[Phys-L] Re: Light bulb

[Bernard Cleyet <anngeorg@PACBELL.NET>]

About time!

There are altogether too few practical Physicists on this list.

bc, who confirms the camera transient response noted by JS.  This
applies to the old (vidicon) and film technologies also.

p.s. incidentally, Levi discusses starting and cooling transients in
incandescents (about four pp. including five graphs).  None of the
graphs show luminous overshoot, but the text reads:  "In many 6-V lamps
the intensity first rises above the rated value and drops slowly as
thermal equilibrium is approached.  This overshoot amounts to about 10%
in the higher current lamps[18]."

[18] is W. E. Forsythe, et al.  "Time Constants of Incandescent Lamps",
J. Appl. Phys. 9 209-214 (1938);  easily available to majority, but not
to me to verify my suspicion that intensity should be current.  However,
I have a bunch of high power 6-Vers and photodiodes, someday.

John SOHL wrote:

> If I get the chance (I need to do a bunch of grading today) I'll measure
> it in my optics lab with a photodiode.
>
> Jack writes:
> - - - - - - - -
> Hi Michael-
>         Turn it on while running a VCR and compare adjacent frames.
>                         Regards,
>                                 Jack
> - - - - - - - -
>
> Don't be fooled here by a common circuit in the video camera. Just like
> your eye, the video camera adjusts to light levels. It might well show a
> rapid brightness surge followed by a drop to a "steady state" level.
>
> I'll try to measure it today and post the results on the web.
>
> John
>
> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> John E. Sohl, Ph.D.
> Professor of Physics
> Weber State University
> 2508 University Circle
> Ogden, UT 84408-2508
>
> voice: (801) 626-7907, fax: (801) 626-7445
> e-mail: jsohl@weber.edu
> web: http://physics.weber.edu/sohl/
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