Effective messages
Many sign codes prohibit flashing, scrolling or moving messages on digital screens. Instead, a static image must be displayed for a certain minimum duration—e.g. five seconds—before the next one appears. These codes usually take their cues from the digital billboard industry, where large screens are viewed from vehicles moving at high speeds.
A more comprehensive approach to determining how changeable messages will appear should also be based on the size of the billboard and the complexity of the desired messages. Research suggests brief messages should comprise no more than three lines of text, with no more than 20 characters per line. It should be possible for each message to be read twice by a driver moving at the speed limit, which typically requires four seconds
of viewing time for every 10 seconds the sign itself is visible to the viewer. Each message should convey a complete thought.
“Eight seconds between messages will produce the strongest results in terms of legibility,” says Garvey. “The average driver can digest two messages from when they first see a message until they pass the sign. That usually is a 16-second period, at typical driving speeds and sign sizes.”
In other words, even putting sign codes aside, industry guidelines themselves suggest digital billboard content should be basic, clear and not especially dynamic. The ads must be short, but also relevant, to be effective. Ultimately, most legibility issues for digital billboards are the same as for traditional signs.
For pedestrian-facing digital signage, on the other hand, content may be much more complex, with a mix of advertising, information and even interactivity. Storytelling can give ad campaigns a strong impact.
SRF studies show messages that are poorly designed often go ignored. The increased ubiquity of digital displays has made viewers accustomed to them, so if content is not visually stimulating, compelling and relevant,it will remain invisible. Certainly, imagery should be at the same level of quality as printed graphics.
Hardware issues
The legibility of content will depend not only on how it is designed, but also on how it is displayed, in terms of the hardware used. Lower-resolution screens have come to be seen as detrimental to their owners’ brand identity, to the point where some municipal governments are beginning to look into regulating resolution the same way they do with illumination levels.
This is one of the reasons LCDs, which provide the highest resolutions, are dominant at the pedestrian level, while arrays of red, green and blue (RGB) LEDs, which are brighter and more easily seen from a distance, are integrated into buildings and used as billboards. Content needs to be designed accordingly.
“LED screens with a tighter pixel pitch become more legible,” says Garvey. “A pitch between 10 and 12 mm (0.39 and 0.47 in.) is quickly becoming the standard outdoors and some manufacturers are pushing the envelope with 8.5 mm (0.33 in.).”
Nighttime digital projections, on the other hand, tend to map three-dimensional (3-D) images on large-scale surfaces, rather than focusing on text. The technology is generally better-suited for dramatic visual effects than for messages.
Environmental integration
The success of exterior digital signage networks has not come without considerable conflict with urban and suburban communities, particularly where there is a perceived lack of integration with the landscape or architecture of the surrounding environment. As a result, some governments have worked to develop new codes that require the overall design of a sign to be considered before approving the use of a large screen.
