Savings in the Spotlight

Dimmable ballast technology gives managers options for improving lighting systems and lowering energy costs

By John L. Fetters  

Controlling lighting levels gives organizations many advantages, including operational savings that result from lower energy use and the flexibility to change light levels for different activities. Controlled lighting is one of the most cost-effective ways to improve the quality of new or existing buildings and enable people working in them and using them to be more productive and satisfied.

For example, productivity rises when occupants in private offices can change light levels in their workspaces, according to recent studies by the Lighting Research Center (LRC). The studies also found that lighting controls save energy — in some cases, up to 46 percent.

Dimmable ballast technology offers one increasingly popular option for controlling lighting levels in commercial and institutional facilities.

A Closer Look at Dimming

Most dimming systems today use electronic dimming ballasts, which operate fluorescent lamps at high frequency, just like fixed-level electronic ballasts. A control circuit, either in the form of separate low-voltage control leads from each ballast or incorporated in the line circuit, differentiates them from fixed-light ballasts.

Dimming ballasts fall into two categories based on dimming ranges. For energy-management applications, the available range is 100 percent down to 5 percent. For applications requiring lower lighting levels, architectural dimming models provide a range of 100 percent down to 1 percent.

Recent developments in dimming electronic ballasts bring their promise closer to reality. Most electronic-ballast manufacturers now offer dimming products, including one-, two-, and three-lamp versions. Ballasts are available for dimming most linear fluorescent lamps, including T5 high-output (HO) lamps.

Most new-generation ballasts provide either dual- or multi-line voltage models. They also provide overvoltage protection of low-voltage control leads in case line voltage is applied accidentally.

Until recently, the most common lighting control method was low-voltage control. But a new group of dimming ballasts accepts AC line-phase control signals from incandescent wall-box dimmer controls, dimming fluorescent lamps accordingly. Many of the new products start lamps at any dimmer setting, and most units available today measure less than 15 percent total harmonic distortion throughout the dimming range and come in a small package.

Several manufacturers also offer new dimming ballasts for rapid-start, four-pin compact fluorescent lamps (CFL). Most of these offerings are for the higher-wattage CFLs — 26-42 watts. Dimming ranges vary by manufacturer, and currently, the lowest dimming limit is 10 percent, though some models dim to 20 percent.

Addressing Cost

Cost is the only disadvantage maintenance and engineering managers cite when asked about dimming technology, but advances in dimming-ballast technology have enhanced the benefits while reducing the cost.

For example, the latest generation of electronic dimming ballasts has a low-end of 5 percent light output. But only a few years ago, dimming ballasts for energy-management applications could dim down only as far as 20 percent. Five percent is satisfactory for many manual-dimming applications, such as conference or presentation rooms.

Until recently, these applications required two systems. One system provided a fixed-light ambient level, usually a fluorescent system, and the other provided dimming, usually an incandescent system. Now, facilities can install one fluorescent system with affordable fluorescent dimming ballasts and meet the needs of the space.

In many cases, managers can modify the lighting system for an existing space by replacing a fixed-light ballast with a dimming ballast. The user can select ballasts that have low-voltage control, which allows control of groups of fixtures independent of the power wiring constraints, or the user can select power-line control, which allows all ballasts on the system to be controlled by an existing or new wall-box dimmer.

Line-voltage control, using phase control from wall-box dimmer, is a simple way to upgrade a two-system conference room. The main advantage for upgrading an existing system is lower operating cost. New installations benefit from lower installation costs.

Compact fluorescent dimming ballasts also are available in either 0- to 10-volt, low-voltage control or line-voltage dimming. This approach is another option for replacing an incandescent downlight system with a fluorescent dimming system. In this case, managers need to purchase new CFL downlights with dimming ballasts.

Classrooms in the Spotlight

Classroom lighting also can benefit from dimming technology. Schools can save energy and money with both manual and automatic dimming. Teachers can improve classroom environments by using handheld remote controls to dim classroom lights for computer use or when showing visuals. This strategy can reduce glare and eye fatigue and generate energy savings.

The previous example of manual control also can be extended to automatic dimming systems, such as daylight-harvesting control in offices, where there is sufficient daylight to obtain savings from dimming electric lights.

Daylight harvesting uses electronic lighting controls to automatically adjust electric lighting output based on the amount of daylight entering a space. The control must meet occupants’ visual and comfort needs, because daylight varies over each day and through the seasons.

Occupants often report problems related to low light levels or sudden changes in levels. Using a fade control can slow the response time, and commissioning can prevent too-low light levels. When well-designed systems are in place, occupants usually are not aware that the lighting system is being controlled.

The two main elements of state-of-the-art daylight harvesting systems are photosensors and electronic dimming ballasts, connected with low-voltage wiring. A system in which a photosensor detects and responds to both daylight and light output from the lighting system it controls is called a closed-loop system.

The light detected by the sensor forms a feedback path that controls the system output to keep the light level at a setpoint. Another example of a closed-loop feedback system is a thermostat that controls a heating or cooling system.

Daylighting and controls are an ideal match that can help managers maximize peak electrical demand savings from lighting systems operating at reduced power and the associated reduction in the chiller plant power. When lighting controls respond to occupant needs, dimming strategies can provide savings and improve the work environment.

When applications involve multiple lighting systems in one room, many facilities choose preset dimming systems. This set-up allows users to change light levels for each system for a specific function, such as showing visuals, at the touch of one button. With separate dimmer controls, each system must be set by changing each dimmer individually.

A Digital Dimming Standard

Digital dimming uses electronic ballasts that are designed to accept digital control commands over a network akin to those used by computers. These digital commands set the lighting levels for individual fixtures. Because lighting-control requirements are rather undemanding — compared with complex computer networks — the resulting digital-command controls are simple networks.

The most promising standard for digital dimming, the digital addressable lighting interface (DALI), is just starting to show up in the U.S. market. This digital standard gives ballast and fixture manufacturers common rules for controlling ballast operation. Building management systems, DALI controllers, or PCs equipped with appropriate software can address specific fixtures equipped with DALI ballasts without rewiring, as is required now for present low-voltage, analog dimming systems using 0- to 10-volt control.

Individual fixtures can be assigned through the software to more than one zone, enhancing control flexibility. Scenes then can be programmed with zones set at different lighting levels. Two-way communications provides additional features.

In addition to digital dimming ballasts, DALI systems can communicate with sensors to obtain information on light levels, occupancy or fixture status. For example, system users can track lamp burnouts, schedule maintenance or apply sensor input to the control logic, further expanding control flexibility.

While some manufacturers introduced DALI ballasts late in 2001, most major U.S. ballast manufacturers plan to have DALI ballasts available in 2002. Costs are expected to be about 1.5 times the cost of analog — 0- to10-volt — dimming ballasts.

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  posted on 4/1/2002   Article Use Policy

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