You may think that your TV screen is simply a flat panel of illuminated images and colors, but there is a lot more to it!
Television screens are composite structures with complex components including
- liquid crystal
- color filters
being key to the quality of your viewing experience.
In particular, the backlighting transforms the intensity of the lighting of the television screen so that you have comfortable viewing, whatever your setting. There are several types of backlight technology, each using a different light source and with its own pros and cons. Popular options include:
- LED (light-emitting diodes)
- ELP (electroluminescence panels)
- Hot CFL (cathode fluorescent lamps)
- Cold CFL (cathode fluorescent lamps)
- Incandescent light bulbs
LED-backlit LCD, which uses light-emitting diodes for backlighting is a common type of display on televisions and laptops. Unlike pure LED screens these LCDs are not self-illuminating and are reliant on the backlighting for illuminating the display. It is an advancement on the preceding cold cathode fluorescent technology and some manufacturers and retailers may advertise this type of screen as an LED TV.
In this article, we are going to look at the importance of the arrangement of this lighting, rather than the type, as this is crucial for how light is directed into color filters and other critical layers. The three arrangements available are:
- Full Array
We’ll take a closer look at Edge-Lit vs Direct-lit backlighting, sharing which is best for your viewing experience.
What is Edge-Lit?
Edge-lit is a type of screen backlighting that has LED lights lining either the top and bottom edges of the screen or the perimeter of the screen. This form of backlighting differs from others as the screen is not lit from behind, and often produces a more muted effect. An opaque piece of plastic called a diffuser light guide distributes the lighting across the rear of an LCD panel.
Individual control of LEDs
Edge-lit LEDs can be individually brightened or dimmed to provide the high degree of backlight control that screened content demands. Edge-lit screens can achieve this in one of two ways:
- The focal LED dimming affects LEDs at the top and bottom of the display to create up to 12 dimming zones made up of vertical bands
- Independent dimming of the top and bottom rows of LEDs creates up to double the number of vertical dimming zones.
The dimming zones created are broad and diffuse, limiting the HDR effect considerably, and creating haloing, a phenomenon where unwanted portions of the display are illuminated.
What is Direct-Lit?
Direct-lit backlighting uses LED lighting across a television back panel. This form of backlighting initially used Cold Cathode Fluorescent Lamps (CCFLs) before transitioning to LED. The lighting is behind the LCD panel to provide consistent lighting across the entire screen.
Dark colors are a challenge
The use of LEDs creates an extremely bright picture. This can lead to black and naturally dark tones appearing too bright, a phenomenon known as ‘elevated black levels’. This appearance can really affect wide-screed films, especially as there is no way to alter the backlight of specific portions of the screen. This has led to the development of alternative backlighting arrangements that minimize the greying of black sections of the screen.
Edge-Lit vs Direct-Lit: Side-by-Side Comparison
|What it is:||A backlight panel arrangement||A backlight panel arrangement|
|Primary use:||Lighting for an LED-backlit LCD screen||Lighting for an LED-backlit LCD screen|
|Conceived:||The 1980s||The 1980s|
|Initial release:||The late 1990s||The 2000s|
|Technical committee:||Samsung||Philips LG Samsung TCL|
|Influential developers:||Samsung||Lumex Quantum Brite|
|Technologies influenced:||Televisions, desktop monitors laptops||Televisions, monitors, laptops|
The Differences Between Edge Lit and Direct Lit
Both types of backlighting provide the illumination LED screens required to produce a visible image. The main difference is that direct-lit backlights sit behind the LCD panel to provide the necessary lighting whereas edge-lit screens have LEDs sitting at the perimeter of the screen. Here are some other notable differences:
- The first generation of LED backlighting was edge-lit. However, this early form of edge-lit technology caused the development of hotspots on the screen and the overall lighting was inadequate. As LED design became more efficient and effective, Samsung revisited this type of backlighting with a market-leading edge-lit LED television in 2009.
- Direct-lit panels use a simple array of LEDs to provide uniform lighting across an entire LCD panel. The adoption of direct-lit screen technology in the 2000s was driven by the availability of white LEDs that could replace existing CCFL technology.
- Direct-lit performs across a range of viewing angles and colors, but it is limited by not being able to increase contrast, as the entire backlight has to be dimmed to change color intensity. This affects the ability of a screen to achieve a deep black tone. Full array lighting and flexible backlight technologies have superseded direct-lit lighting. They are more advanced and can achieve more nuanced imaging effects.
- Edge Lit screens can achieve full, deep blacks as they can use local dimming technology to reduce lighting in areas of the screen that display black or dark colors.
|Cost-effective||No pinpoint dimming|
|Thin screen||Picture quality can be variable|
|Compact, integrates into thin screen designs||Local dimming is not as effective as a full array|
|Low energy consumption||Less contrast than a full array|
|Can dim sections of the screen image|
|Easy installation because the screen is lightweight|
|Better picture quality||Bulky screen|
|More even lighting||Greater power consumption|
|Cheapest television backlight panel||Struggles with rendering darker shades|
|Uniform brightening and dimming|
|Poorer contrast ratios|
|More expensive to run|
|Potential for screen burn|
|Can cause screen burn-in|
Edge-Lit vs Direct-Lit: Six Must-Know Facts
- Samsung pioneered edge-lit technology. They launched the world’s first edge-lit TV back in 2009.
- LED TVs can have up to 1500 individual LEDs in an array, lighting 2 million pixels of a 1080p TV.
- A single led light may illuminate 1400 pixels.
- Direct-lit TVs don’t have local dimming, but newer, more advanced full array technology does.
- The local dimming on LED TVs is a key way of introducing contrast. With this technology, the intensity of lighting adapts to the image shown achieving contrast ratios.
- Direct-lit backlighting can make black or dark areas of the screen appear too light, rendering them gray.