fluorescent light question please.

[chris765]

Hi All,

Yesterday my neighbour called me round (they are quite elderly) and asked me to have a look at their fluorescent light. Its a 70w single tube 8' in length. The tube would turn on and be fine for about 30seconds. Then it would start flickering. I was sure it was the bulb as the starter got the bulb going. Once it was on I thought the starter was redundant.
So we put a new bulb in and sure enough it started flickering.
Then we replaced the starter and its been ok.

Does the tube rely on the starter all the time it's on?
Thanks for your help.

 

[bongos]

Once it was on I thought the starter was redundant. Does the tube rely on the starter all the time it's on?
Thanks for your help.

I thought this too. Maybe a problem with the ballast but as you say replacing the starter seems to have solved the problem.

Have a look here. It does say if there isn't enough current to kick start the bulb then the process repeats.

 

[RF Lighting]

Once the tube has struck, you can remove the starter completely and it will stay lit until the power is turned off.

It sounds like that although it had lit, the tube hadn't been started properly.

 

[ericmark]

No once started you can remove the starter and tube will remain lit. However if the starter tries to re-fire an already lit lamp it will extinguish it. Norm is replace starter if works great. If not replace tube as well. If tube goes it normally takes starter with it so always replace starter when replacing tube.

Lucky 8' works as they are right on the edge for 240vac and with 230vac have problems starting so in the main they have gone.

 

[bernardgreen]

From the source that bongo gave

The most common fluorescent starter is called a "glow tube starter" (or just starter) and contains a small gas (neon, etc.) filled tube and an optional radio frequency interference (RFI) suppression capacitor in a cylindrical aluminum can with a 2 pin base.

Changing from aluminium to plastic cased starters can create a problem for long tubes. The striking voltage of a neon "glow tube" is affected by the amount of light entering the glow tube, more light lower strike voltage. So in fittings where the starter is fitted close to the tube and the plastic is not UV opaque then as the tube warms up and gets brighter the striking voltage of the starter gets lower and can in extreme cases become low enough that the lamp is re-started.

Related History
==========
One piece of early GPO electronic equipment used in telephone exchanges depended on neon tubes striking reliably. Lots of equipment faults occurred at night but few if any during the day. Never went wrong on the test bench, The equipment needed some light to ensure the neons struck reliably. Flourescent lamps had to be fitted to illuminate the neons to keep the equipment working at night.

Neon screwdrivers ( wash my mouth with soap ) can also react differently when used in a dark room to when used on the same voltage in daylight.

 

[vsynth]

We tend to use electronic starters at work now, I'm not sure the expense is justified but they do seem to strike the lamp more efficiently and I haven't ever had one fail.

As for 8' tubes, we have hundreds of 100W and 125W single and dual fittings at work so I hope the tubes aren't going out of fashion!

 

[333rocky333]

Are you sure it is a 70 watt 8 foot.

If it is a 70watt 6ft the starters can be temperamental.
Only use a starter that has 70 watt included on it, even a 75 watt starter can cause a problem.

An 8ft tube would normally be 85 watt, 100watt or 125 watt.