LED vs. LCD as a Sign Technology

For nearly 20 years, light-emitting diode (LED) displays have been developed and refined as a sign-industry technology. Arguably, it’s now a mature product for most programmable-display applications and the best possible solution. However, select applications remain where LEDs aren’t viable. Most noteworthy are near-distance, high-resolution displays, because even in the tightest resolution, LED displays suffer from pixilation issues.
A pixel is an individual lighting element which, when combined with other display pixels, creates the full image. More pixels create greater resolution — the greater the resolution, the clearer the image. When closely viewed, the screen pixels may become individually recognizable. Unless this was done to achieve a particular effect, the resolution needs to be increased, meaning, for close viewing, pixels need to be smaller and more closely aligned.
With LEDs, physical limitations say how small each pixel can be, while still generating sufficient and consistent light for the display image. Today, the smallest available pixel pitch (the space from one pixel center to each adjacent pixel center) is 1.8mm. Although this is extremely tight, it’s insufficient for many close-viewing applications. Likewise, for most applications, the cost of close- resolution LED displays isn’t justifiable.
The world’s first, liquid-crystal display (LCD) color television was produced in 1985. As with many technologies, the development cost impeded the product from reaching its potential until the mid-2000s. In 2007, LCD systems became the most widely sold television format, resulting in production-related price reductions, which, in turn, expanded the development of commercial applications.
As digital-signage networks came into existence, LCD displays became the de facto vehicle for such applications. However, as many LCD networks began to spill over into outdoor environments, sellers learned that unaltered systems were incapable of competing with sunlight.
Unlike LED-lamped systems that emit light, the LCD system doesn’t produce light in any form. It requires illumination from either the front or the rear to produce an image. Earlier LCD televisions used cold-cathode fluorescent lamps, equipped with diffusers and polarizers, to create and distribute the face illumination. The process required a bulky and expensive inverter that converted voltage to a level necessary to operate the fluorescent lamps.
The latest technological iteration uses white LED lamps distributed along the display edges, with a diffuser in place that evenly distributes the light. Because LED lighting is less costly and more space confined than the earlier fluorescent systems, modern LCD displays are produced in thin cabinets at a lower price.
Outdoor LCD-technology applications suffer from numerous problems. The most notably are insufficient illumination, temperature control and water-related electrical problems. These issues are similar to those found in early LED technologies.
In recent years, some companies have created specialty products by modifying LCD technology with various illumination enhancements, and special enclosures that control heat and seal against water penetration. The first of these products were small, with modest gains in illumination. Soon after, however, a few companies began to experiment with large-format solutions.
One such pioneer was Troy Dodson. In 2004, he purchased open-frame LCD televisions from Samsung, and added an array of proprietary fluorescent lamps and upgraded power supplies, to produce the Suncutter display product. Suncutter’s LCD-based signs were successfully installed in numerous applications and fared reasonably well as “trail-blazing” technology. However, the displays suffered from heat buildup and water-incursion problems, especially when unknowing installers drilled into the cabinetry to provide connection points.
Ultimately, Suncutter replaced the fluorescent illumination with LEDs, to reduce the cost, maintenance and heat factor. All following providers use white LEDs as the light source.

LCD displays as signs
Today, outdoor-brightness LCD screens are viable for various, programmable sign applications. Because the price point is significantly less than high-resolution LED systems, the LCD products make sense where high-quality images are required for close viewing.
But, make no mistake — the outdoor LCD products are not as mature as standard LED systems. Further, innate challenges exist that cannot be overcome — primarily, the glass that comprises the face.
Glass is heavy. Consequently, the weight of an LCD display may be a consideration for delivery and installation. For example, an outdoor-use, single-face, 80-in.-diagonal LCD display will weigh approximately 850 lbs.
Unlike traditional sign measurements, LCD display sizes are quoted in the television vernacular of diagonal length, so another issue is size and aspect ratio. Because few manufacturers produce LCD glass, limited sizes are available; most choices reside in the 16:9, high-definition television-aspect ratio. Available LCD display sizes range from 32 to 80 in. (diagonal).
Heat is an enemy of liquid crystals. In LED-lamped, backlit displays, one challenge is to configure a heat-synch solution into the lighting source. Air conditioning units may be used, but they are cost prohibitive and cumbersome. In such hot climates as Las Vegas, the combination of internal heat and solar gain can cause an isotropic reaction in the LCD, which manifests itself as a black spot at the hottest location. If the heat persists, the black spot will expand across the entire screen. While this doesn’t permanently damage the display, it renders it temporarily useless.
The reflective nature of glass causes another outdoor LCD difficulty. Although many providers offer reflection-resistant materials, the reflective issue isn’t eliminated. Reflected whites are a particular problem.

When to use LCD instead of LED
Dozens of applications for programmable signs in outdoor environments exist. An outdoor-advertising firm that wanted to incorporate digital advertising in bus shelter signage sparked my first concern. Although an LED system was the logical solution in terms of size, flexibility and brightness, the resolution was insufficient, and the cost couldn’t be justified.
Since that time, more than 1,000, high-brightness LCD displays have been placed in commercial environments. However, the lingering issue is aspect ratio. A traditional, bus-shelter sign is approximately 45 x 60 in. The nearest LCD option is a 72-in. screen that becomes a 62.75 x 35.3-in. sign (16:9 aspect ratio). A lesser-sized, 65-in. screen falls short at 56.65 in. high. Be aware that both aspect ration and cabinetry can change such dimensions.
Many other applications offer more size flexibility. Environments where pedestrians approach a facility are logical applications, for example, as are entrances to casinos, movie theaters, retail centers and convenience stores. Further, amusement parks, outdoor sports facilities and settings adjacent to ticket windows provide important visual-communication locations that are best served with LCD-based signs.

LCD outdoor display providers
LCD-based sign screens are in development stages at many companies. While researching this column, I discovered numerous firms have entered the market, but with residential-type products. Note that commercial-use products require robust lighting technology, plus durable power supplies, efficient cooling and industrial-grade cabinetry.

Companies that market commercial, outdoor LCD products:
DynaScan (www.dynascanusa.com).
Manufacturing Resources Intl. (www.mri-inc.net)
Global Display Solutions (www.gds.com)
Suntronics (www.suntroniclcd.com)
YESCO (www.yesco.com/lcd/outdoor)

 

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