Lighting Control Options for Warehouse and Industrial Lighting
Now that the old high-intensity discharge lights in many warehouses have been replaced by fluorescents and LEDs, facility managers are taking their energy-savings efforts to the next level and installing control systems. You could have the most energy efficient lights on the market, but if they are burning brightly in unoccupied areas, or in rooms fully lit by natural daylight, you are wasting energy and missing out on significant utility savings.
One of the most common types of controls are occupancy sensors, which turn lights on automatically when they detect motion and then turn them off when the area is vacated. Along the same lines, “vacancy sensors” require occupants to manually switch on the lights when they enter a room, but as soon as they leave, the lights automatically switch off.
Sensors detect occupants in several different ways. Passive infrared sensors (PIR) are designed to respond to infrared light radiating from a person (or any other heat-emitting source) in their line of sight. Ultrasound sensors produce low intensity, inaudible sound and detect changes in sound waves caused by motion. Because they are not line-of-sight dependant, these sensors are useful in enclosed hallways and bathrooms with stalls.
Occupancy sensors can be installed in various ways – wall-mount, ceiling-mount, corner-mount or on the light fixture itself. One of Leviton’s best-selling PIRs, for example, mounts directly to a high-bay industrial fluorescent fixture. It can be set at any time without requiring power to the sensor; time delay is variable from 30 seconds to 20 minutes. And it automatically adjusts the PIR sensitivity as ambient temperature rises to increase detection of heat movement through the field-of-view.
In areas where people are doing work that entails small movements – computer or paperwork for example - the sensitivity of the occupancy sensing system should be as high as possible to ensure detection. In hallways, body movements are not hard to detect, so the system does not need to be as highly reactive.
Daylight harvesting systems supplement artificial light with ambient light in areas where there is a sufficient amount of it available, such as near large skylights or windows. Although this can be done manually, automatic systems tend to result in greater energy savings over the long run. In an automated system, optical sensors called photocells read ambient light levels and send this data to controls that raise or lower light levels to maintain a base level of illumination.
Another way to assure that lights are turned off when unneeded is through time-scheduling. This can be done with a simple time clock or with computer controls, used to turn lights on and off at specific times. These systems, which work well in large open areas, often include overrides that allow occupants to turn on the lights after hours.
Using any of the control systems above, lights can either be lowered or shut off entirely when unneeded. In areas where safety and security is a concern, such as stairwells used for emergency exits, lights should never be switched off completely. Here, an additional control can be built into the system – a dimmer that allows you to capture energy savings but keeps lights on at a constant low level when areas are unoccupied. When an integrated or separately mounted occupancy sensor detects that someone has entered the space, it signals the dimmer to raise light levels to full brightness.
Another alternative to shutting lights off completely is dual-switching, also referred to as bi-level or step-switching. With this approach, multiple lamps in a single light fixture can be switched on and off independent of each other. This allows for typically one or two steps between full and zero output.
Exterior Light Controls
Control systems can also be used to conserve energy in exterior applications. The Maxlite 14-watt LED wall-pack, for example, is built with a dusk-to-dawn photocell, eliminating the need to turn lights off in the morning. Most parking lot pole lights are also equipped with photocells, but they can be programmed to dim down or shut off at a certain time of night. At building entrances and driveways, you can install motion detectors to turn flood lights on after dark when people approach an entrance to the building. In all exterior applications, you will have to find a balance between conserving as much energy as possible and meeting safety and security requirements.
Benefits of Lighting Controls
There are multiple benefits and incentives for installing control systems. First and foremost, they save a significant amount of energy, although exactly how much is difficult to quantify. Many factors come into play, including occupant behavior and the placement of windows and skylights. However, the Lawrence Berkeley National Laboratory analyzed 240 energy savings estimates from 88 papers and case studies, and came up with “best estimates” of average lighting energy savings for each strategy. The average savings for occupancy sensors was 24%, while the average savings for photosensors was 28%.
Controls also reduce maintenance costs, since dimming or turning lights off when they are unneeded prolongs lamp life. These “life cycle savings” should be factored into the equation when you tabulate your initial investment in a control system. That initial cost can also be reduced with the help of generous utility rebates. PPL, for example, one of the utility companies servicing Pennsylvania, provides a $45 rebate for fixture-mounted, remote-mounted and wall-box occupancy sensors. According to the Lighting Controls Association, the average rebate for photocells is about $28. The controls may be required to be listed by UL or other OSHA-approved testing laboratory to qualify, and pre-approval is often required before equipment is purchased.
Finally, lighting controls, and daylight harvesting in particular, can contribute to the comfort of a work environment. Studies cited in the GreenGuide published by the American Society of Heating, Refrigerating and Air-Conditioning indicate that greater use of natural daylight resulted in a 40% improvement in sales in retail settings. In school settings, increased daylight resulted in a 20% improvement in math scores and a 26% improvement in reading scores. It’s not unreasonable to assume the same would hold true for industrial settings – so let the sunshine in.