As with many lighting options, the lamp type you choose and the addition of controls can help save energy dollars.
In a facility that’s lit with old probe-start MH lamps, installing newer, pulse-start lamps can gain you savings, but fluorescent lamps or LEDs can raise the savings even higher.
HID lamps (high-pressure sodium and metal halide) were the mainstays of high-bay lighting for many years, but in about 2000, advances in the performance and color quality of fluorescent lighting made high-intensity fluorescent (HIF) lamps the most efficient, cost-effective choice in many cases. Compared to HID lighting, fluorescent lighting (predominantly T5 high output and high-performance T8 lamps) offers many pluses, including higher efficiency, longer life, lower lumen depreciation rates, better dimming options, faster start-up and restrike times, better color rendition, and less glare, but they are also more sensitive to temperature variations. On the HID side, higher-wattage ceramic metal halide (CMH) lamps and compatible higher-wattage electronic ballasts have made CMH a competitive choice in some applications.
Induction lamps, a type of fluorescent lamp that uses radio-frequency energy rather than an electric arc to excite phosphors and produce light, are also a viable option. Induction lights offer very long life but are less efficient than LEDs and high-performance fluorescents. In addition, lamp-life ratings for LEDs and some fluorescents are approaching those of induction lamps.
Despite their higher initial costs, LEDs are starting to make inroads into high-bay applications. Compared to fluorescents, LEDs offer comparable or higher efficacy (and the technology is still rapidly improving), longer life, similar color quality, more controllability, and more flexibility with light-distribution patterns. The most promising early applications for LEDs were in cold storage because LEDs perform better in cold conditions than other lamp types. Since then, LED products have become more efficient, and with less heat to dissipate and better techniques for handling the heat that LEDs do create, high-bay applications have expanded to more general warehousing applications.
A large high-bay site might have the lights on across the whole facility, even if only a small portion is occupied at any given time. In these cases, the ability to turn lights on when they’re needed and off when they’re not can have a substantial impact on consumption. Occupancy sensors and timers can capture these savings, but they need to be combined with lighting systems that are effective when controlled. HID light sources have long start-up and restrike times and so can’t be shut off based on occupancy, but they can be dimmed to about 50 percent of initial power. Fluorescent lighting is a better choice for controllability due to its faster startup time, but frequent on-off switching can reduce its life span. LEDs are the most amenable to control—they react instantly and suffer no degradation of life with frequent switching—but they are more costly.
For some facilities, skylights and daylighting controls—which modulate electric light levels based on available daylight—can also be big energy-savers. In addition, lighting control systems can automatically turn lights on and off based on a preset schedule, rather than relying on personnel to remember to turn lights off.