From: a0s5108@titan.ucs.umass.edu (Neal and Mara Priestly)
Newsgroups: rec.arts.movies
Subject: Re: PEEVES at MOVIE THEATERS !
Date: 21 Jan 1993 11:20:42 -0500
Organization: University of Massachusetts, Amherst
Distribution: world
NNTP-Posting-Host: titan.ucs.umass.edu


[Deletia...well, more like article cut to ribbons...]

>>>I'd like to know if I'm the only one who notices this:  Theaters that
>>>turn down the brightness of the projector bulb, supposedly to keep
>>>the film stock from wearing out sooner, so that the whole movie looks
>>>like it was filmed at night.
>

>>Are different-strength
>>bulbs required for different theater configurations (e.g. different
>>sizes/types of screen, different distances between projector & screen)?
>
>Most certainly.  Actually, the correct term is "lamp".  The problem of
>putting enough light on the screen is an old one.  When the theatre is
>originally configured, the lamphouse (light source) is selected as
>being the optimum for the particular configuration of throw (distance
>between lense and screen) and screen size.  

Well, it's a nice theory.  It can be hosed fast if someone has some
equipment from a closed/upgraded site somewhere else.  My sister 
theatre across the street has an interesting mismatch (which does
work) because there was about 50k in equipment available from an
aquisition.  It was not the ideal equipment for thier site tho...

>                                            However, what seems to
>never be taken into consideration is the fact that components age, and
>as they age, performance declines.

There is a fix for this...we'll get to it...

>
>With carbon-arc lamphouses, the reflectors darken.  With xenon
>lamphouses, the lamp's output drops with age.  Within limits, the
>amperage to the lamp can be raised to brighten the screen.  This
>however, reduces the lamp's life expectancy.  Further complicating
>matters is the fact that replacement lamps are expensive - $1,000 for
>some of them.  Even worse, when xenon lamps fail, they sometimes fail
>catastrophically - resulting in damage to the lamphouse.  Changing

For those of you who don't do this for a living, fail catastrophically
is techie for 'explode and trash the machines guts.'  I've had to replace
2 reflectors because the newer lamphouses use bulbs that give less
warning that they are about to fail.  Until the new reflector is installed
the picture looks like hell.  And you shouldn't open the lamphousing
for a while after the lamp dies due to the heat...can't do anything til
it cools anyway.

>those lamps is a hazardous procedure - although I have no knowledge of
>this happening, theoretically, an accident during a lamp change could
>kill the projectionist.  Last time I changed one, I wore a face shield,
>kevlar vest, and a pair of thick gloves of the type normally worn by
>firemen in steam locomotives.

It's the same as a fragmentation grenade.  Small, very sharp, bits of 
quartz (lamps are made of quartz envelopes, not glass) travel at 
explosive velocities.  I've blown up a few throwing them away.  One
of the old 2200 watt vertical bulbs visibly dented the dumpster.

>
>Sometimes, as a cost-cutting measure, the lamps are de-rated - they're
>run at an amperage below their rating.  They last longer and tend to
>die gracefully.  Unfortunately, you get a nice dark picture for their
>efforts.
>

The answer to this...what we do... is to get a bulb rated over what is
needed and run it lower than it is rated.  The math says we need a 1300
watt bulb for our theatres, it actually works out to be 1200w when the
bulb is brand new.  So we buy 1600w lamps, and crank them down to about
1200w.  (well, we set the lamp amperage with a light meter at the screen
to a published standard.  But we start tuning at 1200w and usually don't
have to move it much...) When we do our regular maintenance routines, we
check the bulbs output, and adjust to the standard.  We toss the bulb 
when it hits it's lifetime rating...cheaper than a new reflector, and 
people call me fewer obcene things if bulbs don't fail.  Since starting 
this regimine, we havn't lost a bulb to explosion, and everything looks
the way it is 'supposed to.'

Still have people tell us it looks 'dark.'  Some films are dark, some
prints are dark, but we have yet to show more than 6% off standard when
we readjust the lamps.

Still waiting for the video guy to post the 'why video tape looks so much
brighter' article.....  I didn't pay a whole lot of attention, 'cos vid
ain't what I do for a living.

-Neal
Disclaimer:  I talk for me, they talk for them.  We probably don't agree on
     this either.  Nuff said?


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