Lightbooth temp
Lightbooth temp
- Subject: Lightbooth temp
- From: "Mark Rice" <email@hidden>
- Date: Sat, 27 May 2006 15:57:15 -0400
I have found the color temperature measuring capability the eye one to be
highly suspect. As I mentioned in another post, I visited GTI with my EyeOne
and a monitor. My Eyeone gave a color temp reading of their light booths of
about 5600K, while their Minolta colorimeter showed a temp of 4950K. Not
that the Minolta is necessarily correct, but after 25 years in the prepress
business, I have a pretty good idea of what the color of a light booth
should look like.
I find I have to get my monitor set to about "5800K" (by the EyeOne)
to match a 5000K light booth. And in all practicality, what a light booth
looks like is what matters to most prepress users.
In addition, most light booth manufacturers recommend changing lamps
about every six months. GTI offers a service to monitor it for you. I know
from experience that lamps start out very cool - magenta-blue. They should
be burned in for at least 24 hours before they are even usable. Then, over
time, they drift toward green-yellow. Over six months of constant use, The
color temp shift will be about 500 degrees warmer, and if the lamps are
older than six months, all bets are off. In addition to that, when the lamps
are first turned on, they will be cooler than when they are warmed up.
Also, when I was at GTI, we dimmed the lamps in the booth and tested
with both the EyeOne and the Minolta color meter. The Minolta told us the
both was moving toward a higher color temperature as it was dimmed, but the
EyeOne said the opposite. Our eyes (Bob McCurdy and myself) agreed that the
Minolta was correct - higher color temperature as it was dimmed.
Mark Rice
Incidentally, speaking of viewers for graphic arts, has anyone found
that the GTI booths and the GTI fluorescent lamps never hit the 5000K
mark when measured (EyeOnePro and BabelColor in ambiant mode)? I'd be wiling
to compare notes printers sites and "institutions" like GATF, and I
must say that I have never gotten better than 4650k to 4800K out GTIs
-- tops. Close to 5000K, granted, but never quite the 5000K CIE u' v'
chromatiticies called for in the ISO-3664:200x standard, and,
according to my measurement, almost always on the border of the 0.005
tolerance CCT radius, if not flat outside. Which baffles me.
measurements. That would undoubdetly affect the results, I don't
debate it. But as you know, many printers on this side of the pond
stick with GTI lamps while many in Europe, Asia and the rest of the world
stick with JUST-Normlicht lamps. Yet, many printers who operate newer
Heidelberg presses (Goss Sunday 4000, Speedmasters), which all come
equipped with their very own luminaires, use a third kind of 5000K
fluorescents, made by Phillips B.V. As it turns out, I never heard
anyone questioned the legitimaty of those Phillips lamps. No the pressmen,
nor the clients. People are just happy or unhappy about the matches.
And you should see the ranges of the proofs that make their to modern press
rooms -- it's laughable some times. Anyway, contrast this with the
prevailing attitude in the industry that, when considering the addition
or replacement of a press luminaire, only GTIs lamps should qualify. The
argument goes that since many design studios and agencies have GTI booths
for color viewing to begin with, so should the printer to maximize the
chances of color matching on press. It makes sense in a way but why do the
GTI systematically never measure the 5000K published chromaticities
whereas the JUST always do? At least in measurements. That's why I'd
like to hear other people's comments and compare notes.
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