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

[James Taylor]

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!

James

 

[DarkMatter]

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!

James

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.

 

[Cubus]

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.

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.

 

[Romy]

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.

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).


Romy

 

[Ross Mac]

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!

James

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

 

[Andrew Gabriel]

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.

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

No, it's a compact fluorescent.

 

[Cubus]

How?

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.

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.

 

[Brian Su]

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.

 

[Peter Clifton]

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

Regards

Peter Clifton

(Electronic Engineering Student)

 

[cuno]

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!