The Continuing Digitization of Outdoor Media

The technical possibilities of digital signage in outdoor advertising are seemingly overwhelming, but the widespread implementation of these technologies is moving slowly. In addition to technical, logistical, and legal obstacles that need to be overcome, financial issues are slowing down the breakthrough of digital signage into the outdoor-media business. Here, we will evaluate the available approaches from the point of view of an out-of-home media company.

by Michael Schmid and Dennis Löffler

ALTHOUGH electronic media utilizing displays in outdoor advertising is becoming increasingly common, they have thus far been concentrating mainly on highly frequented places such as sporting arenas, airports, train stations, etc. However, the largest percentage of sales in the out-of-home media market still is comprised of traditional concepts such as billboards, pillars, and city-light posters in places such as bus shelters. But recent history indicates that it is only a matter of time before the out-of-home media market becomes predominately digital. To wit:

• Digital information systems are increasingly penetrating many aspects of our civilization. In the private domain, the Internet has become widely used as an alternative to libraries, shops, call centers, and post offices, to name but a few. In most companies, Internet-based technologies (intranet) are used to exchange corporate business data, and thus increase the productivity of the company's processes. The Internet allows the maximum "up-to-dateness" imaginable; the speed of the medium is only limited by the speed with which content editors can upload content. Since content generation for the Internet has become simple even for semi-expert users, the costs have become affordable even for private customers.

Michael Schmid and Dennis Löffler work in the R&D Departmemt at Ströer Out-of-Home Media, Ströer Allee 1, D-50999 Köln, Germany; +49-02236/88 46-534, fax -337, e-mail:


Fig. 1: Two examples of symbiosis between digital and non-digital signage. On the right is a City Light Pillar that includes a monochrome LED ticker plus multiple interactive information terminals. On the left is an interactive City Light Poster (iCLP) containing a transflective LCD with a touch pad.

• Cell phones have virtually replaced public phone boxes and they offer mobile communications in all its known forms, including Internet access, video conferencing, and myriad other information services.

Despite the wide variety of applications and services offered by both Internet and mobile telephony, only a fraction of them is commonly used by the customer. There are various examples of services that are still striving for common acceptance: E-paper, video-telephony, multimedia messaging service (MMS), and many others. Most of the technologies developing slowly lack one essential criterion for success: They contain hardly any added value for most clients. This obstacle can only be overcome when either synergy with other commercial technologies can be used to achieve a significant cost reduction or the market spread of the application is subsidized. In the long run, this can create profit by volume-led cost reduction.

To accelerate the establishment of digitization in outdoor advertising, it is essential to understand where the potential is from the point of view of an out-of-home media client.

Improving the speed and cost situation is of interest to every private company. For outdoor advertising, the target aspects of this productivity optimization are mainly through reduction of the maintenance costs of the advertisement carriers (on-line quality control, on-line proof of service) and in the production and distribution of the advertisements. Digital technologies can support such process improvement in every discipline and have already been integrated into state-of-the-art outdoor-media systems.

For example, let's examine Mega-Lights, the stand-alone billboard scrollers that carry up to four different posters behind a glass screen. The maintenance and logistical processes of Mega-Lights are simplified by linking them via GSM/GPRS modems to the advertiser's network (e.g., Ströer WPC). The poster size can be as large as 18 m2, and with the backlight concept, they do not need external lighting, which creates excellent design opportunities. The WPC network technology allows on-line proof-of-service, simplifies the coordination of maintenance and distribution activities, supports claim management, and also allows for the remote change of the displayed advertisements.

Whereas cost saving is a high priority of every business, the essential goal of any advertising is to enhance sales volume. The volume of out-of-home media is considerably lower than that of other media such as TV and print. Good advertisements communicate the product message and evoke emotional connections between the product and the customer. Many campaigns work best on a multimedia level, and some even require interactivity. If such requirements are introduced, they simply cannot be fulfilled with the traditional static and non-multimedia techniques that currently dominate this market.

Niches for digital signage occur in applications that either allow interaction between the passer-by and the medium or are furnished with sufficient dynamic to carry the campaigns' messages. Advertisements that encourage the passers-by to spend more than a short glimpse at it, increase eye contact time, and delve into them can apparently only be successful when they are located at sites that are highly frequented and where the targeted viewers can spend a reasonable amount of time in contact with the media (e.g., pedestrian zones, train/bus stations, trains, or busses, etc.).

Experiences with interactive City Light Posters (iCLP) have been made in the last 2 years by Ströer. A CLP is a mid-sized showcase that can carry posters of 1200 x 1750 mm. CLPs are generally installed at the pedestrians' eye-level and are also a standard feature of modern passenger shelters. The interactive concept uses a regular CLP with an added liquid-crystal-display (LCD) screen, which shows an attractive animation (Fig. 1). Multimedia content (ring tones, video trailers, etc.) can be downloaded via Infrared Data Association (IrDA) and/or Bluetooth to a cell phone. In this way, campaigns can be implemented that would not have been considered by advertising agencies for going outdoors if only the standard non-interactive CLPs had been available.


Fig. 2: A Com Centre integrated into a passenger shelter. Both screens are transflective AMLCDs. The right screen shows advertisements, whereas the left screen hosts an interactive city guide.

Another trend that can be seen in public-space signage is an increasing demand for information. Dynamic passenger information in public transport is a very fine example of the range of low-to-high–end information systems that need to be part of an Out-of-Home Media Company's portfolio. Simple display systems will be installed in suburban shelters, whereas the high-end interactive systems will be installed at central junction points with high foot traffic. These Web-based interactive terminals (also called Com Centers and City Guides, shown in Fig. 2) can be integrated into various out-of-home media products such as advertising pillars and shelters and are also available as stand-alone solutions. This type of interactive media can thus incorporate information services as well as interactive campaigns such as those described above.

