Posted by <normanstrong on 10/24/05 15:10

"NunYa Bidness" <nunyabidness@nunyabidness.org> wrote in message
news:k32pl1t61hq2mdeeagbra5spe16e1it0di@4ax.com...
> On 23 Oct 2005 23:20:53 -0700, "Jim Reid" <jimreid56@aol.com> Gave us:
>
>>There's another possiblilty. There's a theater chain here in Dallas
>>that I have caught turning the lamp power down on the projector when
>>it's not a full house. The picture looks dark and has what appears to
>>be lag in it. I go get the mangager and yell at him and a few minutes
>>later it brightens up.
>
>
> Do you even know what would be required to reduce the voltage going
> to the projector bulb?
>
> Also, the amount that would decrease the brightness significantly
> would not be a very big change in wattage requisite at all. The
> interplay between voltage input to the bulb and light output is not
> linear at all. So, there is no valid reason they would need to "turn
> it down". In fact, it would likely NOT cause any significant increase
> in bulb life either. It could even shorten it.
>
> The mere task of making a circuit that allows one to alter the
> voltage of a device *inside* the projector, a very delicate piece of
> machinery, is a very difficult one indeed.

He said they turned the "lamp power down". He said nothing about the
voltage. Is there any reason to think that the "lamp" is an incandescent
bulb? It might be a xenon arc lamp run with a current pulse. The length of
the pulse is proportional to the light output as well as the power.

Norm Strong

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