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Times Square Sign Uses 12 Million LEDs
Low-cost LEDs enable video operation on a grand scale
Charles J. Murray, Senior Technical Editor -- Design News, October 13, 2008
The sign's statistics are almost unimaginable: 16 miles of electrical cable; six miles of structural steel; half a million nuts and bolts. It stretches to a height of 340 ft, wraps around three sides of New York City's One Times Square building and takes up about as much space as 60 regular-sized billboards.
And, oh, it uses 12 million light-emitting diodes (LEDs). Yes, LEDs — those miniscule lamps commonly used in big screen TVs and Christmas lights. But here, they're illuminating an electronic billboard that covers nearly 16,000 sq ft.
Moreover, they're changing the face of multi-story building architecture by breathing life into one very large, very inanimate object. Gilmore Group, the New York-based designers who laid out the concept, sought to deliver an air of energy to One Times Square.
“They envisioned a building that would come alive with choreographed, inter-linked animations,” says Meric Adriansen, founding partner of D3 LED, the digital display engineering firm that turned the design in a technological reality for Walgreens Co. “All of the sides work together and the whole building lights up with color.”
When the “Walgreens' sign” lights up for the first time this fall, however, its engineers will know one big secret about the 30-story LED billboard: It's incredibly complex. Synchronizing 12 million LEDs on three sides of a skyscraper and displaying coherent animations requires more than the flip of a switch. To make it work, engineers had to choose the right LEDs, keep costs and power under control and develop a system that enables 20 computers to “talk” to 10,000 electronic modules at gigabit speeds.
“The Walgreens' sign had some incredible challenges as far as technology is concerned,” Adriansen says. “You have to remember: This isn't a still photograph. You've got all these controllers talking to the electronics and you're displaying an animation at 30 frames per second.”
Balancing the Budget
Luckily for D3 LED, the company designed big LED-based signs before, albeit none as gargantuan as the Walgreens' model. A year earlier, it completed a 3,200-sq-ft “super sign” for the American Broadcasting Co. (ABC), also in Times Square, which used 2 million LEDs in a complex pattern of curves.
“Typically, when you finish a sign like that one, you figure your glory will last for at least three or four years,” Adriansen says. “But a month after we finished, the Walgreens' job came along and suddenly we had to beat the ABC sign in technical sophistication, and deal with the fact that the new sign would be at least four times as large.”
While the ABC sign was far smaller than the Walgreens' version, it provided valuable lessons. Most importantly, it taught D3 LED engineers that the signage game was quickly changing. Because the cost of LEDs was dropping so fast, the company found it could push the technological envelope in ways it couldn't have only a few years earlier. Engineers learned they were able to quintuple the dot pitch (distance between LEDs) without raising the price. As a result, they could achieve a 25-fold increase in LEDs (five times in the vertical and horizontal directions), which, in turn, meant the display's resolution could be far greater.
On the Walgreens' sign, they quickly put those lessons to work. The sign, which consists of smaller main screens flanked by two giant slash-shaped displays on the building's sides, called for an entirely different design perspective. Teaming with Nichia America Corp., D3 LED engineers laid out a plan to vary the dot pitch and brightness of the devices at different locations around the sign. Near the top of the display, more than 300 ft above street level, they employed the brighter Nichia Super Oval 546 LEDs at a dot pitch of 24 mm. In the middle, they used Super Oval 346 LEDs at 12 mm and at the bottom, they wrapped the building in Nichia's 026 LEDs at dot pitches of 6 and 10 mm. In essence, they were trading resolution for brightness as they moved up the building.
Nichia engineers say LED brightness is an important factor for the sign, especially over time. “These displays run five, seven, even 10 years,” says Hideki Kaneguchi, a senior manager for Nichia America Corp. “Initially, the brightness isn't so important. But every year, the brightness can go down. So, generally speaking, the brighter the LEDs, the better.”
Still, budgetary constraints prevented design engineers from universally selecting the best and brightest devices at every level of the sign. “At the top, we wanted to keep the brightness up, so we went with a brighter diode,” says George Pappas, managing partner of D3 LED. “But we didn't need the higher resolution up there. When something is that far away, you could have a 12-mm or a 24-mm pitch and your eye wouldn't be able to tell the difference.”
“On the Walgreens' sign, we wanted to create an absolutely spectacular display with incredible resolution,” adds Adriansen. “But at the same time, you still have to make the project fit in terms of budget, so the viewing distances come into play.”
Quest for Low Power
For designers, however, the greatest challenge may have been animating the giant sign. To do that, they employed 15 x 15-inch electronic modules and placed them throughout the display. In all, they installed 10,987 modules, each containing between 1,024 and 1,600 pixels, for a total of approximately 12 million LEDs.
All of the modules are controlled by a bank of 20 to 30 computers located in the sign's command center. Xilinx field programmable gate arrays (FPGA), each with their own IP addresses, serve as the controllers for the individual modules. The FPGAs communicate with the command center across miles of Gigabit Ethernet cabling. In all, an HD video can move about 150 Gbytes of data across the Ethernet pipes during the playing of a 30-sec video, engineers say.
“When you add everything together, you end up with an animation that requires tremendous data throughput,” Adriansen says. “You have huge files and lots of pixels and you need to have a way of handling it all.”
Moreover, engineers needed a way to deal with the power issues.
“Our initial calculation was about 1 megawatt of power,” Adriansen says. “But early on, we discovered that there was not that much power available in the building. So we spent a lot of time and engineering effort figuring out how to create a sign that would be more economical and could live within the building's power parameters.”
The main way of accomplishing that was to boost the voltage of the power supplies from 208 to 265V. By doing that and making other power adjustments, they lowered the power requirement to 350 kW and were also able to reduce the size of transformers and cables used throughout the building.
“It really turned out to be a huge economical boost to run the displays at 265V,” Adriansen says. “It's unheard of to be able to run a sign this size at 350,000W.”
'Getting Better and Better'
Construction of the sign spanned the spring and summer, performed mostly on weekends after midnight. In all, the display required 20 tractor-trailers carrying 250,000 lb of steel and electrical apparatus, not to mention the 12 million diodes.
“It was so big that installers had to have permits to block off the street and use a crane, and the only time they could do the construction was after midnight.” Pappas says. “Nothing like this had ever been done before.”
D3 LED engineers say nothing like it could have been comprehended a decade ago. Back then, D3 LED built an LED-based sign for ABC that used less than a half-million diodes in combination with slower, lower-bandwidth data pipes. The idea of running HD video on a 16,000-ft screen was unimaginable.
“Fifteen years ago, a blue diode was a dollar,” Pappas says. “Six or seven years ago, Ethernet wasn't available for this type of application. Now the diodes are a fraction of the cost and we're using Gigabit Ethernet.”
The next step could be wireless, Pappas says. With wireless speeds climbing and LED prices still dropping, engineers could employ more devices and not have to worry about making connections via physical cabling.
“The sophistication is very high today,” Pappas says. “We know that we need to stay on the cutting edge of this because it's just going to keep getting better and better.”
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Times Square Sign Uses 12 Million LEDs
