Lighting the Way to Lean
November 30, 2007
Santa always uses Rudolph to light his way this time of the year. While assemblers can’t fly like reindeer, they can turn to task lighting to boost productivity and error-proof their work.
Many manufacturers have acquired lean, ergonomic workstations to improve takt time and increase operating efficiency. However, without the right type of light, that investment can result in waste, which is a serious sin in the lean realm.
“The advent of lean manufacturing and built-in quality places a higher level of emphasis on just-in-time defect detection by workers,” says Josh Kerst, vice president of Humantech Inc. (Ann Arbor, MI), an ergonomics consulting firm. “Lighting is really a big deal, because 85 percent of the information that humans gather comes through our eyes. Poor lighting can affect the quality of work and overall productivity, specifically in situations where precision is required.”
To address ergonomic concerns, reduce defects and improve quality, lighting is critical to the design of any lean workstation. Inadequate lighting will force assemblers to shift workpieces or adopt awkward body postures. While this may provide temporary relief, it eventually leads to back pains, eyestrain, fatigue, headaches and other ailments.
“Poor lighting leads to production inaccuracy and decreases in efficiency,” warns Erica Rice, marketing director at Production Basics (Watertown, MA). “Operators are generally not comfortable and not able to do their jobs correctly, which is counter-productive for any business.”
Although lighting is an important element of workstation design, it’s often overlooked. Lighting is usually a check-the-box type of activity for engineers, who often underestimate its importance.
“Many people think that a low-cost solution of purchasing a $20 light from a hardware store will accomplish the same task as a highly engineered product,” says Kurt Greissinger, product marketing manager for manual production systems at Bosch Rexroth Corp. (Buchanan, MI). “In fact, lighting may even be at best an afterthought; at worst, not thought about at all.”
“If you are going to the expense of designing an ergonomic workstation, you must consider the benefits of optical ergonomics as well,” contends David Seay, national sales manager in the industrial division of Sovella Inc. (Kennesaw, GA).
Lighting is often overlooked because engineers feel that the work area has adequate lighting. “The reality is, even if an area has adequate lighting, overhead cabinets and cantilever shelving mounted to a modular workbench can cause shadows and reduce light at the work surface,” notes Bob Simmons, national sales manager at Pro-Line (Haverhill, MA). With overhead frames and fixtures, light can be tilted toward the surface and positioned so that it avoids shadows.
“Too much light can make assembly and inspection tasks more difficult by creating shadows and causing visual discomfort for the user,” explains David Verrill, applications support manager at IAC Industries Inc. (Brea, CA). “Excessively bright light can also wash out visual gradients.
“Too little light can contribute to longer task times and increased errors,” adds Verrill. “It is important to keep in mind that the amount of artificial overhead and natural light reaching a workstation can vary significantly from station to station, because of the relative location of the station to the light source, obstructions, time of day, and so on.”
New Lighting OptionsEnvironmental and energy conservation initiatives, such as the EPA’s Energy Star program, have prompted many manufacturers to invest in new lighting systems. High-efficiency lighting can offer significant cost benefits and energy savings.
The lighting industry has responded by using new technology, such as cold cathodes. “The latest trend has been to use T-8 energy-efficient ballasts instead of the traditional T-12 ballasts,” says Simmons.
Traditionally, workstation lighting choices were limited to either overhead fluorescent tubes or halogen task lamps. But, new light-emitting diode (LED) technology offers another option.
“Overhead fluorescent fixtures are still the most common supplemental light used at workstations,” claims Verrill. “We build our own fixtures using high-efficiency ballasts, and most of the fluorescent light fixture manufacturers have also made the transition to electronic ballasts from magnetic.”
Fluorescent lights basically consist of a phosphor-coated glass tube filled with argon or argon-krypton gas and traces of mercury, capped at both ends with electrodes. Electrical current excites the mercury atoms and causes them to emit ultraviolet radiation, which the phosphors then convert into visible light.
“Fluorescent lights provide the lowest cost-per-light output ratio of any of the light sources. They run cool and may be placed close to an operator,” explains David Trinks, sales manager at Sunnex Inc. (Natick, MA). “[However], they do represent hazards, based on the mercury components that they contain. [And], they are easily broken, thus not well-suited for [some] industrial applications.” Another potential drawback on the plant floor is that fluorescent lights can contribute to radio frequency interference.
