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Slightly OT. Heat and a Bench Light ...

A

Arfa Daily

Jan 1, 1970
0
For twenty odd years, I have had the same Terry's Anglepoise bench lamp in
service. I have always used perfectly normal 60 watt incandescent lamps in
it, without any problem at all. Although the metal shade used to get quite
warm, it was never enough to actually burn you when your forehead
accidentally connected with it.

Recently, the light bulbs I've been seeing and buying, seem to have reduced
in size from the old 'tennis ball' size, to something closer to a snooker or
pool ball (but not as small as the established 'golf ball' types often used
in multibranch ceiling lights and light / fan fittings.)

I have noticed that these new smaller bulbs run a whole quantum leap hotter
than the older larger size, and they hot up the shade on the bench light
until it is unbearably hot to touch. Today, I left the workshop for a while,
and when I came back, the air was full of that 'fishy' sort of smell you get
when something like a wall socket or the plug that's in it, is burning. A
hunt around for the source, brought me to the bench lamp, which was still
alight. When I moved it, it went off. When it had cooled down a bit, I took
the bulb out (a UK bi-pad bayonet cap rather than a U.S. edison screw type)
and I was horrified to see that one of the solder pads had just about burnt
away completely, and the black insulation material in the base had started
to burn as well. Fortunately, the brass lampholder was undamaged.

So, has anyone else noticed how hot these smaller bulbs run ? Are we talking
dangerous here if they are used in any fitting where they hang downwards ?
Any suggestions as to why there is such a large increase in temperature ?
Yes, I can see that the glass envelope is closer to the filament, and that
it has somewhat less surface area to radiate the heat away from, but I'm not
sure that either of those are enough to account for just how much hotter
they seem to run. And why had one pad burnt away?Anything to do with the
solder being lead-free and less malleable than before, reducing the spring
loaded contact area maybe ?

A bit worrying as I'm sure that there will be many situations where a
fitting that has previously been quite happy with a 60 watt bulb in it, will
now overheat, with possibly catastrophic consequences ...

Arfa
 
N

N_Cook

Jan 1, 1970
0
Arfa Daily said:
For twenty odd years, I have had the same Terry's Anglepoise bench lamp in
service. I have always used perfectly normal 60 watt incandescent lamps in
it, without any problem at all. Although the metal shade used to get quite
warm, it was never enough to actually burn you when your forehead
accidentally connected with it.

Recently, the light bulbs I've been seeing and buying, seem to have reduced
in size from the old 'tennis ball' size, to something closer to a snooker or
pool ball (but not as small as the established 'golf ball' types often used
in multibranch ceiling lights and light / fan fittings.)

I have noticed that these new smaller bulbs run a whole quantum leap hotter
than the older larger size, and they hot up the shade on the bench light
until it is unbearably hot to touch. Today, I left the workshop for a while,
and when I came back, the air was full of that 'fishy' sort of smell you get
when something like a wall socket or the plug that's in it, is burning. A
hunt around for the source, brought me to the bench lamp, which was still
alight. When I moved it, it went off. When it had cooled down a bit, I took
the bulb out (a UK bi-pad bayonet cap rather than a U.S. edison screw type)
and I was horrified to see that one of the solder pads had just about burnt
away completely, and the black insulation material in the base had started
to burn as well. Fortunately, the brass lampholder was undamaged.

So, has anyone else noticed how hot these smaller bulbs run ? Are we talking
dangerous here if they are used in any fitting where they hang downwards ?
Any suggestions as to why there is such a large increase in temperature ?
Yes, I can see that the glass envelope is closer to the filament, and that
it has somewhat less surface area to radiate the heat away from, but I'm not
sure that either of those are enough to account for just how much hotter
they seem to run. And why had one pad burnt away?Anything to do with the
solder being lead-free and less malleable than before, reducing the spring
loaded contact area maybe ?

A bit worrying as I'm sure that there will be many situations where a
fitting that has previously been quite happy with a 60 watt bulb in it, will
now overheat, with possibly catastrophic consequences ...

