"Normal" compact fluorescent bulb in 3-way lamp safe?

[Duffy Tweedy]

I've seen some mixed messages, even from labs and government sites,
about whether "normal" CFL bulbs can be used safely in 3-way lamps.
Some say flatly Yes, others No. But I haven't seen much about this in
general. Can someone point me to a definitive site, or answer this
one? The reason I'd like to be able to use regular CFLs is, of
course, lower cost. But unless I can determine finally that it is
safe to do so, obviously I'll have to assume otherwise and use the
(much) more expensive 3-way CFLs, or stick to incandescent in my
3-ways. Thanks.
--Duffy Tweedy

[Ian Stirling]

Post by Duffy Tweedy
I've seen some mixed messages, even from labs and government sites,
about whether "normal" CFL bulbs can be used safely in 3-way lamps.

What do you mean by a 3-way lamp?

[Daniel J. Stern]

Post by Ian Stirling

Post by Duffy Tweedy
I've seen some mixed messages, even from labs and government sites,
about whether "normal" CFL bulbs can be used safely in 3-way lamps.

What do you mean by a 3-way lamp?

That is a term used in North America for A-line lamps with two filaments
and three possible intensities made possible by powering one, the other,
or both filaments.

[Duffy Tweedy]

Post by Ian Stirling

Post by Duffy Tweedy
I've seen some mixed messages, even from labs and government sites,
about whether "normal" CFL bulbs can be used safely in 3-way lamps.

What do you mean by a 3-way lamp?

A lamp with a three-way switch, to take the usual 3-way incandescent
bulb ("50 watt, 100 watt, 150 watt").

--Duffy

[Ian Stirling]

Post by Duffy Tweedy

Post by Ian Stirling

Post by Duffy Tweedy
I've seen some mixed messages, even from labs and government sites,
about whether "normal" CFL bulbs can be used safely in 3-way lamps.

What do you mean by a 3-way lamp?

A lamp with a three-way switch, to take the usual 3-way incandescent
bulb ("50 watt, 100 watt, 150 watt").

Hmm, not something I've ever seen.
I guess they diddn't make it over the pond for some reason.

[Andrew Gabriel]

Post by Ian Stirling

Post by Duffy Tweedy

Post by Ian Stirling

Post by Duffy Tweedy
I've seen some mixed messages, even from labs and government sites,
about whether "normal" CFL bulbs can be used safely in 3-way lamps.

What do you mean by a 3-way lamp?

A lamp with a three-way switch, to take the usual 3-way incandescent
bulb ("50 watt, 100 watt, 150 watt").

Hmm, not something I've ever seen.
I guess they diddn't make it over the pond for some reason.

It's US-only AFAIK.
It's designed to be compatible with single filament US ES lampholders.

Use of ES GLS (A-line) lamps in UK is much rarer (and only on imported
fittings), and the European ES thread is slightly different size from
US anyway (not to mention different voltage and insulation requirements)
which means US fittings aren't likely to be directly imported into EU.

[Ian Stirling]

Post by Andrew Gabriel

Post by Ian Stirling

Post by Duffy Tweedy

Post by Ian Stirling

Post by Duffy Tweedy
I've seen some mixed messages, even from labs and government sites,
about whether "normal" CFL bulbs can be used safely in 3-way lamps.

What do you mean by a 3-way lamp?

A lamp with a three-way switch, to take the usual 3-way incandescent
bulb ("50 watt, 100 watt, 150 watt").

Hmm, not something I've ever seen.
I guess they diddn't make it over the pond for some reason.

It's US-only AFAIK.
It's designed to be compatible with single filament US ES lampholders.
Use of ES GLS (A-line) lamps in UK is much rarer (and only on imported
fittings), and the European ES thread is slightly different size from
US anyway (not to mention different voltage and insulation requirements)
which means US fittings aren't likely to be directly imported into EU.

I was more meaning the concept, rather than the exact lamp.
For example, a couple of smaller bumps on the outside that form a diamond
pattern with the existing bumps, and are connected to another filliment
internally.

[Daniel J. Stern]

Post by Duffy Tweedy
I've seen some mixed messages, even from labs and government sites,
about whether "normal" CFL bulbs can be used safely in 3-way lamps.
Some say flatly Yes, others No. But I haven't seen much about this in
general.