“The advantage of fluorescent lighting over halogen or LED lighting for workbenches is that the tubes are longer and can be spread out over the length of the surface,” says Simmons. “Most workbenches are 5 or 6 feet long. With fluorescent tubes that are 4 feet long, they can be centered and light the complete work surface.
“Halogen or LED lighting is brighter, but the light source is more centralized,” adds Simmons. “When working on small parts that require additional lighting, other sources can be used. But, to light a complete surface, fluorescent tubes still work the best.”
Despite those advantages, LEDs are becoming more popular. The rugged, cool-burning, long-lasting light source offers unique advantages. For instance, it allows workstations to be illuminated by individual arrays of light or by distributive light pipes.
According to Mark Rea, director of the Lighting Research Center at Rensselaer Polytechnic Institute (Troy, NY), LEDs are made of semiconductor chips and emit light when a current passes through them. Lighting applications that use LEDs are referred to as solid-state lighting. The U.S. Department of Energy (Washington, DC) estimates that this technology may save as much as $98 billion in energy costs over the next two decades.
“LEDs offer many benefits, including energy and maintenance savings, long life, durability, safety and flexibility,” says Rea. “LED lighting systems are very effective in applications where brightness, visibility and small size are important.”
One unique feature of LEDs is that they can provide color wash to surfaces, creating ambient and indirect lighting effects. This ability to mix and match or tune light can be done with great precision, providing sophisticated control over color, tone and brightness to generate an infinite variety of effects.
“The LED trend is very hot in assembly workstations, because LEDs are vibration-, switching- and temperature-tolerant, with extremely rapid response times,” says Kerst. “LED lighting can be installed in places currently unavailable to traditional lighting sources.”
But, cost is a potential drawback. “It is hard to compare an LED module to a standard halogen bulb, as the technology is not as simple as unplugging one and plugging in the other,” explains Trinks.
“A LED module or package normally consists of the diode lighting element; a lens or mirror to focus the light being emitted; a heat sink to pull heat generated by the element away from the source diode; connection cables; and a power conversion source or driver,” Trinks points out. “Provision of all these components are what makes the LED option one of the most expensive lighting solutions in the marketplace.” A
Consider These Factors When Choosing LightsDavid Verrill, applications support manager at IAC Industries Inc. (Brea, CA), says workstation lighting requirements depend on three key factors:
Level of detail required for the task. Assembling a large control box with 0.25-inch bolts, for instance, can be accomplished easily enough with whatever ambient light is available. As the level of detail increases, so, too, does the need for brighter lighting with less glare. “This is especially true for fine-pitch work in the electronics industry,” explains Verrill. “Many of our customers add magnifying lights at the work surface level to ensure accuracy.”
When it comes to glare, only so much can be controlled with the type of lighting diffuser selected. The choice of work surface colors and materials often comes into play. For example, fiber optics manufacturers often select black laminate surfaces because the added contrast helps operators perform splicing operations. Conversely, white wires on a white work surface become nearly invisible with bright lighting.
Age of the operators performing the task. “Even in this day of corrective lenses, laser surgery and lens replacement therapy, the fact remains that our vision deteriorates as we age,” notes Verrill. “It’s important to evaluate the age differences within a work group to ensure that lighting is appropriate. There is no one-size-fits-all solution.”
If there is a great variance in age, an adjustable-output light fixture may be the best solution. For instance, fluorescent fixtures equipped with remote dimmer controls give operators absolute control of lighting at their workstation. “These are especially useful if the level of detail increases throughout the day,” Verrill points out. “The ability to [increase light] can reduce fatigue.”
Amount of ambient light. Over the past few years, architects and facilities managers have given more thought to facility lighting, claims Verrill. Newer construction typically addresses current and future lighting needs by use of modular grid systems, which makes it easier to rearrange lighting when assembly lines are reconfigured.
However, even with those systems, task lighting at the workstation may be necessary. Older buildings with tall ceilings and high-pressure sodium or mercury vapor fixtures almost always require supplemental lighting at the workstation.
Learn more about workstation lighting by clicking "Web Extra."