>>
>> 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?) cir***stances. 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)
>
Hi Dave
I haven't measured the actual power consumption of the new bulbs. A few
years ago, I would have been surprised if the figure quoted on a lamp was
not at least within say 5% accuracy, but these days, with the reduction in
integrity of just about everything, and the fact that much manufacturing
is
now done in 'emerging' industrial countries, I would be less sure of that.
As to whether the new bulb's envelope is small enough to reduce the
dissipation of the heat by the amount noted, I'm not really a good enough
theoretical physicist to make a call of any real value, but given that
this
appears to be the only mechanism by which this could be happening, I would
have to say that is probably the answer.
I don't dispute what has been said about 60 watts being 60 watts, or that
heat and temperature are not the same thing. However, radiation efficiency
is key to the relation****p between the two, as we both know. A 60 watt amp
with a small silver heatsink on its output transistors will not get rid of
the unwanted heat anything like as well as if that heatsink is black, and
force air cooled.
For all I know, my bench lamp may be a 'special case', and the fitting of
the smaller bulb might just screw up the dynamics of the air circulation
within the shade. As anyone who knows the Terry's Anglepoise will agree,
the
shade is not particularly well ventilated. Perhaps it would benefit from
having a ring of 5mm holes drilled around its top ... ??
Arfa
> Experience: What you get when you don't get what you want
>
>
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