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re A head light comparison

 "Romeo Shayne Pavlic'" <bcpi@arias.net> provided a copy of a useful
evaluation of lamps, not repeated here.  A couple of comments.

For a hotter color, i.e., closer to the sun's 6000K color temperature,
either the filament has to be run hotter, or the color has to be shifted by
a transmission coating.

A hotter filament will have a shorter lifetime.

For implied visibility comparisons, the actual luminosity of the lamp has to
be measured.  This requires an appropriate filter over the photometer
detector.  Most photographic meters measure lux assuming the color
temperature of the source is that of the sun, and if the sources being
compared have different color temperatures, the results cannot be directly
compared.  Tektronix makes a true luminosity meter I believe.  Note that the
peak output of a 3200K source is at 0.9 micrometers, in the near infrared.
Measurement with a detector such as silicon that also peaks in this region
will lead to big measured luminosity errors.

                .... Kirby   (Kirby A. Smith)
                              2 x 1988 90q
                          New Hampshire USA