Fluorescent lamp is by far the most widespread of all discharge lamp type. It is employed almost universally especially in office lighting. The most common type of fluorescent lamp is tubular linear in shape ranged from 600mm (18W) to 1500mm (58W) in length. The discharged tube has an electrode sealed into each end and is filled with an inert gas and a small amount of mercury, the latter being present in both liquid and vapour form. The inside of the tube is coated with a mixture of fluorescent powders.

Fluorescent Lamp Operating Principle

These convert the ultraviolet radiation of the mercury discharge into longer wavelengths within the visible range. A great many different fluorescent powders or "phosphors" are available for any desired colour temperature and colour rendering characteristics.

Unlike an incandescent lamp, a fluorescent lamp cannot be connected directly to the mains. Some device to limit the electric current flowing through it must be included in the circuit. This device can be electromagnetic (conventional) ballast with starter or electronic ballast operating at high frequency.

Fluorescent Lamp Circuits Fluorescent Lamp Circuits

The basic construction of typical electronic ballast involves a low-pass filter, rectifier, buffer capacitor and a high frequency (HF) oscillator. The basic operation principle is that after passing a low-pass filter, the mains voltage at 50Hz power frequency is rectified in an AC/DC converter. This converter also contains the buffer capacitor, which is charged with a DC voltage. In the HF power generator this DC voltage is transformed into a HF voltage, which provides the power to the lamp.

The ballast takes advantage of a characteristic of fluorescent lamp whereby greater efficacy is obtained at high operating frequency above 10kHz. Efficacy due to high frequency operation is increased by about 10% thereby enabling the lamp to be operated at a lower input power than at 50Hz mains power frequency. Ballast losses are reduced compared to conventional (electromagnetic) ballast, as the solid state circuit contains no copper windings. In the case of a twin 1200mm 36W lamp circuit the losses can be reduced from 24W to a mere 6W when using an electronic ballast. The overall achievement in a suitable luminaire, therefore, is an energy reduction in the region of 20% to 30%. These energy saving features enable lighting levels to be maintained with a dramatic cut in electricity costs. With less heat generated, the cooling load on air conditioning equipment will also be reduced.

The overall lighting system efficacy can be increased by 20 to 30 percents due to three main factors:

  1. Improved lamp efficacy at high frequency operation.
  2. Reduced circuit power losses.
  3. Lamp operates closer to optimum performance in most enclosed luminaires.

Other benefits electronic ballast offered include:

Common Lamp Wattage of Fluorescent Lamps

Nominal Lamp LengthT12T8T8 (HF)T5
600mm 20W 18W 17W 14W
1200mm 40W 36W 32W 28W
1500mm 65W 58W - 35W

Suitability of Ballast Types for various Fluorescent Lamp Groups

Lamp GroupLow Loss BallastElectronic BallastDimmable Ballast (Magnetic)Dimmable Ballast(Electronic)
T12 (38mm) Yes No Yes No
T8 kryton-filled (25mm) Yes Yes No Yes
T8 argon-filled HF (25mm) No Yes No Yes
T5 (16mm) Yes Yes No Yes

Product Range available for Electronic Ballasts

Product Range of Electronic Ballasts Available for T8 Lamps
1x18W 2x18W 3x18W 4x18W 1x36W 2x36W 3x36W 1x58W 2x58W
Product Range of Electronic Ballasts Available for T5 Lamps
1x14W 2x14W 3x14W 4x14W 1x21W 2x21W 1x24W 2x24W
1x28W 2x28W 1x35W 2x35W 1x49W 2x49W 1x54W 2x54W

To ensure quality of electronic ballasts, the following national or international standards must be specified:

The electromagnetic compatibility (EMC) is basically determined by the characteristics of electronic ballast in combination with the luminaire design. The following technical aspects and basic rules have to be considered by designers in applying electronic ballasts in luminaires:

  1. Effective protective earth must be provided for all exposed conductive parts of the metal luminaire.
  2. Functional earth is required to fulfil certain EMC requirements or to guarantee proper operation of the system.
  3. Ensure a firm electrical connection between the electronic ballast and the metal luminaire.
  4. Mains power wiring and lamp wiring inside luminaire must be as short as possible, firmly mounted on spacers and far away from each other to minimise stray capacitance.
  5. Provide good electrical contact between metal luminaire and reflector and/or louvres. Reflector and louvres serve as a shielding around the lamp.

Check List for Electronic Replacement in Existing Luminaires:

For more information about the application of electronic ballasts, please contact the Energy Efficiency Office at tel. no. 2808 3465 .