Fundamentals of LED Backlights
There are two types of LED backlights (in simple terms), edge-lit and direct.
In an edge-lit backlight, there is a row of LED light emitters (usually white) along one, two, or three edges of a backlight with reflective films and coatings to funnel that light across the entire back of an LCD panel in a uniform manner.
- Results in a thin overall LCD display profile. If you see a panel that is very, very thin, most likely it is using an edge-lit backlight design.
- It is lower cost since it uses less LEDs to cover a larger area of display.
- Can have some brightness uniformity issues, creating bright edges of the display and a dark center.
- There are some size limitations to edge lit displays that make them impractical for large format LCDs.
- Limited ability to modulate the backlight based on content to improve contrast and save power. The backlight is on all the time, no matter what content is showing.
In a direct lit backlight configuration, the LEDs are behind the LCD display, not just on the edges. There are many different approaches to this, but the most common implementations is to have arrays of LEDs in “zones” that can be controlled independently based on content.
- Best overall brightness uniformity.
- Local dimming can result in higher contrast and lower power consumption. In a zone where the content is dark, the backlight is turned down. In a zone where the content is bright, the backlight it turned up. Results in a thin overall LCD display profile. If you see a panel that is very, very thin, most likely it is using an edge-lit backlight design. This means that it can be lower power (or high) depending on the content shown.
- No size limitations. You see this approach commonly on very large displays.
- The direct lit style backlights tend to be thicker than edge-lit, resulting in thicker overall display and television sets.
- Higher overall cost due to the use of more LED components.
- Can be higher (or lower) power depending on the content.
- The local dimming can lead to perceived brightness uniformity concerns and a “halo” effect around light content on a dark background.