Effect of Light on Modern Digital Prints Photographs and Documents

by Andrea Venosa, Daniel Burge and Douglas Nishimura, Image Permanence Institute

Summary

This research project, part of a series of digital print preservation projects undertaken by the Image Permanence Institute, examined the light fastness of prints created with the most commonly used digital technologies along with prints created using traditional technologies. The inclusion of traditional prints provided benchmarks for collection care professionals to better gauge the significance of the results. In this study, prints were subjected to two types of lighting used independently to simulate daylight through window glass and artificial indoor illumination. Five aspects of light damage were assessed: fade in the mid-tone neutral, fade in the darkest neutral tone, paper yellowing, changes in paper gloss, and text readability.

Background

With a growing number of digitally printed photographs and documents entering cultural heritage institutions, information about the vulnerabilities of these materials is increasingly important. One of the factors that can cause deterioration is light. The sensitivity of digitally printed materials to light has long been recognized by the printing industry, giving rise to many small scale, brand-specific studies. This was the first comprehensive examination of digital prints, including a large number of samples representing the diversity of digital printing technologies, colorants, and papers used today.

Unlike previous work that was focused only on pictorial images, this study included text-based documents as well.

Our objective was to provide collection care professionals with an understanding of the sensitivities of digital printing materials compared to those of traditionally printed material.This project evaluated the light sensitivities of the primary digital print technologies (inkjet, electrophotography and dye sublimation) and their most common sub-categories (e.g. dye inkjet on porous-coated photo paper, liquid toner electrophotography, etc.) and compared these results to the light sensitivities of threetraditional print materials collection care personnel are already familiar with (silver-halide color photo, B&W electrophotography and offset lithography).

Methodology

Samples were subjected to two types of lighting – xenon arc and fluorescent – used independently, for a total of 12 weeks. Assuming a typical display intensity of 450 lux for 12 hours per day, 12 weeks of constant, high intensity exposure is approximately equivalent to 50 years of typical display. This prediction also assumes that all degradation is caused only by light, and excludes the simultaneous effects of pollutants, high humidity, and heat, which also occur during typical display.

Xenon arc light: A Q-Sun Xenon Test Chamber with an illumination intensity of 50 kilolux was used to simulate daylight through window glass. Window-Q filters were placed between the xenon lamps and the samples. The samples were positioned on the specimen tray mounted in metal holders with metal backings. The samples’ location on the tray was rotated weekly to account for the asymmetry of the position of the light source with respect to each sample. The temperature and humidity across the specimen plane were set to 25°C and 50% RH.

Fluorescent light: A custom-built fluorescent light unit with an illumination intensity of 50 kilolux was used to simulate artificial indoor illumination. The unit uses 42 GE F72T12- CW-1500-0 cool white fluorescent tubes positioned on a cylinder that constantly rotates, changing the relative position of each lamp with respect to each sample. This rotation accounts for possible variations in intensity between lamps. A non-reactive and non-yellowing white material (100% cotton cellulose, 4-ply white mount board) was used as a backing for the sample. The temperature and humidity across the specimen plane were set to 23°C and 50% RH.

For both tests, the ambient air was filtered through a carbon filter to reduce the presence of air pollutants, which are known to affect digital prints. Each sample was evaluated for colorant loss, paper yellowing, changes in paper gloss, and text readability. Evaluations were made after two, six, and twelve weeks of exposure to high-intensity light, which are approximately equivalent to eight, twenty-five, and fifty simulated years under the assumptions described above.

Conclusions

Digitally printed photographs and documents can undergo colorant loss, paper yellowing, and changes in paper gloss when exposed to light for an extended time. In this study, digital prints were, on average, less sensitive than their traditional benchmark; but each major category of digital prints (inkjet/photo paper, dye sublimation, color electrophotography, inkjet/plain paper and digital press) had at least one sample that performed worse than the benchmark in at least one of the aspects of light damage studied.

Current policies for the care of traditional prints should be considered a minimum starting point for the care of digital prints. Providing the most benign environment possible (low light intensity and low frequency of display) and closely monitoring prints for signs of change are essential. It is also important to keep in mind that third party printing materials may be more sensitive than original manufacturer materials, and that earlier dye digital prints are more sensitive than those tested in this study, which dated from 2007.

Depending on the collection, documents may tolerate less stringent care strategies than photographs. Changes tend to be more objectionable in a photograph than in a document, since photographs usually have aesthetic as well as informational value. In a document, the irretrievability of the information within the item may be of more concern than yellowing, changes in gloss, or colorant fade. Provided that the text is readable, the document is usually acceptable – unless it has historic or artifactual value.

Read the entire article at:

https://www.iiconservation.org/node/2930  or  http://www.dp3project.org/webfm_send/620