Do We Need 30 Foot Candles of Light?
Changes in Direction
The question in the title of this post is one that I have heard asked repeatedly in the past 25 years. My answer has always been the same — it depends.
In fact, there have been operations for which I pushed for more light than 30 FC in specific work areas, like receiving, returns processing, price ticketing, inspection, or garment sortation. Each of these tasks can require extensive fine work or reading to perform.
The configuration of the storage systems, and the products being stored in the system, are factors to consider. White boxes reflect light, unlike brown boxes, which absorb it. Garment-on-hanger operations can require more light, depending on the kinds of garments, the fabrics, and the protection used. Tires and other black rubber products absorb light, and therefore work areas where tires are stored require more light.
Changes in technology, building design, equipment, and our distribution processes have the greatest impact on lighting requirements. These changes in direction are our focus today.
Notwithstanding Jack Palance’s character Curley’s assertion that there is just one thing, our warehouses are complex systems where change from multiple directions is the reality. It’s not just one thing; it is many that we must consider when deciding how much light the average person needs to perform well in our operations. To understand the need for light in our operations, we should understand the impact of the changes.
Radio Frequency Data and Bar Codes
In the late 1990s, more distribution centers started using Radio Frequency Communications in conjunction with their Warehouse Management Systems. Initial deployments mainly used RF for fork truck put-away processes. With the promises of higher picking accuracy and lowered equipment costs, more DC operations used RF handheld terminals for picking and receiving. With the integration of bar code scanning and WMS picking processes dedicated to RF terminal use, RF order selection became the norm. With the introduction of voice recognition technology for order selection in the early 21st century, only the most basic of distribution operations still used paper picking documents.
Warehouse Building and Storage Heights
As the size of the warehouse grew, so did the lighting requirements. Taller buildings are not the norm, and it takes more energy to create the intensity of light needed to reach the floor of a modern warehouse. As the floor area grew, so did the power consumption. In the mid-1990s it was common to specify that a warehouse needed to have 1,000 amp service for every 250,000 square feet of area. Today 2,000 is the norm. While conveyor systems drive some of the power requirements, the lighting requirements increased as more operations specified 30 FC minimum lighting standards.
Energy Costs & Carbon Footprint
Another force from outside the warehouse influences the lighting used in warehouses. Energy costs continue to rise, motivating operators to find ways to lower consumption. The concern with carbon emissions from the use of fossil fuel drives additional regulation. Some states, like California, now limit power consumption per square foot of space. As with many regulations, what starts in California often moves to other states.
New Lighting Technologies:
With the introduction of electronic ballasts in the mid 1990s, florescent fixtures started to make a comeback as a lower power consumption option for metal halide fixtures in warehouses. Mainly developed for retail and office applications, T8 (8/8' diameter tubes) and T5 (5/8" diameter tubes) delivered greater lighting output on fewer watts of power than the traditional T12 (12/8" tubes) technology.
The two new tube types offered new options in lighting over the old florescent systems. With electronic ballasts, the frequency of the power used to excite the gasses inside the tubes increased, creating more efficient light output, eliminating the 60 hZ flicker of traditional T12 bulbs. The smaller tubes produced more intense light, and by increasing the frequency, the tubes could produce more light for each watt of power.
T8 technology allows a 4' — 32-watt lamp to create about 30 percent more light output than an older 40-watt florescent light. T8 fixtures and bulbs with the correct electronic ballast can provide a dimmable bulb, eliminating the flash headache effect caused by older florescent systems.
In industrial use, the T5 lamp, powered by a high frequency electronic ballast, can be amped up to produce more intense light. Coupled with high polish reflectors, a 277-watt T5HO produces the same FC output as a 400-watt metal halide. Considering that a large warehouse can require over 300 fixtures, a 123 watts per fixture reduction in consumption adds up very quickly.
The Question: Do we need 30FC?
As I wrote at the start of this post, the need for 30FC depends on a number of factors. The mistake that these early specifications make is the idea that one size fits all. I don’t believe in that concept. An old joke in the garment industry is that the only time one size fits all is when you're making a housedress or a Mumu.
I have specified higher FC requirements in some areas of distribution centers because the activity in that area needed the brighter light. I have also specified lower FC levels. In writing specifications for lighting, I consider a number of factors, including the activity performed, the commodity stored, and the equipment systems used to perform the task.
Activities
If the work requires high visibility, more light is better. Activities like receiving, returns, inspections, and repair all benefit from more light. If the work does not require high visibility, as is the case in places like traffic aisles or large bulk storage areas, I will specify less light. A truck loading area does not need as much light as a receiving dock.
Commodities and materials
All materials either absorb or reflect light. White boxes reflect light, and brown boxes absorb light. Rubber parts, like hoses, belts, and tires suck the light out of a room. A highly polished concrete floor reflects some light, but not as much as an epoxy-coated floor. White walls reflect light better than raw concrete.
Equipment Systems
Think of two different pick methods, picking from a paper pick list or picking from pick-to-light shelves. Which system needs more light in the space? If paper is the method, and 30FC is the minimum light level to consider, I might call for 35FC or 40FC, depending on the quality of the printing on the documents. For pick-to-light, the picker follows the lights on the face of the equipment and reads instructions on the illuminated display, so bright light is not needed, and 20FC may be sufficient.
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