With displays, it is easy to get caught in the hype as technology buzzwords are meant to grab your attention rather than describe the actual screen quality. Super AMOLED, HD-IPS, Super LCD, Retina IPS and whatnot, each claim to offer the best image quality around, but usually find it unnecessary to provide specific numbers, which would make technologies easier to compare.
On the rare occasions that display specs are actually quoted, the numbers are purposely chosen to be misleading and make the real-life performance seem much better than it really is. Which is where our first test comes in.
Perhaps the most important factor when it comes to screen quality is contrast ratio. Contrast ratio is the measure of the dynamic range of the luminance of the display, essentially describing how much darker the deepest blacks are than the brightest whites. A display with a good contrast ratio is able to show richer, more vibrant still images and videos that come to life.
The brightness of a given object is measured in candela (cd), which is the scientific unit for luminance. One candela--which stands for candle in Latin--is the equivalent of the light intensity of one candle as perceived by the human eye. For displays, light is measured per square meter of surface area (cd/m2), which is sometimes also referred to as Nits (nt).
The contrast ratio itself is determined by measuring the cd/m2 of a pure white screen, and dividing it by the cd/m2 of a pure black screen (note that on an LCD a pure black screen is not the same as a screen which is turned off, because even black pixels emit some light). So, a display which has 100 cd/m2 of whites and 1 cd/m2 of blacks will have a contrast ratio of about 100:1.
An important note about AMOLEDs is due here. As AMOLED units have the ability to completely switch off individual pixels, their black level readings are 0, which gives them an infinite contrast ratio under the testing conditions.
When we measure we take two readings off each device - first with the display brightness set to 50% and then with the brightness setting pushed all the way up. We test the handsets in complete darkness, because when ambient light is present, the luminance levels of the blacks displayed goes up, and affects the perceived contrast ratio.
Contrast ratio is very heavily influenced by the black levels of a display. While a brighter display would normally have an advantage, it will usually be unable to compensate for insufficiently deep blacks.
While having a good quality display is important, the reflectivity of the screen is not to be neglected. After all, you rarely use your smartphone in complete darkness, so there's little use of having a premium screen that turns into a mirror in bright environments.
Our sunlight legibility test aims to show you how legible each screen remains in bright environments, where screen reflectivity matters as much as its natural contrast and brightness. We use fixed studio lighting to simulate sunlight falling on the phone screens and measure the contrast ratio of each of them, when faced with this powerful light source. We measure each display with brightness turned up to 100%.
The perceived sunlit contrast ratio is then calculated based on the values of the blacks and whites visible on the display. The higher the value here, the more visible the screen in bright sunlight.
And before you start asking for a "real life" test (typical indoor lighting), you should know that contrast loss is linear, so you should be able to make out the usual performance as an average of the two scores we provide. Our test is obviously based on two extremes: the pitch black room and the bright outdoors. Adding something in between wouldn't make much sense, as there's no standard for how bright a home or office is.