Displays

Confounded by contrast ratios? Doubtful about Delta E? Darien Graham-Smith takes a close look at the specs and capabilities that allow the best screens to shine

When you’re buying a new phone, tablet or laptop, the quality of the screen is a big consideration. And naturally the same applies if you’re buying a new monitor for a desktop PC.

The trouble is, there are many factors that contribute to the overall quality of a screen, and when you’re reading an online specification sheet – or even a review in PC Pro – it can be hard to visualise what they all really mean and how they tie together. Here’s our guide to all the different display features and measurements, and what to look for. Next month, alongside our annual group test of monitors, we’ll dig into the various different display technologies commonly used in modern screens, explore how they work and set out the strengths and weaknesses of each type.

1 Brightness

One of the most immediately obvious qualities of a display, brightness is usually measured in candelas per square metre, or cd/m2 – one candela being roughly equivalent to the light put out by a single candle. Display brightness is also sometimes quoted in “nits”, a term derived from the Latin “nitere” (to shine); the conversion is pretty easy to do in your head, as one nit is equal to 1cd/m2 .

The brightness figures we cite in our reviews represents the measured luminance when the screen is completely white, with the brightness setting turned up to maximum. A brightness of 250cd/m2 is a usable minimum for a desktop monitor, but a display capable of putting out 500cd/m2 or higher will be a lot easier to read in bright sunlight; the latest high-end mobile devices claim a peak brightness well in excess of 1,000cd/m2 . Screens that support HDR may go even higher than their measured “maximum” when showing HDR media, as we’ll discuss below.

By the way, don’t confuse candelas with lumens: lumens are a measure of total light output in all directions, making them useful for devices such as smart bulbs. Candelas measure the intensity of light in a particular direction, which is what we’re interested in for a computer display.

2 Contrast

Contrast represents the difference in brightness between black pixels and white pixels. A bright screen with low contrast will look washed out, while one with middling brightness and excellent contrast might look very bold and clear, as long as you’re viewing it in a dark environment, where the highlights aren’t overwhelmed by ambient light. The ideal, of course, is to combine high brightness with high contrast.

Contrast is expressed as a ratio, with a ratio of 2:1 meaning the brightest areas are twice as bright as the darkest ones. That would be a terrible score, though – a decent baseline is more like 1,000:1, but higher is always better and many phones and laptops get closer to 2,000:1. In the case of OLED screens, where black pixels aren’t illuminated at all, the contrast ratio is effectively infinite.