What Is a Quantum Dot (aka QLED) TV?

What you need to know about Quantum Dot and QLED TVs

Samsung Q900 8K QLED TV Lifestyle Image
Samsung

Despite some shortcomings, LCD TVs are the dominant type of TV sold to and purchased by consumers. The acceptance of LCD TV accelerated the demise of CRT and Rear Projection TVs and is also the main reason that Plasma TVs are no longer with us. In recent years, OLED TV, led by LG, has been touted as the successor to LCD. Although OLED represents a step-up in TV technology, LCD TVs have taken it up a notch with the incorporation of Quantum Dots (aka QLED).

Quantum Dots and QLED refer to the same technology. QLED is a marketing term that Samsung and TCL use in the branding of their Quantum Dot TVs, which combine LED backlighting with Quantum Dots for color enhancement.

What Is a Quantum Dot?

Quantum Dot Structure and How They Are Made

A Quantum Dot is a man-made nanocrystal with semiconductor properties that can be used to enhance brightness and color performance displayed in still and video images on an LCD screen.

Quantum Dots are emissive particles (somewhat like phosphors on a Plasma TV), but when they are hit with photons from an outside light source (in the case of LCD TV application a Blue LED light), each dot emits color of a specific bandwidth, which is determined by its size. Larger dots emit light that is skewed towards red, and as the dots get smaller, they emit light that is skewed more towards green.

When Quantum Dots of designated sizes are grouped together in a structure (more on this in the next section) and are combined with a Blue LED light source, they can emit light across the entire color bandwidth required for TV viewing.

The image above shows both the structure a quantum dot (on the right), a hypothetical example the relationship of Quantum Dot color emission properties according to size (on the left), and the method by which Quantum Dots are actually manufactured (looks like something out of Dr. Frankenstein's lab or college chemistry lab).

How Quantum Dots Can Be Used in LCD TVs

Quantum Dot Applications in LED/LCD TVs
QD Vision

Once Quantum Dots are made, the different size dots can be placed randomly or in a size-organized manner in a casing that can be placed within an LCD TV (with an LCD TV the dots are typically two sizes, one optimized for Green and the other optimized for Red).

The image above illustrates ways Quantum Dots can be placed in an LCD TV.

  • Placed inside of a casing (referred to as an Edge Optic) along LCD panel edges between a blue LED edge light source and the LCD panel (for edge-lit LED/LCD TVs).
  • On a "film enhancement layer" (QDEF) placed between a Blue LED light source and the LCD panel (for Full Array or Direct-Lit LED/LCD TVs).
  • On a chip that is placed over Blue LED light sources along the edge of an LCD panel (for edge-lit LED/LCD TVs).
Samsung Quantum Dots
samsung

In all methods, a Blue LED sends light through the Quantum Dots that are excited so that they emit red and green light (which is also combined with the Blue coming from the LED light source).

The different colored light passes through the LCD chips, color filters, and on to the screen for image display. The added Quantum Dot emissive layer allows the LCD TV to display a more saturated and wider color gamut than LCD TVs without the added Quantum Dot layer.

The Effect of Adding Quantum Dots to LCD TVs

Quantum Dot Color Gamut Boost for TVs

QD Vision

Shown above is a chart and an example of how adding Quantum Dots to LCD TVs can improve color performance.

The chart at the top is a standard graphical representation illustrating the full visible color spectrum. TVs and video technologies can't display the entire color spectrum. Keeping that in mind, the triangles displayed within that spectrum show how close various color technologies used in video display devices approach that goal.

As you can see from the referenced triangles, LCD TVs using traditional white LED back or edge lighting display far less than the NTSC color standard that was adopted in 1953 for color transmission. However, when Quantum Dots are added into the mix, color on an LCD TV can extend out far enough to meet NTSC color standard requirements.

The practical effect: Colors are more saturated and natural, as shown in the comparisons below the graph.

Quantum Dots can also be used to fulfill the needs of both HD (rec.709) and Ultra HD (rec.2020/BT.2020) color standards.

Standard LED/LCD vs OLED

LCD vs OLED Structure

LG Display

 

LCD TVs have drawbacks in color saturation and black level performance, especially when compared to Plasma TVs, which are no longer available. The incorporation of LED black-and-edge-lighting systems has helped somewhat, but that hasn't been quite enough.

As a response, the TV industry (mostly LG) pursued OLED technology as the solution as it can produce both a wider color gamut and absolute black.

