Editing Fluorescent lamp (section)

===Starting===
{{main|Glow switch starter}}
The gas used in the fluorescent tube must be ionized before the arc can "strike" . 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). Many different starting circuits have been used. The choice of circuit is based on cost, AC voltage, tube length, instant versus non-instant starting, temperature ranges and parts availability.

====Preheating====
[[File:Fluorescent Light.svg|thumb|A ''preheat'' fluorescent lamp circuit using an automatic starting switch. A: Fluorescent tube, B: Power (+220 volts), C: Starter, D: Switch (bi-metallic thermostat), E: Capacitor, F: Filaments, G: Ballast]]
[[File:Fluorescent lamp-electronic ballast starter-movie VNr°0001.ogv|thumb|left| Starting a preheat lamp. The automatic starter switch flashes orange each time it attempts to start the lamp.]]
Preheating, also called switchstart, uses a combination [[electrical filament|filament]]–[[cathode]] at each end of the lamp in conjunction with a mechanical or automatic ([[Bimetallic strip|bi-metallic]]) switch (see circuit diagram to the right) that initially connect the filaments in series with the ballast to preheat them; after a short preheating time the starting switch opens. If timed correctly relative to the phase of the supply AC, this causes the ballast to induce a voltage over the tube high enough to initiate the starting arc.<ref name=philipsapp>{{cite book|chapter=Chapter 8. Lighting|title=Power Semiconductor Applications|chapter-url= http://www.nxp.com/documents/application_note/APPCHP8.pdf|archive-url= https://web.archive.org/web/20091122114429/http://www.nxp.com/documents/application_note/APPCHP8.pdf|url-status=dead|archive-date=22 November 2009|access-date=22 November 2009|publisher=Philips Semiconductors}}</ref> These systems are standard equipment in 200–240&nbsp;V countries (and in the United States lamps up to about 30&nbsp;watts).

[[File:Starterp.jpg|thumb|left|A ''preheat'' fluorescent lamp "starter" (automatic starting switch)]]
Before the 1960s, four-pin thermal starters and manual switches were used.{{Citation needed|date=June 2013}} A [[glow switch starter]] automatically preheats the lamp cathodes. It consists of a normally open [[bi-metallic strip|bi-metallic]] switch in a small sealed [[gas-discharge lamp]] containing inert gas (neon or argon). The glow switch will cyclically warm the filaments and initiate a pulse voltage to strike the arc; the process repeats until the lamp is lit.  Once the tube strikes, the impinging main discharge keeps the cathodes hot, permitting continued electron emission. The starter switch does not close again because the voltage across the lit tube is insufficient to start a glow discharge in the starter.<ref name=philipsapp/>

[[File:Pulsestarter.JPG|thumb|Electronic fluorescent lamp starters]]

With glow switch starters a failing tube will cycle repeatedly.  Some starter systems used a thermal over-current trip to detect repeated starting attempts and disable the circuit until manually reset.

A [[power factor]] correction (PFC) [[capacitor]] draws leading current from the mains to compensate for the lagging current drawn by the lamp circuit.<ref name=philipsapp/>

