Lighting Project Boosts Productivity

When Mack Trucks planned the installation of a new cab assembly line in its Macungie, Pa., plant in 1995, the company thought the time was right to look into retrofitting the building's troublesome lighting system. The facility's 20-yr-old, 400W high-pressure sodium (HPS) highbay fixtures needed repairs on a daily basis, and the time and money spent on maintenance and repairs was unacceptably high.

When Mack Trucks planned the installation of a new cab assembly line in its Macungie, Pa., plant in 1995, the company thought the time was right to look into retrofitting the building's troublesome lighting system. The facility's 20-yr-old, 400W high-pressure sodium (HPS) highbay fixtures needed repairs on a daily basis, and the time and money spent on maintenance and repairs was unacceptably high. As a result, the company took a systematic approach to find the retrofit that would fit its plant best.

Mack had installed the HPS fixtures when the million-sq-ft facility was built in 1975. The fixtures began creating problems shortly thereafter. The company had mounted the lights without considering how machinery would affect the lighting, and when it installed the assembly-line equipment, the lights created shadows and low light levels unsuitable for certain jobs.

“The cab lines had very poor lighting with the old fixtures,” says Jerry Vogwill, plant facilities section manager. “Color rendition was a problem, and employees literally could not see to do the job. We were having difficulty matching colors on trucks where we had a cab painted a certain color and small parts painted a different color.”

The plant builds each truck to customer specifications, so mixing up colors wasn't acceptable. Vogwill knew something had to be done.

“When we installed the new cab assembly line, one of our goals was to improve the quality of lighting,” he says. “We knew we could obtain a more natural white light by switching to metal-halide lamps.”

The age of the system only added to the problem. A typical HPS lamp with a conventional ballast loses more than 60% of its initial lumen output after just 20,000 hours of operation. As lighting systems age, the lumens delivered to the work surface decreases significantly. That means more errors, more scrap, and an increased likelihood of personal injury. The lumen output of Mack's system had lowered significantly, and operations were starting to suffer. New ballast and lamp technologies extend lamp life to well over 40,000 hr while still maintaining adequate operating lumen levels. This creates a scheduling buffer zone and results in savings in maintenance — Fewer replacements means less labor and less money spent on new lamps.

Mack Engineer Tom Campbell decided to light the new cab line with a different system than the rest of the plant, and contacted lighting representatives for recommendations. Fromm Electric, Bethlehem, Pa., and Diversified Lighting Associates, Allentown, Pa., offered their expertise.

“We first analyzed the system that was in place, tried to find the correct wattage needed, and then figured out what optics would work best to suit Mack's needs,” says Fred Schuler of Diversified Lighting Associates.

Most lighting engineers would have taken one look at the Mack job and immediately thought “highbays.” But Schuler says he decided highbays might not be the best option because Mack was interested in vertical footcandles (fc) and uniformity.

Mack wanted to test and evaluate different fixtures, so Diversified and Fromm installed several fixtures to see how they worked in the facility. Schuler's team realized generating light on a vertical plane was most important, so they went beyond looking at just horizontal footcandles and concentrated on a fixture that would also deliver a high level of vertical footcandles.

With the need for vertical lighting in mind, they selected a luminaire with a precision optical design and low surface brightness. This allowed them to mount at heights of 10 ft to 25 ft. The fixture's square grid distribution improved overall illumination uniformity with 2-to-1 fixture spacing. The system is a perfect fit for the facility's industrial areas where machinery and other vertical obstructions cause shadows and uneven illumination. What's more, the new system requires 20 to 30 fewer fixtures to achieve the same light levels produced by standard peak lead systems. By doubling the life of standard M59 lamps, the system greatly reduces operating and maintenance costs.

However, the improvements went beyond just vertical lighting. Old standard highbays like those originally installed at the Mack plant do a good job of delivering light to the floor, but they lack the precise optics necessary to distribute the light evenly over that horizontal surface. The highbay fixtures that had been in use at the plant produced light levels that averaged about 50 fc, with peaks as high as 65 fc to 70 fc. However, the level between lights dropped to about 25 fc. This meant workers were always moving between light and dark areas.

The highbay fixtures also focused the light down, so the crossing pattern of light was below the work height. Newer optic systems create a more uniform light pattern over an area even as the lamps begin to degrade and deliver less light. So, fixtures with 3-D optics can maintain light levels higher than those produced by a greater number of older model luminaries. With the new system, uniform footcandle readings are in the mid to high 40's. The lighting design allows light to spill into areas that previously had almost no light — such as, in the cabs.

Most fixtures cast light only onto a horizontal floor surface or table. In areas where workers must see inside or around a machine (such as a printing press or machine tool), or inside assembly operations (such as a car or truck interior), the vertical surface also needs to be lighted. Only specially engineered optics will do this, by directing up to 68% of the light above the 50° level.

“With the old fixtures in place, I measured the light level inside the cab where the employee was mounting the dash, and it was 2 fc,” says Vogwill. “The employees had to work with a flashlight and if they dropped a screw, it was lost. With the new fixtures installed, our readings rose from 2 fc to 28 fc.”

The previous HPS system drove lumens directly toward the ground, giving a dark and uninviting look to the space between the ceiling and fixtures. Now, the new optics push indirect light up to the ceiling to reduce this cave-like effect.

Because the plant builds each truck with thousands of potential variations, increases in productivity are difficult to measure. Production numbers are constantly rising and falling, based on the process resources required for each truck. However, Mack Truck has looked at other variables and seen significant improvements since installing the new lighting system.

“What we have tried to do is look at write-ups,” says Vogwill. “Write-ups are deficiencies we find at the end of the assembly process. We have noticed there is a significant reduction in the number of write-ups.”

Mack used the cab-line area to test the system. The fixtures instantly caught the eye of everyone in the plant. Employees immediately began asking when they could get new lighting in their areas.

Based on the results from the lighting trials, Campbell decided to retrofit the entire plant. The plant retrofit will consist of approximately 1200 fixtures by the time it is complete. The retrofitting project is in the last year of a 5-year plan. The facilities electricians at Mack are converting about ⅕ of the plant each year themselves. Even in the early days of the retrofit, the plant saw a significant improvement in lighting quality and the cost of maintaining it.

“The old fixtures we replaced were being repaired on an average of one per day,” says Campbell. “With the new fixtures in place, we may have a problem every one or two weeks and that includes the remaining HPS fixtures we are slowly phasing out.”

Engle is a product manager with Hubbell Lighting, Christiansburg, Va.

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