Re: Projection lamps

[P3D Larry Berlin <lberlin@xxxxxxxxx>]

>Michael Kersenbrock comments:
>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. ...

Ordinary filament lamps have less flicker than older fluorescent lights, but
they do flicker due to the momentary cooling between cycles. It is very
obvious to an infrared sensor and I believe it has an effect on the nervous
system. It's more like background noise that we learn to ignore, except that
in this case we may not have learned to recognize it at all.

Newer fluorescent fixtures of a special type are more efficient with light
because they have designed the flicker to be around 20,000 Hz instead of 120
Hz. It provides a much more restful light than older fluorescents. However,
fluorescents wouldn't be considered at all for projection applications.

I don't know about tungsten leaving the filament more with DC than AC, but
halogens are designed to reduce the loss of tungsten and that is part of why
they are much brighter. I have been told that they are a perfect choice if
one is planning to run them on DC. Ideally, a DC source for these lights
should do more than rectify the AC current. It needs some level of filtering
to reduce the ripple to a reasonably flat current.

Only extensive testing would ever show whether or not a flickerless light
source is beneficial in any real sense. To my knowledge it's never been
directly studied. It sounds like a good thing and is more *natural* so could
be a sales point where it existed even though unproved in a clinical sense.
It's a feature that's not hard to supply and one that I would consider if I
were designing a projector from scratch.

Larry Berlin

Email: lberlin@xxxxxxxxx
http://www.sonic.net/~lberlin/


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