'''Electronic starters''' use a different method to preheat the cathodes.<ref name="electrostart">{{cite web|title=Datasheet of typical electronic starter (not fast start), with detailed explanation of operation|url=http://www.tabelek.co.uk/datasheets/UM2-UM3-Datasheet.pdf|access-date=2011-04-08 |archive-date=2012-03-22 |archive-url=https://web.archive.org/web/20120322120421/http://www.tabelek.co.uk/datasheets/UM2-UM3-Datasheet.pdf|url-status=live}}</ref> They may be plug-in interchangeable with glow starters. They use a semiconductor switch and "soft start" the lamp by preheating the cathodes before applying a starting pulse which strikes the lamp first time without flickering; this dislodges a minimal amount of material from the cathodes during starting, giving longer lamp life.<ref name="philipsapp" /> This is claimed to prolong lamp life by a factor of typically 3 to 4 times for a lamp frequently switched on as in domestic use,<ref name="faststart">{{cite web|title=Datasheet of typical fast start electronic starter, with detailed explanation of operation|url=http://www.tabelek.co.uk/datasheets/300C-Datasheet.pdf|access-date=2011-04-08 |archive-date=2012-03-22 |archive-url=https://web.archive.org/web/20120322120454/http://www.tabelek.co.uk/datasheets/300C-Datasheet.pdf|url-status=live}}</ref> and to reduce the blackening of the ends of the lamp typical of fluorescent tubes. While the circuit is complex, the complexity is built into an [[integrated circuit]] chip. Electronic starters may be optimized for fast starting (typical start time of 0.3 seconds),<ref name="faststart" /><ref name="type300c">{{cite web|title=Electronic Tube Starter 300C Fastlux for fluorescent strip lights|url=http://www.tabelek.co.uk/product-300C-fastlux-electronic-fluorescent-tube-starter.php|website=www.tabelek.co.uk|access-date=2019-04-26 |archive-date=2019-01-08 |archive-url=https://web.archive.org/web/20190108100850/http://www.tabelek.co.uk/product-300C-fastlux-electronic-fluorescent-tube-starter.php|url-status=live}}</ref> or for most reliable starting even at low temperatures and with low supply voltages, with a startup time of 2–4 seconds.<ref name="um2">{{cite web|title=Soft Start Electronic Starter for fluorescent tubes the UM2 Multi Pulse|url=http://www.tabelek.co.uk/product-um2-multipulse-electronic-fluorescent-tube-starter.php|website=www.tabelek.co.uk|access-date=2019-04-26 |archive-date=2019-04-23 |archive-url=https://web.archive.org/web/20190423140214/http://www.tabelek.co.uk/product-um2-multipulse-electronic-fluorescent-tube-starter.php|url-status=live}}</ref> The faster-start units may produce audible noise during start-up.<ref>{{cite web| title=Fast electronic starters for fluorescent lights| date=20 June 2004<!--from page source-->| quote=All three of the 'FAST' (< .5 seconds) starter brands caused an audible 'BURRRRRRRP' noise in some light fittings as they started and this is an inherent problem caused by their use of the faster 'DC' heating. It is worse with higher wattage tubes and if there is any loose metal in the light fitting.| website=users.tpg.com.au| url=http://users.tpg.com.au/pschamb/light.html| access-date=25 February 2023| archive-date=2012-11-04 | archive-url=https://web.archive.org/web/20121104034555/http://users.tpg.com.au/pschamb/light.html| url-status=live}}</ref>

Electronic starters only attempt to start a lamp for a short time when power is initially applied, and do not repeatedly attempt to restrike a lamp that is dead and unable to sustain an arc; some automatically stop trying to start a failed lamp.<ref name="electrostart" /> This eliminates the re-striking of a lamp and the continuous flashing of a failing lamp with a glow starter. Electronic starters are not subject to wear and do not need replacing periodically, although they may fail like any other electronic circuit. Manufacturers typically quote lives of 20 years, or as long as the light fitting.<ref name="type300c" /><ref name="um2" />

====Instant start====
[[File:T12 Fluorescent lamp electrodes - rapid start and instant strt.jpg|thumb|T12 fluorescent tubes. The first two are rapid start, (for "tombstone" and socket holders respectively) while the third is an instant-start lamp. The instant-start  has a characteristic, rounded, single pin, for plugging into the spring-loaded socket holders.]]
''Instant start'' fluorescent tubes were invented in 1944. Instant start simply uses a high enough voltage to break down the gas column and thereby start arc conduction. Once the high-voltage spark "strikes" the arc, the current is boosted until a [[glow discharge]] forms. As the lamp warms and pressure increases, the current continues to rise and both resistance and voltage falls, until mains or line-voltage takes over and the discharge becomes an arc. These tubes have no filaments and can be identified by a single pin at each end of the tube (for common lamps; compact cold-cathode lamps may also have a single pin, but operate from a transformer rather than a ballast). The lamp holders have a "disconnect" socket at the low-voltage end which disconnects the ballast when the tube is removed, to prevent [[electric shock]]. Instant-start lamps are slightly more energy efficient than rapid start, because they do not constantly send a heating current to the cathodes during operation, but the cold cathodes starting increases sputter, and they take much longer to transition from a glow discharge to an arc during warm up, thus the lifespan is typically about half of those seen in comparable rapid-start lamps.<ref>''Mechanical and Electrical Equipment for Buildings'' by Walter T Grondzik, Alison Kwok, Benjamin Stein, John S Reynolds, Wiley Publishing, 2010, pp. 545–546</ref>

