The scoop on electronic ballasts

Higher light output and energy savings push electronic ballasts to the forefront.

By Athanasios Papademos, PE, technical director of electrical engineering, Albert Kahn Associates, Detroit October 23, 2007

A valuable tool in any sustainable designer’s toolbox, electronic ballasts powering fluorescent light sources offer a plethora of benefits over magnetic ballasts–not to mention incandescent lamps. Not only do they readily lend themselves to being controlled through building management systems, daylight sensors, occupancy sensors, and other similar devices, but such lighting systems controlled by a combination of these devices can actually provide energy savings in the 30% to 40% range.

Taking a quick look at the history of the fluorescent lamp, it was Peter Cooper Hewitt ate the fluorescent lamp.

Years later, electronic ballasts came on the scene. First introduced to the marketplace around 1988, these ballasts use electronic components to convert 60 Hz voltage and current to high frequency to operate the fluorescent lamp. They are more efficient than electromagnetic ballasts, providing energy savings that continue to improve almost on a yearly basis. Even though in 1988, less than 1% of ballasts used in the United States were electronic type, by 1998, approximately 40% of ballasts shipped were electronic.

Electronic ballast advantages
Why all the hype about electronic ballasts? The technology provides higher light output than electromagnetic ballasts at the same power input level and, used appropriately in design calculations, energy savings can be realized by using less fixtures to achieve the same overall light levels.

For peak lighting performance, ballasts should be specified to match the requirements of the lamp types they will drive. Fortunately, most electronic ballast manufacturers have developed a variety of ballast types for the various available lamps. Even though the same can be said of electromagnetic ballasts, the numbers of available ballast types are considerably smaller than the electronic ones.

There are also some advantages that are the direct result of the ballasts’ construction. For example, the familiar “hum” of electromagnetic ballasts has all but been eliminated, color rendering has improved, and lamp flicker has been greatly reduced–and in most instances eliminated.

Yet another advantage is the effect they have on HVAC systems. Because equal or more light can be delivered to the space for lower input wattage, further energy savings can be realized by reducing the heating load on the system.

At the same time, designers should use caution when designing lighting for sensitive electronic areas as the use of electronic ballasts is probably inappropriate for these areas.

Finally, the numerous combinations of lamp and ballasts available from today’s manufacturers provide excellent opportunities for energy savings, increased/decreased light levels within code-mandated parameters, and control for visual comfort in the design of lighting systems.

More recent developments
Although already available for a few years, digital addressable lighting interface (DALI) is a fairly recently developed ballast standard that creates unique building blocks for lighting control, using an open communication protocol. Each DALI ballast, technically considered to be electronic, has a specific address that enables it to be controlled individually or in groups, from a variety of manual or automatic controls, and independently of the circuit wiring. A DALI system has many components that need to be defined precisely, but the flexibility it offers is tremendous.

In general, electronic ballasts use three methods of starting: instant start, rapid start, and programmed start. The first two methods also are available in electromagnetic ballasts, while the last one is offered only by electronic ballasts.

Instant start provides the most energy-efficient operation for T8 lamps and should be used in applications where the lamps will operate more than three hours per start.

Rapid start ballasts are intended to prolong lamp life, with a 15% to 25% increase in switch cycles before failure, depending on individual ballast design.

Programmed start ballasts, the most recently developed—although already around for about a decade—are best suited for applications where the lamps will operate less than three hours per start and offer an increase in switch cycles before failure of 100% or more over the rapid start ballasts. Recent programmed start ballast designs offer energy efficiencies that match those of instant start ballasts.

In terms of specifying lamp/ballast combinations, there are many types and sizes of fluorescent lamps, and a ballast can operate more than one lamp from within the same type. While the lamp characteristics are determined during manufacturing, its performance will depend on the “capabilities” of the ballast that drives it.

Legislative action
With an eye on energy efficiency, in 2000 the Dept. of Energy issued regulations governing the performance of ballasts. The regulations set new ballast standards requiring energy-efficient ballasts to be used in all new commercial fluorescent fixtures manufactured after April 1, 2006, and for most replacement applications after July 1, 2010. As of April 1, 2005, ballasts used for F40T12 and F96T12 lamps had to meet new ballast efficacy factor (BEF) requirements.

Further, ASHRAE /IESNA Standard 90.1 provides guidelines for the design and control of HVAC and lighting systems which, when implemented, should result in the efficient use of energy. Most of the building codes adopt these guidelines into the codes by reference, creating a means of enforcing compliance with the standards. When first issued in 1999, ASHRAE/IESNA Standard 90.1 set upper limits for lighting power density (Watts/square foot) for building types that, in many instances, were 50% of the densities used by previously acceptable designs. The 2004 issue of the standard further reduces the allowable power densities by an additional 15% to 30%, depending on the building area type.

Picking up on the sustainable design wave, many electric utilities also have provided rebates for revisions to building lighting systems that result in reduced energy demand. The Energy Policy Act of 2005 provides federal tax credits for replacement lighting systems that meet certain energy use conditions and electronic ballasts can enhance the chances for compliance with the programs.

The taxonomy of ballasts
When specifying ballasts, it’s important to understand the definitions of certain key terms:
Ballast efficacy factor (BEF) is used to compare the efficiency of various lighting systems.

It is defined as:
BEF = ballast factor x 100/input Watts

It should be used only in comparing ballasts within a given type of lighting system.
Ballast factor (BF) quantifies the light-producing ability of a fluorescent lamp/ballast combination relative to a reference ballast. The reference ballast is defined by ANSI. Note that a ballast can have one BF for standard lamps and a different one for energy-efficient lamps.

Power factor (PF) is a measurement of how efficiently the ballast uses power supplied by the source.

It is expressed as:
PF = input Watts / (input Volts x input amperes)

Ballasts are classified as high power factor (HPF), low power factor (LPF), or power factor corrected (PFC). In most commercial applications HPF ballasts are used to minimize wiring costs.

Total harmonic distortion (THD) is the measurement of the distortion of the sinusoidal voltage or current waveform caused by the ballast’s components. While not directly related to the lighting performance of the fixture, high THD values can adversely affect the wiring system through overheating of the wires. Ballasts should have a THD of less than 20%.