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Function of the Fluorescent Ballast

Fluorescent lamps require the use of a ballast to efficiently transform electrical energy into light. The ballast provides a high initial voltage to initiate the discharge, then limits and regulates the lamp current to stabilize light output.

Starting Modes


This is the most popular mode of operation presently in use. Lamp filaments are heated prior and during operation for optimim lamp life. It is also the only system suitable for wide-range dimming applications.

In this mode, lamp filaments are not preheated and the ballast must provide a starting voltage about three (3) times the normal voltage thus reducing lamp life by 25%. Another similar mode is the cathode cutout ballast which removes filament power after starting - which also reduces lamp life.

Magnetic Ballast

Most of the ballasts currently installed are magnetic type.

The inherent deficiencies of this technology are as follows:

  • - Important energy losses and excessive heat dissapation reduce efficiency and light output.

  • -Flickering: At 60 Hz, the gas inside the lamp is extinguished 120 times per second creating eye strain.

  • -Weight: This ballast is quite heavy because of metal and tar content (approx. 4 pounds).

  • -Noise: In time, noise is audible in offices with this type of ballast.

  • -Light output and lamp life may vary with line voltage variations.

  • -This technology does not permit proper dimming of fluorescent lamps.


    The main difference between the magnetic and the electronic ballast is the frequency at which the lamps are operated.

    An electronic circuit converts the 60 Hz to High Frequency (20 - 40 KHz) with increased lamp efficiency and reduced ballast losses. Combined with the T8 lamp, an electronic ballast will provide evergy savings of 30 to 40%



    The power factor is defined as a ration of the real power to apparent power, the ideal being 1.0. Lamp Current Crest Factor:

    The ratio of the peak to the average (RMS) lamp current represents the current crest factor.

    Lamp manufacturers use and recommend 1.7 CCF maximum to calculate lamp life. Decreasing that ratio (peak) will result in longer lamp life.
    Harmonic Distortion:

    When a current wave shape deviates from the ideal sinusoidal current, harmonics are produced. Harmonic currents are higher multitude of the fundamental frequency and are expressed as a percentage of fundamentals. Harmonic distortions in an electric system are undesirable because of the effects that may result, such as: overloading of transformers and over current in neutral of a 3 phase system, interference with electrical or communication equipment.

    Electromagnetic Interference EMI/RFI

    Since electronic ballasts operate lamps at high frequency, they can generate in the air and the power system RFI and EMI that can interfere with communication and data processing systems. Electronic ballasts nust meet the North American "Standards" that limit the emissions: FCC, PART 18, 15V (Class "A") and CSA 108, 6-M91 for lower frequencies>


    Electronic ballasts are subject to various "STANDARDS" that guarantee minimal industry performances and safety: CSA-CZZ.2-74, UL945, ANSI-C81,11 and C6Z.41, IEE587, FCC-Part 18-15U Class "A" and CSA108, 6-M91.


    The ballast factor determines the light output for the lamp ballast system. It is expressed as a percentage of the measured lumen output of the system compared to the rated lumen measured using a speciallydesigned reference ballast (under "ANSI" test conditions). ANSI C82,11 has set the minimum B.F. at .85 for electronic ballasts.


    The ballast efficacy factor is a ratio of the ballast factor to the watts input to the ballast. The BEF is not a true measure of ballast efficiency as its value depends on the quantity of lamps operated. It is better to use the system efficacy calculation.


    The efficacy of a fluorescent lamp ballast system is better expressed in LUMEN/WATT and can be calculated as follows:

      Ballast Factor (%) divided by Input Power.

    This measurement allows one-to-one comparison between different ballasts by considering both the light output and the correlated power consumption of a lamp-ballast system.