Re: brightness vrs. power

[Barlow Newbolt <NewboltW@WLU.EDU>]

Under those conditions it probably was very nearly linear.  The point is
that the relationship between the potential difference (voltage) and the
current is not linear unless the temperature is held constant.  This,
however, is a different problems from the problem about the brightness
of light bulbs and their power levels.  You have two aspects to the
problem: (1) Total radiant power approximately equal to electrical power
supplied and (2) Spectrum of radiation emitted strongly dependent on the
temperature.
WBN

Barlow Newbolt
Professor of Physics
Washington and Lee University
e-mail: newboltw@wlu.edu
telephone:  540-463-8881
fax:  540-463-8884
Office: Howe 218

"Had I been present at the creation,  I would have given
some useful hints for the better ordering of the universe."

          Alphonso X,  Learned King of Spain  (1252  - 1284)

> > > David_Strasburger-fac@NOBLES.EDU 05/03/00 10:40AM >>>
PHYS-L@lists.nau.edu writes:
> > Radiant energy depends on temperature of a filament. For instance
when
> two
> > similar bulbs are connected in series the net current is
(approximately)
> > halved. The power dissipated in both bulbs is reduced by factor 1/4.
>
> I don't know how you calculated this, but it is incorrect. Light
bulbs
> do not obey Ohm's law. They are extremely nonlinear.

This may be true, but I saw a demonstration about three summers ago in
which the instructor broke the glass on a household bulb and immersed
the
filament in a bath of water with an electric stirrer to keep the
temperature as uniform as possible.  He varied voltage and measured
current -- I have to say the relationship looked awfully linear to me.

David