[Tig] Measuring a DCI-theatre projector - new vs old lamp

Jim Houston jdhouston at earthlink.net
Fri Mar 1 16:04:05 GMT 2013

> Got a question. Has anyone out there done any measurements on a theatre
> projector with a new vs old lamp?


By the fact that your DCP looked overexposed on the one projector but not any  others,
it is pretty clear what happened.   The operator changed the lamp without recalibrating.

*All new lamps must be recalibrated to get the correct power level. color temperature and primaries
for digital cinema projectors*

Also, the operator likely did not even reset the power setting to the lamp which is
 a really basic flub.  Old lamps need more power to hit 14fL where a new lamp could
probably hit 20fL+ easily at 100% power.  This would look overexposed.
 It is possible in some theaters that setting the projector to minimum power (75-80%)
leaves the brightness too high.   There isn't much you can do about that
other than using a lower wattage lamp or putting a glass ND in front of the lens
until the new lamp burns in for a while.  I suspect this might have been what
happened;  the theater just relied on burn-in to bring the new bulb down
to 14fL.

Most digital cinema lamps aren't really stable until about 50 hrs of burn-in, so
 for critical viewing you need to recalibrate again after a couple days.

As a lamp ages, you have to turn the power level up and the color temperature
 will shift towards the red.  You can go from 80% to 90% power before having
 to recalibrate, so recal's are really only necessary about three or four times
 during the life of a lamp until power hits  >105%.  Again this is for the strictest
viewing conditions -- most theaters only check it once after replacement.

Jim Houston
Starwatcher Digital
Pasadena, CA

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