This 27’ tall x 48’ wide LED display scoreboard is an integral part of the game presentation at Milwaukee’s Miller Park.

The history of large-screen display technology is littered with the remains of companies that were certain they had invented “the better mousetrap” with such technologies as hybrid liquid crystal light valves (too unstable and complex), laser CRT projection (which works great in the lab, but…), and analog micromirror imaging (it's not digital).

The struggle continues with existing technologies. In early January, an auction notice crossed my desk informing me of how I could participate in a web auction to bid on the assets of Colorado Micro Displays/Zight, a bankrupt manufacturer of liquid crystal on silicon (LCoS) imaging panels. Other LCoS fabricators continue to fight low yields and financial pressures.

So what is the next big thing in large-venue imaging? Turns out that the biblical saying “the meek shall inherit the earth” isn't too far off. We need to look no further than the light-emitting diode (LED).

LEDs have been around for more than 30 years. This simple junction semiconductor emits continuous light when current flows through its junction at a low voltage. By itself, an LED is quite useful as a power-saving indicator lamp. It is bright, has a fairly wide viewing angle, and can be arranged into matrices to display text, numerals, and even crude pictures.


An LED wall is made of building blocks, small matrices of LEDs — red, green, and blue -— that make up individual pixels.

LEDs also come in a variety of colors, including red, green, and blue — the building blocks of any color imaging system. So how, exactly, can we incorporate them into a display capable of fast refresh rates — fast enough to show SDTV and HDTV?

The answer is to think digital. By employing a pulse-width modulation (PWM) technique, we can switch diodes on and off fast enough to create grayscale values of R, G, and B. Because LEDs have a quick response time and no perceptible lag, PWM should and does work very well with LED imaging, making it possible for LEDs to follow the 30Hz or 60Hz refresh rates required by video. In fact, they can be refreshed several times faster, from 300Hz to 400Hz, if needed, to eliminate picture flicker and allow the display of rapid motion.

The next problem is light output. LEDs are certainly bright enough on our VTRs and cameras. But are they bright enough to use on an outdoor billboard? This task might seem impossible unless we think in terms of LED building blocks — small matrices of LEDs that make up individual pixels. Such matrices would have at least a pair of green and red LEDs, plus a single blue LED. Or it might be expanded to have three red and three green LEDs, and a pair of blue diodes.

These individual matrices are a lot brighter than individual diodes, and make up a much larger pixel, one that appears very coarse to us as we view the LED display up close. The effect is like looking at a magazine photo with a magnifying glass. If you get close enough, all you see is the dot screen and not the image.

Because we have better alternatives for viewing electronic images up close, let's back off, say 20 or 30 feet, and take another look at our LED matrix. Now it appears to be more a large pixel than a collection of dots. Stand even further back and all of a sudden the display takes on the characteristics of a large video screen. We don't see the LED matrix structures as much as we notice the images they form.


A behind-the-scenes look at an LED matrix located at the Baltimore Ravens’ football stadium.

That's the key to using LED displays. They aren't intended to replace small-screen imaging. Rather, they are aimed at larger-than-life electronic displays, particularly those that must work under unforgiving ambient lighting. Typical applications would be at tradeshows, along highways, and in stadiums and arenas under full daylight or nighttime lighting.

What about color fidelity? It's better than you might think. The high refresh rate employed with LED displays allows for a wide color palette. Currently, the industry seems to be hovering around a 1.07 billion-color palette, which is defined as 1,024 colors per channel (or 1,024 shades each of red, green, and blue). This 10-bit color palette far exceeds that of any RGB imaging device, with the exception of specialized electronic cinema projectors. And the displayable RGB color gamut is much larger than NTSC or HDTV gamuts.

The Nuts and Bolts

LED displays are usually manufactured in tiles. Each tile might measure 40in. or so on a side and will contain rows of the pixel matrices described above. Low-voltage drivers for each pixel within the matrices are connected by a simple row-and-column system, similar to that used with plasma panels and older passive-matrix LCD displays. By simply applying a voltage on a given coordinate, the appropriate color LEDs within that pixel will fire.

The resulting panel is quite compact, similar to the individual tiles in a drop ceiling. Also, the tiles aren't very thick. A typical LED tile will have similar dimensions to a plasma monitor, so you can easily fly, hang, or flush-mount LED displays. If individual pixels happen to fail, they can be pushed out the front of the panel and replaced with another pixel. Weatherproof sealants around the pixel face keep the electronics high and dry under the harshest weather conditions.


This curved, interactive LED display from Smartvision is one of 20 major attractions in this New York Toys R Us superstore.

