Mobile lighting systems have come a long way since the first enterprising electrician wired an Edison incandescent bulb to a metal pole and called it outdoor lighting. While earlier efforts to improve task lighting focused largely on producing more light, in recent decades a greater emphasis has been placed on ensuring that the light produced is usable and targets the intended work areas.
“The biggest advancement in light output has been the development of the quartz metal halide bulbs,” says David Price, national key accounts manager for mobile lighting solutions provider AllightPrimax. “No manufacturer of any industrial lamps has signed off on the fact that their product is intended for use expressly in a light tower in an industry where it takes such abuse and where we traditionally see light filaments shaken to pieces. The double-ended metal halide lamps are gas-filled with no internal filaments, so breakage due to vibration is significantly reduced.”
The metal halide lamps use a hot-strike system that reduces the amount of power required to produce light. A generator creates a pulse of energy that ignites the lamp at the precise temperature required to produce light.
Related: Magnalight introduces generator-powered mini light tower for stand-alone illumination
“The linear gas lamps also allow you to control the amount of light produced, while with a filament lamp it’s very erratic and difficult to maintain an even energy flow,” he says.
DESIGN IMPROVEMENTS
The light castings – lamp heads and assemblies – have also been improved over the years. The initial designs and some current models have offered rudimentary concave dishes with a wide lens that could be adjusted backward, forward and from side to side to illuminate various intersections, work areas and mine pits. However, once the light – traditionally measured in lumens – was diverted, it significantly reduced the amount of usable light – measured in lux – cast on the subject. (See sidebar on next page.)
“Companies like Philips and Sylvania really advanced light output and have made significant improvements on the light castings, both in durability and design,” says Price. “These parabolic style castings incorporate reflectors – louver dampers – to direct the light to the ground. This has really improved the lux ratings over lamps producing the same number of lumens.”
The other quality of light that makes it more useful is its color temperature – in this case, its similarity to daylight – measured in degrees Kelvin. Standard daylight contains a large amount of white light. Direct sunlight measures in at 5,500 K while an indoor 40-watt incandescent bulb rates around 2,680 K. A 1.5 kW metal halide lamp can produce a very clear white light at a color temperature of 4,200 K, and is capable of exceeding 24,000 K of pure white light on some light tower models.”
“The white clear light emitted from the quartz metal halide is the closest thing to natural sunlight,” says Price.
POSITION THE LIGHT BAR
The other important factor in getting light into workspaces is the design of the light tower itself. A typical four-head tower is delivered to the site in a folded state, and then mechanically raised to full vertical height.
“For years, these were raised up and the light was distributed evenly around the pole from the four lamps by directing the light assemblies, like a light tree in a shopping center parking lot,” says Price.
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“Our solution to improving on that was to create a light bar that could be tilted 180 degrees parallel to the ground and rotated 180 degrees while also incorporating a mast rotator that could rotate the mast tube 350 degrees simply by actuating switches from the control panel while the light tower was at full operational height,” Price
explains of the AllightPrimax product. “For every degree or two you tilt the head, you can increase the lux factor by 10 percent. Placement and attitude are critical, especially in oil and gas production, because you typically need to locate the tower outside the fence of the crowded production area.”
The company also produces towers with a highwall overhang feature.
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“By positioning the hydraulic mast and light bar horizontally over the work area, for example in an open-pit mine, it illuminates from directly above the work area, greatly improving usable light,” he says. “Our highwall overhang feature allows the mast to be extended horizontally over the fence line or a windrow in an open pit that can provide a 70 to 80 percent increase in lux ratings by directing the light downward and having it positioned
directly overhead.”
RAISING MASTS SAFELY
How the towers are raised into position is also an important safety consideration, says Price.
“Light towers are typically raised using a two-winch system, with one main winch raising the mast from the stowed, transport position into a vertical position and the hoist winch, which extends the mast tube sections upward once it’s in the locked and upright position,” says Price. “However, if the main vertical winch or cable fails when the tower is extended, that mast will come down and could severely injure someone.
