OLED

An OLED screen consists of tiny dots that each generate light on their own. Each of these dots contains a thin layer of organic compounds – that is, carbon-based compounds – that light up as soon as electric current flows through them. This may sound like a minor detail, but it is a fundamental difference from older LCD technology: there, a lamp behind the panel illuminates the entire image evenly, and tiny switches let more or less light through for each pixel. With OLED, this backlight is eliminated entirely. Each dot lights up on its own – or it doesn’t light up at all.

True black levels and their consequences

The most important advantage results directly from this design: an OLED pixel can be switched off completely. Black image areas then emit zero light – they are actually dark, not just very dark. On an LCD screen, even black content shimmers slightly because the backlight is always on.

This difference can be expressed in numbers: the contrast ratio – that is, the ratio between the brightest and darkest displayable value – is theoretically infinite for OLED, because the denominator is zero. In practice, this means: starry skies, dark movie scenes, or black user interfaces appear noticeably more three-dimensional and deeper on OLED panels. For many users, this is the main reason to choose OLED when buying a device.

Another effect: because no backlight is needed, OLED panels can be built extraordinarily thin and even flexible. This is why foldable smartphones function almost exclusively with OLED displays.

How an OLED pixel generates light

The core of each pixel is a stack of ultra-thin organic layers between two electrodes. When a voltage is applied, electrically charged particles move from both electrodes into the organic layer and meet there. This encounter releases energy – not as heat, but directly as light. The color of the light depends on the exact chemical composition of the layer.

A colored image requires three subpixels per pixel: one red, one green, and one blue. Varying the brightness of these three subpixels produces every color in the image. This is, in principle, the same as with LCD – just without a lamp behind it, and with the decisive advantage that each subpixel can be individually dimmed all the way to zero.

A well-known problem with this technology is so-called burn-in: if the same static image remains on the panel for a very long time, the organic compounds in exactly those spots wear out faster. A permanently displayed navigation bar or a channel logo can thus remain visible as a ghost image. Modern panels mitigate this through software tricks, but the problem has not yet been fully solved.

OLED in smartphones, TVs, and wearables

OLED has by now arrived in many device categories. Most high-end smartphones – including all iPhone Pro models since 2017 and the flagship lines from Samsung, Google, and others – rely on OLED. The difference compared to cheaper LCD models is immediately noticeable in a direct comparison, especially with dark content and off-angle viewing.

In the TV market, OLED dominates the upper price segment. LG is the best-known manufacturer here; Sony, Panasonic, and others also buy panels from LG and install them in their own devices. As direct competition, Samsung has developed its own variant called QD-OLED, which combines OLED with an additional quantum dot layer to produce brighter, more vibrant colors.

Smartwatches such as the Apple Watch or Samsung’s Galaxy Watch also use OLED. The reason is pragmatic: because black areas consume no power at all, a dark always-on display on an OLED panel saves considerably more battery than on an LCD. For a device worn on the wrist that runs around the clock, this is a decisive advantage.