Ofcom trace interference to a lightbulb

[John Lee]

Full size related but it just goes to show how interference can be generated from an unexpected source. Ofcom link

[Peter Christy]

On a similar note: **LINK**

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Pete

[Bob Cotsford]

How does that bulb work, some form of arc? Remember the crude spark gap transmitters (I only know of them from museums, honest )

[Capt Kremen]

These type of interference are not as isolated as might seem.

Commercial ovens e.g. Baker's, Confectioners, Biscuit Makers etc. etc. switch these on and off at often set times coinciding with work patterns and shifts. A dodgy connection or two in these or some other component misbehaving, (and other equipment), can easily generate disruptive signals.

Maybe your clubmate 'Old Joe' did suffer a radio glitch on 2.4 after all!

[Geoff S]

Posted by John Lee on 24/09/2020 11:47:49:

Full size related but it just goes to show how interference can be generated from an unexpected source. Ofcom link

That's a very strange light bulb with an ES (Edison Screw) connector. I was involved with selling light bulbs in our family electrical/radio etc shop from childhood in the 1940s onwards and all mains light bulbs were bayonet fittings. Thiis was at a time when many houses had gas rather than electric lighting (and no indoor plumbing) in our small mining town. The only screw fitting bulbs we sold were MES (Miniature Edison Screw) bulbs for torches and bike lamps.

I can only assume there was a loose connection to the filament or perhaps a mechanical connection that wasn't really secure and thus generated a spark. As Bob mentioned early radio transmitters used spark gaps to generate the RF - and that's not so long ago in real terms. I bet it was an interesting investigation and very satisfying to bring it to a successful conclusion.

On the old TV interference I'm guessing it was a valve one with a CRT which needed several kilovolts for the EHT and again the source of the interference was a spark.

Geoff

[kc]

That 'vintage' lightbulb might have been a modern one made to look vintage! But ES bulbs were common back in the 1950.s and 60's - they were used in things such as photoflood lights, photographic enlargers & projectors. Probably used in industrial stuff too where more accurate location of the bulb was needed . Lots of items now use ES bulbs if they come from places like Ikea etc.

[Kevin Wilson]

Most mains powered equipment that have low voltage circuits use switch mode power supplies (SMPS) to generate the low voltages. These SMPS use frequencies typically in the 30>40kHz range in the conversion process. The cheaper units have very poor filtering and cause huge amounts of harmonic energy across the RF spectrum.

Its a big problem for radio amateurs such as myself. Mains powered LED lamps are a particular problem, probably due to being so ubiquitous and built to the cheapest, lowest standard.

[Kevin Wilson]

As KC notes, with the increase in worldwide transport of electrical fittings ES27 lamps (and ES14) are not uncommon. Decorative light fittings are frequently ES or SES.

[Geoff S]

Posted by Kevin Wilson on 24/09/2020 13:41:30:

As KC notes, with the increase in worldwide transport of electrical fittings ES27 lamps (and ES14) are not uncommon. Decorative light fittings are frequently ES or SES.

That's true now but back in 1950s and 60s they were almost unknown in a domestic setting. I much prefer bayonet fittings myself as they're much easier and quicker to fit.

A good point about LED light fittings which have switch mode regulators (and rectifiers) to convert 240v ac to 12v dc or whatever for the LEDs. I'm sure they could well generate all sorts of RF interference. I think eventually houses will be wired with a 12 dc circuit for lighting with a central ac to dc regulator/rectifier and much simpler (and probably cheaper) LED bulbs with greatly extended life.

Geoff

[Martin_K]

The photo in the Ofcom article, linked below, looks like an incandescent bulb. Interesting as they have not been legally for sale in the UK or EU for many years.

Possibly it is a reproduction "Mazda" (General Electric brand) bulb.

The interference from these was known about 70 years ago.

[kevin b]

A good point about LED light fittings which have switch mode regulators (and rectifiers) to convert 240v ac to 12v dc or whatever for the LEDs. I'm sure they could well generate all sorts of RF interference. I think eventually houses will be wired with a 12 dc circuit for lighting with a central ac to dc regulator/rectifier and much simpler (and probably cheaper) LED bulbs with greatly extended life.

Geoff

Good idea Geoff.

Then in the future when power supplies fail because of demand due to vehicle charging, we will at least be able to read RCM&E magazine if we plug our lipos into the house lighting circuit.

