Behind the Scenes of a High Tech Bridge Lighting System

The historic Blatnik Bridge was outfitted with a state-of-the-art bridge lighting system that makes a show-stopping statement on the skyline while reducing energy consumption by 60 percent. How did they design it?

The John A. Blatnik Bridge has been safely carrying travelers over the scenic St. Louis Bay between Duluth, Minnesota, and Superior, Wisconsin, since it opened in 1961.

After more than 50 years of service, the Minnesota Department of Transportation (MnDOT) embarked on a multi-year bridge rehabilitation project, which included replacing the existing lighting system along the 1,140-foot-long main truss span.

The old system had ever-increasing maintenance costs. So MnDOT required a lighting design that provided minimal maintenance and had maximum aesthetic appeal. They were able to accomplish this feat with a state-of-the-art LED system that uses only 92 luminaires.

Infographic of bridge lighting design

 

Designing a low-maintenance bridge lighting system that shines

With the previous lighting system suffering from significant maintenance issues — conduit falling off the structure, many luminaires broken and inoperable — MnDOT wanted a system requiring minimal upkeep.

“MnDOT challenged us to provide a cost-effective, low-maintenance lighting design that still provided aesthetic appeal,” says Ken Taillon, SEH lighting design specialist and project manager.

For Blatnik Bridge, this translated into:

  • Using long-lasting LED luminaires.
  • Employing a dimmable lighting control feature.
  • Protecting the luminaires and electrical distribution system from the elements.
  • Using robust materials and installation methods.
A 3-D model of the Blatnik Bridge lighting system.

LEDs are the logical choice

As recently as five years ago, LED luminaires were still evolving. Not only were they often prohibitively expensive to implement, but they lacked the light output necessary for most projects.

Today, however, LED lighting has significantly lowered in cost and yields many other advantages that make them a logical choice for nearly every project.

How much better are LEDs?

“A typical LED luminaire should operate effectively for at least 100,000 hours, equivalent to about 22 years of actual use,” says Taillon.

The high-performance 140-watt LED luminaires used on Blatnik Bridge have a light output of 10,000 lumens. Compare this number to an average household 60 watt incandescent bulb, which has an output of 800 lumens, and you quickly see how efficient the lighting system is on Blatnik Bridge.

By using high-output, low-energy LED luminaires, combined with proper placement, the design team was able to reduce the total amount of luminaires from 216 to only 92.

LED luminaire for bridge lighting design
Before and after: 216 traditional luminaires, many broken or damaged (left), were replaced with 92 energy-efficient LED luminaires (right).

“Soft on, soft off” system saves more energy

It’s fundamentally simple. Turning lights off saves energy.

A typical roadway lighting system reduces energy consumption by automatically turning luminaires on at night, then off during the day.

However, there is a missed opportunity here because these lamps are either completely on or completely off.  In reality, a luminaire doesn’t need to be as bright during dusk and dawn as it does at night.

“When lighting infrastructure, we don’t want to see the lights, necessarily. We want to see what the lights illuminate. At dusk or dawn, that simply doesn’t require as much light,” says Taillon.

This is why the Blatnik Bridge lighting system has a customized “soft on, soft off” system that accommodates real-time lighting needs. By employing a dimmable lighting control system, lights come on slowly in the evening and gradually increase to 100 percent as it gets darker.

As a result, the bridge gets the right amount of light when it needs it. This approach both stretches the luminaires overall lifetime and reduces daily energy cost.

Location, location, location

Changing a light bulb is a nuisance, even in your home. Now put that same light bulb hundreds of feet in the air, and add about one hundred more. At such a scale, paying staff to change lamps on a bridge like Blatnik could require a significant investment of time and money.

LED bridge lighting system for John A. Blatnik Bridge
Lit from within: The old lighting system (inset) had “outline lighting.” When a lamp went out, you knew it. The new system (outset, photo credit LumenPulse) achieves its signature look by placing luminaires within the skeleton of the bridge, which also protected the luminaries from the elements.

On Blatnik Bridge, long-lasting LEDs eliminate the need to replace old lamps, but the harsh Minnesota climate adds another challenge.

In northern climates, where snowfall, ice, slush and salt (called “spray”) can cover the surface of luminaires and significantly reduce the brightness, keeping luminaires clean can be labor intensive.

The team solved this challenge by putting luminaires inside Blatnik Bridge and pointing them outward. This unconventional approach accomplished two separate feats.

First, it gave the bridge its signature glow-from-within. Previously the lighting system had what is called “outline lighting.” The lights were placed on the outside of the bridge and only visible from a distance. Lit from within, the bridge not only looks great from a distance, but you can experience the bridge and its lighting design as you drive over it.

Second, by placing the luminaires inside, the bridge’s infrastructure acts as a shelter that protects them from the elements, thereby reducing maintenance.

Bridge lighting design for John A. Blatnik Bridge
Lit as predicted: Prior to installation, a lifelike rendering (left) of the Blatnik Bridge lighting design was shown to stakeholders, which  was nearly identical to what it would look like In real life (right, credit LumenPulse).

Long-lasting materials, durable installation

On any project, materials and installation can make a significant difference in quality of the end product. A galvanized steel bracket will do a better job than a twist tie. The Blatnik Bridge lighting system was built with this philosophy.

Special attention was directed toward installing a robust electrical distribution system and conduit. Conduit in the previous system was embedded within the structure, which made it difficult to access wiring in need of repair.

The new system is not embedded, but rather bolted on the exterior where it is easily accessed if maintenance needed. Finally, where conduit in the spray zone suffered from corrosion under the previous system, the new system employs custom-designed PVC-coated galvanized steel conduit to protect against spray in critical locations.

Conclusion

By designing for maintenance and energy consumption first, and reducing the amount of luminaires from 216 to 92, the bridge lighting system for the Blatnik Bridges still makes a strong statement on the skyline, but with a significantly smaller environmental footprint and lower maintenance and energy costs.

About the Expert

Ken Taillon

Ken Taillon is an electrical and lighting design specialist with experience in a wide variety of outdoor lighting projects for government agencies across the upper Midwest. Ken’s work focuses on roadway lighting for state highways, commercial and residential areas, downtown streetscapes, and lighting for parks, parking lots and sports facilities. His areas of expertise include lighting planning and policy development, design, specifications, construction observation, equipment photometric and mechanical evaluation, intelligent lighting management systems, solid state (LED) lighting equipment, and addressing operation and maintenance issues. Contact Ken

The Blatnik Bridge lighting project was recently featured in Architectural SSL magazine. Click here to read more.

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