Ballast is a device which is used with an electric-discharge lamp to attain the necessary circuit conditions for starting and operating lamps by providing starting voltage and current and by limiting the current during normal operation in electrical discharge lamps such as fluorescent lamps. Ballast can be of two types:
- Magnetic ballasts: These are also referred to as electromagnetic ballasts and made up of copper windings on an iron core.
- Electronic ballasts: Ballasts that employ semi-conductor components to increase the frequency of fluorescent lamp operation (normally in the 20-40 kHz range) are known as electronic ballasts.
These are smaller in size as smaller inductive components provide the lamp current control. Besides, they are more efficient as compared to magnetic ballasts since electronic high-frequency ballasts increase lamp-ballast efficacy, leading to increased energy efficiency and lower operating costs. Electronic ballasts operate lamps using electronic switching power supply circuits. They take incoming 60 Hz power and convert it to high-frequency AC (usually 20 to 40 kHz). Furthermore electronic ballasts are more competent than magnetic ballasts in converting input power to the proper lamp power. Also their operating of fluorescent lamps at higher frequencies reduces end losses, resulting in an overall lamp-ballast system efficacy increase of 15% to 20%. Electronic ballasts offer numerous other advantages over magnetic ballasts. They are:
- Electronic ballasts are readily available that operate three or four lamps, allowing the use of a single ballast in 3-lamp and 4-lamp luminaires. This reduces both installation and field wiring labor costs, and may wipe out the necessity of tandem luminaire wiring as required by the 1992 Energy Efficiency Standards for Residential and Nonresidential Buildings.
- Electronic ballasts are designed to operate lamps in either series or parallel mode. The advantage of the parallel mode of operation is that a single lamp failure will not affect the operation of the remaining lamps controlled by the same ballast. However, ballast losses will increase slightly in the parallel mode.
- Reduced weight
- Quieter operation
- Reduced lamp flicker
- Electronic ballasts are directly interchangeable with magnetic ballasts, and they are available to operate most full-size and compact fluorescent lamps.
Ballast Factor (BF)
It is the measured ability of particular ballast to produce light from the lamps it powers. It is derived by dividing the lumen output of a particular lamp/ballast combination by the lumen output of the same lamps on reference ballast. Hence, Ballast factor is the ratio of the luminous output of a lamp when operated on ballast to its luminous output when operated under standardized rating conditions. In other words, it is the percentage of rated lumens from the same lamp using commercial ballast as compared to ANSI reference ballast. Ballast factor is not a measure of energy efficiency. For example, a ballast factor of .96 means the commercial ballast produces 96% of light produced by ANSI reference ballast operating the same lamp. The ballast factor can be referred to in the catalogs from fluorescent or HID ballast manufacturers.
Ballast Efficacy Factor (BEF)
It is the ratio of the ballast factor to input power of the ballast i.e. input watts. It identifies the efficacy of a lamp/ballast system in comparison to other systems using the same type and number of lamps. The higher the BEF within the same lamp-ballast type, the more efficient is the ballast. Unlike Ballast factor, it is the measure of efficiency of fluorescent lamp ballasts.
Transformer hum or noise is inherent in lamp ballast. Most ballast has noise ratings on the label, A thru F, with A being the quietest. Generally a better grade of light will be less noisy. To avoid ballast hum or noise, make sure that the ballast is tightened securely in lamp fixture. Also make sure the fixture itself is tightened securely. Moreover voltage should be within the ballast rating. As soon as the ballast starts to go bad, the noise will get louder.
It is the power or energy dissipated in the ballast as heat which is not converted to lamp energy. Lamps and ballasts experience losses when operating together as a system. Ballast losses vary according to the type of ballast, depending on the design and manufacturer. By reducing ballast losses we can improve the efficiency of a fluorescent lamp-ballast system. In fact the losses in magnetic ballasts have been reduced by substituting copper conductors for aluminum and by using higher grade magnetic components. Ballast losses can also be reduced by using a single ballast to drive three or four lamps, instead of only one or two. Cautious circuit design increases efficiency of electronic ballasts.