To avoid the issues created by the use of this winch-style system, we switched to an all-hydraulic design, as did a few other manufacturers.
“Our hydraulic towers use a cantilever mast-raise design on some models, and a scissor action on others,” Price continues. “This equalizes the weight of the tower as it’s pushed into the vertical position. It then locks and a secondary hydraulic system raises the mast. A system of limit switches and hydraulic safety valves prevents the tower from retracting or coming down. This same system prevents the machine from moving out of its center of gravity and from becoming off balance.”
The tallest hydraulic trailer-mounted tower supplied by the company has a mast topping out at more than 34 feet. A skid-mounted hydraulic model rises to 55 feet.
The mobile light towers are mounted, along with cabin-enclosed generators and a light control panel, on a single-axle or twin-axle mobile trailer, and heavy-duty truck axle variations. The trailers are made of welded plate steel and aluminum and offer four outriggers and a jockey wheel to stabilize the vehicle when the mast is extended. Hydraulic stabilizers are optional.
BUILT FOR DURABILITY
“These trailers have grown heavier and stronger over the years,” says Price. “Ours feature a fully welded base frame and a ballast box that slides out to provide easy service access. You have to keep the design very basic and compact so they can be easily shipped on flatbed trailers or inside shipping containers.”
The trailers are designed with 16-inch ground clearance and equipped with 4-star rated radial tires.
“On rough terrain, ground clearance is critical,” says Price. “The trailers feature leaf springs like you would find on a truck. We also won’t skimp with bias ply tires, because the variations in ambient temperatures in some regions combined with the weight of the load can tear bias ply tires apart.”
The lights are powered by diesel engines supplied by Caterpillar or Perkins. Allight-branded heavy-duty generators are also supplied in all of the units. These generators are fine-tuned and selected specifically to support the ratings of the lamps mounted on the tower mast and the electrical specifications required by each model.
“It’s optimal to keep the generators running at roughly about 75 to 80 percent of the component’s capacity,” says Price. “So on a 6 kW Hydraulic Light Tower, we require the use of 6 kilowatts to power the lamps and keep 2 kW in reserve for auxiliary power. When the generator runs in the sweet spot within a close tolerance of the expected load, it extends the life of the generator over the long run.”
However, Price notes that some contractors are tempted to use the light generator to power auxiliary equipment, both overtaxing the generator and running it outside the sweet spot.
“Even if we were to offer a generator with lots of extra capacity in reserve, the generator would be producing capacity that it may or may not use and you’d be sacrificing generator longevity for something you might only be using for 50 percent of the time,” he says.
Price argues it would be far more economical and efficient to use a standby generator to handle these specific additional auxiliary power needs.
LIGHTING EXPERTISE
Diesel engines powering light tower units require typical maintenance. Price says light tower purchasers should place greater weight on the maintenance time required to swap out lamps. “See a demonstration before you buy,” he says. “There’s a huge difference in downtime between being able to change all four lamps in five minutes or one lamp in 20 minutes. It really isn’t the best option to run a light tower with only two or three of four lamps working, both because of the lack of light in the work areas and because of the toll this will take on the generator.”
Wind velocity ratings are also important and play an increasing role in bid specifications, particularly in Kansas and other states in the Midwest flatlands, says Price. The company’s own towers are rated to 92 miles per hour.
He notes that suppliers are also becoming more involved in helping contractors to design the lighting plan for a site.
“I recently went out to an open-pit mine in Texas where there were as many towers on the left side of a cut as on the right side,” he recalls. “The problem there was a huge shadow at 45 degrees against the side of the cut and lighting was notably poor. We were able to replace those towers with half as many towers with higher output by using hydraulic units that extended horizontally over the pit, which directed the light downward, eliminating shadows and drastically increasing usable light at the work platform. Sometimes the best lighting solution isn’t the most obvious.”
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