"Arfa Daily" wrote in message
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"Jim Adney" wrote in message
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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
I've been following this thread rather loosely for the past several days, so
please pardon me if I repeat previously addressed thoughts.
Arfa, I understand that you've stated that you're using lamps labeled as 60-watt
in your fixture. Have you actually measured the power consumed (for instance,
using a Kill-a-Watt or similar meter) by the lamps? It's a possibility that the
lamps have been mislabeled, and you actually have 75- or 90-watt lamps instead
of 60-watt lamps.
Since an operating incandescent lamp is essentially a resistive element, the
power consumed should be RMS power, which is the heating value of the power.
Sixty watts RMS into a resistive element should produce the same amount of heat,
whether it's in a large glass bulb or a small glass bulb. The temperature of
the bulb might be higher in a small lamp because it has a smaller radiating
surface. Power that is concentrated in a small area will have a higher
temperature than the same power that has been spread over a larger area.
Is the radiating surface area of the new lamps small enough to cause the
increase in temperature that you're experiencing?? I suppose the math could be
done to derive the rise in temperature of your new lamps... would be interesting
to see the results.
My ending thought on the issue is that, IMHO, the telling story would be in the
reading of a power meter in the circuit. If you don't have a power meter such a
the Kill-a-Watt, then you could measure it directly with a voltmeter and
ammeter. V * I = P no need to measure phase since it's essentially a resistor.
--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)
Experience: What you get when you don't get what you want