Digital billboards, comprising arrays of LEDs, are becoming more common across Canada.
Photo courtesy Outfront Media
Pixel-pitch breakthroughs
One of the core specifications for determining
the clarity, effectiveness and cost of an LED-based digital sign is pixel pitch. Also known as dot pitch, this is the measurement of the spacing between clusters of LEDs within an array.
In September 2016, for example, Leyard launched the industry’s finest pixel-pitch LED display to date, delivering a pixel pitch of just 0.9 mm (0.035 in.) for video wall applications. By breaking the 1-mm (0.04-in.) barrier, the display achieves unprecedented resolution for an LED array, offering clear viewing even at close distances of 3 m (9.8 ft) or less. Earlier Leyard video walls ranged in pixel pitch from 1.2 to 2.5 mm (0.047 to 0.098 in.).
Further, LED arrays are now being made available in flat-panel designs and the 16:9 aspect ratio that meet popular high-definition (HD) standards, making them more directly competitive with LCDs in the digital signage sector. They are similarly engineered as factory-aligned, self-contained units with standard HD Multimedia Interface (HDMI) inputs and looping, along with optional redundant configurations, reducing the cost and time required for installation. Larger units mean fewer displays are needed to create a video wall, reducing the potential number of points requiring service and maintenance in the long term.
The advantage of curves
That said, there is also a major trend involving the custom design and engineering of LED-based displays, e.g. incorporating curves and slim profiles to accommodate unique installation settings in different types of buildings or other structures. Manufacturers like NanoLumens, for example, can fit their LED displays to the needs of existing architecture.
An additional advantage of curved digital signage is the ability to catch passersby’s attention. When it comes to connecting with an audience in today’s relatively saturated market, straight planes are not always the best choice. The human eye is naturally drawn to sleek curves, so even if a custom-shaped LED display only offers a pixel pitch between 3 and 9 mm (0.12 and 0.35 in.), it can convey an enhanced experience for the viewer.
Where LEDs meet LCDs
As mentioned, LEDs are also used as BLUs for LCDs in the digital signage marketplace. So,
as LCDs continue to find their way into mass transit vehicles, airports, train and bus stations, retail stores and other locations, the LED market grows at the same time.
LCDs have long overtaken plasma display screens, where there was a much higher chance of image retention and ‘burn-in.’ This is an especially important issue for digital signage, since the text and image templates used for messaging applications are often stagnant. Another concern with plasma screens, as digital signage applications made their way to outdoor installations and other bright locations, was how they could not prevent glare as well as LCDs could.
When backlighting LCDs, there are several significant advantages offered by LEDs over cold cathode fluorescent lamps (CCFLs), including power savings of up to 50 per cent, a superior contrast ratio, broader colour gamut and the elimination of motion blurring.
There are two main configurations for LED BLUs in commercial-grade LCDs—edge-lighting and direct-lighting—and both are available with or without local dimming technology. Each configuration offers its own advantages and disadvantages.
In an edge-lit LCD, the LED BLUs are installed along one or more outside edges of the screen, depending on the size of the display, along with light guides to ensure their illumination is dispersed across the entire screen. The advantage of placing LEDs only along the edges is this allows manufacturers to produce a very thin screen at a reduced cost. The disadvantage of this configuration is it can emphasize brightness around the edge of the screen and reduce the depth of black images, but these issues are usually not noticeable when graphics are viewed in brightly lit rooms. Other minor image uniformity issues, when viewing a screen in a dark room, can include ‘spotlighting’ in the corners and white blotches across the screen. Overall, however, pictured quality is similar to that of CCFL-backlit LCDs.
In direct-lit LCDs, also referred to as full-array LED LCDs, the LED BLUs are arranged behind the entire display panel. As a result, these screens are thicker than edge-lit LCDs, which may be a disadvantage for certain digital signage installation locations. Like their edge-lit counterparts, direct-lit LCDs provide picture quality similar to that of CCFL-backlit LCDs, but they can display deeper black performance on par with plasma displays.
Forecasting OLEDs
Organic LEDs (OLEDs), which are very thin, lightweight and flexible, are expected to eventually make their way into a significant number of displays and screens. They could find a strong opportunity in certain digital signage applications, such as small displays installed in the backs of seats in public transportation vehicles. For the time being, however, they are not yet a threat to the established LED market.
Stephen Montgomery is president of international business expansion for ElectroniCast Consultants, which forecasts market trends in LED illumination and communication networks. For more information, visit www.electronicast.com.
