images progressively fade. Sometimes up to 5 afterglow artifacts remain on the screen representing the visible white trail behind objects.
We capture this LCD defect with a camera at a shutter speed of 1/1000 s by taking 50 pictures per test. We then can see a monitor’s ghosting effects, or the car’s position in the entire process from the moment when afterglow is at its maximum, up until when the next image is about to be created and the previous image is the least visible.
Here are the two extreme states between which each monitor’s afterglow can oscillate.
IPS 8 ms : Dell 3008WFP-HCFrequency of the two states:
We therefore always have a colored afterglow image behind the main image and half the time an additional transparent one.
For comparison, here is what we find on a good quality TN 2 such as a Iiyama 22’’ 2 ms:
There can be more transparent afterglow images but this isn’t a problem as this only slightly increases visible afterglow. It is especially the colored ones that are a factor and determine if a screen is more or less good in this area.
For this reason, the Dell 3008WFP-HC is obviously behind in reactivity. In addition, all of the ‘’average’’ performances start add up here and become a problem. First is was in colors, then depth of black, brightness homogeneity, and now reactivity.
By the way, here is the reactivity of an entry level TN 5 ms :
The 3008WFP is therefore not all that catastrophic and it is more half-way between the best and worst monitors at this time. However, note that its 8 ms announced response still does better than a TN 5 ms. After all, they are just numbers...
Input lag in games
If you didn’t already know, almost all LCD monitors have a small delay in display. To measure this, we photograph a chronometer which is precise to 1/1000th of a second displayed in clone mode on our reference CRT and the LCD we are testing. We take 12 consecutive differences, eliminating the two extremes and then find the average delay.
For this test, we deactivate graphic card / screen synchronization to capture a more precise result instead a value that is rounded to the nearest image. For this reason, the resulting measurements are not dependent upon the fps value. An LCD functions at 60 Hz (even those that claim 75 Hz) and so 17 ms equals an average delay of a single image. In the same way, 33 ms equals 2 images. This may not seem like much, however, to an on-line gamer it could make a world of difference. For example, an adversary with an LCD or CRT will see his character two images before him. This can be compounded by the fact that the mouse can add another 1 to 8 ms (except very poor ones), and the graphic card adds a half image delay (at best and actually this can be 5 to 50 ms). More specifically in our research, we found that this can be a cumulative delay of 110 ms or 6.5 images. In this case, it is indeed noticeable and even bothersome for some gamers. For more details on this subject, see our article on LCD images delayed compared to those of CRTs ? Yes !
IPS 8 ms : Dell 3008WFP-HC
Once again, the 3008WFP-HC scores low while a growing number of screens come with no input lag, even in the entry-level. This screen is consistently 3 images behind.