Display Comparison

Many technologies that were originally developed for the indoor domain will be critically affected when used in extreme climate conditions. Active-matrix LCDs (AMLCDs) show clearing (the liquid crystal changes phase to an isotropic liquid) when operated at temperatures higher than 60°C. A high temperature such as this may on first sight seem unlikely to occur in outdoor applications in many locations. However, vandalism protection requires a solid glass front window for the advertisement, which allows the temperature to easily exceed 60°C when the display is exposed to direct sunlight. At the moment, the clearing effect in AMLCD technology can only be avoided by integrating a ventilation system that cools the space between the display and the front window. Thus, the technology must be resistant against extreme and rapidly changing climatic conditions of temperature, humidity, and rain.

When used for advertising purposes, the displays must also provide saturated bright colors. A wide color gamut is mandatory to assure that the customer's corporate identity is displayed in exactly the right colors. Good readability in both daylight and night-time conditions is another requirement, and some applications (e.g., billboards) demand good performance in direct sunlight. One major driver for readability is contrast and the other is luminance.

Digital signage is being established for various applications in mostly urban environments. Light-emitting-diode (LED) billboard displays are available from a variety of vendors. By producing a luminance of up to 6500 cd/m2, they are ideally suited for outdoor environments and can display pictures clearly even in direct sunlight. Moreover, this technology has full video capabilities, which makes TV spots accessible for outdoor advertising, although post- or re-production of the commercials shown on TV is likely to be necessary in many cases to match the visual characteristics of the LED display. Due to its poor fill factor, LED technology is limited to viewing distances of 10 m or more. Viewed at closer distances, these displays appear very coarse-grained and become more and more uncomfortable to watch. A billboard-sized LED display fulfilling the technical specifications previously mentioned currently requires an investment of around $100,000. Moreover, the power consumption costs are significantly higher than that of a paper poster.

Various LCD technologies have already been introduced into the out-of-home media market: backlit, reflective, transflective, and bistable LCDs, to name a few.

AMLCD technology is already widespread in the consumer marketplace. Simple television-sized panels have been piloted in Infoscreen products either in shelters or on trains. In order to meet the technical specifications of outdoor applications, of course, the available devices from the mass market need to be upgraded. The indoor market is strongly focused on emissive technologies with a typical luminance of around 200 cd/m2, but outdoor applications of such a technology require a luminance significantly higher than 1000 cd/m2to make it suitable for sunlit conditions. Good results have been achieved with transflective LCDs that produce a transmissive luminance of around 500 cd/m2. By virtue of their reflective properties, these LCDs can compensate sufficiently for the significant contrast degradation that would otherwise occur when the display is exposed to direct sunlight.


Fig. 3: Magink billboard installations.


Fig. 4: Two examples of Ströer/Infoscreen installations. On the left is a projector solution in a Munich metro station; on the right is a PDP screen in Frankfurt Central Station.

The LCDs commonly used for public-transport passenger information are tiled trans-flective panels. These panels are available in both monochrome and color, and due to their transflective behavior, they can be used in daylight.

For displaying dynamic passenger information, it will be necessary to integrate digital signage into a bus-stop-stele, which is the minimum furnishing of a bus stop. Conventionally consisting of a pole carrying a bus schedule and bus-stop indication, the designs have been enhanced within the last decade. A bistable reflective LCD seems to be the best approach for displaying information such as timetable information in a stele. Because these cholesteric displays work at low frame rates, they are only suitable for displaying static content. Their daylight capability is excellent, and due to their bistability they only consume energy when the content is changed. However, it is still not feasible to power the display with a solar panel, since the necessary peripheral components of the display system (front light and air-conditioning) has constant power consumption.

Because LCD panels can, in general, not be produced in the very large sizes required by most outdoor applications, large displays are usually made by the tiling of many display panels. When viewed from large distances, the resulting mullions between the single panels are accepted as long as the readability of the screen content is not harmed. In applications working at closer distances, the mullions need to be minimized. For this, optical fibers can be used to artificially expand the active area of each tile.

Several out-of-home media companies have started to create billboard installations using the so-called Magink technology (Fig. 3), which uses matrices of tiled bistable reflective LCDs. Thus far, there are no Magink displays available with the previously described mullion reduction by optical fibers, thus the mullions are clearly visible. The pixel pitch of the technology used at present is roughly 9 mm. These aspects pre-destine Magink for signage watched from large distances. The color gamut is poor compared with transflective LCDs, and design restrictions arise with the need for external illumination. The strictly reflective approach can be interesting for closer distances only when the pixel pitch and the mullion size are significantly reduced (e.g., AEG MIS Geameleon®™).

Plasma-screen technology (PDPs) is also widespread in various out-of-home applications. Signage systems in train stations, airports, and similar environments make use of these displays (Fig. 4). For outdoor applications, PDPs have the ability to deliver a bright image that is rich in contrast at sizes of as large as 120 in. Disadvantages include burn-in effects, low lifetime, color degradation over lifetime, and very high power consumption. PDPs are mainly installed in semi-daylight environments (e.g., train stations).

Another large-screen technology is the LCD projector, which avoids the problems associated with PDPs but does not deliver comparable brightness and contrast. This aspect at the moment limits projection solutions to subway stations or places with indoor-lighting conditions.


Customer and user demand for digital signage in out-of-home media applications already exists. Due to the high level of investment required to establish such signage extensively, most existing installations have been made on a test basis. New marketing concepts, which include optimizing the potential of digital signage in the right places and with the right media, are currently under development. Technologies are available for every application imaginable. But there are different preferences for different functionalities. As in any other branch of technology, there is still plenty of room for improvement and innovation. •