Confused about LED vs. LCD TVs? Here's everything you need to know
 
Creating or upgrading a home theater setup can involve a lot of different things, but it often comes down to one major question: What kind of TV should you get? But what’s the difference? It’s a question we hear a lot from budding home theater shoppers, but shouldn’t. Blame the acronyms. Here’s the quick answer: An LED TV is an LCD TV, but how the two came to be confused with each other might come as a surprise.
 
AN LED TV IS AN LCD TV
Despite having a different acronym, an LED TV is just a specific type of LCD TV. The proper name would actually be “LED-backlit LCD TV,” but that’s too much of a mouthful for everyday conversation, so people generally just refer to them as LED TVs.
 
Both types of TV make use of a liquid crystal display (LCD) panel to control where light is displayed on your screen. These panels are typically composed of two sheets of polarizing material with a liquid crystal solution between them, so when an electric current passes through the liquid, it causes the crystals to align so that light can (or can’t) pass through. Think of each crystal as a shutter, either allowing light to pass through or blocking it out.
 
Now, since both LED and LCD TVs use LCD technology, you’re probably wondering what the difference is. Actually, it’s about what the difference was. The LCD TVs you think of now no longer exist. Here’s why: Backlighting. Older LCD TVs used cold cathode fluorescent lamps (CCFLs) to provide backlighting, whereas LED TV’s used an array of smaller, more efficient light-emitting diodes (LEDs) to illuminate the screen, which gave them a few advantages. Now, all LCD TVs use LED lights and are colloquially considered LED TVs. Here’s how that works.
 
Backlighting
There are three different forms of illumination that have been used in LCD TVs: CCFL backlighting, full-array LED backlighting and LED edge lighting. Each of these illumination technologies is different from one another in important ways, and each has pros and cons. Let’s dig into each.
 
CCFL Backlighting
CCFL backlighting is an older form of technology that has mostly been abandoned, though some manufacturers do use CCFLs in lower tier LCDs since they’re cheaper to make. A series of CCFLs sit across the inside of the TV behind the LCD display. The lights illuminate the crystals fairly evenly, which means all regions of the picture will have similar brightness levels. This affects some aspects of picture quality, which we discuss on the next page. Since CCFLs are larger than LED arrays, CCFL LCDs tend to be thicker than their LCD counterparts. As this is an outdated technology, you won’t find many models using this style of illumination. A few tend to crop up here and there, but they’re almost always on the cheaper end of the spectrum.
 
Full-array backlighting
Full-array backlighting swaps the outdated CCFLs for LEDs. An array of LEDs spans the back of the LCD screen, with zones of LEDs can be lit or dimmed in a process called local dimming (we go deeper into how local dimming works on the next page). TVs using full-array LED backlighting make up a chunk the high-end LCD TV market, and with good reason — with more precise and even illumination, they can create better pictures than CCFLs LCD TV were ever able to achieve. Plus, they’re less of a power drain than CCFL LCDs were. Given these benefits, the shift to LEDs as industry standard made a lot of sense.
 
Edge lighting
Another form of LCD screen illumination is LED edge lighting. As the name implies, edge-lit TVs have LEDs along edges of a screen. Within this lighting type, there are a few different configurations, including LEDs along just the bottom; LEDs on the top and bottom; LEDs left and right; and LEDs along all four edges. These different configurations result in differences in picture quality, but the overall brightness capabilities still exceed what CCFL LEDs could achieve. While there are some drawbacks to edge lighting when compared to full-array or direct backlight, the upshot is edge lighting allows for manufacturers to make thinner TVs which cost less to manufacture.
 
To better close the local dimming quality gap between edge-lit TVs and full-array backlit TVs, manufacturers like Sony and Samsung have developed their own advanced forms of edge lighting. Sony’s technology is known as “Slim Backlight Master Drive,” while Samsung has “Infinite Array” employed in its line of QLED TVs. These keep the slim form factor achievable through edge-lit design but with local dimming quality more on par with full-array backlighting in these cases (though still not quite equal).
 
WHAT IS LOCAL DIMMING?
Local dimming is a feature of LED LCD TVs wherein the LED light source behind the LCD is dimmed and illuminated to match what the picture demands. LCDs can’t completely prevent light from passing through, though, even during dark scenes, so dimming the light source itself aids in creating deeper blacks and more impressive contrast in the picture. This is accomplished by selectively dimming the LEDs when that particular part of the picture — or region — is intended to be dark.
 
Local dimming helps LCD-based TVs more closely match the quality of Plasma (RIP) and OLED TVs, which feature better contrast levels by their nature — something CCFL LCDs couldn’t do. However, the quality of the local dimming effect varies depending on what type of backlighting your LCD uses and the quality of the processing. Here’s an overview of how effective local dimming is on each type of LCD TV.
 
Full-array and direct local backlighting
TVs with full-array backlighting have the most accurate local dimming and therefore tend to offer the best contrast. Since an array of LEDs spans the entire LCD screen, regions can be dimmed with more finesse than on edge-lit TVs, and brightness tends to be more uniform across the entire screen.
 
“Direct local dimming” is essentially the same thing as full-array dimming, just with fewer LEDs spread further apart in the array. It’s worth noting, however, that many manufacturers do not differentiate “direct local dimming” from full-array dimming as two separate forms of local dimming. We still feel it’s important to note the difference, however, as fewer, further-spaced LEDs will not have the same accuracy and consistency as full LED arrays.
 
Edge lighting
Edge lighting is a process by which light from LEDs positioned on the edge or edges of the screen is projected across the back of the LCD screen, as opposed to directly behind it. This works well enough but can result in very subtle blocks or bands of lighter pixels within or around areas that should be dark. Because of this, the local dimming of edge-lit TVs can sometimes result in some murkiness in dark areas when compared with full-array LED TVs. It should also be noted that not all LED edge-lit TVs offer dimming, which is why it is not uncommon to see glowing strips of light at the edges of a TV and slightly lower brightness toward the center of the screen.
 
CCFL Backlighting
Since CCFL backlit TVs do not use LEDs, models with this style of lighting do not have dimming abilities. Instead, the LCD panel of CCFL LCDs is constantly and evenly illuminated, which makes a noticeable difference in picture quality compared to LED LCDs. This is especially noticeable in scenes with high contrast, as the dark portions of the picture may appear too bright or washed out. When watching in a well-lit room it’s easier to ignore or miss the difference, but in a dark room, it will be, well, glaring.
 
OLED AND QLED
As if it wasn’t already confusing enough, once you begin exploring the world of LED TVs, new acronyms crop up. The two you’ll most commonly find — and the two most important — are OLED and QLED.
 
Despite the similar sounding name, OLED TVs are a totally different category than LED TVs. We have an in-depth guide as to the differences between OLED and LED, but here’s a quick overview: Organic light-emitting diode (OLED) displays utilize a panel of pixel-sized organic compounds that respond to electricity, as opposed to LED bulbs. This allows for both deep contrast ratios and better per-pixel accuracy in the picture. OLED displays are often found on high-end TVs in place of LEDs, but that doesn’t mean that LEDs aren’t without their own premium technology either.
 
Source: www.digitaltrends.com