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Fluorescent light toubles

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Fluorescent light toubles

Posted by Kelly Marie on Jan 19, 2020 6:19 pm

My kitchen fluorescent lamp which is 6 foot 100 watt unit wouldn't light tonite the starter flickered but no sign of any tube activity. It was very cold in the kitchen so I put the boiler on which warmed things up nicely I tried the tube again and although a bit sluggish it lit ( maybe my swearing at it helped) my question is do you think it's just because the tubes old and doesn't like the cold  or is there something else going on? 

Re: Fluorescent light toubles

Posted by Potential on Jan 23, 2020 12:24 am

The 'twin packs' of 6ft fittings were produced mainly for commercial projects. They were single 6ft fittings sold in pairs - one lead/one lag - to correct the power factor when used in shops/factories which often had 3 phase supplies and getting the PF as near to unity could save money.

Yes, they had a  capacitor in series with the ballast.
I installed many of them when they first came out and unfortunately for a while the capacitor was prone to failure.
Usually it would become a short circuit, the lamp would not light properly and the short would toast everything else in the circuit so that the whole fitting needed replacing.
The local Edmundsons got a bit fed up with me bringing in returns.

Re: Fluorescent light toubles

Posted by mapj1 on Jan 23, 2020 12:24 am

Resonant starting.
Or to be less terse... On 230V mains to drive a tube that needs 200v to strike and runs at 90, a simple series dropper will do , usually a choke and hopefully a PFC capacitor.
On 110V or so you will not get the striking voltage, so a step up in voltage or a resonant start is needed - in effect the leakage inductance of the transformer and the C conspire, when not loaded by the tube, i.e. before it is struck, to form an LC resonator of modest Q factor, so the voltage magnification is perhaps 4 or 5.
Once the tube is struck, it is such a significant damper on things that the voltages end up about 1:0.9 or so.

It would be perfectly possible to have a step up transformer and then the  UK style series choke and starter, but is largely pointless - why have 2 coils when one would do - but realise they need a significant step up to start and a nearly level voltage step when running.
The 277 US volt fittings look more like ours, though they do still like to transformer couple the heaters, in situations where we would use the starter to flash the heaters in series across the choke limited mains to warm them up, and then leave them to be heated by the emission current once there is some flowing.

and it is all there on wikipedia.
regards Mike

Re: Fluorescent light toubles

Posted by Potential on Jan 23, 2020 12:44 am

Rather than waste power on lossy resistors a lot of the cell saver designs of torches do the dimming from anything other than full brightness by chopping the current waveform, so half brightness is the same as full brightness for half the time. What I do not understand is why the makers elect to do this slicing at low audio frequencies, rather than hundreds of kHz, which is just as easy for the electronics and would avoid the worst of the weird optical illusions.
I do seem to be 'gifted' with the ability to see flicker more than most, and to me the overhead motorway variable speed signs flicker as well, and asking at work, most people have not noticed it, but those of us who do agree it is bloody annoying.

Perhaps the flicker you are seeing is caused by intermodulation between the various circuits rather than that of their fundamental chopped frequency?

Re: Fluorescent light toubles

Posted by Denis McMahon on Jan 23, 2020 8:25 am

Chris Pearson:

I have occasionally noticed flicker from LEDs ...

Now you mention it, whilst drilling the fixing holes for a back box today and using a head torch for illumination (no mains lighting for obvious reasons) I thought of this and noticed that my drill appeared to be going backwards; so clearly, even battery powered LEDs must flicker.


Even with LEDs powered from direct current sources, it has been common practice for many years to deliberately chop the supply to the LED. I understand that the reason for this is in the interests of efficiency. The eye perceives a LED fed from chopped d.c. as almost as bright as one fed from continuous d.c., but much less power is used. One can see this flickering effect on instrument panel indicators, car tail lights and, apparently, LED head torches. I checked my own head torch and can't see any noticeable flicker, but possibly it is strobed at a very high frequency. 
Denis McMahon "There is always a better way."


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