Bridge Jewelry

Feb. 21, 2003

Greg Herd likes to get a table by the window at the River Station restaurant in Poughkeepsie, N.Y., especially after dark. As dusk descends over the Hudson River, the stately Mid-Hudson Bridge comes alive with colored lights dancing along its suspension cables. But while other patrons simply enjoy the show, Herd--with a few clicks on a handheld computer--enjoys controlling it.

Greg Herd likes to get a table by the window at the River Station restaurant in Poughkeepsie, N.Y., especially after dark. As dusk descends over the Hudson River, the stately Mid-Hudson Bridge comes alive with colored lights dancing along its suspension cables. But while other patrons simply enjoy the show, Herd--with a few clicks on a handheld computer--enjoys controlling it.

As manager of Information Technology for the bridge's owner, the New York State Bridge Authority (NYSBA), Herd is chief choreographer for the dancing necklace lighting and was closely involved in the system's design. In addition to its beauty, the lighting system has the distinction of being the first application of LED-bridge necklace lighting in the U.S., and one of the first in the world. 

Lighting up a landmark

When the Mid-Hudson Bridge opened in 1930, it became a symbol for Poughkeepsie, which is 90 miles up the Hudson River from New York City. The structure is a graceful 3,000-ft-long parallel wire cable suspension bridge with a 1,500-ft main span, suspended side spans and two 315-ft-high towers. Ten years ago, the Poughkeepsie Chamber of Commerce urged NYSBA to make the Mid-Hudson Bridge an even more distinctive landmark by dressing it up with aesthetic lighting. NYSBA explored various options--weighing installation, power and maintenance costs--and eventually illuminated the towers with flood lights. It was a start, but the communities of Poughkeepsie and neighboring Highland, N.Y., wanted more. 

With strong support from Executive Director Jack Gaffney, NYSBA issued a request for proposals to develop a lighting scheme that would set the Mid-Hudson Bridge apart--and not cost too much to construct, light up or maintain. NYSBA selected Baker Engineering NY Inc., a unit of Michael Baker Corp., to facilitate the project. 

Adding color

Necklace lighting is not unusual, and even colored lights are becoming more common on bridges. Baker's challenge was to combine proven technologies to create a unique effect that was also cost-effective.

To meet NYSBA's criteria, Baker proposed developing necklace lighting using colored light-emitting diode (LED) lights instead of traditional mercury fixtures. LEDs would cost about the same to construct as conventional lighting, but their power and maintenance demands would be significantly less.  

Multi-colored LEDs also would allow spectacular light-changing effects. But while LEDs are widely used to create exciting aesthetic lighting for casinos, museums and other buildings, they had never before been used as necklace lights. LEDs are flexible and dramatic, but they can be less bright than traditional colored lighting technologies.

They're powerful enough to decorate a building facade, but the bridge towers extend 315 ft up into the night sky and are typically viewed from a distance. Since each LED fixture would put out just 250 lumens (as opposed to the 8,500 lumens of a conventional necklace lighting fixture), the team's primary concern was that the necklace lights might turn out to be dim pinpricks of color rather than the stunning jewels they envisioned.

Even in this era of computer simulation, the only way to truly gauge the effect of the LEDs was to hang a few actual fixtures on the cables, wait until dark and throw the switch. 

The LEDs looked great. During a test of six prototype fixtures the team determined that the LEDs emitted plenty of light for aesthetic purposes. Testing a few prototypes on the bridge also helped NYSBA determine the most attractive arrangement of the lights. The Mid-Hudson's vertical cables are 20 ft apart, and the original plan was to place a necklace light at the top of each cable. After seeing the test fixtures on the bridge, however, NYSBA decided that placing lights at every other cable would create a more dramatic look. 

