This is a very close relation of the U2211H, the only notable difference being the extra 1.5 inches of screen space diagonally. Otherwise, the two models coincide in their specs (except that the 2311H is brighter by a mere 50 nits). Let's see if they are so similar in real life.
Talking about the size of the screen, larger is certainly better when it comes to movies and games but things are trickier with productivity applications. The U2311H has the same native resolution of 1920x1080 pixels as the U2211H, so it has somewhat larger pixels. And I think it’s a plus because some people may find it hard to discern small details on the screen of the 21.5-inch model. The 23-incher is kind of more versatile in this respect, so if you are not sure which of these two screen diagonals to prefer, I'd advise you to choose the larger one.
The monitor’s Brightness and Contrast are both set at 75% by default. I achieved the 100-nit white by selecting 50% Brightness and 56% Contrast. The monitor regulates its brightness through backlight modulation at a frequency of 180 Hz.
The maximum brightness is higher than that of the U2211H by half. It is close to 300 nits, which makes this model suitable for any applications under any ambient lighting. The adjustment range is wide enough to lower the brightness of the screen to such a level that you could work or play comfortably at night with minimum lighting.
The contrast ratio is somewhat lower than that of the previous model, yet is still as high as 600:1 at the default settings. Today’s typical TN-based monitors have a contrast ratio of 600 to 700:1, too. It is PVA-based monitors that are superior to both TN and e-IPS technologies in this respect by delivering a perfect black (not without some inherent defects, though).
The gamma curves of the U2311H and U2211H are almost the same at the default settings. They are satisfactory.
The curves do not change when Brightness and Contrast are lowered in the monitor’s settings.
Rather surprisingly, the gamma curves get better in the Game mode, by getting closer to each other. The Game mode also makes the option of dynamic contrast available. It is indeed odd that the monitor’s color rendering is set up more accurately in a gaming mode than in a standard one.
The gamma curves diverge in the Multimedia mode. The purpose of this mode evades me. It looks the same as Standard, has the same Brightness and Contrast settings and no dynamic contrast. Dell must have introduced it as a kind of placebo: if the user manual claims that the image quality improves in this mode, some users will indeed get the impression of improvement.
Most surprisingly, the gamma curves are almost perfect in the manual setup mode (Custom RGB).
The monitor’s color gamut matches the sRGB color space, being smaller in reds and somewhat larger in greens.
The U2211H’s white point is shifted towards greens but not as much as with the U2211H. The greenish hue is quite conspicuous, though. Building on the correctly shaped gamma curves of the Custom mode, I selected the following values: R=100, G=94 and B=96. This eliminated the greenish hue and improved the monitor's color rendering to a very good, if not perfect, level. I want to remind you here that another sample of the same monitor model may differ (due to such factors as firmware version, LCD panel version, etc.), so you shouldn’t just blindly copy my setup. You always have to make sure with your own eyes that the image quality is good for you.
The average nonuniformity of black brightness is 6.1% with a maximum deflection of 19.7%. The average and maximum for white are 5.1% and 14.5%, respectively. The pictures above, drawn to reflect the test results, make it clear that the monitor has a brighter bottom half of the screen and the corners of the top half. These irregularities in brightness are quite normal and will not distract you in typical applications.
The response time average is 8.2 milliseconds (GtG) with a maximum of slightly over 10 milliseconds (GtG). Although the monitor doesn't set any records, it is quite fast for dynamic games. For example, the NEC MultiSync EA231WMi, based on an e-IPS Matrix without response time compensation, was twice as slow as that!
The level of RTC errors is 8.6% on average, and RTC-provoked visual artifacts (light shadows that appear behind moving objects) are mostly inconspicuous unless you are deliberately looking for them.
Comparing the U2311H with the U2211H, I should say there is no fundamental difference between them other than the size of the screen. Both offer good (but not exceptional) technical specs and setup quality and both have the same downsides which are insignificant or easily correctable. The higher maximum brightness of the U2311H won't matter much for practical applications unless you prefer to watch movies or play games in a brightly lit room. Thus, the screen size is the only factor that matters here. I personally think that the 23-inch model is more versatile in this respect but you may have a different opinion. Besides, the U2311H costs more than its smaller cousin.