ISO 18937-1:2023
(Main)Imaging materials — Methods for measuring indoor light stability of photographic prints — Part 1: General guidance and requirements
Imaging materials — Methods for measuring indoor light stability of photographic prints — Part 1: General guidance and requirements
This document provides information and general guidance about the methods for measuring the indoor light stability of reflection prints, both colour and monochrome, transparent or translucent films, and photographic prints for backlit displays. This document is relevant to the selection and operation of the methods of exposure to radiation and environmental stress factors described in detail in subsequent parts. It also describes general performance requirements for devices used for exposing printed material to laboratory light sources. Information regarding performance requirements is for producers of artificial accelerated lightfastness devices. NOTE In this document, the term “light source” refers to radiation sources that emit UV radiation, visible radiation, infrared radiation, or any combination of these types of radiation. This document does not include test procedures for determining the effects of light exposure on the physical stability of images, supports, or binder materials. However, it is recognized that in some instances, physical degradation such as support embrittlement, image layer cracking, or delamination of an image layer from its support, rather than the stability of the image itself, determines the useful life of a print material. Print image stability results determined for one printer model, software settings, colorant, and media combination may not be applicable to another combination.
Matériaux pour l'image — Méthodes de mesure de la stabilité de la lumière en intérieur des épreuves photographiques — Partie 1: Lignes directrices générales et exigences
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INTERNATIONAL ISO
STANDARD 18937-1
First edition
2023-06
Imaging materials — Methods for
measuring indoor light stability of
photographic prints —
Part 1:
General guidance and requirements
Matériaux pour l'image — Méthodes de mesure de la stabilité de la
lumière en intérieur des épreuves photographiques —
Partie 1: Lignes directrices générales et exigences
Reference number
ISO 18937-1:2023(E)
© ISO 2023
---------------------- Page: 1 ----------------------
ISO 18937-1:2023(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
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---------------------- Page: 2 ----------------------
ISO 18937-1:2023(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
4.1 General . 2
4.2 Significance . . . 2
4.3 Use of accelerated tests with laboratory light sources . 3
4.4 Other limitations . 3
4.5 Safety cautions . 3
5 Requirements for laboratory exposure devices . 4
5.1 Irradiance . 4
5.2 Temperature . 5
5.3 Humidity . 6
5.4 Maximum allowable deviations . 6
5.5 Other requirements for the exposure device . 6
5.6 Air quality in the test environment . 6
6 Test specimens . 7
6.1 Form, shape and preparation . 7
6.2 Specimen selection, preparation, mounting, and conditioning . 7
7 Test conditions and procedure .8
7.1 Allowable deviations from the set points . 8
7.2 Duration of exposure . 8
8 Test report . 9
8.1 General reporting requirements . 9
8.2 Light stability reporting requirements . 9
Annex A (informative) Evaluation of light stability reciprocity behaviour.11
Annex B (informative) Example of chamber uniformity verification method .13
Bibliography .15
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ISO 18937-1:2023(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 42, Photography. This first edition of
ISO 18937-1 cancels and replaces the second edition of ISO 18937:2020, which has been technically
revised.
The main changes are as follows:
— This revision of the existing ISO 18937 separates the International Standard into three separate
parts in a similar way to two other artificial exposure testing series, ISO 4892 (Plastics, in TC 61), and
ISO 16474 (Paints and varnishes, in TC 35).
A list of all parts in the ISO 18937 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.
iv
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ISO 18937-1:2023(E)
Introduction
This document addresses the methods for measuring the indoor light stability of reflection prints,
[10][18] to [23][24] to [30]
and transparent or translucent films, both colour and monochrome .Outdoor light
stability is addressed in ISO 18930, with additional background referenced in ISO TR 18945.
This document focuses on general guidance, which includes aspects of the testing that applies to all of
the other specific parts, including minimum performance requirements of the instruments used, details
of control systems, calibration requirements, test specimen development, and reporting requirements.
ISO 18937-2 focuses on exposures using xenon-arc lamps. ISO 18937-3 focuses on exposures using LED
lamps. Specific testing requirements based on simulation to the defined use cases and capabilities of
the instruments are included in ISO 18937-2 and ISO 18937-3 documents.
The length of time that such photographs are to be kept can vary from a few days to many hundreds of
years and the importance of image stability can be correspondingly small or great. Often the ultimate
use of a particular photograph may not be known at the outset. If display is part of the intended use,
knowledge of the lightfastness level of colour photographs is important to manufacturers to improve
print materials and to many users to match their display longevity expectations for any given use
profile, especially since stability requirements may vary depending upon the application.
