Lighting options for roadways, tunnels and bridges
New technologies in tunnel, bridge and roadway lighting continue to surface, while existing high-intensity discharge (HID) and fluorescent technologies generate mixed reviews from lighting experts.
Glare control is critical. More emphasis is placed on color temperature because of its effect on nighttime driving. As more cities enact dark-sky ordinances, controlling light distribution to save energy and reduce obtrusive light is essential.
The lighting industry recognizes that lamp color temperature has a significant effect on perceived brightness.
“When it is very bright, such as outdoors in the afternoon, our eyes are most sensitive to amber or long wavelengths. As light levels drop, our vision becomes more sensitive to blue or short wavelengths,” said Mark Lien, accredited lighting professional and manager of The Source Educational Center for Cooper Lighting, Peachtree City, Ga.
Lien said studies performed on exterior lighting indicate at low, nighttime light levels some light sources appear brighter because of their color temperature. Metal halide (MH) lamps can appear twice as bright as high-pressure sodium (HPS) lamps at the same foot-candle level due to their white color.
Research has shown a correlation between pupil size and color temperature. The cooler light sources such as MH cause pupils to shrink more than warmer sources such as HPS.
“The smaller pupil size increases visual depth of field and visual acuity,” Lien said. “Increased depth and brightness perception can affect safety.”
The color rendering index (CRI) of a lamp can also impact our perception of brightness, and there is a linear correlation between CRI and perceived brightness. The higher the CRI of a light source, the brighter it will appear compared with another lamp of the same color temperature. Using lamps with higher color temperatures and CRI can make a project appear brighter without increasing energy costs.
When lighting tunnels, electrical contractors should evaluate the width of the tunnel first, according to Owen Shipler, GE Lighting Systems product manager. “In most cases, you cannot light more than four lanes with a wall-mounted fixture. Fixtures for tunnels wider than four lanes must be ceiling mounted. Tunnels with two lanes or less can be lighted from a single wall.”
Counterbeam lighting has reduced wattage requirements and improved visibility of objects in the roadway. Objects are in negative contrast to the driver, according to Mike Owens, lighting systems engineer with GE Lighting Systems.
“The primary tunnel light source is HID, specifically high-pressure sodium, because of high lumens per watt and longer lamp life,” Owens said. “Hot restrike for HID light sources is popular in tunnel lighting to help counteract the dark tunnel effect when power dips occur.”
Setback lighting is a good choice for roadways because it allows contractors to mount fixtures on non-breakaway poles, reducing costs as well as eliminating lane closures to cut fixture maintenance. Fixtures, such as GE’s Tiger, work well for roadway applications because they can light up to eight lanes of traffic, thereby illuminating wider roadways from one side of the road.
White light is a growing trend because the human eye perceives white light more easily in low-light conditions.
“However, if higher CRI is desired, MH lamps do not have the same life rating or efficiency as HPS lamps,” Shipler said.
Induction is another growing trend offering high CRI coupled with a 100,000-hour rated lamp. The downside is that fixtures with this technology are more expensive and require more poles per mile due to the lower wattage offering (165W maximum) and lower lumens per watt.
GE’s M400 can be used with a 100W induction lamp, thus using induction advantages while still maintaining full cutoff light distribution.
Because bridges encounter much higher vibration than typical roadways, vibration is thusly a major concern with bridge lighting.
“Bridges need fixtures that withstand at least 3G vibration ratings,” said GE’s Owens. “Another method for reducing fixture vibration is to pole-mount instead of arm-mount. Mounting a fixture to a pole-top tenon dramatically reduces fixture vibration.”
Full-cutoff distributions have become widely accepted because of growing concerns about light pollution. A fixture with full-cutoff optics that can withstand higher vibration ratings is a good choice for bridges.
GE Lighting Systems offers a wide variety of bridge lighting fixtures. The M400 Cobrahead, which withstands 3G vibration, includes lamp supports to help sustain higher vibration conditions. Often used for interchanges and tollbooths, the Tiger fixture’s flexible design enables glare control and offset lighting. Tiger features a variety of mounting options including pole-top tenons.
Lighting the way
According to Andrew Holt, lighting engineer for U.S. Traffic Corp.’s Nu-Art Lighting Division, Salt Lake City, HIDs and fluorescents are the two major light sources for roadways and tunnels. Both create challenges for maintenance crews who must ensure the lights keep operating. Whenever a light needs repair or replacement, maintenance must close lanes, which takes time and puts crews in danger of moving traffic.