Illuminating collaboration

The Mid-Hudson Bridge lighting scheme is the result of collaboration by industry leaders in lighting design, engineering and manufacturing. Baker facilitated the combination of technologies by Color Kinetics of Boston, a leader in intelligent LED-illumination technologies and developer of ColorPlay light show authoring software, and MagniFlood Inc., North Amityville, N.Y., a lighting developer and manufacturer well known for its expertise in necklace lighting fixture design and production. 

"Due to ongoing developments in the manufacturing processes of LEDs, brighter LEDs become available each year," explained Mike Blackwell, principal electrical engineer for Color Kinetics. "That fact, along with the development about five years ago of blue LEDs, opened up a lot of new applications for LED technology to be used as an intelligent source of illumination."

Color Kinetics has pioneered and patented an intelligent digital method of illumination, called Chromacore, that uses LEDs to generate and control millions of colors and a variety of lighting effects. Unlike traditional methods of generating colored light, this digital technology does not require filters, dimmers or moving parts, but incorporates a microprocessor to control the mixing of multi-colored LEDs to create colored light.

Although Color Kinetics had developed LED fixtures for outdoor applications, the demands on a necklace lighting fixture are much more severe than those on typical architectural lighting projects. 

"Necklace lighting fixtures are exposed to extreme conditions," explained MagniFlood President Ken Greene. "They are baked in the sun all day and are subjected to wind, bridge vibrations, moisture and pollutants from vehicles on the bridge."  

Electrostatic charges can develop in the bridge, which also can affect the fixture. The light housing must protect the LED assembly from such hazards while being easy to install and maintain by crews working high above the bridge. 

Based on extensive experience in necklace lighting, MagniFlood designed the fixture, lens, castings and power supplies to accommodate LEDs. The housing is water-resistant rather than water-tight, which allows moisture to escape. Components are coated with TGIC polyester powder to create a protective film and are electrically isolated with a nylon bushing to insulate the fixture from static charges that could build up on the bridge. Isolating the fixture also eliminates electrolytic action between dissimilar metals, which can cause severe corrosion. 

"One challenge was handling the fluctuations in the bridge's power supply," said Greene. "It varies from 200 to 260 volts AC. The lights had to see exactly 24 volts DC, so we used an electronic voltage regulating device to convert the incoming AC and regulate the output at exactly 24 volts DC."

MagniFlood's housing design is foolproof to install and easy to maintain. Because the fixtures require a power cable plus a data cable to control the lights, MagniFlood used clear male/female connections with a different size for power and data to prevent confusion, and with quick disconnects that don't require tools. If maintenance is needed, the fixture opens easily with a simple latch and components can be replaced without tools.

To further facilitate installation, MagniFlood requested that the contractor measure the distance along the suspension cable between each pair of vertical cables (which varies due to the curve of the suspension cable). MagniFlood pre-made wires the exact length needed, complete with data cable connections, and marked them according to their precise location on the bridge. Because MagniFlood has its own foundry and produces its own castings, the fixture could be designed, created and tested very rapidly--it took less than six months to move from concept to finished product.

Baker designed two 3,000-ft-long messenger cables with more than 1,000 hangers that support the power and data cables. The LED fixtures are attached to stanchions that are attached to the suspension cable. Structural engineers specified the hangers along with the steel rope used as the messenger cable. Baker's design also included power conditioning, distribution and surge protection at the power panel that provides the 24-volt power for the LED fixtures.

Digital communications

On traditional architectural lighting projects, the computer that controls the lights can be located in that very building, well within the 1,000-ft limit for copper wire. On the Mid-Hudson Bridge, however, the lights are controlled by a computer in the bridge's administration building, nearly a mile away from the bridge itself, so copper wire was inadequate. However, NYSBA had run fiber-optic cable to the bridge several years previously as part of a closed circuit television traffic monitoring project and had the foresight to install a spare fiber for future use. The team was able to use that extra fiber for necklace lighting data communications.

