Display Technologies Evolve for Indoor Digital Signage
Effective signage needs to grab people's attention in order to convey information. In the case of digital signage, getting that attention means using the right choice of display technologies, which are constantly evolving to suit the needs of the burgeoning market.
by Don Shaw
THE indoor-digital-signage market is currently dominated by flat-panel displays that are virtually no different from the HDTVs we buy at the big-box stores and install in our living rooms at home. Indeed, flat-panel displays were the technology breakthrough that allowed the digital-signage market to begin in earnest during the late 1990s. With a high-quality displayed image, brightness of 300–700 nits, and economies of mass production alongside TV-grade panels, it is no wonder that this technology has been so successful in digital signage. However, one could now argue that flat-panel displays have become ubiquitous and easily ignored, presenting a stumbling block in an industry that needs to engage and captivate viewers. This has created an opportunity for display manufacturers to develop new technologies that can attract attention, as flat-panel displays were able to do in the past. Some of the clearest opportunities for innovation are in display sizes and shapes, but it is equally important to consider advancements in resolution, color fidelity, and brightness. Beyond these visual characteristics, it is also key to consider factors such as acceptable viewing distances, serviceability, and calibration.
Bigger is Better
Perhaps the most obvious way to build a more exciting digital-signage display is to make it bigger than the TV in everyone's living room. In fact, liquid-crystal-display (LCD) and plasma-display-panel (PDP) manufacturers have been going down this path for several years now, with a continuing battle of one-upmanship on the trade-show floors, culminating in monolithic displays up to 150 in. on the diagonal. This is nine times the size of a more conventional 50-in. display, but also comes with orders-of-magnitude higher production costs due to manufacturing yield realities. Also, setting aside cost for the moment, there are significant challenges involved in (carefully) transporting these glass behemoths from the manufacturer, through the doors of their intended venue, and then up onto a wall or display stand. One notable success in this category is the 103-in. plasma display from Panasonic with 1080p resolution, a pixel pitch of 1.18 mm, and a weight close to 500 lbs. Somehow, Panasonic has managed to ship several thousand of these units since their commercial debut in late 2006. Figure 1 is just one example of how companies are using digital signage in new ways (in this case, as part of a giant "camera") to catch the eye of passers-by.
Displays in Arrays
Another common approach for building larger digital-signage displays is to combine several conventional flat-panel displays into an array. Everyone has seen examples of these installations at trade shows and in public spaces. They are relatively inexpensive to set up, but always need some type of custom structure to support and align them. Once installed, their most obvious drawback is the existence of large mullions between the individual display panels. Not only do these mullions provide a visual distraction, but they necessitate special care when developers are creating content and playback systems to make sure no vital messages get lost in the non-viewable or "null" display areas. It should be mentioned that reduction of bezel size among flat-panel-display manufacturers has been reasonably successful in recent years, resulting in smaller mullions, two examples of which will be discussed below. Also, as flat-panel-display technology has generally been designed to operate in isolated units, it is very difficult to achieve and maintain color and brightness uniformity across multiple units, especially as they age. As a final consideration, arrays of flat-panel displays are inherently time-consuming and labor-intensive to maintain. A typical repair involves manipulation/ replacement of a large screen that is often attached to all of its neighboring units, necessitating a tear-down of a substantial portion of the array to address even single-unit failures.
Despite the difficulties of attempting to configure and maintain conventional flat-panel-display technologies in arrays, two specific efforts to address the issues are worth mentioning. One product is an adaptation of EDTV-resolution (852 x 480) 42-in. plasma displays, from Orion PDP Company, whereby the bezel around the screen is substantially reduced, allowing for a 4-mm seam between adjacent displays. Featuring a pixel pitch of 1.08 mm and a claimed brightness level of 1000 nits (although some parties have reported actual measurements substantially lower than this), the image quality is quite good, although newer displays feature better black levels and less glare. Furthermore, there have been numerous reports of brightness, uniformity, burn-in, and reliability issues, especially as these units age. Despite these issues and a per-unit selling price at an order of magnitude above standard 42-in. EDTV screens, Orion plasma displays have achieved a remarkable number of installations since they were first introduced in 2003; certainly due to their early-to-market advantage where no other flat-panel manufacturers had shown any interest or progress.
More recently, Samsung has introduced a 46-in. LCD panel, with a WXGA resolution (1366 x 768), that features bezels of 2.4 mm (right, bottom) and 4.3 mm (left, top), which leaves a 7.3-mm seam between adjacent displays when they are mounted in an array configuration. With a pixel pitch of 0.75 mm, a brightness of 700 nits, and visibly better contrast than the Orion plasma displays, the image quality is excellent. Interestingly enough, several other major manufacturers (NEC, Barco, Planar, etc.) announced their own products, with identical seam and image specifications, just after Samsung announced its offering. Selling at a lower price than the Orion plasma displays, these LCDs seem like a viable solution if the end user can accept the 7.3-mm seams, but only time will tell how the various manufacturers are able to wrap the Samsung panels with enough "tiling" technology (for mounting, uniformity, cooling, etc.) for success in this market.