Arfa

I usually use circular fluourescent lamp of an anglepoise inspection lamp
for bench illumination but sometimes use a traditional one (Luxo for those
over there). In that I have a 60Watt one that is conical in shape, like
Apollo earth lander capsule, that has silvering on the cone so directs both
heat and light forwards unlice dichroic which is designed to pass heat
through to the rear and light forward. The cover gets about as hot as
something less than a 40W standard bulb. They may be used for shop display
purposes these silvered bulbs. As most of the rearwar light is directed
forwards more efficiently than a cluttered white cover then perhaps
equivalent to standard 150W illumination in the direction where you want it

The ones I have are coloured but I scrape the varnish off the front, Endon
Accessories Reflector R080 type
 
A

Arfa Daily

Jan 1, 1970
0
N_Cook said:
I usually use circular fluourescent lamp of an anglepoise inspection lamp
for bench illumination but sometimes use a traditional one (Luxo for those
over there). In that I have a 60Watt one that is conical in shape, like
Apollo earth lander capsule, that has silvering on the cone so directs
both
heat and light forwards unlice dichroic which is designed to pass heat
through to the rear and light forward. The cover gets about as hot as
something less than a 40W standard bulb. They may be used for shop display
purposes these silvered bulbs. As most of the rearwar light is directed
forwards more efficiently than a cluttered white cover then perhaps
equivalent to standard 150W illumination in the direction where you want
it

The ones I have are coloured but I scrape the varnish off the front, Endon
Accessories Reflector R080 type

I'll have a look for some. Without any desire to re-open the CFL thing
again, I currently have one of those in it, as it was all I had to hand. The
light from it is useless in this application ...

Arfa
 
N

N_Cook

Jan 1, 1970
0
As far as appearance, like a bayonet version of the leftmost one of these
http://www.global-b2b-network.com/direct/dbimage/50135433/Reflector_Lamp.jpg
Perhaps 80 percent of the rearward cone is silvered, so reflecting that part
forwards, both heat and light.

Anglepoise is one of my favourite made-up words, precisely giving its
mechanical function , unlike Luxo which could be anything involving light.
If the workroom gets too hot I have an 6 inch fan mounted on the anglepoise
arms of an ex-light.
 
B

Baron

Jan 1, 1970
0
Arfa Daily Inscribed thus:
For twenty odd years, I have had the same Terry's Anglepoise bench
lamp in service. I have always used perfectly normal 60 watt
incandescent lamps in it, without any problem at all. Although the
metal shade used to get quite warm, it was never enough to actually
burn you when your forehead accidentally connected with it.

Recently, the light bulbs I've been seeing and buying, seem to have
reduced in size from the old 'tennis ball' size, to something closer
to a snooker or pool ball (but not as small as the established 'golf
ball' types often used in multibranch ceiling lights and light / fan
fittings.)

I have noticed that these new smaller bulbs run a whole quantum leap
hotter than the older larger size, and they hot up the shade on the
bench light until it is unbearably hot to touch. Today, I left the
workshop for a while, and when I came back, the air was full of that
'fishy' sort of smell you get when something like a wall socket or the
plug that's in it, is burning. A hunt around for the source, brought
me to the bench lamp, which was still alight. When I moved it, it went
off. When it had cooled down a bit, I took the bulb out (a UK bi-pad
bayonet cap rather than a U.S. edison screw type) and I was horrified
to see that one of the solder pads had just about burnt away
completely, and the black insulation material in the base had started
to burn as well. Fortunately, the brass lampholder was undamaged.

Don't count on the lampholder being undamaged ! The springs in the
holder that apply pressure to the contact pads on the bulb, weaken with
both age and heat. It would be wise to replace the lamp holder.
So, has anyone else noticed how hot these smaller bulbs run ? Are we
talking dangerous here if they are used in any fitting where they hang
downwards ? Any suggestions as to why there is such a large increase
in temperature ? Yes, I can see that the glass envelope is closer to
the filament, and that it has somewhat less surface area to radiate
the heat away from, but I'm not sure that either of those are enough
to account for just how much hotter they seem to run. And why had one
pad burnt away?Anything to do with the solder being lead-free and less
malleable than before, reducing the spring loaded contact area maybe ?

