Foreword

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This document was prepared by Technical Committee ISO/TC 42, Photography.

The first edition of ISO 21139-22 cancels and replaces the first edition of ISO/TS 21139-22:2023 , which has been technically revised.

The main changes are as follows:

the Technical Specification was developed into an International Standard.

A list of all parts in the ISO 21139 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A complete listing of these bodies can be found at www.iso.org/members.html.

Introduction

Backlit display of prints is a market segment in the context of commerce (advertisement, brand shops) and information (maps, directories). In this use profile the backlit prints are irradiated from their frontside and from their backside, with irradiations on both sides typically differing by their intensity and spectral distribution.

Backlit display applies with prints on transparent or translucent foils and/or prints on a textile. This document focusses on LED-based backlit units and provides information about fluorescent-based backlit units for reference. These backlit displays may be installed indoor or in shaded outdoor display conditions, for examples backlit display units in shelters and patios. Backlit displays which are subject to solar radiative heating or precipitation, introducing extensive temperature cycling, are excluded.

Prints on backlit display may fade or otherwise change in appearance due to various environmental stresses, including irradiation, heat, humidity, atmospheric pollutants, or biological attack, and the combination of these factors. One of the most critical degradations is light fading caused by intense irradiation from the backlit unit as well as by the general irradiation from the viewing environment, which may represent various levels of intensity and spectral distribution, depending on the installation site in a building, near to a window or in a shaded outdoor display condition.

The irradiation of the backlit print is therefore typically different from its frontside (oriented towards the viewing environment) compared to its backside (oriented towards the backlit unit).

In this document, the intensity of the irradiation from either frontside or backside is characterized in terms of illuminance, Ev, and the accumulated dose by luminous exposure, Hv. Spectral distributions, which cause varying rates of light fading due to their different UV content, are accounted for by a dimensionless factor called "relative severity". This factor compares the fading rates of a specific type of irradiation condition to those under the standardized exposure condition called "general indoor display" (according to ISO 18937-2 ), both evaluated at the same illuminance, Ev, as explained in Annex A.

The lighting design of the backlit display unit may cause inhomogeneity of the backside exposure of the print, which may in turn introduce inhomogeneous patterns of colour fading or discoloration leading to enhanced visibility of degradation (an example is illustrated in Annex B). The test method described in this document does not include the assessment of the impact from inhomogeneity of the backside exposure.

This document provides information about the test conditions for colour fading and discoloration applicable for the different types of display materials, including transparent films or translucent films, papers, and fabrics. Furthermore, this document gives guidance for estimation of an equivalent luminous exposure for the intended time of display, acknowledging the limitations of such generic extrapolations. The display use profile applies for digital and analogue prints.

The test method described in this document does not address the adverse effects of exposure to atmospheric pollutants, including ozone, and is also limited to the evaluation of colour changes and therefore does not require specific methods for the evaluation of physical properties, including changes of tensile strength, cockling etc. In the case that backlit materials are constructed from laminates, the aforementioned factors are of less importance.

The general concepts for the exposure characterization of prints on a backlit display provided in this document may also be considered in museum context with details defined by ISO/TS 18950 .

1 Scope

This document specifies the test method for light stability measurements of prints on transparent or translucent foils, transparent or translucent film, and paper or printed on a textile, which are displayed on backlit units installed in indoor or in shaded outdoor conditions, which are protected against direct precipitation and radiative heating. Installations of backlit display units in outdoor areas without shading, which are exposed to direct weathering and/or radiative heating, are excluded.

This document is applicable to the various product classes of “commercial prints” that are suitable for backlit display. These commercial prints often contain combinations of text, pictorial images and/or artwork.

This document provides guidelines for colour measurements, data analysis, and also provides guidance for translation of test results into suitable image permanence performance claims considering the variability of backlit designs and environmental conditions.

This document is applicable to both analogue and digitally printed matter. Methods and principles apply to both colour and monochrome prints.

NOTE The test method in this document does not address the specific requirements for testing museum backlit display, however, some of the elements in this test method (such as exposure in both directions) can also be considered in museum context with details defined by ISO/TS 18950 .

2 Normative references

3 Terms and definitions

3.1 Symbols and abbreviated terms

3.2 Measures of exposure severity

3.3 Surroundings of backlit display

3.4 Orientations of the backlit print

3.5 Colour evaluation

4 Use profile

4.1 General

4.2 Parameters of backlit display

4.3 Frontside exposure and environmental conditions

4.4 Equivalent test conditions

4.5 Relevance of use

5 Test method

5.1 General

5.2 Sample preparation

5.3 Common test conditions

5.4 Testing of the frontside of the print

5.5 Testing of the backside of the print

6 Measurement

6.1 General

6.2 Measurement conditions

7 Data analysis

7.1 General

7.2 Image quality parameter for data analysis

7.3 Equivalent test conditions

7.4 Estimation of the time to reach a certain change

8 Test report

Bibliography