The effective pixel pitch of a tiled display depends on the number of LEDs and their size, plus the diagonal measurement of each RGB diode grouping. They can resemble the face of playing dice. Smaller pitch sizes, such as 4mm, 6mm, and 8mm, are used for displays with close-up viewing, while larger-pitch 10mm, 15mm, 20mm, and even 40mm matrices are reserved for super-large screens with long viewing distances.

Brightness is proportionate to pitch. Panels sized 4mm will carry specifications of 700cd/m2 to 1,000cd/m2 (candelas per square meter), while 8mm panels can deliver from 1,000cd/m2 to 1,200cd/m2. If you are interested in more light output, you can get up to 6,000cd/m2 from 25mm, 30mm, and 40mm pixel arrays. That makes for a blinding display and, certainly, one that's impossible to miss.

Achieving those brightness levels with tiled rear-projection cubes is possible, but requires more space and doesn't always work under high-ambient lighting. Front projectors are at an even bigger disadvantage — light spilling on any imaging surfaces degrades contrast and raises black levels too high. Plus, projectors require a two-piece install with the screen, making the job more complex.

LED displays are always driven with progressive-scan signal sources, most often converted to SVGA (800×600) resolution. Scan converters and scalers are employed downstream from all video and RGB sources to provide constant output. So, all mixing, dissolve, wipe, and superimposition effects happen just as they would with interlaced and progressive-scan video.

LED displays are scalable. You can make them as big as you wish, and there have been some monster LED arrays constructed for public-display applications. One installation I visited a few years back was in the stadium where the NFL's Baltimore Ravens play their home games. This stadium featured a pair of 25'×100' LED tiled displays (4:1 aspect ratio) at both ends of the stadium.


Milwaukee’s Miller Park is one of several professional sports stadiums to feature large LED video displays.

The Ravens media staff produced live coverage of games with a full production studio that would be the envy of any remote crew. Standard 480i cameras were run in 16:9 mode to provide the widescreen images, and a marked reticule in the viewfinder indicated the “safe” 4:1 area for action. Downstream scalers converted the main 480i feed to 600p to drive the LED walls. The display was quite impressive even in full daylight (more than 20,000lux).

LED installations usually incorporate some sort of ambient light sensors. There's no reason to run a panel at full power when ambient light levels are low. Super-bright LED displays also are hard on the eyes in darkened rooms. Similar technology can be found in plasma monitors, but they aren't capable of producing anything near the levels of an LED matrix without first going up in flames.

Who's Got Them?

The market for tiled LED displays has really taken off in the past five years. Some of the major players in LED include Barco, Lighthouse Technologies, Smartvision, Daktronics, and Electrosonic. The differences from one product to another aren't substantial (an LED is an LED, after all) and lie mostly in the size of the individual tiles and the number of LEDs in each pixel matrix.

Stadiums and arenas are obvious choices for LED displays, but LEDs also are gaining popularity in public concourses and malls. Themed retail stores are installing LED displays to pull shoppers in the door and keep them there. Live entertainment venues have hopped on the bandwagon with numerous touring musical acts using static and dynamic LED set pieces, including one that actually separated in half during the show.

Smartvision recently built a 9'×48', 15mm curved interactive LED display for the exterior of a new 110,000-sq.-ft. Toys R Us superstore located on Broadway in New York City and occupying the facade of an existing movie marquee approximately 13ft. off the ground. The display is divided into two sections. The smaller of the two sections is 9' tall × 16' wide facing uptown and the larger is a curved 9' tall × 32' wide section facing downtown. Show & Tell Productions of Manhattan will be developing and producing programming software and content for this display.


Nasdaq Marketsite Tower’s curved, exterior LED display by Smartvision features a radius of 45ft.

Phil Lenger of Show & Tell says, “We are very excited to be working with such a versatile display and intend to use it to its full potential to engage Toys R Us customers — both inside and outside the store.” Examples of interactive content include showcasing live events in the store, promoting special events, Toys R Us branding, toy trivia, movie trailers, and even a realtime “stock ticker” of major toy stocks written in crayon. The Smartvision LED display is one of 20 major attractions contained in the 110,000-sq.-ft. flagship toy store.

The Toys R Us display is one of several curved, LED installations that Smartvision has completed recently. Perhaps the most famous is the Nasdaq Marketsite Tower display, which has a 45ft. radius. Another is a convex and concave display for Paul Allen's Experience Music Project Museum in Seattle, which possesses an even tighter curve.

In 2001, Smartvision installed a 27' tall × 48' wide LED video display at Miller Park in Milwaukee, which is often described as the most technologically advanced, aesthetically appealing ballpark in the world. The 270×484-resolution display contains 653,400 pixels using a 30mm dot pitch and is specified to deliver 5,000cd/m2. According to Smartvision, the screen is bigger than a standard basketball court.

