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Results: Brightness And Contrast

Dell P2714T 27-Inch Touchscreen Monitor, Reviewed


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.

Our comparison group consists of the last six desktop monitors reviewed at Tom’s Hardware.

The P2714T is not an exceptionally bright monitor, but it is bright enough for any indoor environment we can think of. It wouldn't work well during an outdoor photo shoot, for example, but that's not really the role it was designed to play. The capacitive layer does exact a penalty in our measurements. Dell specifies a panel brightness of 300 cd/m2 and a monitor brightness of 270 cd/m2 in its manual. Therefore, we can say the touchscreen reduces light output by about 10 percent.

Hopefully, that results in a nice low black level.

The P2714T’s max black level is a bit on the high side compared to our test group. This is the third screen we’ve tested in the last 12 months based on a Samsung-made PLS part. The other two displays demonstrated lower black levels.

And here’s the final contrast result.

While 883.6:1 is a respectable number, it has upward potential. If the P2714T were brighter while maintaining the same black level, or if the black level could be made lower without sacrificing output, its contrast would be greatly improved

All the computer monitors we have reviewed this year lack a true black level control. The brightness slider actually changes the level of the backlight. Therefore, we can use its full range without clipping any detail at either end of the brightness scale. For our minimum luminance tests, we leave the contrast control at its default and reduce the brightness to zero.

We believe 50 cd/m2 is a practical minimum standard for screen brightness. Any lower and you risk eyestrain and fatigue. Many monitors will measure under that level. While the comparison chart shows the absolute lowest brightness for a given monitor, we also comment on the contrast and black level results at a 50 cd/m2 setting.

The P2714T has a maximum output of 41.4961 cd/m2 when brightness is set to zero.

With the backlight set to its minimum, the P2714T’s black level becomes quite good. With just over 41 cd/m2 max output, the monitor is usable, though it might be a little fatiguing. Fortunately, turning up the backlight to 50 cd/m2 only increases the black level slightly. Use a brightness setting of six to achieve this.

We’ll wrap up this section with the minimum contrast comparison.

The P2714T’s minimum contrast measurement is only a little lower than its maximum, which shows solid and consistent performance. Setting the output to 50 cd/m2 improves the contrast figure to 834.9:1 for a small gain.

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), this brightness level provides a sharp, punchy image with maximum detail and minimum eye fatigue. It's also the sweet spot for gamma and grayscale tracking, which we'll look at on the next page. In a darkened room, most professionals prefer a 120 cd/m2 calibration. We have found this makes little to no difference on the calibrated black level and contrast results.

We start with the calibrated black level. This can sometimes rise a bit from the monitor’s default state. We consider the tradeoff in contrast well worth the gain in color accuracy.

Dell's P2714T has the highest calibrated black level in our test group, but finishes just below mid-pack for all of the monitors we tested in 2013. That's decent performance.

Here are the final calibrated contrast numbers.

Contrast ratio takes a small hit when you calibrate the P2714T. Given its excellent out-of-box grayscale accuracy, we can’t strongly recommend calibrating this monitor. Your choices are a perfect white balance with decent contrast, or almost-perfect white balance with slightly more decent contrast. We’re splitting hairs here!

ANSI Contrast Ratio

Another important measure of contrast is ANSI, which we measure with a checkerboard pattern of sixteen zero and 100 percent squares. This is somewhat more real-world than on/off readings because it tests a display’s ability to simultaneously maintain both low black and full white levels, and factors 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.

The P2714T maintains an ANSI contrast level very close to its on/off value, highlighting the solid engineering that went into Dell’s choice of a high-quality grid polarizer. Minimizing light leakage between adjacent pixels means the image is more crisp and clear to the eye.

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