LG utilizes a system referred to as WRGB, which is a combination of white light-emitting OLED subpixels and color filters to produce images, while Samsung incorporated true red, green, and blue light-emitting OLED subpixels.

Samsung dropped out of consumer OLED TV production in 2015, leaving LG and Sony, as the sole sources for OLED TVs in the U.S. market. Samsung has devoted its resources to bringing Quantum Dot (QLED) TVs to market, along with Vizio and TCL.

OLED TVs look great, but the major issue slowing many TV brands from bringing OLED TVs to the market on a mass scale is cost.

Despite the claim that LCD TVs are more complicated in structure than OLED TVs, OLED TV is more expensive to manufacture in large screen sizes.

This is due to defects that show up in the manufacturing process that result in a large percentage of OLED panels being rejected from use for large screen sizes. As a result, most of OLED's advantages (such as displaying a wider color gamut and deeper black level) over LED/LCD TVs haven't resulted in wide manufacturer adoption.

Taking advantage of OLED's production limitations and the ability to incorporate Quantum Dots into currently executed LED/LCD TV design (with little change needed in the assembly line), Quantum Dots are seen as the ticket to bring LED/LCD TV performance closer to that of OLED — but at a lower cost.

Samsung is spearheading a move that combines quantum dots with OLED (dubbed QD-OLED) for even better color performance and brightness without the drawbacks of current QLED and OLED TVs. No word on when or if such sets would come to market.

LCD With Quantum Dots (QLED) vs. OLED

Samsung QLED TV vs LG OLED TV
Samsung and LG

Adding Quantum Dots to an LCD TV brings its performance closer to that of an OLED TV, but there are areas where each has advantages and disadvantages. Here are examples of some of those differences.

Quantum Dot/QLED TV
  • Color performance on par with OLED.

  • Maintains excellent color saturation as brightness changes better than OLED.

  • Can't display absolute black.

  • Uneven screen uniformity – Blacks and whites are not even across the entire screen surface.

  • Narrower viewing angle when compared to OLED TVs.

  • High light output capability consumes more power.

OLED TV
  • Excellent Color Accuracy.

  • Not as good as QLED at maintaining color saturation as brightness changes.

  • Can display absolute black.

  • Not as bright as a QLED TV – Best to use in a dimly lit room.

  • Better Screen Uniformity (blacks and whites are even across the entire screen surface) than QLED TVs.

  • Lower power consumption than most QLED TVs.

  • More expensive than QLED TVs when comparing equivalent screen sizes and other features.

Quantum Dots: A Colorful Present and Future

Quantum Dot Tech Demo and QD Vision Models - CES 2016

Lifewire / Robert Silva

The main providers of Quantum Dot Technology for use in TVs are Nanosys and 3M, which provide the Quantum Dot film (QDEF) option for use with Full Array backlit LED/LCD TVs.

In the photo, above, the TV on far left is a Samsung 4K LED/LCD TV, and just to right and the bottom is an LG 4K OLED TV. Just above the LG OLED TV is a Philips 4K LED/LCD TV equipped with Quantum Dot technology. The reds pop out more on the Philips than on the Samsung set and is slightly more saturated than the reds displayed on the LG OLED set.

On the right side of the photo are examples of Quantum Dot-equipped TVs from TCL and Hisense.

The use of Quantum Dots has taken big leap forward as several TV makers have shown off Quantum Dot-enabled TVs at tradeshows including Samsung, TCL, Hisense/Sharp, Vizio, and Philips. Of those, Samsung and Vizio have brought models to market in the U.S., with TCL also jumping in – Samsung and TCL brand their Quantum Dot TVs as QLED TVs, while Vizio uses the term Quantum.

LG displayed some Quantum Dot TV prototypes in 2015 but backed away from bringing them to market to put more resources into their own Nano Cell technology in select LCD TVs as well as making more expensive TVs using OLED technology.

With LG and Sony (as of 2020) as the only makers of OLED TVs (Sony OLED TVs use LG OLED panels) for the U.S. market, the Quantum Dot alternative for color enhancement offered by Nanosys and 3M might enable LCD to continue marketplace dominance for years to come.

Next time you go shopping for a TV, check to see if it has the "Color IQ", "QLED" "QD", "QDT", "Quantum" or similar label on the set, or in the user guide – that will tell you that the TV is utilizing Quantum Dot Technology.