Relighting the NC State University Library bookBot: A Case Study in Addressing Lighting Maintenance Challenges
Lighting systems don’t last forever. Regardless of the type—be it fluorescent, LED, or another technology—eventually, the system will reach the end of its operational life. Moreover, the longer the system operates, the more it is exposed to unusual situations and the greater the likelihood of something going wrong. Failure of design and construction professionals to consider factors such as resilience and maintenance leads to missteps when implementing lighting systems, often resulting in costly replacement projects.
In 2010, as the design phase for the James B. Hunt, Jr. Library at North Carolina State University (NCSU) was nearing completion, solid-state lighting technology was just coming into the mainstream. Various LED luminaires were available on the market, but lumen packages and efficacy were still in competition with linear fluorescent and only available at substantial premiums.
That’s when it was decided that the overhead work lights for the automated archive retrieval system used to house the library’s collections, known as the bookBot, would be conventional fluorescent. No one involved in the original design could have predicted the reaction of patrons, staff, and visitors to the bookBot nor the subsequent change in how the work lights for the bookBot system would eventually be used.
Insufficient Illumination Led to Lighting Breakdown
The bookBot is a group of robots and the governing software that locate, retrieve, and return items within the Hunt Library’s collection. Staff scan the items in and out of the bins, but the rest of the process is completely automated. The four robots glide down 120-foot-long aisles, using a crane and carriage arm to reach bins stacked 50 feet high.
When the center opened in 2013, the bookBot’s original lighting systems were designed not for the robots but for the humans who maintained and worked with them. It included LED cylinder downlights with integral drivers for mandated 24/7 emergency lighting, as well as fluorescent high-bay luminaires intended to operate eight hours per month for maintenance and repairs. Due to the extremely light duty cycle, no maintenance access plan was envisioned for the fluorescent work lights.
Anticipating that this innovative system would draw fascinated spectators, large viewing windows were installed at the first occupied level of the library to allow visitors and staff a peek behind the curtain. An item request feature was also installed, allowing visitors to call for an item and observe the robots at work. A third lighting system was coordinated with the robot supplier to include PAR lamps mounted on the carriages, highlighting the robots’ actions.
Unfortunately, the lighting proved insufficient to illuminate the robots at work in the vast darkness of the archive retrieval system. The library began to field questions and comments from patrons about the status of the bookBot and whether it was closed. To assuage the community’s concerns, the library staff began leaving the overhead work lights on during open hours, which exponentially increased the burn hours for the fluorescent system, resulting in the lights rapidly fading out.
Several ideas were proposed for accessing and relamping the work lights, including lifts, climbing the racking, and using the crane ladders. However, no lift existed that could navigate the aisles, and the racking system was not designed to accommodate live loads. Moreover, the ladders were not within reach of the fluorescent luminaires. As a result, not a single lamp was changed over the next decade, resulting in their dimming, discoloring, and dying. A catwalk or a coordinated ladder system could have been included in the initial design to prevent the decline in visibility for the bookBot and possibly facilitate improvements.
From Blackout to a Maintainable Lighting System
In 2023, Pivotal Lighting Design was tasked with studying and subsequently implementing a replacement lighting system with a longer lifecycle, along with an “archi-tainment” component to enhance the viewer experience. Execution involved shutting down the library for approximately two months to erect and remove scaffolding, change the luminaires and associated wiring, disconnect existing building controls, and install and commission a new control system dedicated to the bookBot. The resulting design was a complete replacement of the overhead lighting.
A primary design criterion for the high-bay luminaires was the ability to remotely access the LED drivers for regular maintenance. In some cases, the drivers would be located up to 200 feet away from the fixture, ganged into an array of 64 driver boxes on the wall alongside the archive storage area.
With that determination made, the general lighting was designed for overlapping coverage from the existing layout, allowing half as many lights to be in regular use, with bi-diem cycling to reduce burn time. The output was overdesigned to dim to 40%, enabling the system to ramp up the setpoint over time as the lumen output depreciates. The lifetime of the new lighting system is estimated to exceed 30 years.
Although still operational after 10 years of continuous use, the LED emergency lights were replaced to reset the lifecycle. This time, the fixtures would have remote drivers and a custom dual-board fixture that was half emergency white and half Wolfpack red. Unlike the unswitched predecessors, the new cylinder lights burn white only after hours when normal lighting is extinguished, as afforded by the UL 924-listed control bypass. The red LED boards, which are separately zoned by aisle, bathe the individual aisles in striking red when the respective robot is activated.
Traditional motion sensors and even wireless goniometers were suggested to track the robots’ movements, but the robots did not have a home base. Adhering to NCSU’s control requirements led the team to laser position sensors at the ends of each aisle to track the motion as a function of distance. Now, the light show begins whenever a robot moves as much as a meter from its position. The white lights shut off, and the red lights engage. After the robot comes to a stop, the general white lights turn back on, and the red cylinders shut off.
Adding to the sense of motion, channels of red LED tape light were added along each side of the crane ladders, directing light onto the book bins as the robot travels. Utilizing an existing beacon light relay on the robots, these 120V tape lights synchronize with the robot's activity and visually enhance its movement. Based on estimated usage, these lights have a life expectancy of over two decades; however, the tapes can be removed and replaced using the crane ladders without extraordinary measures.
Anticipating Future Needs is Key in Lighting Design
The new lighting for the Hunt Library bookBot archival retrieval system has reinvigorated interest in the innovative system, which has been the pride and joy of the university and the state of North Carolina since it first came online. However, the underlying deficiency remains. The lights will start fading out in about a generation, prompting an encore performance with an all-new cast.
The unexpected lighting challenges in this case underscore the importance of foresight in lighting design and the necessity of considering long-term maintenance needs in any facility. Incorporating maintenance solutions into lighting design projects acknowledges the inevitability of change, thereby ensuring more resilient systems. Not doing so is tantamount to expecting the system can be abandoned in place at the end of its operational life. This begs the question, if a system is so easily discarded, why build it in the first place?