Yes the smaller glass envelope does increase the heat considerably !
The bulb produces a little more light as well. I don't know that being
lead free makes a lot of difference, the heat sure does though !
A bit worrying as I'm sure that there will be many situations where a
fitting that has previously been quite happy with a 60 watt bulb in
it, will now overheat, with possibly catastrophic consequences ...

Arfa

Yes I agree, overheating is a problem. I enlarged the vent holes on my
desk lamp for that reason. I used a nibbling tool that I bought at
Radio Shack when I was in the USA a few years ago.
 
A

Arfa Daily

Jan 1, 1970
0
Baron said:
Arfa Daily Inscribed thus:


Don't count on the lampholder being undamaged ! The springs in the
holder that apply pressure to the contact pads on the bulb, weaken with
both age and heat. It would be wise to replace the lamp holder.


Yes the smaller glass envelope does increase the heat considerably !
The bulb produces a little more light as well. I don't know that being
lead free makes a lot of difference, the heat sure does though !


Yes I agree, overheating is a problem. I enlarged the vent holes on my
desk lamp for that reason. I used a nibbling tool that I bought at
Radio Shack when I was in the USA a few years ago.

The lampholder is ok. Oddly enough, I renewed the cable to the lamp a few
weeks ago, as it had gone intermittent at one of the bend loops, and as the
holder was original, and looking a little worse for wear, I put in a new
one, and a new pressel switch as well, which had failed and been bypassed
long ago ... :)

Arfa
 
B

Baron

Jan 1, 1970
0
Arfa said:
The lampholder is ok. Oddly enough, I renewed the cable to the lamp a
few weeks ago, as it had gone intermittent at one of the bend loops,

Yes ! The middle one. The original cable was fabric woven sheath over
rubber. I replaced it with "electric iron" cable but that didn't last
as long as the original one. I've now got a modern plastic insulated
cable in there. Its much thinner and more flexible. I used cambric
spaghetti over the wires at the bulb holder end just in case the heat
damaged the plastic insulation.
and as the holder was original, and looking a little worse for wear, I
put in a new one, and a new pressel switch as well, which had failed
and been bypassed
long ago ... :)

Arfa

That little push on push off switch went a very long time ago ! There
is just the hole now, adding to the ventilation !
 
A

Arfa Daily

Jan 1, 1970
0
Yes ! The middle one. The original cable was fabric woven sheath over
rubber. I replaced it with "electric iron" cable but that didn't last
as long as the original one. I've now got a modern plastic insulated
cable in there. Its much thinner and more flexible. I used cambric
spaghetti over the wires at the bulb holder end just in case the heat
damaged the plastic insulation.


That little push on push off switch went a very long time ago ! There
is just the hole now, adding to the ventilation !

I too have a thin plastic cable in there. There was a good reason that I
changed it apart from the intermittency. Over the years, it has had a lot of
'half-arsed' repairs done to it. I'm sure if you have one, you know exactly
what I mean. It's half past two, and the guy is coming to pick up his
amplifier that you have assured him will be ready at half past four, and the
bench light starts going on and off ... Well, a long time ago, some silicon
sheathed heat-resistant wire had gone into the lampholder, and been joined
to the feed cable (via the pressel switch bypass ...!!) with a bit of
plastic choc-bloc. Yes, I know, but I didn't have a ceramic one to hand.

Anyway, it had been fine until I started using these small very hot bulbs in
it, whereupon the nylon insulation on the bloc had crisped up. Well, a
couple of weeks ago, I had one hand on the (earthed) chassis of an amp I was
working on (no, it wasn't plugged into the bench isolation tranny as it
should have been !) and I grabbed the Anglepoise shade to pull it into a
more convenient position. A microsecond later, the air turned blue as a
stream of profanity flowed from my mouth ...