The images of most modern analogue and digitally-printed colour photographs are made up of cyan,
magenta, yellow, red, green, blue, orange, black, grey, white or other colourants. Colour photographic
images typically fade during storage and display; they will usually also change in colour balance because
the various image colourants seldom fade at the same rate. In addition, a yellowish (or occasionally
other colour) stain may form and physical degradation may occur, such as embrittlement and cracking
of the support and image layers. The rate of fading and staining can vary appreciably and is governed
principally by the intrinsic stability of the colour photographic material and by the conditions under
which the photograph is stored and displayed. For silver halide prints, black and white or colour, the
quality of any chemical processing is another important factor. Post processing treatments and post-
production treatments, such as application of lacquers, plastic laminates, and retouching colours, also
may affect the stability of colour materials.
The light stability of colour photographs is influenced primarily by the intensity of the radiation/light
source, the duration of exposure to light, the relative spectral irradiance of the light source, and the
ambient temperature and humidity conditions. However, the normally slower dark fading and staining
reactions also proceed during display periods and will contribute to the total change in image quality.
Ultraviolet radiation is particularly harmful to some types of colour photographs and can cause rapid
fading as well as degradation of the underlying substrate. Information about the light stability of colour
photographs can be obtained from accelerated light stability tests. These require special test units
equipped with high-intensity light sources in which test strips can be exposed for days, weeks, months,
or even years, to produce the required amount of image fading (or staining). The temperature and
moisture content of the specimen prints should be directly or indirectly controlled throughout the test
period, and the types of light sources should be chosen to yield data that can be correlated satisfactorily
with those obtained under conditions of normal use.
Accelerated light stability tests for predicting the behaviour of photographic colour images under
normal display conditions may be complicated by “reciprocity failure." When applied to light-induced
fading and staining of colour images, reciprocity failure refers to the failure of a colourant to fade, or
to form stain, equally when irradiated with high-intensity versus low-intensity light, even though the
total light exposure (intensity × time) is kept constant through appropriate adjustments in exposure
duration. The extent of colourant fading and stain formation can be greater or smaller under accelerated
conditions, depending on the photochemical reactions involved in the colourant degradation, on
the kind of colourant dispersion, on the nature of the binder material, and on other variables. For
example, the supply of oxygen that can diffuse into a photograph’s image-containing layers from the
surrounding atmosphere may be restricted in an accelerated test (dry gelatine, for example, is an
excellent oxygen barrier). This may change the rate of colourant fading relative to the fading that would
occur under normal display conditions. The magnitude of reciprocity failure may also be influenced by
the temperature and moisture content of the test specimen prints. Furthermore, light fading may be
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ISO 18937-1:2023(E)
influenced by the pattern of irradiation — continuous versus intermittent — as well as by light/dark
cycling rates (see Annex A).
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INTERNATIONAL STANDARD ISO 18937-1:2023(E)
Imaging materials — Methods for measuring indoor light
stability of photographic prints —
Part 1:
General guidance and requirements
1 Scope
This document provides information and general guidance about the methods for measuring the indoor
light stability of reflection prints, both colour and monochrome, transparent or translucent films, and
photographic prints for backlit displays. This document is relevant to the selection and operation of the
methods of exposure to radiation and environmental stress factors described in detail in subsequent
parts. It also describes general performance requirements for devices used for exposing printed
material to laboratory light sources. Information regarding performance requirements is for producers
of artificial accelerated lightfastness devices.
NOTE In this document, the term “light source” refers to radiation sources that emit UV radiation, visible
radiation, infrared radiation, or any combination of these types of radiation.
This document does not include test procedures for determining the effects of light exposure on the
physical stability of images, supports, or binder materials. However, it is recognized that in some
instances, physical degradation such as support embrittlement, image layer cracking, or delamination
of an image layer from its support, rather than the stability of the image itself, determines the useful
life of a print material.
Print image stability results determined for one printer model, software settings, colorant, and media
combination may not be applicable to another combination.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 18913, Imaging materials — Permanence — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 18913 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
1
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ISO 18937-1:2023(E)
4 Principle
4.1 General
4.1.1 Specimens of the samples to be tested are exposed to laboratory light sources under controlled
environmental conditions. The methods described include the requirements for the measurement of
the irradiance (or illuminance) and radiation exposure in the plane of the specimen, the temperature of
specified black panel sensors, the chamber air temperature, and the relative humidity.
4.1.2 The test methods in this series can be useful as stand-alone methods for comparing the stability
of image materials with respect to one specific failure mode. Data from the test methods in this series
can be used in stand-alone reporting of the absolute or comparative stability of image materials with
respect to the specific failure mode described in this document, when reported in accordance with the
reporting requirements of this document.
