Editing Fluorescent lamp (section)

====Electronic ballasts====
[[File:Fluorescent-lamp-electronic-ballast.webm|thumb|left|Fluorescent lamp with an electronic ballast]]
[[File:EL 2x58ngn.jpg|thumb|Electronic ballast for fluorescent lamp, 2×58&nbsp;W]]
[[File:Fluorescent Lamp Inverter.png|thumb|[[Electronic ballast]] basic schematic]]
[[File:TCS lamps2.jpg|thumb|[[Electronic ballast]]s and different compact fluorescent lamps]]Electronic ballasts employ [[transistor]]s to change the supply frequency into high-[[frequency]] [[alternating current|AC]] while regulating the current flow in the lamp. These ballasts take advantage of the higher efficacy of lamps, which rises by almost 10% at {{nowrap|10 kHz}}, compared to efficacy at normal power frequency. When the AC period is shorter than the relaxation time to de-ionize mercury atoms in the discharge column, the discharge stays closer to optimum operating condition.{{sfn|Kane|Sell|2001|p=182}} Electronic ballasts convert supply frequency AC power to variable frequency AC. The conversion can reduce lamp brightness modulation at twice the power supply frequency.

Low cost ballasts contain only a simple oscillator and series resonant [[LC circuit]]. This principle is called the [[Resonant inverter|current resonant inverter]] circuit. After a short time the voltage across the lamp reaches about 1&nbsp;kV and the lamp instant-starts in cold cathode mode. The cathode filaments are still used for protection of the ballast from overheating if the lamp does not ignite. A few manufacturers use positive temperature coefficient (PTC) [[thermistor]]s to disable instant starting and give some time to preheat the filaments.

More complex electronic ballasts use programmed start. The output 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.

Many electronic ballasts are controlled by a [[microcontroller]], and these are sometimes called digital ballasts. Digital ballasts can apply quite complex logic to lamp starting and operation. This enables functions such as testing for broken electrodes and missing tubes before attempting to start, detection of tube replacement, and detection of tube type, such that a single ballast can be used with several different tubes. Features such as dimming can be included in the embedded microcontroller software, and can be found in various manufacturers' products.

Since introduction in the 1990s, high-frequency ballasts have been used in general lighting fixtures with either rapid start or pre-heat lamps. These ballasts convert the incoming power to an output frequency in excess of {{nowrap|20 kHz}}. This increases lamp efficiency.<ref>{{cite web|title=Energy Conservation Standards for Fluorescent Lamp Ballasts|url=http://www1.eere.energy.gov/buildings/appliance_standards/residential/pdfs/flballast_preanalysis_ch3.pdf|archive-url=https://web.archive.org/web/20120803184327/http://www1.eere.energy.gov/buildings/appliance_standards/residential/pdfs/flballast_preanalysis_ch3.pdf|url-status=dead|archive-date=3 August 2012|publisher=US Department of Energy|access-date=29 January 2012|pages=3–23}}</ref>  These ballasts operate with voltages that can be almost 600 volts, requiring some consideration in housing design, and can cause a minor limitation in the length of the wire leads from the ballast to the lamp ends.