Lightbox
A Lightbox
for viewing prints is an essential part of the CdCC's monthly competitions.
It provides a properly illuminated environment for competition
entries to be viewed by the judge and the audience.
The CdCC
Lightbox was constructed based on a
set of
plans prepared by the Photographic Society of America. The PSA
Lightbox was designed to accommodate matted prints up to a maximum
size of 29" wide x 22" high. For the CdCC Lightbox we wanted to be able to
accommodate larger prints as some of our members are routinely
making prints that are 19" x 13". This required that the
CdCC Lightbox be
able to handle mattes as large as 24" x 18". To achieve this we
scaled up the PSA plans by increasing the height, width and depth of
the Lightbox to give a maximum displayable area of 36" wide x 27"
high.
The PSA
plans call for the illumination of the prints to be provided by a
mix of fluorescent and incandescent lights. The purpose of using two
different light sources was to try to get a color balanced light
source - the fluorescent lights provide a cold light source while
the incandescent lights give out warm light. By mixing the two light
sources, the designers hoped to achieve color balanced illumination.
Some research on the Internet told us
that color corrected lighting technology has improved recently and that properly
color balanced fluorescent tubes are now available that would meet the
PSA specifications for lighting color prints. The
January 2005 edition of "Focal Plane", the newsletter of the
Ridgewood Camera Club,
had an interesting article about "New Lighting in our Print Box".
It was the inspiration to build the CdCC Lightbox to meet the PSA
specification using the latest lighting technology.
The PSA publication
"UNIFORM PRACTICE – JUDGING PRACTICES". specifies the
color temperature of the light source to be used for print display,
the Color Rendition Index (CRI) of the light source, the
illumination level required and the uniformity of the light source.
It also has some interesting information about the judging setup and
room conditions for a competition.
One interesting point to note in the
PSA document is as follows:
"The illumination level provided by PSA international
Exhibitions, and other Competitions, for judging photographic prints
is higher than that used for general viewing. Print
exhibitors, therefore, should make their prints slightly darker than
for general viewing, which makes the highlights, color and detail in
a color print and the highlights and tones of a monochrome print
stand out."
 The
CdCC Lightbox was constructed by Tony Paxton over a couple of weeks
in February 2006. The Lightbox was made larger, in accordance with
our modified PSA plans, and the fluorescent lighting system was
installed. The Fluorescent tubes used were purchased from
topbulb.com.
We decided to use their F25T8/TL950
36" 25Watt T8 Fluorescent tube which
has a color temperature of 5000K and a Color Rendition Index of 95.
These tubes are made by Phillips and, at the time, cost $9.99 each.
We determined, by trial and error, that a total of 8 tubes would be
required to meet the PSA illumination specifications. This meant
mounting four tubes above and below the display area. To power the tubes
we purchased two (4 lamp) F25T8 Electronic Ballasts from
ProLighting.com. The
ballasts cost $49.98 each and were mounted
underneath the tubes. The tubes were held in place using Medium Bipin Fluorscent sockets also purchased from ProLighting.
When the Lightbox was completed, the tubes provided a
very even level of illumination across the print display area with good color
rendition and adequate illumination. The tubes
have proven to run quite cool even
after several hours of
operation. An additional metal plate was installed under each
ballast to spread the heat generated and to keep the ballast from
direct contact with the wooden box. The entire electrical
installation was carefully grounded and earthed.
 The
original PSA plans were a good guide to building the Lightbox.
However, the increase in size of the CdCC box, and the weight of the
fluorescent lighting fixtures, caused the top part of the box to
lean forward. This was corrected by adding two vertical metal
brackets to the back of the Lightbox to keep it straight up. If we
were to build a Lightbox again, using the same modified plans, we
would probably use 2" x 4" lumber for the frame construction instead
of the 2" x 1" lumber called for in the original PSA drawings.
We also extended the depth of the shelf
that the prints rest on. The PSA plan called for a 1" deep shelf but
this proved to be too narrow and we modified it to be 2" deep. The
entire print area was painted with a flat gray paint that was a
close match to the 18% reflectance gray card that we took to the
paint shop. The two light boxes were painted white inside and out.
All other components were purchased at our local Home Depot.
The unit folds up for storage and
transportation as per the original PSA design.
For more information about the CdCC
Light Box please contact
Tony Paxton.
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