"Jim Adney" wrote in message
...
On Fri, 4 Jul 2008 01:23:49 +0100 "Arfa Daily"
wrote:
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.
-
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Jim Adney
Madison, WI 53711 USA
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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