The crisped up insulation on the choc-bloc had left a mains leakage path to
the metal shade. I decided there and then that no such thing was going to
happen again, so I have now rewired it with a thin three-core cable, and
grounded the metalwork to mains earth, via the earth connector on the brass
lampholder. Silicon sleeving has also been fitted to the wire ends in an
effort to proof them at least some, against future heat problems.

I've got to admit that the shock I got from the setup was a bit of a wakeup
call, as it's often the case that your forehead brushes agains the lamp
shade, as you try to stick your head inside some recalcitrant item that's on
the bench for repair. At least now, if there should be any future leakage
issues, it should just whack the RCD out.

Arfa
 
A

Arfa Daily

Jan 1, 1970
0
Jeff Liebermann said:
As I understand it (possibly wrong), the higher the temperature of the
filament, the more efficient the incandescent light bulb in lumens per
watt. There's a bit of a clue at:
<http://en.wikipedia.org/wiki/Incandescent_light_bulb>
During ordinary operation, the tungsten of the filament evaporates;
hotter, more-efficient filaments evaporate faster. Because of this,
the lifetime of a filament lamp is a trade-off between efficiency
and longevity. The trade-off is typically set to provide a lifetime
of several hundred to 2000 hours for lamps used for general
illumination. Theatrical, photographic, and projection lamps may
have a useful life of only a few hours, trading life expectancy
for high output in a compact form. Long-life general service lamps
have lower efficiency but are used where the cost of changing the
lamp is high compared to the value of energy used.

In other words, the newer smaller bulbs are trading efficiency for
lifetime, which is the result of running hotter. I'm not sure why the
bulb is smaller. My guess(tm) is that it's simply thicker, which
allows the use of a smaller bulb size, which can withstand the heat
better than a thin bulb and can handle a higher internal gas pressure
(which is necessary to prevent filament evaporation).

More on the subject:
<http://en.wikipedia.org/wiki/Luminous_efficacy>
<http://members.aol.com/ajaynejr/lumen.htm>

--
Jeff Liebermann [email protected]
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Interesting thoughts. Really not a good thing though, I am thinking. It's
only been a matter of a few months that I have been using these small bulbs,
and they have already caused a problem with a lamp that had previously been
running daily, without heat-related problems, for years. It seems to me that
in certain domestic applications, these could represent a significant fire
hazard. Take for instance, a 'standard' pendant room light fixture,
suspended on normal plastic cable. There is not normally enough heat
generated, to cause a problem with the insulation, but I'm sure that with
the increased temperature that these things run at, there's going to be.

Take also, a typical lampshade made from either plastic or paper based
sheet. These will typically have a sticker in them saying something like "60
watt max lamp". Now that figure is a fire safety one, based on the heat
generated by a typical 60 watt bulb. What about when you put one of these
new ones in ? I would guess that the heat steaming off them, is at least
equivalent to what you would be expecting from a traditional-sized 100 watt
bulb. So even putting in a correctly rated 60 watt bulb, you could be
thermally overloading that shade, by 60 odd % . Potential fire hazard, or am
I just being paranoid ? Does this need bringing to someone's attention ?

Arfa
 
B

Baron

Jan 1, 1970
0
Arfa said:
I too have a thin plastic cable in there. There was a good reason that
I changed it apart from the intermittency. Over the years, it has had
a lot of 'half-arsed' repairs done to it. I'm sure if you have one,
you know exactly what I mean. It's half past two, and the guy is
coming to pick up his amplifier that you have assured him will be
ready at half past four, and the bench light starts going on and off
... Well, a long time ago, some silicon sheathed heat-resistant wire
had gone into the lampholder, and been joined to the feed cable (via
the pressel switch bypass ...!!) with a bit of plastic choc-bloc. Yes,
I know, but I didn't have a ceramic one to hand.

Ooo shudder !
Anyway, it had been fine until I started using these small very hot
bulbs in it, whereupon the nylon insulation on the bloc had crisped
up. Well, a couple of weeks ago, I had one hand on the (earthed)
chassis of an amp I was working on (no, it wasn't plugged into the
bench isolation tranny as it should have been !) and I grabbed the
Anglepoise shade to pull it into a more convenient position. A
microsecond later, the air turned blue as a stream of profanity flowed
from my mouth ...

