Buzz
Large screens like these are commonly seen in sports stadiums around the world.If you've attended a live sporting event with a giant screen in the venue, you've experienced the incredible and massive displays that make following the action a breeze. These screens show instant replays, player highlights, and close-ups. You can also find such giant screens at race tracks, concerts, and major public spots like Times Square in New York City.
Ever wondered how they manage to build a television that towers at 30 or even 60 feet (10 to 20 meters)? In this article, we will explore the LED technology that makes these enormous screens a reality!
Understanding the Signal
A jumbo TV that stands 60 feet (20 meters) tall operates in the same way as a regular television set -- it takes a video signal and turns it into light points. If you're familiar with How Television Works, you'll know that a television using a cathode ray tube (CRT) achieves this. Here's a brief summary of how an old black-and-white TV functions:
- The electron beam in a CRT scans the screen line by line. As it travels, the beam excites small dots of phosphor, which then emit light visible to the human eye.
- The video signal directs the CRT beam to adjust its intensity as it moves, as shown in the diagram that follows, which illustrates how the video signal conveys intensity information.
- The initial pulse of five microseconds at zero volts (the horizontal retrace signal) signals to the electron beam that it's time to begin a new line. The beam starts at the left side of the screen and races across in 42 microseconds. The voltage fluctuations after the horizontal retrace signal adjust the beam's brightness as it sweeps across.
- The electron beam paints lines down the CRT's face and then receives a vertical retrace signal to return to the top right corner and start again.
[A color screen works in a similar way, but uses three distinct electron beams and three phosphor dots (red, green, and blue) for every pixel on the screen. A unique color signal tells each pixel's color as the electron beam moves across the display.]
As the electron beam moves across the screen, it strikes the phosphor with electrons. These electrons excite tiny dots of phosphor, causing the screen to light up. By rapidly painting 480 lines on the screen at 30 frames per second, the TV screen ensures that our eyes perceive everything as a smooth moving image.
CRT technology performs well indoors, but once you move a CRT-based TV outdoors into bright sunlight, the display becomes unreadable. The phosphor on the CRT just isn't bright enough to rival sunlight. Additionally, CRT displays are restricted to a maximum screen size of around 36 inches. To create a large outdoor screen that can match sunlight's brightness, a different technology is required.
Giant Screens
An outdoor jumbo television screen located in Shibuya, JapanThere are two major differences between a jumbo TV screen found at a stadium and the television in your living room:
- Clearly, it is enormous compared to your home TV. It could stand 60 feet (20 meters) tall rather than a mere 18 inches (0.5 meters) in height.
- It is incredibly bright to ensure visibility even in direct sunlight.
To achieve these remarkable feats, nearly all large-scale outdoor displays rely on light emitting diodes (LEDs) to generate the image.
LEDs are essentially tiny, brightly colored light bulbs. Modern LEDs are compact, exceptionally bright, and consume relatively little power for the light they emit. You can also spot LEDs in use outdoors, such as on traffic signals and car brake lights.
In a color CRT television, red, green, and blue phosphor dots are used to create each pixel on the screen:
In a jumbo TV, red, green, and blue LEDs replace the phosphor. A 'pixel' on a jumbo screen is a small module containing at least three or four LEDs (one red, one green, and one blue). For the largest jumbo TVs, each pixel module could have dozens of LEDs. These modules generally range from 4 mm to 4 cm (about 0.2 to 1.5 inches) in size.
To construct a jumbo TV, thousands of these LED modules are arranged in a rectangular grid. For instance, the grid might contain 640 by 480 LED modules, which totals 307,200 modules. The final size of the screen depends on the size of the individual LED modules:
LED Module Size 4 mm
- Screen size: 2.56 x 1.92 meters
- Screen size: 8.4 x 6.3 feet
LED Module Size 25 mm
- Screen size: 16 x 12 meters
- Screen size: 52.5 x 39.4 feet
LED Module Size 40 mm
- Screen size: 25.6 x 19.2 meters
- Screen size: 84 x 63 feet
Managing a massive LED screen like this requires a computer system, a power control setup, and a lot of wiring.
- The computer system processes the incoming TV signal, determining which LEDs to activate and how bright they should be. It samples the intensity and color data and converts it into brightness information for the three LED colors at each pixel module.
- The power system supplies electricity to all LED modules and adjusts the power so each LED has the correct brightness. With so many LEDs on, power consumption can be significant. A typical 20-meter jumbo TV can consume up to 1.2 watts per pixel, totaling approximately 300,000 watts for the entire display.
- A number of wires run to each LED module, meaning there’s a complex web of wires behind the screen.
As the price of LEDs has decreased, jumbo TV screens are now appearing in more places and in a variety of sizes. You can find LED TVs indoors (in shopping malls and office buildings) and in numerous outdoor locations, particularly in tourist-heavy areas.
