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Digital Ballasts, also called solid-state ballasts are the newest technology when it comes to High Intensity Discharge lighting (HID). They are known to provide significant energy savings over magnetic ballasts. Aside from greater efficiency, the voltage regulation is far superior allowing for much longer bulb life. This is an outstanding advancement in technology within the ballast manufacturing industry when considering the savings for large scale users such as municipalities. These end users will see benefits worth billions of dollars, with a 20-30% reduction in energy costs.

The technology has only been in use for a few years now, however technology advancements are shaping the industry to replace old style magnetic core-and-coil ballasts that account for 99% of a multi-billion dollar industry. Electronic ballasts are used more often than one would imagine. Such uses pertain to train lighting, street lighting, aircraft lighting, greenhouse lighting, stadium and building lighting, and many other applications that use HID lighting systems.

One of the most apparent benefits of digital ballasts is that the HID bulb life cycle is increased as compared to using a magnetic ballast. Magnetic ballasts reduce the HID bulb life by as much as 50-60% after one year, whereas electronic ballasts reduce the HID bulb life by 20-25% after one year. These figures are averages for normal use of HID bulbs, with industries such as greenhouses having a much shorter life cycle for their bulbs due to strenuous use of bulbs to mimic the sunlight. Yet another reason why digital ballasts are favorable when it comes to reducing costs. It is a rather interesting concept that many users are beginning to realize – spend a little more now, save a lot more later.

Use

Digital ballasts and magnetic ballasts are used in many applications ranging from lighting systems in streets, trains, airplanes, stadiums, greenhouses, warehouses, and many more. Magnetic ballasts are still used in a wide range of applications where noise, heat, EMI, and power loss aren’t major concerns to users. However, many of the new applications require the use of the more technologically advanced electronic ballasts that control voltage fluctuations, have higher BFs, and reduce heat and noise for its operators. Some of the first users of electronic ballasts were greenhouses due to the reduction in flickering and the ability of the Digital ballast to imitate the sun so closely through the full spectrum of light colors. Some of the newer generation ballasts can operate both High Pressure Sodium lamps as well as the Metal Halide lamps, thus saving money for the greenhouse users who are in need of both types of lamps.

History

To better understand the evolution of ballasts that spurred the innovation and transformation from magnetic ballasts to digital ballasts we must first look at the characteristics of different ballast forms.

Magnetic Ballasts

Magnetic ballasts are core-and-coil electromagnetic ballasts. They contain magnetic core of several laminated steel plates wrapped with copper windings. The power loss of these ballasts is greater than electronic ballasts due to their need to consume 20%-30% more power than electronic ballasts. Magnetic ballasts operate at line frequency of 60 hertz (Hz) in North America. They are also least expensive ballasts. However due to their high power consumption characteristic the Department of Energy plans to eliminate magnetic ballasts in new construction and renovation of commercial and industrial buildings. Currently many governments across the world concerned with energy efficiency are looking forward to replacing the older magnetic ballast technology in lieu of keeping with energy saving initiatives.

Hybrid Ballasts

Hybrid ballasts use magnetic core-and-coil transformer and an electronic switch for the electrode-heating circuit. Much like magnetic ballasts, hybrid ballasts operate at line frequency of 60 Hz in North America. These types of ballasts, which are also referred to as “cathode-disconnect ballasts”, disconnect the electrode-heating circuit after they start the lamps. These ballasts were the intermediate step to dealing with issues caused by magnetic ballasts and are in the mid range when thinking about costs.

Digital Ballasts

Digital Ballasts, also known as “solid-state” ballasts allow manufacturers to replace the core-and-coil transformer with electronic components that operate lamps within a 20,000 Hz (20 kHz) to 60,000 Hz (60 kHz). This essentially translates to nearly half the power loss of magnetic ballasts. Lamp efficacy also increases by approximately 20% as compared to 60 Hz operation when a lamp operates at a frequency above 20 kHz. Other benefits of using digital ballasts are reduction in noise, light weight, and reduction in lamp flickering.

Physical Characteristics

Digital ballasts use either a metal or plastic casing, however aluminum casing seems to be a preferred choice with heat sinkers included in the design surrounding the ballast. This in turn reduces the ambient atmosphere more significantly than the plastic casing, or casing that uses insufficient heat sinkers.

Dimensions

Digital ballasts can be smaller than magnetic ballasts in most cases. Ballast shape also affects heat dispersion and more cylindrical shapes disperse heat better than cubic shapes, especially when fans are involved as internal cooling components.

Weight

Digital ballasts tend to be lighter than magnetic ballasts. Top of the line Digital ballasts weigh less than 5 lbs. Some electronic ballasts are filled with a resin that protects the circuit board and capacitors from outside factors such as moisture and humidity. However, carefully designed ballasts with resin coated components can still weigh less than magnetic ballasts.

Sound

Magnetic ballasts produce a humming noise caused by vibration of the laminated magnetic core. Digital ballasts on the other hand are significantly less noisy because they are made of different materials and operate at higher frequencies, thus reducing vibrations. Although electronic ballasts are usually quieter than magnetic ballasts, factors such as mounting method, location of the ballast, and even loose parts in the fixture can enhance the noise a ballast may produce.

Flicker

Operating lamps on alternating current modulates the light output, such that a noticeable modulation is called a flicker. Electronic ballasts operate at frequencies of 20 kHz or higher, refreshing the phosphors so rapidly that the light modulation is imperceptible. The flicker index is used for measuring perceptible light modulation ranges from 0-1, with 0 indicating lower possibility of flickering and 1 indicating the highest. Lamps operated on magnetic ballasts have a flicker index between 0.04-0.07 while digital ballasts have a flicker index of below 0.01. Ballasts in Use

References http://www.lrc.rpi.edu/nlpip/publicationDetails.asp?id=129&type=1 http://avionlighting.com/index.php?product=test http://www.esource.com/escrc/0013000000DP22YAAT/BEA1/PA/PA_Lighting/PA-55 http://www.bghydro.com/bgh/static/articles/0506_digiballasts.asp

• Proposed deletion as of 18 June 2012