LCD Backlight Technology

Liquid crystal displays (LCDs) do not generate light of their own. The liquid crystal layer in a panel works by selectively blocking or passing light, acting like a controllable shutter for each pixel, so a separate light source is required behind or beside the panel to make the image visible. This light source is the backlight, and its design strongly affects a display's brightness, colour and energy use.

In a thin-film-transistor (TFT) LCD, each pixel contains coloured filters and a liquid crystal element whose orientation is controlled by an applied voltage. Combined with polarising layers, this allows the panel to vary how much backlight passes through each sub-pixel, producing the full-colour image. Because the crystals only modulate light rather than emit it, a uniform and stable backlight is essential for good picture quality.

For many years the standard backlight was the cold-cathode fluorescent lamp (CCFL), a thin fluorescent tube that, like a fluorescent lamp, produces light from a gas discharge and a phosphor coating, requiring a high-voltage inverter to drive it. CCFL backlights were later largely replaced by light-emitting diode (LED) backlights, in which arrays or edge-mounted strips of LEDs illuminate the panel. LED backlighting offers lower power consumption, thinner panels, longer life and the ability to dim regions of the screen locally for improved contrast. Displays using LED backlights are often marketed as “LED TVs,” although the image is still formed by an LCD panel.

Frequently asked questions

Why does an LCD need a backlight?

The liquid crystal layer only blocks or transmits light rather than producing it, so a backlight is needed behind the panel to make the image visible.

What is a CCFL backlight?

It is a cold-cathode fluorescent lamp used as the light source in many older LCDs, working on the same gas-discharge and phosphor principle as a fluorescent tube.

Is an “LED TV” different from an LCD TV?

Not fundamentally. An LED TV is an LCD television that uses LEDs for its backlight; the picture is still formed by a liquid crystal panel.