The answer is "flatly yes". Any other answer comes from those who do not
understand how 3-way lamps work, probably arising from fear that some
resistor or PWM box inside the socket would underdrive the CFL and cause
early death. Of course, that's not how 3-way lamps work at all. Rather,
3-way lamps and their intended sockets have two filaments of differing
wattage and flux characteristics and three contacts (central "tip"
common to both filaments, intermediate "ring" to feed one filament, and
outer shell to feed the other filament, rather than just two (central
"tip" and outer shell). As the 3-way switch is turned through its
positions, power is applied in sequence:

-Off (no power to either switched contact -- open circuit upstream of both
filaments)

-Low (power to low-wattage filament only, across e.g. ring and shell)

-Med (power to high-wattage filament only, across e.g. tip and shell)

-High (power to low-wattage filament across ring/shell and power to
high-wattage filament across tip/shell)

When a standard single-filament lamp (or a non-3-way CFL) is installed in
a 3-way socket, there is no compatibility or safety issue; single-filament
lamps (or non-3-way CFLs) have only the tip and shell contacts and so the
socket's ring contact doesn't touch anything. The only artifact is a
somewhat odd switching sequence (off-off-on-on-off-off) as the 3-way
switch is rotated through its positions.

DS

[John D. Bullough, Gurley Building]

Post by Daniel J. Stern

Post by Duffy Tweedy
I've seen some mixed messages, even from labs and government sites,
about whether "normal" CFL bulbs can be used safely in 3-way lamps.
Some say flatly Yes, others No. But I haven't seen much about this in
general.

When a standard single-filament lamp (or a non-3-way CFL) is installed in
a 3-way socket, there is no compatibility or safety issue; single-filament
lamps (or non-3-way CFLs) have only the tip and shell contacts and so the
socket's ring contact doesn't touch anything. The only artifact is a
somewhat odd switching sequence (off-off-on-on-off-off) as the 3-way
switch is rotated through its positions.

This is exactly how it works in the two 3-way table lamps I have with
CFLs in them.

JB

[Duffy Tweedy]

Post by Daniel J. Stern

Post by Duffy Tweedy
I've seen some mixed messages, even from labs and government sites,
about whether "normal" CFL bulbs can be used safely in 3-way lamps.
Some say flatly Yes, others No. But I haven't seen much about this in
general.

The answer is "flatly yes". Any other answer comes from those who do not
understand how 3-way lamps work, probably arising from fear that some
resistor or PWM box inside the socket would underdrive the CFL and cause
early death. Of course, that's not how 3-way lamps work at all. Rather,
3-way lamps and their intended sockets have two filaments of differing
wattage and flux characteristics and three contacts (central "tip"
common to both filaments, intermediate "ring" to feed one filament, and
outer shell to feed the other filament, rather than just two (central
"tip" and outer shell). As the 3-way switch is turned through its
-Off (no power to either switched contact -- open circuit upstream of both
filaments)
-Low (power to low-wattage filament only, across e.g. ring and shell)
-Med (power to high-wattage filament only, across e.g. tip and shell)
-High (power to low-wattage filament across ring/shell and power to
high-wattage filament across tip/shell)
When a standard single-filament lamp (or a non-3-way CFL) is installed in
a 3-way socket, there is no compatibility or safety issue; single-filament
lamps (or non-3-way CFLs) have only the tip and shell contacts and so the
socket's ring contact doesn't touch anything. The only artifact is a
somewhat odd switching sequence (off-off-on-on-off-off) as the 3-way
switch is rotated through its positions.
DS

Thanks for the quick response. That seems to be the prevalent I've
seen. The lamp itself had a sticker saying in no uncertain terms that
"ONLY 3-way bulbs should be used, not standard bulbs"--hence my
reluctance. Some federal government site said that CFLs "may fail" in
3-way fixtures, but mentioned no fire danger. bulbs.com warns only
that CFL's should NOT be used "w/ dimmers, timers,
photosensors/photocontrols, or other special switching devices." Lots
of warnings about dimmers.
--Duffy

[Travis Evans]

Post by Duffy Tweedy
I've seen some mixed messages, even from labs and government sites,
about whether "normal" CFL bulbs can be used safely in 3-way lamps.
Some say flatly Yes, others No. But I haven't seen much about this in
general.

Interestingly, I seem to remember reading an article about someone who
actually had a CFL explode when placed in a 3-way lamp, but I can't find
it at all. I think the general guess was that the way the lamp base was
designed somehow caused a short circuit to occur in a 3-way lamp socket.

I'm pretty sure something like that would be extremely rare and
exceptional. I don't see any reason why a CFL would cause any problem in
a 3-way lamp, as long as it isn't one of those lamps that actually
creates three brightnesses by using a dimmer (rather than using "3-way"
socket contacts).

[Daniel J. Stern]

Post by Travis Evans
Interestingly, I seem to remember reading an article about someone who
actually had a CFL explode when placed in a 3-way lamp, but I can't find
it at all.

If it actually happened, it was a tremendously good illustration of the
very first principle taught in Stats classes: Correlation does not imply
causation.

Post by Travis Evans
I think the general guess was that the way the lamp base was designed
somehow caused a short circuit to occur in a 3-way lamp socket.

A short circuit in the socket would blow the fuse or breaker, not explode
the CFL.