Hi Guys,
The other day, I bought a whole heap of compact fluorescent lamps to fit my house out with.
These are Philips 20W BC type things.
Anyway, I was reading in bed last night and as it was getting late I turned out the room lights and proceeded to get some sleep.
Now I know that fluorescent lamps of any kind have a faint glow after you turn them off. However, I happened to notice out of the corner of my eye that the lamps were actually flashing at about a 0.3Hz rate.
Anyone ever struck this with compact fluorescents before?.
I was rather freaked out by this when I first saw it, you naturally assume that lights should not emit light with the switch turned off.
I woke up about an hour later and they had stopped, which was a relief, I was beginning to think the lamps might be haunted.

Could it be a residual discharge stored in the electronic ballast components.

Some sort of low-frequency resonance effect? 0.3Hz seems very slow for the components involved though.

Interesting Mike,

I have seen a similar effect with green indicator lamps. These are not the Neon ones but got a different gas in them, probably Argon.

If they were turned of a glow remained for a while,
then,
when they were dark, and once in a while they flickered back on very briefly but not at a regular rate.

These indicator lamps did not have any electronics in them , only a 68 k Ohms resistor.

Trumpy I reckon those compact fluorescents are better for outdoor lighting and garages etc. They take a while to warm up, so they probably take a while to cool down, partially re-igniting several times after switch-off.

I guess you'll be changing the bedroom lights back to incandescants then ?

These have electrolytic capacitors in them, that tend to charge up all by themselves due to their chemistry. A high voltage one that's been discharged can reach 30 volts or so. (Kilovolt caps need safety shorting straps if you are working inside equipment with them, eg high power radio transmitters.)

When the volts get high enough the circuit will burst into life momentarily, discharging the capacitor, and start over again...

I have seen this effect with neon and fluorescent lamps...the reason is that such lamps will show a visible glow with microamps of current. How can such a current flow with the switch off? The wiring (especially if it's the usual twin cable) capacitance will be enough if there's a reasonable distance from light fitting to switch. Two ways to get over the problem are don't use a looped in switch wiring; ie. have the supply come to the switch before it gets to the light fitting, or simply put a high value resistor across the fitting; something like 470K 1W.
Why the pulsed effect with a compact fluoro?
Again, the slight current flowing will slwoly charge up the electrolytic filter capacitor in the CFL. At a certain voltage the lamp will attempt to start (hence the short glow). But in doing so it draws lots of current discharging the filter cap again...voltage drops and lamp can't fire. Now that the lamp isn't drawing current again the procedure repeats itself and functions as a crude relaxation oscillator.

Yeah,
It's interesting stuff, I've always associated an after-glow to a degree with the Cathode Ray Tube (or TV screen or oscilloscope screen).
Is it to do with the phosphor coating on the inside of the tube face that causes this or is it the fact that it takes a while for the EHT voltage in a TV to "die down" after intial turn-off?.
Anyone with knowledge of the old B&W sets would be familiar with the centralised dot in the middle of the screen.
Anyway,
It's actually stopped now (the flashing), I'd more or less put it down to "new-ness"
Kiwi,
I'm just doing my bit for the country, sure I won't save a wind farn being built, but every bit helps.
To be honest I like this 6500Kelvin colour and I'm saving power too!.
I'm not going back to incandescents, ever.

Trumpy its cosing me a small fortune replacing the "Spotone" incandescants here at my place. My whole house has downlights, 20 all up, and those Ro-80 lamps are always dying. Light Bulbs are a permanent fixture on our grocery shopping list ! !

My wallet wants me to put in long life compact fluorescents but I just don't like Fluorescent lights inside my house.

The dot in the center of the screen was there for a short time while (a) the EHT voltage leaked away and (b) the cathode of the electron gun cooled to the point at which it would stop emitting electrons. This took much longer than the time needed for the vertical and horizontal scanning fields to disappear, hence just the dot and not a full raster.

Many manufacturers actually added a section on the on/off switch (or used some other similar method) to bias the tube into cut-off to prevent the dot.

The overall faint glow right across the tube face you can see in a darkened room after it's switched off is the persistence of the phosphor. I remember doing that with "Test Card F" as a kid! Turn off all the lights, then switch off the set and see how long I could still make out Carol & her companion!