====Rapid start ====
[[File:Magnetek Watt Reducer HPF Rapid Start Ballast.jpg|thumb|right|A rapid-start "iron" (magnetic) [[electrical ballast|ballast]] continually heats the [[cathode]]s at the ends of the lamps. This ballast runs two F40T12 lamps in series.]]
Because the formation of an arc requires the [[thermionic emission]] of large quantities of electrons from the cathode, ''rapid start'' ballast designs provide windings within the ballast that continuously warm the cathode filaments. Usually operating at a lower arc voltage than the instant start design; no inductive [[voltage spike]] is produced for starting, so the lamps must be mounted near a grounded (earthed) reflector to allow the glow discharge to propagate through the tube and initiate the arc discharge via [[capacitive coupling]]. In some lamps a grounded "starting aid" strip is attached to the outside of the lamp glass. This ballast type is incompatible with the European energy saver T8 fluorescent lamps because these lamps require a higher starting voltage than that of the open circuit voltage of rapid start ballasts.

====Quick-start====
Quick-start ballasts use a small auto-transformer to heat the filaments when power is first applied. When an arc strikes, the filament heating power is reduced and the tube will start within half a second. The auto-transformer is either combined with the ballast or may be a separate unit. Tubes need to be mounted near an earthed metal reflector in order for them to strike. Quick-start ballasts are more common in commercial installations because of lower maintenance costs. A quick-start ballast eliminates the need for a starter switch, a common source of lamp failures. Nonetheless, Quick-start ballasts are also used in domestic (residential) installations because of the desirable feature that a Quick-start ballast light turns on nearly immediately after power is applied (when a switch is turned on). Quick-start ballasts are used only on 240&nbsp;V circuits and are designed for use with the older, less efficient T12 tubes.

====Semi-resonant start====
[[File:65W SRS fluorescent lamp starting.ogv|thumb|left|A 65-watt fluorescent lamp starting on a semi-resonant start circuit]]
[[File:semi resonant start circuit.png|thumb|right|A semi-resonant start circuit diagram]]
The semi-resonant start circuit was invented by Thorn Lighting for use with [[fluorescent-lamp formats|T12]] fluorescent tubes. This method uses a double wound transformer and a capacitor. With no arc current, the transformer and capacitor [[electrical resonance|resonate]] at line frequency and generate about twice the supply voltage across the tube, and a small electrode heating current.<ref>Thorn Lighting Technical Handbook</ref> This tube voltage is too low to strike the arc with cold electrodes, but as the electrodes heat up to thermionic emission temperature, the tube striking voltage falls below that of the ringing voltage, and the arc strikes. As the electrodes heat, the lamp slowly, over three to five seconds, reaches full brightness. As the arc current increases and tube voltage drops, the circuit provides current limiting.

Semi-resonant start circuits are mainly restricted to use in commercial installations because of the higher initial cost of circuit components. However, there are no starter switches to be replaced and cathode damage is reduced during starting making lamps last longer, reducing maintenance costs. Because of the high open circuit tube voltage, this starting method is particularly good for starting tubes in cold locations. Additionally, the circuit power factor is almost 1.0, and no additional power factor correction is needed in the lighting installation. As the design requires that twice the supply voltage must be lower than the cold-cathode striking voltage (or the tubes would erroneously instant-start), this design cannot be used with {{nowrap|240 volt}} AC power unless the tubes are at least {{convert|1.2|m|abbr=on}} length.  Semi-resonant start fixtures are generally incompatible with energy saving T8 retrofit tubes, because such tubes have a higher starting voltage than T12 lamps and may not start reliably, especially in low temperatures. Recent proposals in some countries to phase out T12 tubes will reduce the application of this starting method.

====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.