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LED vs. LCD Part 2: The competitive landscape of visualization technologies

LED will rarely, if ever, outsell the LCD single-panel solutions in units. In fact, LCD or emerging OLED single panels enjoy all of the momentum and growth of the $50 billion consumer TV market.

July 21, 2016

By Gary Feather, CTO, NanoLumens

In part 1 of this series, I discussed the recent innovations in the LED digital signage industry with reference to pixel pitch. In part 2, I will discuss the competitive landscape of LCD technology.

The comparison to the LCD TV is an important one. Various applications of LCD panels are currently less than 80 percent of all units shipped in the digital signage business today. The future of our industry will benefit from LED tiled displays as the resolution meets the needs currently satisfied by LCD panel implementations. Determining how LED will benefit and why requires a little perspective on what the customer desires for a solution. 

LED will rarely, if ever, outsell the LCD single-panel solutions in units. In fact, LCD or emerging OLED single panels enjoy all of the momentum and growth of the $50 billion consumer TV market. Visual video performance is stellar on the most critical LCD systems such home theater with a brightness limitation of 500 nits, which is overcome through upgraded backlights. When one single display panel is sufficient for the customer for a digital signage application, LCD is most often the solution of choice. 

An LCD typically supports an equivalent pixel pitch of 0.7 millimeters. UHD or 4K displays, which are rarely used in signage but prominent in the consumer TVs seen this year, are typically pixel pitches of 0.35 millimeters. The fill factor of the LCD TV is greater than that of the seamless-tile style LED modular display walls. Today's LCD TV supports flat displays with bezels, those black cross-hatch lines found between individual displays when areas larger than one square meter are desired. Despite the narrow bezel solutions of 0.9 millimeters, tiled LCDs have noticeable black dividing lines that are objectionable if the customer wants a single video display experience.   

With regard to resolutions, initial thinking might suggest that competitive LED digital signage solutions must track LCD and get down to 0.7-mm or even 0.35-mm pixel pitches in order to be a viable replacement. This is simply not true. 

Pixel pitch is only one of three factors creating the demand for to replace LCD and provide solutions exceeding its capabilities. More must be accomplished, and only some people in the LED digital signage business are addressing these factors. 

Second is efficacy. Efficacy, measured at watts per meters squared, for the desired level of nits for the viewing environment, must be comparable or better than that of the LCD.  Digital signage applications — new or replacement — cannot support two to three times the power for the same level of nits on the display. Today industry leaders are still challenged with obtaining efficiencies that get the brightness without disproportionate increases in power, especially at the finest pitch. 

Higher power dissipation translates to a higher operating temperature for display electronics such as components, power supplies and LEDs. This translates to mean time between failure and ppm failure rates of the individual LEDs to a level far below the requirements for a true LCD replacement. For example, current 6-mm pixel pitch LED digital signage with 6,500K white point average around 7-cd/W. High-contrast 4-mm displays can be 4-cd/W, dissipating almost twice the power for the same per-unit area brightness. The industry challenge will be to keep the efficacy above 3-cd/W as pixel pitches drop from 2.5 millimeters to 1.25 millimeters. 

Third is the LED display's visual performance and if it can compare favorably to the LCD panel.  Digital signage has built its core applications on large, bright, high-color displays. However, earlier industry targets were focused on bright imagers, not on video quality.

This year, however, the world changed. Today viewers expect LCD (or OLED) image quality in the finest-pitch LED display. Colors must align to BC2020 or REC709, or the display is unacceptable for the critical corporate customer or content creator. Because of video frame rates as well as the multiplexed addressing for LED, it is critical to operate at LED frame rates 10 times that of a normal video rate. This will work to avoid motion or image perception artifacts. 

Most important here is true delivered grayscale as content is critical from the brightest to the darkest images. Grayscale brightness is built based upon a "time-on" approach with constant-brightness LEDs leveraging the eye and integrating the quantity of light in the frame to see the higher and lower brightness exactly. This digitally precise "on-off" methodology allows exact luminance reproduction when displays are calibrated at their initial commissioning and is most important for the perception of natural images. With exact RBG colors set at the initial design/sourcing, exact color can be reproduced and presented by the display.

With the precise control of brightness at each step level being 100 percent reproducible, systems can replicate true-life perception. However the entire video data path, drive electronics and the LEDs must be carefully designed to achieve true-life images. Many in the industry do not yet understand how to achieve this performance in their products. 

Content consistency is critical from the brightest to the darkest images. Color balance of RGB can and must be perfect to avoid "color in the black and white" at the lowest bit depth or "cartooning lines" in the lifelike images in the source when delivered to the viewer's eye. Video must strive to match LCD in recreating lifelike images, and system uniformity and linearity is critical as LED matches to reality. Precise control will drive each pixel to the optimal level, creating true-life images.

One additional area of image quality that helps bring images to life is high dynamic range.  Recent studies have demonstrated the dynamic range of three orders of magnitude typically falls woefully short of what the human visual system desires in true-life-like images. Scenes that include sun scintillation on the sand, reflections off a window or the expansiveness of the sky's color and brightness require nearly six orders of magnitude to fully satisfy the viewers. In tests viewers see the difference and note how images displayed properly emulate true life. 

LED digital signage at its fundamental design has all the capabilities to support compelling high dynamic range. However implementation and system control is required to deliver these compelling images. The future solutions for the highest image quality will provide compelling visual displays.  

The competitive nature of the industry can be seen in a "glass half-full" mentality, viewing the LCD market as simply out of reach. But it is this type of driver that will propel the future developments and technological advances that LED digital signage needs. Fully satisfying the requirements and capabilities of image quality, efficacy and fine pitch will open the future market to all current and future LCD and projection markets. Additionally, market growth will also be accelerated in the current state as performance improves. Focusing on pixel pitch, efficacy and visual performance will drive the future of the LED marketplace for true innovation rather than form over function.