The mercury atoms in the fluorescent tube must be ionized before the arc can "strike" within the tube. For small lamps, it does not take much voltage to strike the arc and starting the lamp presents no problem, but larger tubes require a substantial voltage (in the range of a thousand volts). In some cases, that is exactly how it is done: "instant start" fluorescent tubes simply use a high enough voltage to break down the gas and mercury column and thereby start arc conduction. These tubes can be identified by the facts thatthey have a single pin at each end of the tube and the lampholders that they fit into have a "disconnect" socket at the low-voltage end to assure that the mains current is automatically removed so that a person replacing the lamp can not receive a high-voltage electric shock.
In other cases, a separate starting aid must be provided. Old fluorescent designs used a combination filament/cathode at each end of the lamp in conjunction with a mechanical or automatic switch that would initially connect the filaments in series and thereby "preheat" the filaments prior to striking the arc. Because of thermionic emission, the filaments would readily emit electrons into the gas column, creating a glow discharge near the filaments. Then, when the starting switch opened up, the inductive ballast would create a voltage surge which would (usually) strike the arc. If so, the impinging arc then kept the filament/cathode warm. If not, the starting sequence was repeated. If the starting aid was automatic, this often led to the situation where an old fluorescent lamp would flash time and time again as the starter repeatedly tried to start the worn-out lamp. More advanced starters would "trip out" in this situation and not attempt another start until manually reset.

Newer lamp and ballast designs (known as "rapid start" lamps) provide true filament windings within the ballast; these rapidly and continuously warm the filaments/cathodes using low-voltage AC. Unfortunately, there is no inductive voltage surge produced so the lamps must usually be mounted near a grounded (earthed) reflector to allow the glow discharge to propagate through the tube and initiate the arc discharge. Electronic ballasts often revert to a style in-between the preheat and rapid-start styles: a capacitor or other electronic circuit may join the two filaments, providing a conduction path that preheats the filaments but which is subsequently shorted out by the arc discharge. Generally this capacitor also forms, together with the inductor that provides current limiting in normal operation, a resonant circuit, increasing the voltage across the lamp so that it can easily start. Some electronic ballasts use programmed start, the output AC frequency is started above the resonance frequency of the output circuit of the ballast, and after the filaments are heated the frequency is rapidly decreased. If the frequency approaches the resonant frequency of the ballast, the output voltage will increase so much that the lamp will ignite. If the lamp does not ignite an electronic circuit stops the operation of the ballast.

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