I must admit I don't plug mine into the isolated side ! Doesn't/didn't
yours have an earth connection then ? Mine does and had one from new !
The crisped up insulation on the choc-bloc had left a mains leakage
path to the metal shade. I decided there and then that no such thing
was going to happen again, so I have now rewired it with a thin
three-core cable, and grounded the metalwork to mains earth, via the
earth connector on the brass lampholder. Silicon sleeving has also
been fitted to the wire ends in an effort to proof them at least some,
against future heat problems.

I've seen electric heaters repaired with those plastic choc-blocks put
in them. I once had an old lady ask me to look at one. She said it
smells funny and there is something dripping out of the back. The
plastic surround had almost compleatly gone and the connections were
hanging in mid air. I had a go at the guy who repaired it and was
un-politely told to sod off........ Sadley there weren't the consumer
protections in those days !
I've got to admit that the shock I got from the setup was a bit of a
wakeup call, as it's often the case that your forehead brushes agains
the lamp shade, as you try to stick your head inside some recalcitrant
item that's on the bench for repair. At least now, if there should be
any future leakage issues, it should just whack the RCD out.

Arfa

Its a good thing you didn't touch it with your forehead ! I can't
imagine the possible injury it could have caused. At least it
shouldn't happen again.
 
B

Baron

Jan 1, 1970
0
Jeff said:
You might have a point, however I find it odd that you're using a 75
or 100 watt incandescent bulb in a desk lamp. I have a few here and
they all specify 60 watts maximum. I guess that applies only to the
old large bulbs.

I don't know about Arfa's lamp, but mine never had any warnings about
bulb size ! I do know that at a pinch you could get a 150 W bulb in
there. Indeed on the odd occasion I have done just that.
Interestingly I recall that the light output was actually poorer with
the bigger bulb. Probably because the filament was considerably
further away from the shade/reflector.
 
N

N_Cook

Jan 1, 1970
0
Dave Plowman (News) said:
There's no difference from a choc block than any other screw connector -
like those found in sockets, etc. Make a poor connection or use an
incorrectly rated one and it *will* give trouble.

--
*Certain frogs can be frozen solid, then thawed, and survive *

Dave Plowman [email protected] London SW
To e-mail, change noise into sound.


One general thing to be aware of these Anglepoise lamps. Well the stronger ,
older , all metal ones.
Make sure all the little rubber grommets are present and correct, not
perished, at each of the channel holes that the mains cable passes through.
 
B

Baron

Jan 1, 1970
0
Dave said:
There's no difference from a choc block than any other screw connector
- like those found in sockets, etc. Make a poor connection or use an
incorrectly rated one and it *will* give trouble.
I couldn't agree more !

However I was referring to the fact that some Id10T had replaced the
original ceramic terminal block with a plastic one ! The fact that the
plastic over the course of a couple of weeks had just melted away with
the heat, rather than just a bad joint. Its likely that the original
had one or more seized or broken grub screws, leading to its
replacement.
 
B

Baron

Jan 1, 1970
0
Dave said:
If it's old enough it will have silk covered rubber cable too - which
perishes.
Yes mine did ! That was one of the reasons that I used cotton braided
electric iron flex as the first replacement. I found it less durable
than the original.
 
A

Arfa Daily

Jan 1, 1970
0
N_Cook said:
One general thing to be aware of these Anglepoise lamps. Well the stronger
,
older , all metal ones.
Make sure all the little rubber grommets are present and correct, not
perished, at each of the channel holes that the mains cable passes
through.

I was a little concerned that these would not still fit, when I put the 3
core cable in, but they did, just fine.

