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."