Ballast

[garcia]

What is ballast, in the context of florescent lights, and what purpose does it serve? Thank you.

[Kerplunk]

A ballast serves two functions: 1. Provide the starting kick. 2. Limit the current to the proper value for the tube you are using. In the old days fluorescent fixtures had a starter or a power switch with a 'start' position which is in essence a manual starter. Some cheap ones still do use this technology. The starter is a time delay switch which when first powered, allows the filaments at each end of the tube to warm up and then interrupts this part of the circuit. The inductive kick as a result of interrupting the current through the inductive ballast provides enough voltage to ionize the gas mixture in the tube and then the current through the tube keeps the filaments hot - usually. You will notice that a few iterations are sometimes needed to get the tube to light. The starter may keep cycling indefinitely if either it or one of the tubes is faulty. While the lamp is on, a preheat ballast is just an inductor which at 60 Hz (or 50 Hz) has the appropriate impedance to limit the current to the tube(s) to the proper value. Ballasts must generally be fairly closely matched to the lamp in terms tube wattage, length, and diameter. All taken from http://members.misty.com/don/f-lamp.html#fb1

[mac309]

If that sounds complicated hopefully this will be clearer. the ballast is just a coil, which creates magnetism within itself.The starter is just a switch will allows the two ends of the tube to heat up the Gas(Low preassure mercury vapour) when the starter switches the circuit becomes open and the magentism in the ballast collopses and gives a voltage of approx 300V across the ends of the tube. IIf the gas atoms are warm enough the voltage will cause a flash across the middle, heating up the rest of the gas.in the tube. Being that it is a metal vapour gas electric current will flow through the tube without wires.After the tube has lit the ballast serves absolutly no purpose as its only there to create the initial 300v..

[IndieSinger]

... and if that sounds complicated, hopefully this will be clearer. It is a little pixie who strikes a bright match when you flick the switch.

[BenDToy]

Indiesinger I definitely prefer (and understand) your answer - I award you 3 stars!

[garcia]

thanks folks.