How Important is 30 Foot Candles of Light in a Warehouse?

A client sent me a warehouse specification package that he wanted me to review before it was released to real-estate brokers. In the middle of this specification package, under the heading Lighting, appeared a simple one-line specification: “The lighting shall produce 30 foot-candles (30FC) of output when measured 36" above the floor.”

While this appears to be a simple specification, it causes a great deal of trouble for the people who design and build distribution centers. Warehouse workers need sufficient light to work, but how much light is sufficient? The answer to this question really depends on the tools, tasks, and processes that drive the work, and how much light the tasks require. Safety is another concern, and many make the argument that a bright environment is a safe environment. Still, does bright light make a job safer?

The 30FC lighting specification is so prevalent in warehouse specifications that some consider it one of the industry’s biblical, carved-in-stone truths. I myself was once a believer in the 30FC specification, but research has led me to question it. While I believe we need light to do our jobs in a warehouse, I no longer believe that 30FC is an absolute necessity.

To help you understand how I became a 30FC heretic, I should share with you the history of the specification as I have come to understand it.

The Legacy

The 30FC lighting specification in general warehouse applications dates back to the mid 1980s. I myself have used it in Distribution Center specification documents since 1988. If you examine the specification packages of many distribution center projects in the past three decades, the 30FC requirement appears in almost all of them.

The typical lighting used in warehouses and distribution centers in the 1970s through the late 1980s consisted of eight-foot-long single- or two-lamp strip fixtures hung by jack chain from the roof. In most applications the roof levels provided a clear height between 20 and 25 feet. The light levels were poor, often under 10 FC.

Warehouses of the era used paper documents for all warehouse functions, and early material-handling engineers considered the ambient light levels to be a leading cause of picking and stocking errors in the operations. Florescent lights were often used due to their low cost. In the mid-1980s, however, the clear height of warehouses climbed to 30 feet, and the florescent lights of the era just did not have the lumen punch of other technology, like high wattage metal halide lamps.

The cost of the metal halide fixture, including the wiring, was significant. The fixtures were expensive, as was the wiring. Some developers substituted lower-cost sodium vapor light fixtures for metal halides, looking at the lower cost of both fixture and bulb. Sodium vapor lights cast a warm yellow light. It is hard for people to read and see clearly under the yellow light of sodium vapor lights, so the warehouses still looked dark. In an effort to control the costs of warehouse space development, developers installed as few fixtures as they could. As a result, warehouses still looked somewhat dark.

In the 1980s and 1990s a number of engineering firms focused on the development of warehouses and distribution centers. These consulting firms pioneered many of the standard concepts that we see in distribution centers today. These firms — Sedlak; James R. Keogh; Garr; Semco-Sweet & Mayers; Tom Zozel; Epstein; Richard Muther; and Gross & Associates, to name a few — led the industry in a number of directions. Each practice developed a standard set of building specifications for warehouses and distribution centers.

To counter the dungeon darkness of old warehouses, the early building specifications created by these leading material-handling engineering firms specified metal halide fixtures with a specific foot-candle requirement of 30FC. My first contact with these specifications came in 1986, when Keogh supplied the building specifications for two distribution centers for which I was managing implementation for my employer. Our project teams discussed lighting fixtures and the FC requirements for each project, with some contention among the engineers, the operators, and the construction department.

We learned an important lesson about sodium vapor lights in one building where the construction team did not agree with the metal halide argument. That 500,000-square-foot building used an abundance of bright yellow sodium-vapor lights, and it was immediately apparent to us that our employees could not see. While erecting a rack in the building one of them drove his forklift head-on into a building column. We had gone to the trouble to paint the bottom ten feet of the column in safety yellow to avoid exactly this kind of accident. But in the bright yellow light, the column disappeared and the installer hit the ten-foot steel column at full speed, shearing the column off at the floor and nearly killing himself. It did not take long to swap out all of the sodium fixtures with metal halides.

We did not have any arguments with the fixture type in the second project.

While we could clearly see the difference the type of light made, the intensity of the lights was a different story. Architects and electrical contractors argued that 30FC was much brighter than what people needed to drive and walk. Typical parking lot illumination is no more than 5FC, often only 2FC. While the light directly under a streetlight is 10FC or more, the space between lights falls quickly to 2FC. In a parking lot, where the task is to get to and from your car safely, and where moving cars use headlights, these lighting levels are sufficient. But more light is needed in a warehouse, where people must read paperwork to do their jobs. How much more light became a subject of argument.

While it may seem simplistic, the prevailing way building designers and electrical contractors approach making a space brighter is to add more fixtures. There are other ways (and we will touch on those in the next part of this series), but in most cases the lighting designers will either add more fixtures or increase the wattage of the fixtures. The key consideration is the investment cost, which is important to the building developer or owner, but not as important to the managers of the future operation.

More light = more fixtures = more investment cost. So getting 30FC on a warehouse floor drives up the cost of the space, prompting the green eyeshade moneymen to argue the point. I know, because I have watched many of these meetings in my career. One often-used argument centers on the question of what research backs up the 30FC requirement.

The fact is, the 30FC requirement was never a tested specification. After one of these many arguments I went looking for and failed to find any relevant research. So I started to ask the consultants for the research. When I asked the question from the client side of the desk, the engineering consultants responded with letters citing their own research, which indicated generally lower error rates with brighter operations. But none of them could provide actual data.

It was after I crossed over to the consulting engineer side of the desk that I discovered an inconvenient truth. There was no research to back up the claims. Several of the engineering principals of the era admitted to me that they chose 30FC because “it was a good, round number.” As a project manager at Keogh, I questioned our partners about the FC requirements, and they all fell back on the general, common-sense idea that brighter is better, and 30FC was as good a measure as any.