Sadly, we haven't seen Test Card F here for about 20 years with 24hr broadcasting from all the commercial stations. Unfortunately our only remaining non 24hr broadcaster stopped using the Philips PM5544 pattern and replaced it with images off a weather satellite. Not much use for aligning your set! Just as well I made a 3hr recording of the Philips pattern before it was gone.

to Kiwi, I have used compact flourescents all over my new house but have installed them in oyster fittings so the glass of the fitting acts like a filter. I cant tell the difference except at bill time, I will admit that not all the flourescent lights are the same with the coulors ranging from a welding flash, (cheap chinese one i tryed) to a soft warm light from a nelson globe that is the same size and shape as an incandescent. I am currently using Mirabella lights that come from woolies. They are cheaper than the philips at the wholesaler and have a nicer light.

Teleivision topic split into new thread here:
https://www.electrical-contractor.net/ubb/Forum9/HTML/000980.html

Mike,

I noticed the same the other day. I was using a potmeter-switch, and turned it down, while the lamp started flashing. I asked our EC, and he said, it slowly collects the energy and burn out in a flash. That repeats over and over again.
So I changed the switch to an on-off type.

Hi Gloria,
I take that you were trying to use a dimmer on a fluorescent lamp?.
Fluorescent lamps are not made to be dimmed.
A compact fluorescent lamp will flash if there is not enough current to maintain the gaseous discharge within the tube.
Dimmers will only work on an Incandescent (Filament) type lamp.
In some cases you can do the Diac and Triac some damage by switching fluorescents on and off with a dimmer in line.
Other side of the coin,
Having installed these lamps in my bedroom, there is one feature that I like about them.
Having been to a few night-time fire calls, I like the fact that they don't come on instantly to full brightness.
A nice soft white glow is enough for me to throw some clothes on and be gone, instead of being blinded with an instant 200W of incandescent light, which takes a wee while for your eyes to adjust to.
And I'm saving power!.
Mind you the Heat-pump has had a hiding lately.

Operating CFL's with electronic control gear at reduced voltage kills them. I discovered this while repairing a couple of them. Running via a current limited power supply and lower voltage while testing them revealed the switching transistors getting very hot. I couldn't see anything wrong so applied full mains voltage and everything ran cool. Obviously at lower voltages the transistors were not being driven into saturation.
The point is don't run them on a supply of less than 340V peak...light dimmers and square wave inverters with a 240V peak output. The original Philips CFL's with a proper iron cored choke were much more immune to this sort of thing but don't seem to have been available for quite a few years.

Now, I don't know about you, Mike...but a 60 watt bulb hanging from the ceiling throws out enough light for general purpose use.

200 watts? Dang!

What's that, Mike !

200 watts !! Lamp or Heater

Takes the nite chill out of your room I guess.

Well Ray,
Now that you come to mention it, for an Electrician, I'm pretty slack as far as my own lighting needs at home go.
I've been here for like 12-13 years and although I've trebled the number of socket outlets in the place, I'm left with the original lighting fixtures in the place.
Most of them are them gaudy brass-looking fittings.
80% of my light fittings are wall-mounted, even when I moved in here, the lights in the kitchen were on the walls, I took them out and replaced them with a single 5ft fluoro over the sink.
Both the bedrooms have wall-lights and that is the reason for the 200W (2 x 100W lamps), because on the other side of the room, you can't see to read things.
This room that I'm using as my office, is a prime example, the original Architect couldn't have put the lights on the plans in a worse place.
One day I'll get around to installing some proper downlights and stuff.
But as my catch-phrase has become in the last few years, "It'll be a while".
Eh, Paul.

Tell me about it. I could use about 48 hours in a day at the moment.

BTW,
For the benefit of our NZ members and readers,
I thought I would relate this little tale about CF lamps.
My next door neighbour (an elderly lady), rang me up in a huge panic yesterday evening, as I was about to go off to work, saying that one of her lights was on fire.
Naturally, a fire in a light would take precedence over having a first cup of coffee and a smoke at work.
I got there and she had turned the thing off but there was still smoke coming out of it.
Apparently, like most elderly people here, she is on a fixed pension and wanted to reduce her power bill, so therefore got her son to purchase and install some "Energy-Saving" lamps.
Now, I rang the son once I got to work and asked him where he got the lamps, because I'd never heard of this brand before and he said he bought them at ************.
(Think Red Shed, folks)
Now here is a pic of the lamp that had burned out:




