Photos courtesy Vertigo Digital Displays
By Ralph and Jennifer Idems
As marketers have long recognized the benefits of displaying their messages in public environments, out-of-home (OOH) advertising has grown to become a multi-billion-dollar industry with a far-reaching scope of influence around the world. While static billboards, posters and wall murals have traditionally dominated the OOH landscape, digital signage has rapidly made its mark on the industry in recent years, due to its versatility and eye-catching visuals.
Indoor deployments of digital signage have become ubiquitous, while outdoor installations are less common. Nevertheless, many of the same organizations that have hosted indoor digital signage—including retailers, hospitality venues and the transportation sector—have also recognized the benefits of deploying digital signage outdoors, where it can be seen by more people and bring them in for business to achieve a return on investment (ROI).
The outdoor digital signage market has taken longer to develop than indoor installations because of environmental challenges, including sunlight, variations in temperature, inclement weather, dust and dirt. Today, however, there are many major rollouts of outdoor digital signage networks, as these challenges have been considered and addressed through new technologies.
Indeed, while liquid crystal displays (LCDs) installed indoors and outdoors might look the same to a passerby, they are very different, as the latter need to be specially engineered to prevent failures and to reduce the need for expensive on-site maintenance and service over their life cycle.
Sunlight
While content may not differ much between indoor and outdoor digital signage, the displays must be designed and built differently to accommodate for the environmental factors that can affect screen visibility and legibility. Sunlight is one of the most significant of these factors.
In bright or direct sunlight, as well as in high ambient light conditions, standard indoor LCDs will suffer from fading, washed-out colours and poor performance. To be fully visible to passersby under the harsh light of day, digital signs must be highly illuminated.
Another danger of exposure to sunlight is solar loading or isotropic behaviour. This involves an LCD absorbing to much external heat in conjunction with the internal heat from its backlighting,
leading to the degradation of the display. The screen starts to turn black in certain spots and its overall operating life is reduced.
Outdoor display suppliers generally agree a minimum luminance level of 1,500 cd/m2 is required for adequate visibility. High-brightness (HB) screens, which are specially designed to emit more light than standard commercial-grade screens, can provide between 2,000 and 5,000 cd/m2, as well as better contrast levels. Ambient light sensors can be installed to automatically adjust a screen’s brightness at different times of day and night, as appropriate.
As accelerated testing shows, exposure to sunlight can lead to isotropic behaviour, whereby an LCD degrades after absorbing too much heat, leading to black spots and a shorter operating life.
Most LCDs already feature anti-glare surface treatments to diffuse reflected light from external sources like the sun. When light hits the rough-treated surface, it is reflected away at different angles. This reduces the intensity of the light reflected into the eyes of passersby, but the anti-glare coating also reduces the screen’s effective contrast ratio with a hazier appearance.
One alternative to an anti-glare treatment is an anti-reflective coating, which has a smooth, glossy finish. Instead of diffusing the reflection, it actually reduces the amount of reflected light. These types of coatings are also becoming common on high-end personal computer (PC) screens and mobile phones. They ensure a crystal-clear image, improved colours and a high contrast ratio even under high ambient light conditions.