And to Baron. I've had the thing a long long time. It's an orange one that
came from BHS originally, but a genuine Terry's Anglepoise, none-the-less.
Before that, I had the even earlier one with the black 'flying saucer'
shade. I can't remember what happened to that one. Over the years, it has
had much work done on it, but I'm pretty sure that it never had anything
other than a 2 core plastic cable on it. I can't imagine that I would ever
have replaced a three core with a 2 core. The old black one had plaited
cotton-covered rubber cable as I recall, but I still don't remember that one
being earthed, either.

Arfa
 
A

Arfa Daily

Jan 1, 1970
0
Jeff Liebermann said:
You might have a point, however I find it odd that you're using a 75
or 100 watt incandescent bulb in a desk lamp.

You're mis-understanding me, I think. I'm not using a 75 or 100 watt bulb.
I'm using a 60 watt bulb, as specified for the lamp, and always have done.
Up until now, they have always been the 'standard' tennis ball sized type.
The smaller ones that I have been buying lately, are still rated at 60
watts, but in my opinion, put out the *heat* of a standard-sized 100 watt
bulb.

Arfa
 
I

Ian Jackson

Jan 1, 1970
0
Arfa Daily said:
You're mis-understanding me, I think. I'm not using a 75 or 100 watt bulb.
I'm using a 60 watt bulb, as specified for the lamp, and always have done.
Up until now, they have always been the 'standard' tennis ball sized type.
The smaller ones that I have been buying lately, are still rated at 60
watts, but in my opinion, put out the *heat* of a standard-sized 100 watt
bulb.

Arfa

I haven't been following the thread, so apologies if this explanation
has been offered earlier.

I'm guessing, but I reckon that smaller sized bulb may be hotter
because:
(a) The filament may be physically smaller (squeezed in more, and coiled
up tighter). Some parts of the filament may be obstructing the path of
the light from other parts. Similarly, the path for radiated heat may be
being obstructed. As a result, the filament may be less efficient (less
light output, but more heat).
(a) The glass bulb is closer to the hot filament.
(b) The glass bulb has quite a lot less surface area available to
dissipate the heat.

What do you think?
 
J

Jim Adney

Jan 1, 1970
0
I have noticed that these new smaller bulbs run a whole quantum leap hotter
than the older larger size, and they hot up the shade on the bench light
until it is unbearably hot to touch.

Lost in this conversation is the fact that you claim that both the old
and new bulbs have been 60 Watts. Now, if that's true, then there's no
more power available from the new 60 W lamps than there was from the
old 60 W lamps.

Halogen lamps, while they DO have much hotter envelopes, convert
electrical power into visible lighte somewhat more efficiently, so
that should make the shade run slightly cooler, if anything. I would
expect this effect to be small.

Certainly a smaller 60 W bulb will run at a higher glass envelope
temperature, but that envelope will be farther from the shade,
assuming that they both got mounted on the same centers. The end
result is that there will be no difference in the radiant heating of
the shade.

The confusion here seems to be the common one between temperature and
heat. Cram the same amount of heat into a smaller amount of material
and you'll get a higher temperature, but in this case, the shade has
remained the same, so the amount of heat energy collected should be
the same, and the resulting temperature should also be the same.

It may help to think of heat and temperature as having electrical
analogs in charge and voltage.

Really, there are only 2 possible conclusions: Either the new bulb is
actually higher wattage than the old one, or the perception of a
hotter shade is mistaken.

Separate from this is heat conduction thru the base of the bulb. If
the bulb is shorter and hotter, then it will likely conduct more heat
into the socket. Halogen sockets are generally ceramic or some rather
special high temp plastic in order to deal with this, so putting a
halogen bulb in a standard socket will always result in a destroyed
socket.

-
 
A

Arfa Daily

Jan 1, 1970
0
Jim Adney said:
Lost in this conversation is the fact that you claim that both the old
and new bulbs have been 60 Watts. Now, if that's true, then there's no
more power available from the new 60 W lamps than there was from the
old 60 W lamps.

Halogen lamps, while they DO have much hotter envelopes, convert
electrical power into visible lighte somewhat more efficiently, so
that should make the shade run slightly cooler, if anything. I would
expect this effect to be small.