The Miller Park screen will be fed by a combination of SD video and SVGA graphics sources. “It's going to be a big part of the game presentation at Miller Park,” said Michael Bucek, vice president of New Ballpark Development. “That's not something our fans are used to seeing. The clarity on this board is incredible. It's like watching television in somebody's house.”


Barco plans to include a mix of indoor and outdoor LED video displays for Reliant Stadium in Houston, the first retractable-roof NFL football and rodeo stadium.

Barco will install a mix of seven indoor and outdoor LED video displays at the new Reliant Stadium in Houston, the first retractable-roof NFL football and rodeo stadium, in time for its September 2002 opening. The stadium will also host the Houston Livestock Show and Rodeo and the 2004 NFL Super Bowl. The stadium's highlight will be a pair of 27' tall × 96' wide DLite 14mm LED displays for the north and south end-zones. These displays, which are configured in an unusual 32:9 aspect ratio, will be able to display two full-resolution, high-definition 16:9 aspect ratio images side-by-side, as well as a single 32:9 aspect ratio image.

In addition, Barco will hang four 7'×12' ILite LED displays to be located on the club-level areas of the stadium and one DLite 14 LED display in the Bud Plaza for pre- and post-event activities. Images will originate from an HDTV-capable production studio, feeding signals first as SD-SDI and then moving to HD-SDI with 10bit signal processing. Sources will include Digital Betacam, HDCAM, and servers, and all image processing and scaling will be performed in a Barco D320 digitizer.

Steve Patterson, executive vice president for the NFL's Houston Texans, says, “In replacing the Astrodome, the eighth wonder of the world, we felt we needed to create a video presentation that would wow our patrons with 21st century technology the way the Astrodome impressed Houstonians in the 1960s. Barco's video displays and projectors will provide that ‘wow’ factor for us.”

LED screens' ample brightness, wide viewing angle, and performance in less-than-ideal lighting make them a wise choice for large-venue displays — from tradeshows to outdoor billboards to football arenas. It definitely seems as though this 30-year-old technology has found its niche in the 21st century.


Peter Putman, owner of ROAM Consulting in Doylestown, PA and author of The Toastmasters Guide to Audiovisual Presentations, reviews large-screen displays and computer/video interfaces. He is also Senior Contributing Editor for Video Sytems and Sound and Video Contractor.

SIDEBAR

Lighthouse Technologies Blitzes Detroit Auto Show


LED screens are a solution for auto shows, environments where high-ambient lighting is the norm.

The automotive industry has always been quick to adopt the latest electronic display technology for tradeshows and January's North American International Auto Show (NAIAS) in Detroit was no exception. At the show, 15 different automakers used a total of 22 Lighthouse LVP1010 indoor LED screens (10mm pixel pitch, 1000nits brightness). Creative Technology, a United States- and U.K.-based rental and staging company, provided Lighthouse screens for Ford, Volvo, Jaguar, and Mazda at NAIAS.

Performance AV of North Carolina, Video WallTronics of Delaware, and Alternative Video Solutions of Minnesota rigged a complex Lighthouse screen array for Dodge. Michigan's Blue Water Technologies designed screens for GM, Chevrolet, and Pontiac.

Other rental operators with Lighthouse screens included ICT of Germany (BMW, Mini, and Mercedes), Modular Display Systems of California (Suzuki), and Media Rent (Audi). The Audi installation featured three screens in 7×6, 9×12, and 9×9 matrices, all moving on independent tracks.

The Creative Technology LED walls were set up in a variety of matrices from 5×5 to 6×8, and video sources for all of them were mastered in Digital Betacam and played back from a Doremi hard drive. Live video coverage of press events employed a portable production unit with a Grass Valley switcher and four Sony cameras. According to Guy Mapley, located in Creative Technology's London office, “Indoor LED screens are the best solution for displaying large electronic images in high-ambient light environments, such as auto shows. They allow lighting designers to concentrate on lighting the cars and not be worried about ‘washing out’ the video screen — an all-too-frequent problem with older technologies, such as videowalls and projected video images.”

For the American Suzuki booth, Modular Display Systems designed a special shock-mounted shipping cart for the LED panel assemblies, which also acted as an intermediate stand for the screen's setup. Modules were pre-wired and assembled before shipping to make the unit truly plug and play. Modular Display Systems' Randy Nelson says, “We effectively converted the standard large-screen LED screen modules into a single large screen for speed and ease of setup, to reduce truck space and cut setup time to a matter of minutes.”

Video sources for the Suzuki LED screens included prerecorded analog and Digital Betacam video clips mastered to DVD, and live feeds from cameras. The Lighthouse Image Processor and a Snell & Wilcox digital video scaler were used to seamlessly mix the video clips, which were mastered at different aspect ratios and sizes.
PP