Re: a better incandescent light bulb

Ned Simmons wrote:
On Fri, 05 Jun 2009 13:01:16 -0700, Winston <Winston@xxxxxxxxxxxxxx>
wrote:

Ned Simmons wrote:

(...)

That's a pretty remarkable claim -- that, at least in the range where
a normal lamp operates, the current flowing thru a filament is
completely independent of the voltage applied to it.
Your model shows a net reduction of voltage available to the bulb.

Not my model. It's the one you proposed in your previous post ("Model
it as two PTC resistors in series, one of which is about a percent of
the value of the second one"), except I moved one resistance outside
the lamp's envelope and turned a knob rather than tweaking it with a
laser.

But first, you changed R1 to a linear resistance. :)
After thinning, it dissipates much more power than it had before.

As power across R1 increases, it's resistance increases nonlinearly.
As power across R2 decreases, it's resistance decreases nonlinearly.

I'm not going to do the arithmetic, but it's a PTC series circuit with a
constant voltage across it. Is it plausible that net power dissipated
by this network remains fairly constant despite the fact that the
ratio of power dissipated by R1 is inversely proportional to the power
dissipated by R2 over a range of say 3% of P2? I think so.

(...)

Exactly. If treating a spot on the filament changed its resistance (as
I changed the resistance in series with my filament), the resistance
of the adjacent untreated filament would change in the opposite
direction, but the magnitude of change would be smaller. In other
words, there'd be a net change in the lamp's resistance, which would
show up as a change in power.

I ain't so sure. My cheapo SPICE simulator does not have a PTC
thermistor component, else I would ask the computer for an answer.

--Winston

--

We now return you to the economic collapse, already in progress.
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