Holt said lighting for short tunnels, bridges and roadway sections is primarily HID fixtures. Lamps are metal halide, low-pressure sodium, high-pressure sodium and mercury vapor—all single-point sources that emit significant light.
“HID is desirable for shorter tunnels and requires fewer fixtures. Although HID can have a strobe effect, it doesn’t cause serious problems for drivers because fixtures are spaced farther apart.”
A preferred source of lighting for longer tunnels is linear fluorescent, Holt said. “In a long tunnel, depending on fixture spacing and driver speed, the HID strobe effect could have a hypnotic effect on drivers. This is why engineers specify fluorescent fixtures in longer tunnels, bridges or roadway sections.”
ICE fluorescent technology
Emerging inductively coupled electrodeless (ICE) lamp technology offers five times the life of HID or fluorescent, from five years to an average of 25 years, Holt said.
“ICE is an exciting lamp source for contractors, departments of transportation [DOTs], municipalities and private roadway authorities for applications requiring maintenance reduction.”
Although users are moving toward ICE technology in tunnel applications, the globe-shape package size is a drawback. ICE’s initial cost is two to three times higher than conventional fluorescent. However, electrical contractor benefits include less maintenance and reduced-risk lamp replacement.
The Baltimore Harbor tunnel is retrofitted with ICE fluorescent lamp technology. Authorities there are not as concerned with difficulty of shape because in the long run, fewer workers are needed to replace lamps.
The highest available wattage in ICE lamps is 150W. DOTs are telling manufacturers that if they can make a 250W ICE lamp, DOTs will install them on new projects and recommend them for retrofits.
A popular tunnel lighting product from Quixote Traffic Corp., Marietta, Ga., TNL-A is more than a heavy-duty fluorescent luminaire. Designed for hose-down applications, TNL-A was water-spray tested in excess of 100 PSI. Branch circuits can be installed and terminated before the fixture is installed, making fixture installation to branch circuits more efficient. A diffuser doorframe hinging from either side provides easy access. Because the TNL-A is waterproof, vapor-tight and corrosion resistant, it is the mainstay in the Boston Central Artery Interstate 90/93 tunnels.
LEDs: a viable future option
Because light-emitting diodes (LEDs) are perceived as energy efficient, they have gained popularity.
“In reality, this is not true,” said Holt. “It’s true for signal lights using an energy-consuming incandescent lamp that only lasts 5,000 hours. LEDs are great for signal applications because they are more energy efficient and last up to 100,000 hours.”
Holt said LEDs are not the best product to illuminate larger areas. “LEDs need more energy because lumens per watt [about 50] are only half as good as fluorescent or HID. When LEDs can get into the fluorescent reach, which is about 80–100 lumens per watt, LED technology will begin to take center stage for large area lighting applications. Plus, no one has standard form factors for LED [sizes, wattages, etc.] at present.
“Although the contractor/distributor wants to buy the least expensive light source, he should ensure the lighting manufacturer produces a quality product,” Holt said.
How do you go about bidding on a road, bridge or tunnel lighting project? Holt recommends that the electrical contractor clearly define a timetable for the proper submittal sample and lay it out with the people who won the contract so it is clear, concise and does not hold up any part of the project. The contractor needs open communications with the specifier. If an EC determines that a package for a particular fixture doesn’t lend itself to the project, try to convince the specifier there is a better solution. Take a logical approach, explain it will not work as specified and suggest a better solution. Ask the specifier, “How can we approach changing the spec?”
For profitable projects, Holt said ECs should look at every specified product that is not off the shelf for all aspects of the job, not just lighting. Get with your various suppliers and distributors to define a timetable that will allow them to succeed. Missing deadlines and milestones can be very expensive for ECs. For successful project bids, Holt advises the following:
1. Get the spec.
2. Determine if you can do it and if you have a fixture that will work, get the correct rating, have the proper certifications, and determine costs.
3. Bid it.
4. Win the job.
5. Assemble a submittal package and sample, with all the certifications the specifier wants.
“Some smaller contractors see the numbers on large contracts and rush into it without doing the ‘7 P Rule’: Prior proper planning prevents piss-poor performance,” Holt said. “Contractors who rush into bids don’t outline their needs adequately or establish workable timetables and milestones for each distributor and manufacturer involved. This can result in liquidated damages for not hitting milestones and late projects.” EC
WOODS writes for many consumer and trade publications. She can be reached via e-mail at firstname.lastname@example.org.