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 (40W) 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.

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.

The basic construction of typical electronic ballast involves a low-pass filter, rectifier, buffer capacitor and a high frequency 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 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:

• Rapid or instant starting of lamp without flickering.
• Single ballast can be designed to drive one, two, three or even four lamps.
• Increased lamp life due to lower lamp operating current.
• Quiet operation without audible noise.
• No visible flicker during operation.
• No stroboscopic effect and HF operation.
• Lower total harmonic distortion (THD)
• High total power factor due to low THD and cosq .
• Cooler ambient temperature inside luminaires for optimum operation of lamp, control gear, capacitor and batteries for emergency lighting.
• No carbonisation and blackening to luminaire and decoration in the vicinity.
• Less effect on variation of luminous flux due to mains supply voltage fluctuations.
• Much lighter in weight.

Common Lamp Wattage of Fluorescent Lamps

Suitability of Ballast Types for various Fluorescent Lamp Groups

Product Range available for Electronic Ballasts

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

• IEC 928/EN 60928/GB 15143-94 A.C.-supplied electronic ballasts for tubular fluorescent lamps - General & safety requirements
• IEC 929/EN 60929/GB 15144-94 A.C.-supplied electronic ballasts for tubular fluorescent lamps - Performance requirements
• IEC 1000-3-2/EN 61000-3-2 Limits for harmonic current emission (equipment input current £ 16A per phase)
• EN 55015 Limit and method of measurement of radio disturbance characteristics of lighting and similar equipment
• FCC, 47 CFR Part 18: non-consumer equipment: conducted interference and radiated interference > 30Mhz

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:

• T8 fluorescent lamp uses 10% less energy than its T12 or T10 counterparts. If the existing lamps are T12 or T10, it is more beneficial to change them to T8 prior to retrofit with electronic ballast.
• Electronic ballast is designed for specific lamp type and lamp wattage, make sure that the appropriate type of electronic ballast is selected for replacement.
• It is more cost effective to use electronic ballasts to operate multi-lamps in luminaires with more than one lamp.
• For location where frequent switching is required, warm or rapid start electronic ballasts have to be specified.
• For location where frequent switching is not required, cold or instant start electronic ballasts could be used. Cold start electronic ballasts do not require preheating for starting and are more energy efficient.
• To avoid high inrush current and incidental MCB tripping, a lighting switch should not operate more than 10 luminaires with electronic ballasts.
• All existing conventional ballast, starter and power factor correction capacitor must be removed from the retrofit luminaire.