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Hi there,

I am currently reading through the different methods used to start a fluorescent tube. I have come across the glow type starter and the thermal starter circuit. In my course book the glow type starter is described as follows "Contained within the starter can are a set of normally open contacts which are mounted on bi metal strips. when switched on a glow discharge takes place around the open contacts and heats up the bi metal strips causing them to bend and touch each other. The glow starter ceases once the contacts are touching so that the bi metal strips cool down an they spring apart again. Their opening momentarily breaks the circuit, causing the magnetic field of the choke to collapse. The collapsing magnetic field induces a high voltage across the circuit enabling the arc to be established...."

However the thermal starter circuit is described as follows "in the lamp's starter, a pair of normally closed contacts are mounted on bi metal strip. A small heater coil heats one of these when the supply is switched on. This causes the strop to bend and the contacts to open causing a momentary high voltage from the lamps choke, thus initiating the discharge in the lamp.

I am slightly confused as it seems that they both work on the principle of high voltage being induced in order for the lamp to work, but differ in the respect that the contacts either start by being open or closed. Please could someone explain how this works? Thanks :)
 
The 'glow tube' starter is a 2-stage start. Firstly, immediately when power is switched it causes a small gas tube in the starter to glow which heats up a bi-metallic contact. About half a second later the bi-metallic contact in the starter gets hot and it closes which stops the internal gas tube from making heat and also causes current to flow through the heating filaments inside the fluorescent tube. After a second or so the bi-metallic contact cools down and re-opens which causes a high voltage spike due to the changing current in the inductive ballast. This momentary high voltage in theory causes the ignition of the tube. Once the tube is lit the ballast just acts as a current limiter.

In practice however if the contact in the starter opens when the AC supply wave happens to be at or close to zero then ignition can fail because insufficient current would have been diverted through the starter at that point in time so insufficient voltage spike is achieved from the ballast to ingite the tube in which case the whole start cycle would just repeat.

Not sure if this makes sense... I'll see if I can find a better written tutorial somewhere.

**edit** Maybe this will help explain better; http://www.st.com/content/ccc/resou...df/jcr:content/translations/en.CD00003901.pdf
 
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A work of pure genius in my mind - another good place to learn about starting methods of different lighting types SOX SON Neon and her sisters is the Eddison techcentre on YouTube.


Such hard work and failure must have gone into the development of these systems only for us to come along now and change it all to LED.
 
There are a number of videos of different lighting systems - scroll til your hearts content!
 
I have come across the glow type starter and the thermal starter circuit
You're reading an old book. Thermal starters were superseded by glow starters many decades ago, you will probably never see one in your life. From the tube's viewpoint the starting method is basically the same: Make series connection through filaments to preheat then open the connection to strike. The thermal type would begin with the contacts closed, using a small heater in series with the fitting supply to heat the bimetal contacts to make them open after the preheat time. The glow starter has to begin with the contacts open as it is the discharge between them that generates the heat to make them close, thereby extinguishing the discharge and making them cool and open again. Once the fluo tube is struck, the end-end voltage is too low to restrike the starter discharge (unless you used the wrong type of starter!). Electronic replacements for glow starters are quicker and have additional benefits but again from the tube's viewpoint the starting process is the same.

Other types that are mostly obsolete:

'Quickstart', which used an autotransformer to deliver a boost voltage to the filaments that was removed once the tube struck. These rely on the mains voltage striking the tube hence required striped tubes or close-fitting earthed reflectors. AFAIK they were only suitable for T12 tubes and could not be made for 110V. They did however get rid of the need for a starter and hence improved reliability of fittings provided starting conditions were reasonable.

Semi-resonant, which used a capacitor and choke tuned to resonate and deliver an increased end-end voltage until the tube struck. These were more reliable in the cold and again avoided the need for a starter.

'Instant Start', which I think caught on best in the USA, which produced a yet higher still end-end voltage from the ballast and did not need filaments at all as the gas would ionise immediately at any realistic temperature. The tubes only have one pin at each end and they really do start instantly. Again I think only T12 versions were produced.

Now of course fittings are usually either switch-start using a glow starter or electronic equivalent, or HF which starts the tube much like a semi-resonant by having high open-circuit volts.
 
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