Re: Projection lamps

[P3D Michael Kersenbrock <michaelk@xxxxxxxxxxx>]

> One could argue that since the ideal light is sunlight, which doesn't
> alternate or flicker, the ideal projector system would be powered by Direct
> Current voltage. A power supply could be designed for any voltage system
> that delivers ripple free current to the projector lamp. There are safety
> concerns with DC, but the light output would seem cleaner and could provide
> a subtle but important benefit of reducing potential eye stress.

Except for fluorescent bulbs, most lamps should flicker little or not at
all.  Not becuase they are flickering too fast to see, but that they
aren't flickering as strongly, or at all.

Fluorescent bulbs actually turn completely on and off at 120Hz (for a 60Hz
line) rate.  For light created by heating some tungsten wire, the tungsten 
is being powered off and on at 120Hz, but it probably doesn't cool down
completely in the 9 milliseconds between peaks.  I'd imagine heaver filaments
with would have a larger smoothing effect due to larger thermal mass.  So 
perhaps part of the design  would be to maximize the mass of the filament
which would seem to be more massive (per inch...) in a lower voltage lamp.

I understand that at least with earlier designs, bulbs lasted longer with AC
rather than DC power because DC caused metal migration in one direction which
tended to thin out the "from" end of the heated wire faster, while AC current
"evened" things out.  May not be a limiting factor any more.  Told to me by
an old timer engineer when I was a young pup engineer.  So, it's OLD info.  :-)

Mike K.



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