Both tablets earned a "very good" score when DisplayMate tested color and brightness variations among different viewing angles as well as overall brightness, although the iPad mini is slightly brighter: 450 nits compared to 424 for the iPad Pro.
You'll get a better contrast ratio in low ambient lighting situations with Apple's larger tablet though. DisplayMate measured a 1,631:1 contrast ratio on the iPad Pro compared to 957:1 for the smaller iPad mini 4. This compares the brightest whites to the darkest blacks on a display.
In terms of color, each of the tested iPads skewed towards a blue-white light as the color temperature of both measured in the 7,109K to 7,164K range. For comparison, a "natural daylight" white bulb has a color temperature of 5,000K to 6,500K while a soft white bulb is typically around 2,700K. That explains the blue tinge on both iPads when looking at whites.
While the iPad Pro has very good color accuracy overall - the average color error in a Just Noticable Color Difference test is 2.6 (a lower number is better) - the iPad mini 4 earned an "excellent" score with a 1.9 JCND. It's a more accurate representation of actual colors on the display.
Surprisingly, the iPad Pro's larger screen wins the power efficiency battle against the iPad mini 4. Setting both tablets to 415 nits of brightness and scaling the results to the same screen area of an iPad Air 2, the iPad Pro uses 3.8 Watts of power while the iPad mini 4 uses 4.2 Watts.
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That's likely due to the new dynamic refresh rate on the iPad Pro, which can vary based on what's on screen. It's worth noting, however, that in the same test, Microsoft's Surface Pro 4 scores even better than both iPads: DisplayMate says it's 27 percent more efficient even than the iPad Pro with 3 Watts of power.
DisplayMate says no tablet display beats the iPad Pro and iPad mini 4 in the average screen reflectance test, though. Both earned "oustanding" marks with the lowest reflected glare.
Most tablets still have 5 percent or higher reflections that can interfere with viewing, the company says. Not so with the iPad Pro and iPad mini 4, which reflect 2.6 and 2.0 percent of ambient light, respectively.