Question: Should a light bulb ever flash when the switch is turned off?

Hi, just a quickie until I can contact my local electrician in the morning. Apologies in advance for my limited understanding of things electrical!

A little earlier on I fitted a Philips energy saving bulb into a standard bayonet cap fitting replacing a regular light bulb. This light socket is on a double switched circuit i.e. the bulb is at the top of my stairs and there are switches controlling it at both the top and bottom of the stairs.

I was a bit disturbed to notice that this energy saving bulb tends to flash on and off every two or three minutes or so. The regular bulb doesn't flash.

I've tried the energy saving bulb in a variety of other sockets on the downstairs, upstairs and in my extension and the only socket it flashes on is the double-switched one at the top of the stairs.

I assume this means the problem is not with either the bulb or the upstairs ring circuit and lies somewhere between the two switches and the socket.

I asked my father, who seems to think that double switched circuits are always live regardless of whether the switches are both off. Is this the case? I wonder whether this means that there is a pulse of current every couple of minutes or so and the energy saving bulb is sensitive enough to light up when this current is applied whereas the regular bulb is not.

Or could the circuit be dangerous? I've removed the bulb from the socket as a precaution.

Any ideas?

Thanks in advance!


Reply to
James Taylor
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On Thu, 1 Jan 2004 17:25:08 -0000, "James Taylor" Gave us:

It sounds like one of the switched has a pitted set of contacts.

For a few bucks each, just replace both switches.

Safer yet to call an electrician to analyse that branch, and put in new switches, and also ensure that it was wired correctly.

You seem from the "call the electrician" segment. Safest bet.

Call a bunch for quotes on that exact job I mentioned, and you may find some competition for your task, and good price may emerge.

Could get screw'd by the fine print as always tho. These guys always seem to want a weeks pay for an hour's work (max).

Sad that they have grown toward that in a once respectable service industry.

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"James Taylor" skrev

Are there any small glow discharge lamps placed together with the switches (to orientate where the switches are in darkness)? If there are it might be the answer why it works fine with a traditional bulb but not the energy saving one.

Reply to

Isn't an energy saving bulb just a lower wattage lamp? i.e.. 52W vs. 60W?

Even so, the little indicator lights are illuminated when the light is off (and vice versa), wouldn't that mean that the indicator is shorted when the switch is on? (thereby having no impact).


Reply to

How does the connection area on the bulb look....I picked up some similar bulbs that had lousy connection areas on the bulbs and flashed a lot....They may work on other sockets because the one you are placing the bulb into is a bit oxidized too....good luck, Ross

Reply to
Ross Mac

Any electronic switches which power themselves through the lamp (such as electronic dusk-dawn, timeswitch, or PIR switches) can have this effect with compact fluorescents.

No, it's a compact fluorescent.

Reply to
Andrew Gabriel


Sorry, but since the neon glow discharge lamps are always wired in series with a high value resistory, I really don't see any possibility of a connection between the lamp flashing and the glow discharge lamp.

My best guess is that the original poster has purchased an energy saving bulb with an intermittent (possibly thermal) problem. The bulb will likely exhibit the identical problem when put into any similarly oriented lamp socket in his home.

The obvious first test would be to switch the bulb having the problem with a different (preferably known good) bulb. If his "energy saving bulb" is of the fluorescent variety, the possiblity that the bulb is itself faulty increases over that of, say, an energy efficient bulb of the quartz halide type.

Harry C.

Reply to
Harry Conover

Some are, but on the other hand some fluorescents and quartz halide bulbs are also marketed with the same of closely related claims.


Harry C.

Reply to
Harry Conover

"Harry Conover" skrev

Because the tiny little current going through the system because of the small glow discharge lamp(s), will accumulate in the electronic ballast in the energy saving bulb and suddenly give a flash as described.

Reply to

Hey there, yes energy saving bulbs flash when you switch them on... actually you should refer to that as 'flicker' just like when you turn on any other flouro lamp, the starter starts it up by magnetizing the magnetic ballast for a few times. Energy saving lamps ARE flourocent lamps in a small package so they work basically the same.

If this is not what you are talking about, well maybe you have a light 'dimmer' knob on one of the switches which controls that lamp? Dimmers shouldn't be used with energy saving bulbs because flourocent lamps work only with 1 specific voltage.

Reply to
Brian Su

Exactly the same happens in my house with Philips energy saving light bulbs - it happens in two sockets in particular at the moment, both of which have two light switches (top of stairs and living room). I have no idea why it happens but it has only ever happened with Philips energy saving bulbs, never with any other type of bulb or any other brand of energy saving bulbs. I am also wondering if it is dangerous!


Reply to

Are you in fact posting about light bulbs, or fluorescent replacements for light bulbs?

The original poster did not make this point clear, and for many of us an "Energy Saving" light bulb is simply a normal bulb with reduced wattage that claims to emit the same luminous flux as a full wattage bulb, or a quartz-halide bulb that really does produce more light with lower wattage than a conventional light bulb (sure, but at $5 a pop!).

Fluorescent substitutes for light bulbs are another item entirely. I believe a number of us in crafting our responses neglected that possibility entirely. (Me be bad!)

Hopefully though, in the future, posters will do a better job of clarifying the nature of the device about which they are posting.

Harry C.

Reply to
Harry Conover

I've noticed this effect too with some of our energy saving flourescent tubes. i don't know what makes they were, but Philips rings a bell.

I believe that the effect is caused by the tiny capacitance between the switch contacts when they are off. You only notice the effect on 2-way lighting circuits because they have many meters of cable with the live feed and the wire to the bulb running in parallel (with the earth in between (UK), which would screen some of the effect).

I've tested this theory by placing a small 250V rated AC capcitor in series with one of these lamps in a table lamp. They flash at a rate determined by the series capacitance. (Large capacitance, frequent flashing, since the capacitors impedance is lower.)

I suspect that its the Flourescent lamps trigger circuit charging through the small capacitive impedance provided by the long switch wires (or series capacitor in my case), and once it reaches a particular threshold, the trigger circuit fires, causing a little flash inside the tube.

Almost certainly not dangerous though


Peter Clifton

(Electronic Engineering Student)

Reply to
Peter Clifton

if cold you can observe that effect, once warm it is gone.

depending if the manufacturer used electronics (tranformer or electronics) it will be more or less. but at the end, It is still a tube light!

"Peter Clifton" schreef in bericht news:bu4704$hjg$

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