Certainly a smaller 60 W bulb will run at a higher glass envelope
temperature, but that envelope will be farther from the shade,
assuming that they both got mounted on the same centers. The end
result is that there will be no difference in the radiant heating of
the shade.

The confusion here seems to be the common one between temperature and
heat. Cram the same amount of heat into a smaller amount of material
and you'll get a higher temperature, but in this case, the shade has
remained the same, so the amount of heat energy collected should be
the same, and the resulting temperature should also be the same.

It may help to think of heat and temperature as having electrical
analogs in charge and voltage.

Really, there are only 2 possible conclusions: Either the new bulb is
actually higher wattage than the old one, or the perception of a
hotter shade is mistaken.

Separate from this is heat conduction thru the base of the bulb. If
the bulb is shorter and hotter, then it will likely conduct more heat
into the socket. Halogen sockets are generally ceramic or some rather
special high temp plastic in order to deal with this, so putting a
halogen bulb in a standard socket will always result in a destroyed
socket.

-

OK. The bulb does not claim to be a halogen type. It was sold as a 'bog
standard' light bulb. It looks like a standard light bulb. It is stamped 60
watts on the packet, and on the bulb itself. The glass envelope and bulb in
general, is identical in every way to what any of us would recognise as a
'standard' incandescent light bulb given, of course, the obvious difference
between a UK bi-pad bayonet cap, and a U.S. edison screw cap. However, it
has one major difference in that instead of the glass envelope being the
size of a tennis ball, it's more like the size of a pool ball. When
installed in my bench light, which is the only 'closed in' place that I've
used one so far, I did not notice any change in light output from any other
60 watt bulb that I have used in the light. Bear in mind that this light is
used every working day to illuminate whatever piece of kit I am working on,
and has been for the last 20 years, so I am pretty confidant that I know its
'normal' operating characteristics.

So, if we believe the rating stamped on both the bulb itself, and its box,
and you are prepared to believe me when I tell you that with this bulb
fitted, the temperature of the shade was a whole heap hotter, then
somewhere, there must be another explanation than the two that you believe
are the only possibilities. There must be a greater degree of heat being
conducted into the base cap, in order for the temperature to have been
raised to the point where the insulation material within the lamp itself's
base, to have started to fry itself and to have destroyed the connection
pad, which is where this thread started from. There must be considerably
more heat steaming off the bulb itself, to have raised the temperature in
the upper part of the shade, to the point where the nylon insulation around
the choc bloc which was located there, has fried. That piece of choc bloc
had been there for a couple of years, and trust me, before fitting this
bulb, it was not even discoloured, let alone crisped.

The physical contact area between the brass lamp holder, and the bracket to
which it is attached, is small, so it would seem unlikely that heat
conduction is playing much of a part in raising the temperature of the
shade. So that would leave only radiation as the mechanism for raising the
shade's temperature. I'm pretty sure that it must be a combination of the
area of the glass envelope being - what, I don't know, 30% smaller maybe? -
making for a less efficient radiator, and exacerbation of this by that glass
being nearer to the filament.

It still seems to me that this has potentially far-reaching consequences
under the right (wrong?) circumstances. The bulb was a B&Q own brand BTW. I
don't have any more in stock at the moment, but I will try to get to the
store and pick some more up, and do some further tests and measurements.

Arfa
 
A

Arfa Daily

Jan 1, 1970
0
Ian Jackson said:
I haven't been following the thread, so apologies if this explanation has
been offered earlier.

I'm guessing, but I reckon that smaller sized bulb may be hotter because:
(a) The filament may be physically smaller (squeezed in more, and coiled
up tighter). Some parts of the filament may be obstructing the path of the
light from other parts. Similarly, the path for radiated heat may be being
obstructed. As a result, the filament may be less efficient (less light
output, but more heat).
(a) The glass bulb is closer to the hot filament.
(b) The glass bulb has quite a lot less surface area available to
dissipate the heat.

What do you think?

Yes, all valid thoughts. See my further discussions of it all in my reply
below to Jim

Arfa
 
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