![Various types of Glow starter](https://upload.wikimedia.org/wikipedia/commons/1/11/Various_types_of_Glow_starter.jpg)
A glow switch starter or glowbottle starter is a type of preheat starter used with a
fluorescent lamp
A fluorescent lamp, or fluorescent tube, is a low-pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor, which produces short-wave ultraviolet lig ...
. It is commonly filled with
neon
Neon is a chemical element with the symbol Ne and atomic number 10. It is a noble gas. Neon is a colorless, odorless, inert monatomic gas under standard conditions, with about two-thirds the density of air. It was discovered (along with krypton ...
gas or
argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abu ...
gas and contains a
bimetallic strip
A bimetallic strip is used to convert a temperature change into mechanical displacement. The strip consists of two strips of different metals which expand at different rates as they are heated. The different expansions force the flat strip to be ...
and a stationary electrode. The operating principle is simple, when current is applied, the gas inside ionizes and heats a bimetallic strip which in turn bends toward the stationary electrode thus shorting the starter between the electrodes of the fluorescent lamp. After about a second the starter's bimetallic strip cools and opens the circuit between the electrodes, and the process repeats until the lamp has lit. One disadvantage of glow switch starters is that when the lamp is at the end of its life it will continuously blink on and off until the glow switch starter wears out or an
electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials de ...
on the fluorescent lamp burns out. Glow starters have a relatively short life, and light fittings enable the starter to be changed easily.
Electronic starters, being interchangeable and using the same casing as a glow starter, last for many years.
The glow switch starter was invented by E. C. Dench in 1938.
Operation
![Fluorescent Light](https://upload.wikimedia.org/wikipedia/commons/e/e1/Fluorescent_Light.svg)
# When power is first applied to the circuit, there will be a
glow discharge
A glow discharge is a plasma formed by the passage of electric current through a gas. It is often created by applying a voltage between two electrodes in a glass tube containing a low-pressure gas. When the voltage exceeds a value called the str ...
across the electrodes in the starter lamp. This heats up the inert gas (
argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abu ...
or
neon
Neon is a chemical element with the symbol Ne and atomic number 10. It is a noble gas. Neon is a colorless, odorless, inert monatomic gas under standard conditions, with about two-thirds the density of air. It was discovered (along with krypton ...
) inside the starter and causes one of the
bi-metallic strip
A bimetallic strip is used to convert a temperature change into mechanical displacement. The strip consists of two strips of different metals which expand at different rates as they are heated. The different expansions force the flat strip to be ...
to bend towards the other terminal.
# When the contacts touch, the two filaments of the fluorescent lamp and the ballast will be switched in series to the supply voltage. The current through the filaments of the tube heats them up and emit electrons into the tube gas by
thermionic emission
Thermionic emission is the liberation of electrons from an electrode by virtue of its temperature (releasing of energy supplied by heat). This occurs because the thermal energy given to the charge carrier overcomes the work function of the mate ...
.
# In the starter, the touching contacts
short out the voltage sustaining the glow discharge, extinguishing it so the gas inside the starter cools down and no longer heats up the
bi-metallic switch, which switches off within a second or two.
# The current through the filaments and the inductive ballast is abruptly interrupted, leaving the full line voltage applied between the filaments at the ends of the tube and generating an
inductive kick
A snubber is a device used to suppress ("snub") a phenomenon such as voltage transients in electrical systems, pressure transients in fluid systems (caused by for example water hammer) or excess force or rapid movement in mechanical systems.
Elec ...
which provides the high voltage needed to start the lamp. The lamp will fail to strike if the filaments are not hot enough, in which case the cycle repeats; several cycles are usually needed, which causes flickering and clicking during starting (older thermal starters behaved better in this respect). A
power factor
In electrical engineering, the power factor of an AC power system is defined as the ratio of the '' real power'' absorbed by the load to the ''apparent power'' flowing in the circuit. Real power is the average of the instantaneous product of v ...
correction (PFC)
capacitor
A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals.
The effect of ...
draws leading current from the mains to compensate for the lagging current drawn by the lamp circuit.
# Once the tube strikes, the impinging main discharge keeps the cathodes hot, permitting continued electron emission without the need for the filaments to continue to be heated. The starter switch does not switch on again because the resistance in the tube drops and the voltage across the starter is insufficient to start a glow discharge again.
Automated starters
With automated starters such as glow starters, a failing tube will cycle endlessly, flickering as the lamp quickly goes out because the
emission mix is insufficient to keep the lamp current high enough to keep the glow starter open. This runs the ballast at higher temperature. Some more advanced starters time out in this situation, and do not attempt repeated starts until power is reset. Some older systems used a thermal over-current trip to detect repeated starting attempts and disable the circuit until manually reset. The switch contacts in glow starters are subject to wear and inevitably fail eventually, so the starter is manufactured as a plug-in replaceable unit.
References
Gas discharge lamps
{{energy-stub