[Martin Harris - Moderator]

Far from being a rarity, I think the lamps* ("Bulbs? Bulbs is wot you plant in your garden" was indelibly knocked into me by our storemen at work) used in my house have at least reached parity between ES and bayonet and I suspect ES are well in the majority.

*Full title: Lamps, incandescent.

Edited By Martin Harris on 24/09/2020 16:02:01

[Simon Chaddock]

Could the great length (300 mm?) of that single strand filament in that bulb be significant rather than the much shorter "coiled coil" used in a conventional incandescent bulb.

I don't know ES or SES fittings are that rare in the UK. I have an ES in my desk lamp and all oven bulbs are SES as far as I am aware.

[Martin Harris - Moderator]

The link hidden at the bottom of Martin_K's post gives a very plausible explanation...essentially, yes - the filament length is at the root of the phenomenon.

[Former Member]

[This posting has been removed]

[Martin Harris - Moderator]

We told apprentices to pop into the stores and ask for a long weight (after explaining how the return weights for switchboard cords came in different sizes of course).

The word bulb probably only appeared in the stores rate book (roots deep in GPO/Civil Service origins) in connection with wet and dry bulb hygrometers.

[leccyflyer]

Posted by Geoff S on 24/09/2020 13:17:11:

Posted by John Lee on 24/09/2020 11:47:49:

Full size related but it just goes to show how interference can be generated from an unexpected source. Ofcom link

That's a very strange light bulb with an ES (Edison Screw) connector. I was involved with selling light bulbs in our family electrical/radio etc shop from childhood in the 1940s onwards and all mains light bulbs were bayonet fittings. Thiis was at a time when many houses had gas rather than electric lighting (and no indoor plumbing) in our small mining town. The only screw fitting bulbs we sold were MES (Miniature Edison Screw) bulbs for torches and bike lamps.

I can only assume there was a loose connection to the filament or perhaps a mechanical connection that wasn't really secure and thus generated a spark. As Bob mentioned early radio transmitters used spark gaps to generate the RF - and that's not so long ago in real terms. I bet it was an interesting investigation and very satisfying to bring it to a successful conclusion.

On the old TV interference I'm guessing it was a valve one with a CRT which needed several kilovolts for the EHT and again the source of the interference was a spark.

Geoff

Lots of the ceiling mounted spotlights have Edison screw fittings these days Geoff, we used to have to carry two sizes for years until we got rid of them.14mm and 27mm IIRC.

[ron evans]

A bit off topic, but lightbulb related.

A few days ago the lightbulbs in the dining lit up with a low glow without being switched on.

They switched on & off normally but the low glow remained and fluctuated for a few minutes before going out.

Any explanations out there.

Thanks.

Ron

[martin collins 1]

Space Aliens

[J D 8]

What sort of bulbs were they? If you hold a fluorescent tube under a high power cable it will glow.

[Robin Colbourne]

I can just imagine the next generation of 'Wild Weasel' radar-jamming aircraft, festooned with old lightbulbs and an ancient TV set on each underwing pylon...

[Simon Chaddock]

Most discharge lamps not only emit light in the visible spectrum but also in the non visible ultra violet range. To make use of this the inside of the glass is coated with materials that absorb the UV and emit visible light hence the term fluorescent lamp. This process has some 'persistence' so it will continue to glow dimly for a short while after the light is switched off.

The quality of the light a fluorescent lamp produces can be changed by using different types of coatings hence warm, cool and daylight types.

[ron evans]

J D 8, The bulbs were 3x low energy candle type.

Ron

[ron evans]

Simon, this occurred in the morning, before the lights had been switched on that day, so would any residual have lasted from the previous evening.

Ron

[Geoff S]

Posted by J D 8 on 25/09/2020 09:54:01:

What sort of bulbs were they? If you hold a fluorescent tube under a high power cable it will glow.

When I was still at school (1953 ish) I went on a visit to the Rugby Long wave transmitter facilty with a local radio club. There was a large hall-like room where the feeds to the aerial arrays left the buildings and I was amazed to see how fluorescent tubes lit when suspended form bits of string. Very useful for maintenance I suppose.

Of course it was all thermionic valves and the big transmitter power output ones had removable glass covers so that elements that failed could be repaired, the covers replaced and the valve evacuated.

All very impressive to a 13 year old and quite impressive to an 80 year old, too

Geoff