Gas discharge lamps have been widely used in various residential, commercial and industrial sectors because of their high efficacy (lumen per watt). However, as they cannot be directly connected to the ac mains, they are driven by a device called a ballast. The ballast generates a high voltage and applies it across the two ends of the lamp to ignite it. The ballast also regulates the current flowing through the lamp.
Ballasts can be categorized into two main types, namely electromagnetic and electronic ballasts. Electromagnetic ballasts have the advantages of extremely high reliability and long lifetime, and robustness against transient voltage surge (e.g. due to lightning) and hostile working environment (e.g. high humidity and wide variation of temperature). Particularly, they offer superior lamp-arc stability performance in high-intensity discharge (HID) lamps. Also, the inductor core materials and winding materials are recyclable.
Electronic ballasts for fluorescent lamps (low-pressure discharge lamps) have been widely used and it has been shown that their use has an overall economic benefit. They also have good performance characteristics, such as high input power factor, low input current total harmonic distortion, low electromagnetic interference (EMI), good lamp current crest factor, and low flickering. Moreover, operating at high frequency (typically above 20-kHz) electronic ballasts can eliminate the flickering effects of fluorescent lamps and achieve a higher efficacy than mains-frequency (50 Hz or 60 Hz) operated electromagnetic ballasts. Therefore fluorescent lamps driven by electronic ballasts consume less energy for the same light output when compared with lamps driven by electromagnetic ballasts.
Fluorescent lamps contains mercury vapor inside the glass tube. This is a serious concern for landfills and waste incinerators where the mercury may be released and contribute to air and water pollution.
With recent advancements in microelectronics technology, solid-state lighting, such as LED, has become popular in general lighting and special purpose lighting. Compared with fluorescent lamps, LEDs have a long life expectancy, are resistant to vibration failure, consume low amounts of power, operate on a low voltage, are highly reliable, and contain no mercury. It would be advantageous to have LED lamps that can directly replace the gas discharge lamps in existing light circuitry or fixtures. However, where this has been tried before, although the existing fluorescent lamp fixtures may remain unchanged, the ballasts installed inside the lamp fixtures have to be removed or changed. Moreover, it requires rewiring of the lighting circuit.
The key challenge in designing an LED lamp for use with an electronic ballast is the way of handling the difference between the rated power delivered by the electronic ballast and the required power of the LED lamp. In general, the required power of the LED lamp is only about one-half of the rated power of the electronic ballast.