China manufacturer of magnetic ballasts for metal halide flood lights & hps flood lights

Fluorescent light fixtures are popular because of their energy efficiency and long lifespan compared to incandescent bulbs. However, fluorescent lights produce light in a different way from lights that use resistors, and they require specialized equipment in order to operate. The ballast is one of the most important parts of the fluorescent lamp, and a magnetic core was part of its original makeup.
One characteristic of core and coil magnetic ballasts operating at 60 Hz, is the generation of audible noise. Noise can be increased by high temperatures, and it is amplified by certain luminaire designs. The best ballasts use high quality materials and workmanship to reduce noise. Noise is rated A, B, C, or D in decreasing order of preference. An "A" rated ballast will hum softly; a "D" rated ballast will make a loud buzz. The number of ballasts, their sound rating, and the nature of ambient noise in the room determine whether or not a system will create an audible disturbance.

Virtually all energy-efficient magnetic ballasts for F40T12 and F32T8 lamps are "A" rated, with a few exceptions, such as low temperature ballasts. Still, the hum of magnetic ballasts may be perceptible in a particularly quiet environment such as a library. Well-designed electronic high-frequency ballasts, on the other hand, should emit no perceptible hum. All electronic ballasts are "A" rated for sound.
A gas that reacts to an electrical current passing through it fills fluorescent lights. As the electrical current jumps across the gas bulb, the gas atoms become energized and release energy particles, which hit the coating on the inside of the bulb. This coating also becomes energy, but when it releases energy particles it releases them as light waves, providing fluorescent light.

Today, fluorescent electronic ballasts have replaced many of these older versions.