If you're buying a TV this year -- and it's a good year to buy a TV -- then you have only a few choices to make before you've picked out a great screen. As well as working out whether you want 4K or HDR, and what screen size you're after in the first place, and what inbuilt smart features you want, your main choice is what TV backlighting technology you want your new big-screen telly to use. We're here to tell you the difference between edge-lit and back-lit LED, LCD and OLED, quantum dot and local dimming, and more.
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LED Vs OLED: Very Different Approaches To Screen Lighting
For the last seven or eight years, most LCD TVs have used LED backlighting. LEDs are a more energy-efficient, more powerful and more colour-accurate lighting source than the cold-cathode fluorescent lighting tubes that were previously used, and they have the additional advantage of making screens much slimmer for the same level of brightness. Modern TVs use either a full backlighting array of LEDs at the rear of the LCD panel, or an edge-lighting frame of LEDs around the perimeter of the LCD panel with reflective channels moving light around the entire back of the display.
With an OLED display, every pixel in a screen's 1920x1080- or 3840x2160-dot array is its own lighting source. As the name suggests, OLED is similar to LED in circuit design, but the pixels are fabricated via printing rather than built in the traditional sense. Because every OLED pixel is its own backlight, it can adjust its brightness to suit the content that it is displaying on a per-pixel basis rather than the slightly larger zones covered by LED backlighting or edge-lighting -- but because each individual light source is smaller, its maximum full-power luminance is comparatively limited.
LED televisions are significantly cheaper than OLED screens, because the technology inside them is more cost-effective to create. Because the LCD panels themselves are built separately to the LED light sources, they're easier to repair if an individual element -- like a single LED or zone of LEDS -- malfunctions. Because LEDs are designed to produce only one white or blue colour temperature of light -- rather than an OLED pixel that must create red, green, blue or white -- they consume significantly less power at full brightness than an OLED of the same luminance. LED TVs can also reach much higher peak brightness levels than OLEDs, which is useful for displaying high dynamic range content.
Edge-Lit Vs Back-Lit LED: Same Technology, Different Effect
If you've decided on a LED back-lit LCD TV versus an OLED, there are two further sub-sets of LED backlighting technology to make the distinction between. You can choose a super-slim LED TV with a LCD panel that's illuminated by LED edge-lighting, or a slightly thicker but usually more visually-impressive LCD TV with an LED back-lighting system. One uses a strip of LEDs arranged around the edge of the LCD panel, while the other uses another panel -- often called an array -- of LEDs behind the LCD panel itself shining directly through. Both have the main advantages and disadvantages associated with LED TVs, but take a slightly different approach to operation that might make one more suitable for your needs.
Edge-lit LED TVs are easy to spot because their design makes it possible to produce an extremely thin chassis that nonetheless offers excellent levels of brightness and contrast across the entire panel. Edge-lit LED TVs are also some of the most energy-efficient screens on the market today, because the technology used inside them allows for a small number of highly powerful LEDs to produce enough luminance to light even large, 65-inch-plus displays without any obvious bright patches. Edge-lit TVs occupy everything from the affordable to the super-premium price range, mainly because they're very slim and attractive, making them an ideal candidate for wall-mounting.
Back-lit LED TVs are generally slightly thicker than their edge-lit counterparts, but make up for that slight physical premium with a full array of LEDs across the entire LCD panel. That generally translates into more consistent lighting across the complete width and length of the screen, as well as the ability on premium LED back-lit TVs to adjust the brightness of LEDs on specific screen areas, known as local dimming. Because back-lit LED TVs generally have a larger array of more LEDs at their disposal, maximum screen brightness levels are higher, which translates into higher contrast levels overall. Back-lit LED TVs are usually slightly more expensive for that slightly superior viewing experience.
Backlight Brightness: It's All In The Nits
If you're buying a new TV, regardless of whether it's an edge- or back-lit LED or whether it's an OLED panel, the most important criteria for a display is its brightness. Brightness directly informs a LED or OLED screen's contrast level, and contrast is the number one factor in your enjoyment of whatever movie or TV show content your television is displaying -- it's more important than the difference between Full HD and Ultra HD resolution, for example. In simple terms, the more versatility that a backlight has in displaying the lowest possible luminance level and the highest possible luminance level will determine its contrast level: this is the difference between the darkest possible blacks and the brightest possible whites.
And, inevitably, you'll have to balance a low minimum brightness and a (relatively) low maximum brightness against a (relatively) high minimum brightness adn a high maximum brightness. Because LCD panels are effectively an array of quickly-changing filters on the top of an always-on, quickly-adjusting LED backlight, they can't always display perfectly dark black levels -- but they're extremely good at displaying high, super-white maximum brightness. OLED screens, on the other hand, can turn each individual pixel off for excellent blacks, but because each pixel is so small the maximum brightness that each is able to display can't compare with LED. With LED, you're getting in the region of 1000 nits maximum brightness and 0.1 minimum, and OLED tops out for the time being at 500 nits and 0.0 minimum.
Of course, it all depends on where and when you watch TV. Most TVs in Australian houses are situated in living rooms and communal spaces, covering a large area -- often the largest room in the house with the largest distances between seats and screens. While we mostly watch TV during the afternoon and evening hours, where ambient light levels from the sun are relatively low, we're increasingly watching TV in rooms with bright overhead direct or indirect lighting sources. If you can guarantee control over the lighting in your viewing area, and can minimise it, you'll value a lower minimum brightness level. If you're watching in the daytime or in a bright room, a brighter maximum is always going to give you a better viewing experience overall.
What Is Local Dimming?
Local dimming is a technology specific to LED backlighting -- but that applies to both edge- and back-lit LCD TVs -- that lets individual LEDs in an edge-lit strip or small zones of LEDs in an entire back-lit array adjust their brightness dynamically. Local dimming means LED TVs can have a dark image displayed on one part of the screen and a bright image displayed on another, without the entire display having to adjust its LED lighting to the level of the brightest image. It maximises the contrast possible, as well as reducing overall power consumption.
What Are Quantum Dots?
Quantum dots are a relatively new invention in the world of television. Conventional LED backlights use either white LEDs or a combination of red, green and blue LEDs to create white light, which is then filtered by the LCD to create the closest approximation of colour required. Quantum dots are tiny nano-scale structures that produce monochromatic light, making them perfect for filtering blue LED backlights into perfectly red or green light, making quantum dot displays far more effective at displaying accurate, bright colours during video playback.