Direct-View LED
In large venues, such as indoor sports stadiums, sunlit atriums, and concert settings, the technology of choice for signage is direct-view light-emitting-diode (LED) displays. These displays have the advantage of being able to produce extremely bright images, up to 7500 nits, and they feature vivid-color palettes. Also, because LED displays are generally made up of relatively small tiles, they are easy to configure in unusual shapes and look nothing like the HDTV in your living room. Originally developed for scoreboards and sunlight-viewable billboards, this outdoor technology has been adapted by numerous companies to be used indoors. Indoor usage allows the brightness to be lowered (to 1000–2000 nits) to save power and reduce cooling requirements. Also, due to the closer viewing distances, pixel pitch is typically lower than outdoor products, with 3 mm being the (very expensive) lower limit of technical feasibility, and 6–10-mm displays occupying the mainstream indoor market space. A major drawback of this technology is that these displays all become pixelated when the viewer is up close and are generally not suitable for high-resolution content unless they are very large and it can be ensured that the viewer is a sufficient distance away from the screen. A general rule for selecting LED displays is that the viewer needs to be at least 1 m back for each 1 mm in pixel pitch. It is also important to note that although this type of display will burn brightly for up to 100,000 hours, it is very difficult to maintain uniform color and brightness as the LEDs age.
Projection Displays
Conventional projection technologies, which can produce brilliant images in dark environments, are often dismissed in digital-signage applications for a number of reasons. First of all, the integrator must carefully consider how to design a projection-based solution that maintains reasonable contrast levels in the high-ambient light environments typical for digital signage, such as in retail. Another consideration is the physical space, often at a huge premium in retail and commercial settings, which needs to be allocated to satisfy line-of-sight requirements for projection-display systems. Finally, because conventional high-brightness projection systems are illuminated with lamps that only last a few thousand hours, the cost of maintenance and spares must be considered carefully, especially for 24/7 (or 16/7) digital-signage installations. Despite all of these issues, if the end user can control the ambient light levels and space is not an issue, a high-quality projector and carefully selected screen can be very cost-effective in terms of screen size. Also, the world has seen some novel examples of what can be done with special optical films on glass surfaces in conjunction with projection.
Fig. 1: A 103-in. plasma display appears as part of an innovative digital-signage exhibit at London Waterloo station. (Photo courtesy Panasonic UK & Ireland.)
Tiled Displays
An example of another recent development in digital display technology is a product called MicroTiles from Christie Digital Systems. Designed as a series of 20-in. (diagonal) building blocks, MicroTiles can be configured in any shape and size, as shown in Fig. 2. The tiles use a direct-throw DLP rear-projection engine with solid-state LED illumination, which enables a large color gamut with no lamps to change over time. With no theoretical limit to the number of tiles in a display, MicroTiles make possible an 800-nit (calibrated) digital canvas with tiny (1 mm) seams and an unlimited number of super-fine pixels (0.57-mm pixel pitch). This product has the shape, modularity, size, and color-reproduction capabilities of direct-view LED displays, but also offers impressive image quality from any viewing distance. Furthermore, through innovative engineering and light-sensing technology, MicroTiles are the first (of hopefully many) tiled display products to feature a closed-loop calibration system, which can automatically set up and maintain brightness/color uniformity throughout the life of the display. The rated lifetime is 65,000 operating hours, and Christie claims that any service that is required on a MicroTiles display unit can be performed in less than 15 minutes by a single technician. MicroTiles are positioned at about the same price point as mainstream high-resolution indoor LED products.
New Technologies
Of course, as the display world continues to evolve over time, there will be new entrants with new technologies competing in the large-area and digital-signage display space. One new company, Prysm, recently announced a technology called Laser Phosphor Display (LPD) technology, from which it is building a product that it claims is ideal for commercial applica-tions such as digital signage (as of this writing, Prysm had not yet published product specifications). LPD is said to use an array of modulated solid-state lasers, combined with a high-speed scanning mechanism similar to that used in CRT displays, to excite a patterned array of phosphors layered onto a rigid screen surface.
Another new entrant is Nanolumens. Using a new type of specially designed, thin-film phosphor-based electroluminescent display modules, and mounting them on a thin-polymer-film display substrate, the company claims to be able to efficiently manufacture uniformly bright (between 500 and 1000 nits) and highly scalable displays. Nanolumens has publicly demonstrated a 112-in. display unit at less than 1-in. thick that is flexible enough to wrap around curved walls and columns or roll up for easy shipping and install. However, at the time of this writing, Nanolumens had not publicly published actual product specifications.
The past year has brought about some exciting display technology innovations that will certainly contribute to the growth of the digital-signage industry. With display options that move well beyond the TV-like screen in terms of size and shape, the creative community (in advertising, retail design, and architecture alike) now has more ways than ever to captivate and engage an audience with digital signage. Beyond freedom in size and shape, we continue to see progress in resolution, brightness, color fidelity, and diminishing seams in tiled-display arrays. Furthermore, with the emergence of purpose-built signage display products across a range of technologies, manufacturers are finally starting to offer viable technical solutions for the maintenance and calibration issues long affecting large-area and tiled displays. •
Fig. 2: The MicroTiles technology allows for displays in a variety of non-uniform shapes.