The Infinite Contrast of the Finite OLED

[Jeffrey Rodman (Jeff Rodman)]

OLED display panels look gorgeous. Where LCD's must create images by laying a grid of tiny, partly adjustable sunglasses on top of a screen that's always fully-lit, OLED's work in the opposite way: by controlling how much light gets emitted from each sub-pixel organic light-emitting diode (OLED) in the first place, from fully off to fully on.

The first commercial OLED displays began to emerge around 2004, and are now available in a variety of sizes, although still with higher price tags and (often) smaller sizes than comparable LCD displays. To offset these shortcomings, their vendors point out that OLEDs have the distinctive advantage of infinite contrast.

Infinite contrast is a lot of contrast. Contrast compares the brightest to the dimmest that a picture element (pixel) can be, and is usually expressed as the ratio of the two. The screen setting has to be stable, of course (you can't crank up the screen's brightness to measure its white and then kick out the plug to measure black). Even so, when measured fairly, while good LCD displays today have a static contrast of around 4,000, OLED's can claim a contrast of infinity because they can turn individual pixels off completely - fully black, zero light emitted - and any number divided by zero is infinity. Don't be too awestruck, of course; the same arithmetic proves that any bargain-store flashlight also has infinite contrast. And sadly, LCD's can't do that. They can't go completely black because a little bit of light will always sneak through those millions of pixel-sized sunglasses - they can't block out that backlight completely. But does it really matter?

An OLED display indeed emits zero when it wants to, but the display is only one component in an application.  When it's being used as a tool in collaboration, it has to be placed in a room of some sort, and there are other lights and windows around. So it usually doesn't matter whether the panel's blacks are emitting an OLED's 0.000% or an LCD's 0.025% because there's lots of room light bouncing around and that perfect OLED black becomes some kind of darkish grey no matter what you do.

If you've seen a well-prepared OLED demonstration in a store or at a trade show, you know that OLED makers often play a trick on us rubes.   In these settings, ambient lighting is usually carefully controlled so blacks are indeed very close to black and the OLED advantage is exaggerated. That's not the real world, though; UC applications differ from staged demonstrations and home theatres because they’re not lit to meet the display manufacturer's ideal specs, they’re lit to collaborate and get work done.   Modern LCD’s solved LCD's larger historic shortcomings (compromised blacks and view–angle variation, for example) years ago, and a contrast ratio of 4,000 is actually excellent. This means that in collaboration work, OLED's have no practical advantage over LCD's. In a real room, doing real work, you'll never notice it.

Like everything else, contrast is only important in the context of where it's applied. Go ahead and splurge on OLED for your new home theatre if you want, but for offices, huddle rooms and most workspaces, a good LCD will offer more choices, lower costs, and perform admirably.