You will note that in the top middle of the photo, that there is blackening near where the spiral tube exits the body of the lamp.
Apparently, the lamp got quote "very bright and then there was a large bang and lots of smoke".
I could smell the smoke as soon as I walked in the front door, armed with a CO2 Fire Extinguisher just in case.
For those of you that may have these lamps, here is a pic of the brand and type number:





{Sorry about the poor colour quality of these pics, my camera is having a bad hair day}

If you do have them, remove them, they may be a bad batch or whatever, but from what I've just said, they could pose a fire risk, especially if they are being used as an un-attended security lighting source.
I'm going to go down to the vendor of these lamps later on today as I believe that this should not be happening with a lamp that is only 2 months old, or any lamp for that matter.
I'll keep you folks posted.

{Message edited to fix up typo's}


[This message has been edited by Trumpy (edited 10-20-2006).]

They sell some strange, interesting, and downright tacky things there. Always have a wander through if I'm going past with time to spare...but I often wonder about the electrical things they sell there and what approvals they may have been subjected to. Last catalog had a toaster for just under $10 which is hard to comprehend. While I've never bought CFL's there I have noticed incandescent bulbs that aren't fused in the stem. Actually, before I forget, have we heard about the HPM power points? Apparently there was a Chinese forgery of the local product. http://www.current.com.au/news/article/LVHZBYNUQJ.html
I wonder if a certain hardware chain has been selling them.

Thanks Mike for the fire safety advise.
I make a note of the brand, and will tell our crews on monday that certain brand of these lamps may have a potential for a fire.
It could have been a bad batch but you never know.

My Philips CFL lamps in the lounge have done 12447 hrs and still going well, a little blackening can be noticed at the end but the light output is good.

I personnaly don't like unknown branded lamps from unknown manufacturers.

240,
Yeah mate,
How on earth can you build, test and manufacture and give decent quality control to an item that will sell at the store for $10??.
I do know that appliances are made as cheap as dirt these days, which is a shame, because at the end of the day, the consumer is not getting the life span out of an appliance that they would have expected say, 10 years ago.
And we have had this argument here before, you can't fix anything economically anymore.
There is actually an Electronics Tech here working at the local Service Station (Garage) for some ungodly wage, because he went out of business because the companies he used to service TV's and the like for, got meaner and meaner with respect to manuals and the price of replacement parts.
I know this guy well and he is a top class technician, but he is too over-priced for the "throw-away" society we live in these days.
We had a problem with our (get this RODALCO), new Plasma screen TV at the Fire station about a month ago, the guy woke me up at 9am to have me let him in, he was done by 9:10 and this was not a small fault, apparently the unit had a lot of dry joints in it, he even showed me and I agreed.
It was still under warranty but he said it was hard to get warranty payments out of a lot of companies these days.
I think that is what killed his business in the end, suppliers don't like being not paid and if the companies that you are servicing gear for with-hold money until they have to pay, what is the guy in the middle supposed to do?.
This is not good, it's totally up-side down from what it was a few years back.
I don't like where we are heading.

RODALCO,
That is not a problem at all mate,
I'd sooner institute a warning rather than wait for results from the vendor.
I've also put a warning on the FireNet for people to watch out for.
I'm first and fore-most a FF, secondly an Electrician.
If this could cause people harm, that source of harm should be eliminated, as far as possible.
Good call on telling your crews, Ray, the more people that know the risk, the better off we all are.
BTW, with the large amount of smoke that issued from that lamp, the smoke detector in the house never triggered.
That needs to be rectified.

Did the smoke alarm have a working 9 volts battery ?
No doubt that you checked that, but just in case.

Ray,

I installed in not only my own house, but I asked my nieghbours if they wanted permanently wired smoke alarms, I said that you lose protection once the battery runs down, hence the chirping that I've heard when doing the odd domestic job.
Now, they all went for it and I did the install.
I was paid almost nothing, but I didn't do it for the money.
With houses being joined together there is a real risk of inter-house fires occuring if a fire did start in one of the town-houses.
Think of the common roof space and convected heat, add to that tar based building paper.
It's very hard working in a roof space with BA on in a lot of older houses.
Even getting through the Man-hole can be a task.