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Jumbo Screens

There are two big differences between a jumbo TV screen that you see at a stadium and the TV in your home:

• Obviously, it is gigantic compared to your TV. It might be 60 feet (20 meters) high instead of 18 inches (0.5 meters) high.
• It is incredibly bright so that people can see it in sunlight.

An outdoor jumbo TV screen in Shibuya, Japan

To accomplish these feats, almost all large-screen outdoor displays use light emitting diodes (LEDs) to create the image.

LEDs are, essentially, little colored light bulbs. Modern LEDs are small, extremely bright and use relatively little power for the light that they produce. Other places you now see LEDs used outdoors are on traffic lights and automobile brake lights.

On a color CRT television set, all of the colors are produced using red, green and blue phosphor dots for each pixel on the screen:

In a jumbo TV, red, green and blue LEDs are used instead of phosphor. A "pixel" on a jumbo TV is a small module that can have as few as three or four LEDs in it (one red, one green and one blue). In the biggest jumbo TVs, each pixel module could have dozens of LEDs. Pixel modules typically range from 4 mm to 4 cm (about 0.2 to 1.5 inches) in size.

To build a jumbo TV, you take thousands of these LED modules and arrange them in a rectangular grid. For example, the grid might contain 640 by 480 LED modules, or 307,200 modules. The size of the ultimate screen depends on the size of the LED modules:

To control a huge LED screen like this, you use a computer system, a power control system and a lot of wiring.

• The computer system looks at the incoming TV signal and decides which LEDs it will turn on and how brightly. The computer samples the intensity and color signals and translates them into intensity information for the three different LED colors at each pixel module.

   

• The power system provides power to all of the LED modules, and modulates the power so that every LED has the right brightness. Turning on all of those LEDs can use a lot of power. A typical 20-meter jumbo TV can consume up to 1.2 watts per pixel, or approximately 300,000 watts for the full display.

   

• Several wires run to each LED module, so there are a lot of wires running behind the screen.

As LED prices have dropped, jumbo TV screens have started to pop up in all sorts of places, and in all sorts of sizes. You now find LED TVs indoors (in places like shopping malls and office buildings) and in all sorts of outdoor environments -- especially areas that attract lots of tourists.