Light Box

A light box 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 light box was constructed based on a set of plans prepared by the Photographic Society of America. The PSA light box was designed to accommodate matted prints up to a maximum size of 29" wide x 22" high. For the CdCC light box 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 light box 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 light box was constructed by Tony Paxton over a couple of weeks in February 2006. The light box 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" 25-Watt 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 light box. 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 light box 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.