How do you choose a panel technology for a display that's bigger--at 33 by 33 feet--than the side of a barn? The liquid-crystal and plasma technologies used in large-screen home TVs are out of the question. CRTs are out too, and organic electroluminescence doesn't even merit mention as a candidate.

There is only one existing technology that can be tapped to display images large enough for arena use and are viewable even in direct sunlight: the light-emitting diode.

Building humongous panels is very difficult. Today, the largest LCD that can be manufactured is 108 inches on the diagonal. For plasma display panels (PDPs), the largest possible screen size is 150 inches (diagonal). To go larger than that, special production equipment would have to be developed.

Projection technology might seem like a solution, but it's not. Indoors, front-projection is feasible. But in big, enclosed arenas such as those at the Beijing Olympics, the presence of competing light sources tends to dull the projected images. Naturally, things get even worse for a front projector in an outdoor stadium.

That is why Matsushita Electric Industrial Co. is installing its LED Astrovision technology in China. The Japanese consumer electronics giant will supply the Beijing Games with 25 LED Astrovision video display screens, delivering a total of almost 4,000 square feet.

Each Astrovision screen consists of hundreds of LED units in one of two sizes--7.5 x 7.5 inches or 14 x 14 inches -- arranged in a grid. Assembling 1,296 LED units in a 16:9 widescreen format, for example, creates a display measuring 551 square feet. Up to 58,000 LED units can be installed per Astrovision screen.

One advantage of the LED, a self-emitting diode, is that it's easy to increase the brightness. Astrovision's luminance is as high as 5,000 candelas/ square meter; the brightest PDP can offer only 1,600 cd/m². And the Astrovision panels are not flat, so slanting sunlight is deflected to the ground and away from the audience. That isn't possible with LCD or plasma flat panels

A display installed in an arena must be able to deliver excellent images to the audience regardless of where they sit. Here too, LED displays have advantages.

Because an Astrovision screen consists of a number of LED units, each serving as light source, it can offer a horizontal viewing angle as wide as 150°. Further, there is hardly any color degradation in images on the screen, regardless of angle. A spectator viewing a 33 x 33-foot LED display can clearly see not just moving images, but also race results and athletes' names on the screen from as far away as 656 feet.

An Astrovision screen consists of as many as 1,728 LED units, snapped into a metal latticework frame. Each unit contains a layer of LEDs in a grid of red, blue and green diodes placed at 8-mm intervals. When the screen is viewed from a distance of 10 feet, three primary-color diodes, driven together, blend to form what appears to be a full-color pixel, reproducing realistic images in vivid hues. Because each LED unit operates at 1.6 kHz, it offers a very fast response time.

For displays smaller than 23 square feet, however, LCDs and PDPs remain far more effective. Because LED panels comprise discrete arrays of individually mounted RGB diodes, they're tough to miniaturize.

By: DocMemory
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