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[Phys-L] Re: light bulb transient



Michael hits the nail on its head, as usual. The filament temperature
increases monotonically in time, and so too does the brightness of
the filament. However, before Michael pointed out what the actual
question was I didn't see it. John Denker's question would be a good
one to use on students for teaching purposes, but not on examinations
to test their knowledge of physics.

Leigh

Michael Edmiston said:

What's the primary point of interest here? Is it the question of
whether the light bulb is momentarily brighter when turned on?

If that's it, I am aware that some people believe they observe this.
But I think it's because the light bulb got to its full brightness
before the irises of their eyes closed down. If the room is not real
bright, and you stare at a bulb as it is turned on, you will have the
impression that it got real bright at first and then dimmed. I think
this is a biological phenomenon in the eye rather than physical
reality
in the light bulb. I don't see how the bulb could overshoot the
equilibrium brightness, but I have to admit I have never recorded the
brightness of a light bulb turning on.

Michael D. Edmiston, Ph.D.
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