Chances are you’re familiar with HDTV. Most of us have one of these in our living rooms. In fact, according to a recent study, more than 80% of US residents probably have at least one HDTV in their homes. And there’s a good possibility these sets are LCDs. They may be a few years old but they’re thin, look great hanging on the wall and basically do their job well. Some of these HDTVs also have 3D capabilities but the required glasses have long been lost to the couch cushions or the dog ate them or they just never made it out of the packaging due to lack of content support by broadcasters.

Quantum-dot enhancement film (QDEF) is designed to replace the diffuser in an LCD backlight unit (BLU) and is placed between the BLU and the LCM. The QDEF contains red- and greenemitting quantum dots that are tuned to each display system and is illuminated by blue LEDs in the BLU. In the above image, a sheet of QDEF (right) can be seen converting some of the blue light emitted by a blue BLU (left) into white.
If you’ve heard of Ultra HD TV (or UHD) at all, you probably know that UHD means a big increase in resolution. Just like the jump to HDTV, UHD promises to show us a lot more pixels — four times more pixels in fact. What you may not know is that UHD brings with it a number of other improvements in image quality that may get consumers excited about TV again.

Technology has changed tremendously since we first started broadcasting HD in the late 90’s. It’s now possible for content creators to capture not just higher resolution but more colorful, dynamic and lifelike images than ever before with powerful production tools. At the same time, new display technologies like quantum dots make it possible to actually see everything that these cameras can capture.

This sounds great, you’re probably thinking, but how does the UHD experience really compare to the HD set in my living room today? Will I be able to see the difference or is this just the next 3D?

UHD Experience

Let’s take a look at UHD’s top three image quality features — resolution, color and dynamic range — to get a sense of how they compare to HD.

Resolution is probably the most talked about new UHD feature and just about all UHD sets will ship with a super-sharp resolution of 3840 by 2160 pixels. That’s four times the resolution of today’s 1920 by 1080 HDTVs. It’s a big improvement, but it’s actually not the most noticeable feature of UHD. This is because HDTV was already close to the limit of what the average human eye can resolve from a distance of nine feet away (the distance most of us sit from our TVs).

Color is a different story. The standard for today’s HDTV color broadcast was set in the early 90’s, around the time that cellphones were brick-sized, and it was designed to work within the limited capabilities of the CRT computer monitors of the day. As a result, HDTVs can only display about one third of the range of colors our eye can detect. So there’s a lot of room for improvement in color. UHD sets with wide color gamut will deliver about 5,000 times more color information to consumers in terms of both a wider range of colors and more accuracy. The difference is striking.

The size of a quantum dot determines its wavelength and therefore its color output. Dots of different sizes are seen here emitting light from cyan (500nm) to deep red (640nm).
Finally there’s High Dynamic Range (or HDR). You’ve probably heard that a good “black level,” a measure of just how inky-black a TV can make a black pixel, is important to look for when choosing a new TV. This is because black level translates directly to contrast ratio — the deeper the black, the better the contrast, the richer and more lifelike the image, especially in darker scenes.

You can think of HDR like contrast ratio on steroids. HDR TVs push the dynamic range in both directions with deeper blacks and brighter whites. Most HDR UHD sets will deliver about 1,000 nits of brightness, which is roughly two and a half times brighter than the average HDTV. Sounds almost painfully bright but the idea here isn’t to blast users into snow blindness with full white screens at full brightness. Having extra brightness headroom available can add tremendous depth and realism to the kinds of tough-to-capture scenes that used to make cinematographers lose sleep. Think super bright stars popping out against a black sky or a bright candle in a dimly lit room or sunlight glinting off of a suit of armor.

Display Technology

The UHD experience sounds awesome but how will we deliver it to consumers in a cost effective way? Can the venerable LCD technology platform that worked so well for HD step up and deliver UHD or do we need to look to totally new approaches like OLED?

LCDs have faced a practical limit in terms of color performance, at best reaching about 50% of the UHD color standard, because of the white LED light source used in most LCD backlights. While LCD makers have experimented with other wide gamut backlight technologies, such as discrete RGB LED and cold cathode fluorescent (CCFL), all have proven too costly, too power hungry, or too bulky to be viable. It has seemed that high brightness, portability and wide gamut color performance simply could not be had in the same LCD package at the same time.

Although emerging technologies, like OLED, continue to promise great things for the future, the technology has yet to capture a large share of the overall display market. LCD remains the standard in nearly all display product categories and with good reason. With over a decade of explosive growth in manufacturing capacity by LCD makers, and over $180 billion in capex in the ground, the cost of LCDs of all sizes is tough to beat for upstart technologies like OLED.

Photonics Tech Briefs Magazine

This article first appeared in the November, 2015 issue of Photonics Tech Briefs Magazine.

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