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a better incandescent light bulb

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.

(...)

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

Reply to
Winston
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But the voltmeter was connected only across the lamp, the point being to determine how an unmodified filament behaves when the voltage across it varies in small increments. And for that purpose, as long as the measurements are taken at equilibrium, it doesn't matter whether R1 is temperature dependent or not.

So we know that small changes in the voltage across a lamp result in proportionally smaller, but measurable, changes in current. Now replace R1 (my variable resistor) with a second lamp. Apply the appropriate voltage to the string and note the current. Thin the filament in the second lamp with a laser, or a genie with an angle grinder. As we agreed before, the network will reach a new equilibrium, with the voltage divided according to the new ratio of the filament resistances, such that the voltage across the unmolested lamp is slightly higher than it was before. Consequently, the current in the circuit will have increased a small, but detectable amount, and so has the sum of the power consumed by the two lamps.

Which is contrary to what was reported in the article. In other words, a localized thinning of the filament can't explain an increase in brightness without an increase in power.

Reply to
Ned Simmons

The point remains that:

1) Mr. Guo and Mr. Vorobeyv's claim that they 'improved' a light bulb by subjecting it to laser light does not pass muster.

2) Their explanation that the laser improved lamp efficiency by creating surface features (independent of a reduction in filament cross sectional area) is far less likely than a simple reduction in the cross sectional area of the filament, causing a hot spot.

3) Thinning of the filament will produce: A) Some aggregate spectral shift towards the blue in the hot spot. B) Increased power dissipation in the thinned area. C) Decreased power dissipation in the unmolested area. D) A reproducible decrease in the life of any lamp thus modified.

We can worry this subject to death, but let's please not lose sight of the fact that Mr. Guo and Mr. Vorobeyv have apparently made a technical boo - boo.

It matters bigtime. We should not draw a conclusion based on a circuit in a given state of equilibrium and apply it to a different circuit in a different state of equilibrium.

Slightly lower, yes? The resistance of the thinned portion of the filament will increase, causing more voltage to be dropped across it rather than the unmolested length of the filament. Power shifts.

I disagree. Power shifts away from the unmolested portion of the filament to the thinned portion of the filament.

Is this fun or what? :)

--Winston

Reply to
Winston

none of listed places have any relevance to light bulbs in any way at all.

Reply to
Cydrome Leader

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