With indoor environments, everything is nice and comfortable. It does not rain inside, temperatures and humidity are controlled, the sun does not shine indoors, ambient light conditions do not change, the air is clean, power is consistent, the wind does not blow, and vandalism is rare. Basically, digital displays that are deployed indoors are in a controlled environment in virtually every respect.
However, in transit-type settings, everything changes – and it changes dramatically. Most transit venues are outside or semi-outside. Even when they are underground, these venues are not as clean and controlled as true indoor environments like shopping mall. Not even close. Brake dust from trains/buses is also a major concern. Digital displays that are to be deployed in these areas are in an uncontrolled, harsh environment that is constantly changing. Anything can happen to them. Therefore, it’s important to consider the following factors and how they will affect your digital display initiative before choosing and deploying digital LCD displays:
|Temperature||65 to 75°F||-30 to 120°F|
|Humidity||Under 30%||Over 80%|
|Rain, snow, dust, dirt||None||Yes|
|Brake dust, car fumes||None||Yes|
|Wind Load||None||Yes - up to 100 MPH|
|Ambient Light||Same all day||Changes throughout the day|
|Duty Cycle||8-12 hours/day||16-24 hours/day|
The table above shows just some of the severe conditions outdoor digital displays have to endure over their indoor counterparts. They must be built to withstand direct sunlight, extreme temperatures, high humidity, rain, snow, dust and dirt, brake dust, harsh windy conditions and they also need to be protected from vandalism. It’s imperative to keep all of the above factors in mind when evaluating outdoor / semi-outdoor displays. While all of these factors must not be ignored, special attention should be given to the impact of the sun.
The sun puts out an incredible amount of energy that cannot be overlooked. Before placing displays in direct and indirect sun conditions, please consider:
- Sunny environments require high-bright displays for optimum viewing.
- Display luminance should normally be between 1,500-2,500 nits or candelas.
- Brightness should be measured through cover glass/film, not just at the surface of the LCD.
- Displays that maintain set brightness levels over time are highly preferred.
- Some displays will lose 10-12 percent brightness/year; this is not good.
- Some displays will lose 10-15 percent brightness in hot or cold ambient conditions; also not good.
Solar Clearing of the LCD screen is a concern. With direct sunlight and a backlight at full brightness, the LCD crystals receive a large amount of heat and could go through a phase change causing black blotches on the screen. This solar clearing will cause degradation in the display thereby reducing the operating life. To prevent solar clearing several factors must be addressed.
- LCDs are rated to different temperatures; 68°C, others 80°C and some at 110°C. The higher the better, so ask your hardware provider which LCDs they use and what the clearing point temperature is.
- CCFLs are inadequate for outdoors. Only use LED direct backlight systems. More reliable, longer life, less power consumption, better uniformity.
- Ambient light sensors should be used to automatically adjust backlight brightness based on light conditions.
- Avoid digital displays that are optically bonded to cover glass. If glass is broken then the expensive LCD is also lost.
- Cooling systems must be robust and reliable and consume minimum power and take up little space.
- The sun is worse in winter with clear skies/lower haze.
- East/West orientations are worst. North/South orientations are best.
- Rising and setting sun are the worst times of the day, not high noon.