Backlight

Backlight is a light source placed behind or around a display to illuminate images produced by the display panel. In most transmissive displays, such as liquid crystal displays (LCDs), the image itself modulates light from the backlight to create visible content. Without backlighting, LCDs would appear dark because the pixels do not emit light.

Traditionally, backlights use cold cathode fluorescent lamps (CCFL) or, more commonly today, light-emitting diodes (LEDs). LED backlights can be edge-lit, where LEDs are arranged at the edge of a light guide plate to spread light across the panel, or direct-lit (full-array), where LEDs are distributed behind the entire active area. LED backlights offer higher efficiency, broader color control, and thinner profiles, while CCFLs are being phased out in many devices due to lower efficiency and environmental concerns. Color temperature and brightness levels are adjustable, and LED backlights are often dimmed using pulse-width modulation (PWM), which can cause flicker for some users.

A typical backlight system includes a light source, a light guide plate to distribute light, diffusion layers to even out brightness, brightness-enhancing films, and a reflective backing. The aim is uniform illumination with good color accuracy and contrast. High-end displays may feature local dimming zones, where groups of LEDs are controlled separately to improve black levels and contrast.

Backlighting is central to LCD technology; emissive display technologies such as OLED and microLED do not require a backlight.