Staying bright, keeping cool: Keys to outdoor LCD displays
By Fritz Esker
Contributing writer, DigitalSignageToday.com
Over the past few years, more and more media companies, advertisers, retailers and content providers are turning to large-format digital LCD displays to get their message delivered to the consumers. These 32- to 82-inch displays can be seen in the form of "street furniture," on the side of a bus shelter, on the back of a newsstand, in a shopping mall, in a quick-service restaurant showing menus, in transportation terminals, in store windows and even inside trains or on the side of a passing bus. Outdoor signage also can be seen as "arrays," creating a virtual digital wall/billboard that is very impressive.
The obvious advantages to digital LCD displays versus static displays or light boxes are the ability to change content with a few keystrokes, vary the type of content and support multiple advertisers or programs.
The ability to now provide dayparting also is significant. A single digital display can run coffee ads in the morning, food ads mid-day and beer ads in the evening to pique interest based on the time of day.
The initial cost will be understandably higher for these digital displays. However, the impact and versatility of these dynamic, eye-catching large-format LCD displays have proven to provide the needed ROI.
As these displays are being deployed "outside," there are several new factors that must be considered. In an indoor environment, conditions are generally stable: the ambient temperature usually is the same, the ambient lighting is known, clean and reliable power is available and the environmental conditions are consistent (it doesn't rain inside). However, outside, things change ... and they change dramatically. Temperatures will vary greatly throughout the year, rain will fall, winds will blow, humidity levels will change, vandalism may increase, cloudy days will occur and direct/indirect sunlight will affect the viewability of the outdoor digital display.
"Indoor displays are designed for certain ambient light conditions, certain humidity levels and certain temperature levels," said Peter Kaszycki, vice president of business development for Alpharetta, Ga.-based Manufacturing Resources International, a company that creates both outdoor and indoor digital signage displays. "When you go outside, everything changes."
How bright is bright enough?
The first major technical issue that must be addressed in selecting an effective outdoor digital display is how viewable is the content when exposed to direct sunlight. Anyone who has ever tried to use a laptop or watch television outside knows that the brightness of the screen impacts visibility, whether the screen is in direct sunlight or even in the shade. A screen with inadequate brightness and poor anti-reflective treatment makes the image difficult to see. If the image cannot be adequately seen, then a business' capital investment in an outdoor digital display solution is wasted.
Outdoor displays need to be significantly brighter than their indoor counterparts. An average indoor digital display will feature a brightness measurement of 350 to 600 nits. MRl's Kaszycki said outdoor digital displays should have, at the bare minimum, a brightness measurement of 1,500 nits.
While brightness is important, increasing it beyond a certain level may actually wash out the image. If the image is too bright, it becomes difficult for a viewer to tell what is on the screen and the advertisement is no longer appealing.
"Just because something's bright does not mean you can see it well," Kaszycki said. "It's a combination of the brightness level, contrast ratio and the AR treatment on the cover/safety glass that provides for the best image."
For outdoor displays, the preferred method of backlighting the LCD is through the use of LED backlights versus older CCFL bulbs. LED backlighting provides longer life, consistent brightness, lower power consumption and more uniform lighting – all of which helps provide for a lower total cost of ownership.
Merely installing an appropriately bright screen with a high contrast ratio does not guarantee a win in the war against outdoor conditions. While the brightness of the sun can affect the viewability of the display, so can weather conditions and the length of time the display is operating. Brightness will be lowered as much as 20 percent in adverse conditions, such as extreme heat or cold, Kaszycki said. And since most environments are not perfectly temperate for the entire year, temperature will be an issue with most outdoor digital deployments. In addition, normal backlighting systems will naturally lose about 10 percent brightness every year of operation.
Newer LCDs using power-efficient LED backlight technology (as opposed to CCFLs), though, can function in temperatures ranging from -30° Celsius to 50° Celsius without any loss of brightness.
Over time, the brightness of the screen will wear down. A typical CCFL-backlit LCD display loses 10 percent to 12 percent of its brightness from year to year because the half-life of the backlights are typically rated at 50,000 hours. This means that the brightness will be cut in half after five years and the picture will get progressively dimmer as the years go by.
Kaszycki likens this to buying a car that gets 33 miles per gallon when purchased, but gets only 16.5 miles per gallon after five years of moderate driving. Such a decrease in brightness represents a significant loss for the company, and lowers the return on investment. LED-backlit displays can allow for full brightness operation for significantly longer, he said.
While it is clear that protecting an outdoor digital display from environmental conditions such as heat or cold is important to keep the display functioning at an optimal level, the question of how to maintain the display at ideal temperatures must be addressed.
On their own, outdoor digital LCD displays work best in cool, dry conditions. But considering that outdoor signage will inevitably be placed in hot, humid locations such as New Orleans or Miami and considering the fact that the signage must be sealed to protect it from certain conditions, such as rain, snow or dust, cool, dry conditions are not always possible to achieve. Keeping the signage protectively sealed traps heat and moisture, making cooling an even greater challenge.
Enhancing brightness in outdoor digital signage often creates a cooling problem. Outdoor signage needs additional backlights to reach the ideal measurement of 1,500 to 2,000 nits, but these extra lights create extra heat, which adds on to the existing heat created by the sealing and the ambient sunlight.
MRI's Kaszycki said conventional air conditioning is not the best way to solve this problem. While a standard air-conditioning unit can indeed work in keeping a display cool, it will use a lot of power, cost more to operate and does not address the real potential of condensation.
A better solution, he said, is to use a closed-loop cooling system to direct air flow and cooling based on ambient temperature conditions and the impact of the direct sunlight on the screen. This alternate system has a few key benefits. It consumes 60 percent less power than a traditional air-conditioning unit, saving money and reducing the impact on the environment. This closed-loop cooling system also weighs 90 percent less than a traditional air-conditioning unit. Lastly, and perhaps most importantly, it provides a greater thermal capability — it can protect the display in temperatures of up to 50 degrees Celsius.
The closed-loop cooling system also eliminates the need for outside air to be circulated through the display, eliminating the possibility of bringing elements such as dirt, excess moisture and humidity into the display, all of which can damage the unit.
(Excerpted from the recently published DigitalSignageToday.com guide, "Outdoor Digital LCD Displays," sponsored by MRI. To read more, download the free publication.)
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