Photos courtesy MRI
By Peter Kaszycki
Digital displays deployed indoors enjoy a comfortable, controlled environment. There is no rain or wind, vandalism is rare, the air is clean and the ambient light levels, humidity and temperature remain consistent. For outdoor installations, on the other hand, digital signage needs to be designed with the assumption none of these factors can be controlled.
With outdoor environments, everything is constantly changing. As a result, almost anything can happen to an installed digital display, with harsh effects.
Dealing with change
Outdoor displays must be built to withstand high humidity, rain, snow, wind, dust, dirt, particulates and occasionally even vandalism, particularly when installed on transit platforms or along sidewalks, in transit shelters and other ‘street furniture.’ They will need to operate in both heat and cold, including extreme temperatures ranging anywhere from -30 to 50 C (-22 to 122 F).
Compared to indoor displays, they are also more likely to operate between 16 and 24 hours a day, rather than a simple workday duty cycle of only eight to 12 hours. And to be effective at communicating their messages, outdoor displays need to be visible even as ambient light levels change throughout the day.
Ambient light sensors can be installed to automatically and gradually adjust a screen’s brightness at different times, based on the surrounding conditions. This function is also helpful at night, when signs that are too bright can annoy the public and digital out-of-home (DOOH) advertisers alike.
Outdoor displays need to operate across a wide range of temperatures, especially in climates like Montreal’s.
Cold-cathode fluorescent lamps (CCFLs) are not recommended for LCD backlighting outdoors. Only light-emitting diode (LED) backlighting systems should be used. They can ensure better uniformity of illumination and create less additional heat to deal with, but can also be adjusted in blocks as needed.
Finally, a glass cover laminated with an anti-reflective coating is recommended to help ensure the screen is as visible as possible when hit by direct or reflected light, whether coming from the sun, nearby buildings’ exterior lights or passing vehicles’ headlights.
Sunlight
One of the most significant factors is the impact of the sun. In a sunny environment, high-brightness displays will be needed for optimal viewing, achieving luminance of between 1,500 and 2,500 candelas per square metre (cd/m2). The displays’ brightness should be measured through their cover glass and/or film, of course, not just at the surface of the liquid crystal display (LCD) itself.
When positioning outdoor digital displays, east and west orientations are the worst, as they will receive the most direct sunlight. North and south orientations are best.
Also, given digital displays face perpendicular to the ground, sunrise and sunset are the worst times of day, whereas high noon will not affect the screen much at all. Sunlight is also harsher in winter, when skies are clearer and haze lower.
