How Dimmers Save Energy

The magnetic dimming systems first introduced in the 1970s were cumbersome, noisy, and inefficient. And the electronic fluorescent dimming ballasts produced in the late 1980s were cost prohibitive and often excluded from Demand Side Management program rebates. However, today's systems provide a viable alternative that has, in turn, made daylight harvesting and energy management more attractive.

Many facilities install skylights or large window walls with photocells and dimming ballasts to reduce lamps when natural light is available. Using a full system-including T8 lamps, electronic fluorescent dimming ballasts, and a control mechanism-can result in sizable energy savings from 55 to 80 percent.

A Look At System Features

Fluorescent electronic dimming ballasts can be connected to standard automatic wall switches or relays, photocells and/or occupancy sensors and can be integrated into building energy-management systems that control lighting, heating, and air conditioning. In addition to dimming ballasts, the combination of daylight harvesting, occupancy sensors, load scheduling, and load shedding contribute to reducing energy consumption.

Daylight harvesting uses photocells or light sensors to capitalize on "free" sunlight and lower the cost of supporting light through dimming. Photocells measure the light level in an area, ensuring an adequate number of foot-candles is present. If daylight falls below the required level, the lamps/ballast system is engaged to compensate with artificial light. Typical harvesting applications are in large facilities with window walls and in commercial and institutional buildings using skylights.

Load schedules are used to determine light levels needed in building space(s) to minimize energy consumption. For example, a facility manager may recognize that the conference room is used every day from 10 a.m. to 11 a.m. The lighting system could be programmed to dim the lights for the hours that the room is not occupied.

Load shedding is used to determine appropriate light levels while minimizing energy consumption and lowering operating costs during peak hours. Utility companies often charge premiums for energy usage during these times. Load shedding generally operates with daylight harvesting by employing natural light and dimming the lighting as a system, therefore "shedding" energy. Facilities operating with set schedules can reduce energy consumption with load schedules. Maintaining proper light levels and dimming the lighting system when appropriate also support facility energy management.

Maintenance is easy on these systems. Most fluorescent electronic dimming ballasts now include circuitry that monitors lamp cathode voltage, which protects lamp life and safeguards the ballast against improper installation. The ballasts also ignite lamps at any preset level, so the ballast no longer has to be on 100 percent to ignite the lamp.

Dimming models maintain light levels over the life of a system. Normal systems' levels (at full output) tend to decrease over time due to lamp lumen depreciation and dirt and dust accumulation. Since dimming ballasts used in conjunction with photocells do not usually operate at full output, the system can adjust automatically to maintain light levels even with lamp lumen depreciation and dirt accumulation.

The Right Approach

The two main types of fluorescent dimming systems are continuous and light level switching. Continuous allows the user to set the lighting at any desired level. Light level switching, on the other hand, uses preset levels and standard wall switches that let the user manually adjust the dimming to preset levels or wire the switch with a photocell that will automatically adjust the light to the established preset levels.

Continuous systems maintain full range dimming from 100 to five percent. The user can manually set the light level at a preferred output. Typical applications for continuous systems are conference rooms that require darkness for presentations, but also must yield enough light for writing. They provide a cost-effective solution for new construction as well as renovations, with energy savings up to 80 percent.

Light level switching uses preset levels. This system can operate with two regular wall switches instead of installing a low voltage dimming control. Two types are available: 100 to 50 percent; and 100 to 60 to 30 percent. Light level switching is an ideal alternative for inboard/outboard switching and low voltage dimming controls.

Better aesthetics are achieved because all lamps in the fixture dim to the fixed light level, compared to inboard/outboard switching which turns off one or two lamps. Both new construction and renovations benefit from light level switching with savings of up to 55 percent.

Fluorescent dimming systems provide creative energy-efficient options for lighting commercial, institutional, and even industrial facilities. Every building, no matter how small, can benefit by incorporating such a system. With energy concerns becoming more prominent, the realized energy savings dimming systems provide make them an ideal lighting application solution.