Re: Blue Bulb Physics

[Don Hoefer <hoefer@eng.pko.dec.com>]

Paul,

> If you selectively recycle the "bad" 
> frequencies into "good" frquencies, you don't lose those precious candlepower,

Very unlikely, those photons will be converted into heat wherever they are
absorbed.  If they go back to the filament some energy could be reemitted
at the frequency that you want.

> but you do control which discrete frequencies are eventually projected.

A laser does this for one frequency.

I am curious about this blue light thing.  It can be tricky,  The eye has
a somewhat different focal length for blue light as opposed to other colors
and is not as sensitive either.

The "blue" appearance must be the color temperature of the source (ion or
gaseous discharge) where the spectrum is biased towards the blue as opposed
to the red as with normal incandescent lamps.  A blue filter on an incandescent
or halogen lamp would hurt more than help I would think.  It does not
matter what the color "looks" like, as long as an adequate spectrum is
available to illuminate objects of all colors.  Removing much of that
spectrum with a filter would make some objects harder to see and, in the case
of blue, hard to focus on.

This gets me thinking.  Yellow was often used for fog lights.  A yellow
light is on the red side of the spectrum, less likely to be scattered by
the fog and containing a good deal of green also.  The eye is most sensitive
to green.  I never liked them though, the "picture" just didn't look as clear
to me as it does with white fog lights.

Don Hoefer
'82 Coupe

Massachusetts, USA