LCD

LCD is the abbreviation for Liquid Crystal Display. It is one of the two major techniques that screens today use to produce images. The screen itself does not emit light. Behind the display surface sits a continuous lamp, the backlight, which shines evenly toward the front. In front of it lies a thin layer of a special material that can be controlled electrically. This layer works like a blind: it lets the light through for each individual pixel, dims it, or blocks it almost entirely.

Why almost every screen in the household is an LCD

LCDs displaced the old, bulky cathode-ray tube televisions in the 2000s. The reason was simply the form factor. An LCD is flat, light, and needs little power. This is what made laptops, tablets, and smartphones practically possible in the first place.

To this day, LCD remains by far the cheapest technology for large surfaces. A 55-inch television with LCD often costs only a fraction of a comparable device with self-illuminating pixels. That is why most televisions, monitors, and display boards sold are still LCDs. Car displays, point-of-sale systems, and station displays also use the technology.

Economically, this is a huge market with very thin profit margins. Production today is heavily concentrated in China, after Japanese and Korean manufacturers gradually withdrew. When business news talks about panel prices, it is usually referring to LCD panels.

The blind made of liquid crystals

Liquid crystals are something in between: they flow like a liquid, but their molecules arrange themselves as in a crystal. If a small voltage is applied, these molecules rotate. It is exactly this rotation that an LCD makes use of. It changes how much of the backlight’s light can pass through the layer.

For this to work, two filter films, called polarizers, lie in front of and behind the crystals. You can picture them as two grids that only let light through in a particular orientation. The rotated crystals change the orientation of the light. This way, the applied voltage determines whether a pixel appears bright or dark.

Color is created through filters: each pixel consists of three fields in red, green, and blue. Their mixture produces every hue. The fundamental drawback remains, however: the lamp is always lit. Black therefore never becomes truly black, only a very dark gray. This is exactly where OLED is superior, a technology in which each pixel lights up on its own and can be switched off completely.

LCD, LED, and QLED in the electronics market

In stores, marketing names cause a lot of confusion. An LED television is not a separate screen type but a perfectly ordinary LCD. Only the backlight consists of light-emitting diodes instead of old fluorescent tubes. Samsung's QLED, too, is at its core an LCD with an additional color layer.

A genuine improvement is called Mini-LED. Here, the backlight is divided into hundreds of small zones that can be dimmed individually. Dark image areas thereby become noticeably blacker. Apple uses this, for instance, in pricier iPads and MacBooks.

LCDs are also encountered in a very simple form: in calculators, digital clocks, and microwaves. There are no color filters there, just a few black bars on a light background. These displays use so little power that a button-cell battery can last for years. It is the same basic idea, just with a few segments instead of millions of pixels.