4.2 Significance
4.2.1 When conducting exposures in devices that use laboratory light sources, it is important to
consider how well the accelerated-test conditions simulate the actual-use environment with respect
to the light spectrum for the sample being tested. In addition, it is essential to consider the effects
of variability in both the accelerated test and actual exposures when setting up experiments and
interpreting results from those exposures.
4.2.2 Even though it is very tempting, it is invalid to assign to all materials a “general acceleration
factor” relating “x” hours, megajoules, or klx-hours of radiant exposure in an artificial accelerated
exposure to “y” months or years of actual exposure. Such general acceleration factors are invalid for the
following reasons.
a) Acceleration factors are material-dependent and can be significantly different for each material
and for different formulations of the same material in both actual-use and artificial accelerated
exposures.
b) Acceleration factors calculated based on the ratio of irradiance between a laboratory light source
and filtered daylight or other illuminations representative for specific indoor use profiles (even
when identical passbands are used) do not take into consideration the effects of temperature,
moisture, and differences in relative spectral irradiance between the laboratory light source and
solar radiation.
NOTE Acceleration factors determined for a specific formulation of a material may be valid, but only if
they are based on data from a sufficient number of tests in the end-use environment and artificial accelerated
exposures so that results used to relate times to failure in each exposure can be analysed using statistical
methods.
4.2.3 There are a number of factors that may decrease the degree of correlation between accelerated
tests using laboratory light sources and exposures in end-use conditions:
a) differences in the relative spectral irradiance of the laboratory light source and that representative
for the indoor use case;
b) irradiance/illuminance levels higher than those experienced in actual-use conditions;
c) exposure cycles that use continuous exposure to radiation from a laboratory light source without
any dark periods;
d) specimen temperatures different than those in actual conditions;
e) exposure conditions that produce unrealistic temperature differences between light- and dark-
coloured specimens;
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ISO 18937-1:2023(E)
f) unrealistic levels of moisture in the accelerated test compared with actual-use conditions.
4.3 Use of accelerated tests with laboratory light sources
4.3.1 Results from artificial accelerated exposures conducted in accordance with any of the parts of
this document are best used to compare the relative performance of materials. Comparisons between
materials when tested in different exposure devices must consider variables inherent to the design of
those devices. Results can be expressed by comparing the exposure time or radiant exposure necessary
to reduce the level of a characteristic property to some specified level. A common application of this is
a test conducted to establish that the level of quality of different batches does not vary from that of a
control of known performance.
4.3.2 It is strongly recommended that at least one control be exposed with each test for the purpose
of comparing the performance of the test materials to that of the control.
NOTE A control would be a material of similar composition and construction to the test material. An
example would be when a formulation different from one currently being manufactured for commercial use is
being evaluated. In this case, the control would be the material made with the original, or current, formulation.
4.3.3 In some specification tests, properties of test specimens are evaluated after a specific exposure
time or radiant exposure using a test cycle with a prescribed set of conditions. Results from any
accelerated exposure test conducted in accordance with any of the parts of this document should not be
used to make a “pass/fail” decision for materials, based on the level of a specific property after a specific
exposure time or radiant exposure, unless the combined reproducibility of the effects of a particular
exposure cycle and property measurement method has been established.
4.4 Other limitations
4.4.1 Conversion of data obtained from these methods for the purpose of making public statements
regarding product life should be in accordance with the applicable documents for specification of print
life.
4.4.2 No accelerated laboratory exposure test can be specified as a total simulation of actual use
conditions. Results obtained from laboratory accelerated exposures can be considered as representative
of actual use exposures only when the correlation has been established for the specific materials being
tested and when the type of degradation is the same. Even if results from a specific exposure test
conducted in accordance with any of the parts of this document are found to be useful for comparing
the relative durability of materials exposed in a particular environment, it cannot be assumed that they
will be useful for determining the relative durability of the same materials in a different environment.
4.4.3 Print image stability results from the test methods in those documents, especially in terms
of the amount of acceleration and/or correlation to end-use service life, that are determined for one
printer model, software settings, colorant, and media combination should not be applied to another
printer model, software settings, colorant, and media combination.
4.5 Safety cautions
In light stability tests, a high irradiance level is used, often with significant UV content. Special care
should be taken to avoid eye injury or skin erythema. Precautions should be taken to ensure that the
light source cannot inadvertently be viewed without suitable eye and skin protection.
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ISO 18937-1:2023(E)
5 Requirements for laboratory exposure devices
5.1 Irradiance
5.1.1 Laboratory light sources are used to provide irradiance for the test specimens. In ISO 18937-2, a
xenon-arc lamp for use with dedicated optical UV filters is specified and in ISO 18937-3 an LED lamp is
specified.