Using Color Kinetics ColorPlay software, light shows are developed on a PC in the administration building, then downloaded onto Color Kinetics iPlayer 2 interface, which is plugged into a USB port on the PC. Data is sent as an electrical signal to a fiber-optic modem, where it is converted to an optical signal. The signal travels by single-mode fiber-optic cable to a DMX converter in one of the bridge towers. The DMX signal, which uses the RS485 protocol, can be interpreted by the light fixtures.

The original proposal was to house the iPlayer 2 device at the base of one of the bridge towers. That would have limited NYSBA to eight stored shows, however, and would have required someone to go to the bridge to launch the shows. Controlling the shows from the PC linked by fiber optics is much more flexible and convenient and allows an unlimited number of shows to be stored. However, if a communications problem should occur the iPlayer 2 can be plugged directly into the system at the base of one of the towers.

Guiding the light

Color Kinetics ColorPlay software controls the lights and allows every imaginable color and on-off sequence, so NYSBA can program light shows to change the effect on the bridge. The lights are scheduled to come on at sunset, and the show (as it is called even if it is a subdued effect) is changed at least weekly. NYSBA lights the bridge to correspond with holidays and other special events--it was all purple when an Alzheimer's convention came to town, and it sports school colors when Poughkeepsie's Marist College has a home game.

Herd described the ColorPlay software as similar to using a CAD program. "There is a representation of each fixture on the screen," he said, "and they can be grouped any way you like--south span, east side, etc. Then you choose from a list of effects and drag the effect over a timeline. So I can easily select a rainbow effect across the entire bridge, for example, and make it fast or slow-moving." The effects can be put into a loop to run continuously. Because the LED fixtures can create millions of colors, Herd previews the colors and effects on a row of mini-fixtures he installed in his office.

Remote control

Herd's IT interest and ability have led him to develop controls for the system beyond the standard interface. He can now launch light shows from anywhere in the world--including the River Station restaurant--from his personal digital assistant (PDA) or even a cell phone. First, Herd installed a web server on the computer he uses to design and save the light shows. He then created browser-based screens to display a list of preprogrammed shows on a PDA. Using wireless remote access, he logs on to the NYSBA intranet. Then by clicking a button on the PDA, he can select and launch shows for immediate display. Similarly, by using a cell phone and entering the proper user name, password and launch codes, he can access the control computer and make real-time changes to the show being displayed.

Community support

There was widespread community support for the bridge lighting project, and NYSBA received almost no negative reactions throughout the in-depth approval process that involved 18 different environmental and historical agencies, local governments and even the U.S. Coast Guard. While a few residents questioned NYSBA's investment in a purely decorative project, the response has been overwhelmingly positive, and the project has been a source of pride and interest to the surrounding communities.

That's not the case on the Bear Mountain Suspension Bridge, about 20 miles downstream. NYSBA planned to use necklace lighting at that distinctive span too, however environmental groups were opposed to what they viewed as unnecessary light pollution in an area that wasn't already highly developed.

Bright future

While the current capabilities of the LED-necklace lighting seem remarkable, there is no lack of future developments. Herd, who has experience designing lighting for bands, is working on synchronizing the necklace lights to music. Poughkeepsie frequently has riverfront performances featuring musical groups such as the city's Philharmonic Orchestra. According to Herd, it would be possible to program the lights to respond to the music. The necklace lights could move to the beat, display in a particular way when the music reached a certain tempo or change color when the volume hit predetermined thresholds.

While NYSBA is fortunate to have the in-house expertise to expand the possibilities of their necklace lighting system, owners who aren't interested in that level of tinkering could limit the bells and whistles and just work with a simple interface. 

"NYSBA has done a lot of development beyond the initial project," explained Blackwell, "but because of the digital intelligence inherent in Color Kinetics technologies and products, it would be possible to stick with preprogrammed shows launched traditionally and still have a very nice effect." 

About The Author: Moreau is chief engineer for the New York State Bridge Authority. Ramanan served as Baker's proj-ect manager for the Mid-Hudson Bridge necklace lighting project.

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