Results: Brightness And Contrast
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 the contrast control 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.
We reviewed another 144 Hz screen back in the fall, Asus' VG248QE, so we're adding it to our comparison group. The rest are QHD and UHD displays already evaluated on Tom's Hardware.
Our measurements come pretty close to BenQ’s spec of 300 cd/m2. That's plenty of light for any gaming or productivity application. There is one caveat though. If you engage the blur reduction feature, output is cut by around 58 percent. Whenever black frame insertion is used in any LCD panel, lower brightness is an unavoidable side-effect. You can mitigate this somewhat by using the Blur Busters Strobe Utility, which we talk about on page nine.
TN panels usually render decent black levels, even with the backlight on maximum.
The XL2720Z cranks out excellent black levels. This is one area where TN panels are still superior to their IPS counterparts. The BenQ also edges out its 144 Hz competitor, Asus’ VG248QE by a hair.
The overall contrast result is quite good.
The BenQ’s max contrast ratio isn’t quite at the top, but it’s very close. Only a handful of monitors of any type can exceed 1000 to 1 when the backlight is turned up all the way.
We believe 50 cd/m2 is a practical minimum standard for screen brightness. Any lower and you risk eyestrain and fatigue. The XL2720Z bottoms out at 66.0294 cd/m2, which is great for playing games in total darkness as long as you don’t use the Blur Reduction feature. As you’ll see below, black levels and contrast hold up extremely well too.
Even though the BenQ finishes last in this group, all of the monitors measure extremely low in our minimum black level test. The VG248QE is still the champ.
Here are the contrast numbers:
BenQ's result beats most of the other monitors we’ve tested. Although we’ve seen a couple of screens score higher (like the Asus), once the contrast ratio is over 1000 to 1, it’s hard to tell a difference in perceived image quality. The XL2720Z demonstrates consistently high contrast performance throughout its entire brightness range.
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), this brightness level provides a sharp, punchy image with maximum detail and minimum eye fatigue. On many monitors, it’s also the sweet spot for gamma and grayscale tracking, which we'll look at on the next page. In a darkened room, some professionals prefer a 120 cd/m2 calibration, though it makes little to no difference on the calibrated black level and contrast measurements.
Calibration usually reduces contrast slightly. But unless the change is greater than about 15 percent, you’re unlikely to see a difference. A result of .2183 cd/m2 is excellent.
The final contrast ratio is only slightly lower than the out-of-box figure.
We are happy to see the trend of consistent contrast performance continue with the XL2720Z. It’s always best to have a screen that delivers the same image quality no matter what the backlight setting. This panel is firmly in that category.
ANSI Contrast Ratio
Another important measure of contrast is ANSI. To perform our test, a checkerboard pattern of sixteen zero and 100-percent squares is measured, giving us a somewhat more real-world metric than on/off measurements because it evaluates a display’s ability to simultaneously maintain both low black and full white levels, further factoring in screen uniformity. 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.
Looking over our data for the past year, a vast majority of tested screens are in a range of 800-900 to 1 for ANSI contrast. The checkerboard pattern we measure is a more real-world representation of actual intra-image contrast. Since the XL2720Z is made from a brand-new panel part, it’s not surprising to see such good engineering and quality control.