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).
What a Quantum Dot Is
A quantum dot is a manufactured nanocrystal with semiconductor properties that can enhance the 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). When the particles are hit with photons from an outside light source (in the case of an LCD TV application, a blue LED light), each dot emits the color of a specific bandwidth, which is determined by its size. Larger dots emit light that is skewed toward red. As the dots get smaller, the dots emit light that is skewed toward green. When quantum dots of designated sizes are grouped in a structure and are combined with a blue LED light source, the quantum dots emit light across the entire color bandwidth required for TV viewing.
How Quantum Dots Can Be Used in LCD TVs
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.
Inside a casing (referred to as an edge optic) along the 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).
In all methods, a blue LED sends light through the quantum dots that are excited so that the quantum dots 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 and color filters, then 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
Shown below 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 displays a narrower color range than quantum dot-equipped TVs. Quantum dots display colors that are more saturated and natural, as shown in the comparisons below the graph.
Standard LED/LCD vs. OLED
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 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. Samsung incorporated true red, green, and blue light-emitting OLED subpixels. 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.
LCD With Quantum Dots (QLED) vs. OLED
Adding quantum dots to an LCD TV brings its performance closer to that of an OLED TV. Still, there are areas where each has advantages and disadvantages. Here are examples of some of those differences.
Quantum Dots: A Colorful Present and Future
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 the far left is a Samsung 4K LED/LCD TV. To the right and the bottom is an LG 4K OLED TV. 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 a 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. 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.
