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Overlord Tempest X270OC, 27" 120 Hz IPS Gaming Monitor Review

Results: Brightness and Contrast

The X270OC would not accept a signal from our AccuPel signal generator, so all measurements were taken with Overlord's monitor connected to a PC via DVI. Patterns were rendered by CalPC Client 3. We took default readings with all look-up tables turned off to be sure we were recording raw values. After creating a custom LUT with CalPC, we measured the results.


Before calibrating any panel, we measure zero and 100-percent signals at both ends of the brightness range. This shows us how contrast is affected at the extremes of a monitor's luminance capability. The X270OC does not have a contrast control, so signal clipping is not an issue. Light output can only be modulated using brightness, which affects the backlight level.

Today’s comparison group consists of the high-refresh gaming monitors we’ve reviewed, plus Asus' value-oriented 4K display, the PB287Q. I'm also adding a typical 27-inch IPS screen, NEC’s EA274WMi.

Overlord rates the X270OC at 380 cd/m2. The most light we measured was 258.5601 cd/m2, though. It's probable that Overlord is citing the panel part's specification. Typical gameplay doesn't require a super-bright display, so this shouldn't be a tremendous issue.

A low maximum black level beats the TN-based panels in our comparison. When I checked our database, I found that Overlord's X270OC bests almost all of the other IPS screens as well.

NEC's screen trumps the Tempest only because of its higher white level. The same is true of this group's other models. Among IPS displays, however, Overlord is at or near the top for maximum contrast.

We believe 50 cd/m2 is a practical minimum standard for screen brightness. Any lower and you risk eyestrain and fatigue. The X270OC bottoms out at 83.0312 cd/m2, which is a great light level for playing games in total darkness. As you’ll see below, black levels and contrast also hold up extremely well.

A last-place result in this test isn't a big deal when you’re talking about such low black levels. If all of the monitors were lined up in a row, it'd be a challenge to pick the darkest one.

The Tempest’s contrast remains super-consistent at all brightness levels. We’re seeing a positive trend towards better contrast performance from both TN and IPS screens. That Overlord can offer results this good with a $450 display is impressive.

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. On many monitors, it’s also the sweet spot for gamma and grayscale tracking, which we'll look at on the next page. Many professionals prefer a 120 cd/m2 calibration in darker rooms. We find that makes little to no difference on the calibrated black level and contrast measurements.

We set the maximum output level using the X270OC’s only available adjustment, brightness. Our results reflect the color and gamma adjustments made by the CalPC-generated LUT.

A calibrated black level result of .218 cd/m2 is excellent. Typically, monitors take a small hit after we adjust them. But not the Tempest. Perhaps this is attributable to the finer control possible with a software LUT. Most displays employ OSD controls that aren't as precise.

An improvement like this makes calibration worth the time and expense, though.

The X270OC posts incredibly consistent contrast results. Whether you calibrate or not, and regardless of backlight setting, the contrast ratio is always around 925 to 1.

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. We get a somewhat more real-world metric than on/off measurements because we're testing the display’s ability to simultaneously maintain both low black and full white levels, plus 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.

The Tempest loses no ground in the ANSI contrast test. Since screen uniformity is a factor, some samples will measure better or worse than ours. Even still, it's impressive to come across such strong build quality from a low-priced IPS display.

Christian Eberle is a Contributing Editor for Tom's Hardware US. He's a veteran reviewer of A/V equipment, specializing in monitors.