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[Phys-L] Re: light bulb transient



At 03:03 PM 11/13/2005, Mike Edmiston, you wrote:
///some people believe they observe this.
[momentary inital brightening]
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.

In referring to brightness as a physiological phenomenon, there is a
technical sense in which Mike absolutely correct - so much so, the
comment can be taken as a truism. See this definition, for example.
~~~~~~~~~~~~~~~~~~~~
brightness: An attribute of visual perception in which a source appears
to emit a given amount of light. Note 1: "Brightness" should be used only
for nonquantitative references to physiological sensations and perceptions
of light. Note 2: "Brightness" was formerly used as a synonym for the
photometric term "luminance" and (incorrectly) for the radiometric
term " radiance"


----------
These definitions were prepared by ATIS Committee T1A1. For more
information on the work related to these definitions, please
visit the <http://www.atis.org>ATIS website.

~~~~~~~~~~~~~~~~~~~~~

But in an extract which addresses the public understanding, it is not
to be expected that there is a universal distinction drawn between
luminance and perceived brightness.

If we paraphrase Mike's, " I don't see how the bulb could overshoot the
equilibrium brightness" to "how can the luminous intensity of areas of the
filament be brighter at turn on than at steady state?"
then one could respond with "hot-spots".


Brian Whatcott Altus OK Eureka!
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