Among the key assumptions of the accelerated method for predicting light-fastness is that the rate of fade at high illumination intensities is equal to the rate of fade at the lower illumination intensities present in more real-world conditions. If these two fade rates are dramatically different then a reciprocity failure exists for that image that can lead to misleading light-fastness predictions. According to H. Wilhelm ('The Permanence and Care of Color Photographs, pg.67), “…[M]ost color materials exhibit at least some ‘reciprocity failure’ in light fading or light-induced stain formation in high-intensity, short-term tests.” Thus, high-confidence light-fastness predictions for all color images should check for reciprocity failure.In this paper the authors describe a practical test method for accounting for possible reciprocity failures in Inkjet imaged prints. The media with swellable ink receiving layer (similar to first generation Inkjet photo media) are seen to have little or no reciprocity failure with the ink sets tested thus far. However, the media with micro-porous ink receiving layer tested have all shown significant reciprocity failures (by a factor of the order of 100) that would lead to greatly exaggerated light-fastness predictions if left uncompensated for.A simple method for identifying whether air exposure contributes to the apparent light fade is also presented. Based on this method it is concluded that air exposure significantly contributes to the apparent light fading of the micro-porous media when samples are not protected from air contact.
Shilin Guo, Nils Miller, "Estimating Light-fastness of Inkjet Images: Accounting for Reciprocity Failure" in Proc. IS&T Int'l Conf. on Digital Printing Technologies (NIP17), 2001, pp 186 - 191, https://doi.org/10.2352/ISSN.2169-4451.2001.17.1.art00039_1