Results: Brightness And Contrast
Uncalibrated
Before calibrating any panel, we measure zero and 100-percent signals at both ends of the brightness control range. This shows us how contrast is affected at the extremes of a monitor's luminance capability. We do not increase contrast past the clipping point. While doing this would increase a monitor’s light output, the brightest signal levels would not be visible, resulting in crushed highlight detail. Our numbers show the maximum light level possible with no clipping of the signal.
The greatest light output is available through the 34UM95’s Photo picture mode. The monitor comes from the factory set to Custom, though that only results in a peak white measurement of 249.9291 cd/m2, under LG’s 320 cd/m2 specification.
The black level at maximum brightness is decent, but that’s partially because of the lower white level. We noticed when displaying a zero-percent pattern that the backlight would shut completely off after a few seconds. You probably wouldn’t experience this behavior during normal use. However, it made our black level measurements a little tricky.
The max contrast level is a little lower than most other IPS screens. We like to see displays achieve at least 1000 to 1, so the 34UM95 isn’t too far off. Our results make it pretty obvious that TN still has the edge there, though.
We believe 50 cd/m2 is a practical minimum standard for screen brightness. Any lower and you risk eyestrain and fatigue. The 34UM95 bottoms out at 56.2552 cd/m2, which is great for playing games or working in a completely dark room.
A black level measurement of .0638 cd/m2 is decent, but other monitors we’ve tested go a little lower. The important thing is that the contrast ratio remains fairly constant as we turn down the backlight.
The difference between the 34UM95’s maximum and minimum contrast is negligible. It’s not quite as high as I'd like. Then again, I'm picky. Fortunately, the image quality you can expect from actual content is quite good with plenty of depth and pop.
After Calibration
Since we consider 200 cd/m2 to be an ideal point for peak output, we calibrate all of our test monitors to that value. In a room with some ambient light (like an office), you get a sharp, punchy image with maximum detail and minimum eye fatigue. On many monitors, this is also the sweet spot for gamma and grayscale tracking, which we'll look at on the next page.
In a dark room, many professionals prefer a 120 cd/m2 calibration. We have found it makes little to no difference on the calibrated black level and contrast measurements, though.
The black level is not significantly affected after calibration. Because the RGB sliders default to the center of their range, grayscale can be adjusted in a more balanced manner. When the controls begin at their maximums (like the majority of monitors), you can only reduce contrast as you dial in the grayscale.
We give up some performance here because we have to reduce the Contrast control in order to clean up the 100-percent white point. If you opt to leave Contrast at its default setting, you can expect about 900 to 1 instead. Our result represents the lowest possible grayscale error and is therefore a compromise.
ANSI Contrast Ratio
Another important measure of contrast is ANSI. To perform this test, a checkerboard pattern of sixteen zero and 100-percent squares is measured, yielding a somewhat more real-world metric than on/off readings because we see a display’s ability to simultaneously maintain both low black and full white levels, factoring in screen uniformity, too. The average of the eight full-white measurements is divided by the average of the eight full-black measurements to arrive at the ANSI result.
The ANSI measurement takes a hit due to the 34UM95’s poor black field uniformity, which we’ll show you on page eight. There are hotspots along the panel’s bottom edge that elevate the readings enough to drop ANSI contrast by another 28 percent from the maximum number. If you return the Contrast control to its default setting, the result improves to 773.4 to 1.