5.1.2 The exposure device should provide holders or space appropriate for placement of specimens
and any designated sensing devices in positions that allow uniform irradiance from the radiation
source.
5.1.3 Exposure devices should be designed such that the irradiance at any location in the area used
for specimen exposures is at least 80 % of the maximum irradiance measured in this area. Procedures
for measuring irradiance uniformity by the device manufacturers are given in Annex B.
NOTE The irradiance (illuminance) uniformity in exposure devices depends on several factors, such as the
configuration of the lamp with respect to the exposed samples. In addition, irradiance uniformity can be affected
by the type of specimen and the number of specimens being exposed.
5.1.4 If the minimum irradiance at any position in the specimen exposure area is between 80 %
and 90 % of the maximum irradiance, specimens should be periodically repositioned to reduce the
variability in radiant exposure. The repositioning procedure and schedule should be agreed upon by all
interested parties.
NOTE There are several possible procedures, including random positioning of replicate specimens, that can
be used to reduce the variability in exposure stresses experienced by specimens during exposure. Consult the
device manufacturer for guidance.
5.1.5 If the irradiance at any position in the area used for specimen exposure is at least 90 % of the
maximum irradiance, it is not necessary to use periodic repositioning of the specimens during exposure
to ensure uniform radiant exposure. While periodic repositioning of the specimens is not necessary in
this case, it is nevertheless good practice in order to assure that the variability in exposure stresses
experienced during the exposure period is kept to the minimum.
NOTE 1 Depending on the specific sensitivity of the material to the exposure stress factors, periodic
repositioning of the specimens is good practice to minimize variability of material degradation in replicate
specimens. Minimizing variability in exposure stress levels is especially important when the test involves
relative comparison of prints made with different printing methods or with different colourant/substrate
material combinations.
NOTE 2 Random placement of replicate specimens is also good practice to reduce the effect of any variability
in the conditions within the exposure area.
5.1.6 Follow the device manufacturer’s instructions for lamp and filter replacement and for any pre-
ageing of lamps and/or filters.
5.1.7 General
5.1.7.1 A radiometer for measuring irradiance in a specific wavelength range or a narrow passband
that complies with the requirements outlined in ISO 9370 should be used to measure the irradiance, E,
or spectral irradiance, E , and the radiant exposure, H, or spectral radiant exposure, H , in the plane of
λ λ
the specimen surface.
5.1.7.2 Alternatively, a radiometer for measuring illuminance that has a spectral response
corresponding to the photopic standard luminous efficiency V(λ), which is identical to the colour-
matching function y(λ) specified in ISO 11664-1 should be used to measure the irradiance (illuminance).
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ISO 18937-1:2023(E)
In this case, the irradiance (illuminance) is reported in lux and the radiant exposure is reported in
lux·hours.
5.1.7.3 The radiometer should be mounted so that it receives the same radiation as the specimen
surface. If it is not positioned in the specimen plane, it should have a sufficiently wide field of view
and be calibrated for irradiance at the specimen distance. The radiometer should be calibrated using a
light source filter combination of the same type that will be used for testing or an appropriate spectral
mismatch factor has been taken into account, especially for passband radiometers. The calibration
should be checked in accordance with the radiation measuring instrument manufacturer’s instructions.
A full calibration of the radiometer that is traceable to a recognized radiometric standards body should
be conducted at least once per year. More frequent calibrations are recommended.
[11]
NOTE 1 ASTM G130 provides specific guidance on the calibration of radiometers using spectroradiometers.
This method can be used to calibrate the instrument radiometer(s).
NOTE 2 See ISO 9370 for definitions of field and reference radiometers.
NOTE 3 The definition of passbands is found in ISO 9370.
5.1.7.4 When measured, the irradiance in the wavelength range agreed upon by all interested parties
should be reported. Some types of device provide sensor(s) for measuring irradiance in a specific
wave
...
DRAFT INTERNATIONAL STANDARD
ISO/DIS 18937-1
ISO/TC 42 Secretariat: ANSI
Voting begins on: Voting terminates on:
2022-03-21 2022-06-13
Imaging materials — Photographic reflection prints —
Methods for measuring indoor light stability — Part 1:
General guidance —
Part 1:
General guidance
ICS: 37.040.20
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
This document is circulated as received from the committee secretariat.
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 18937-1:2022(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION. © ISO 2022
---------------------- Page: 1 ----------------------
ISO/DIS 18937-1:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
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---------------------- Page: 2 ----------------------
ISO/DIS 18937-1:2022(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
4.1 General . 2
4.2 Significance . . . 2
4.3 Use of accelerated tests with laboratory light sources . 3
4.4 Other limitations . 3
4.5 Safety cautions . 4
5 Requirements for laboratory exposure devices . 4
5.1 Irradiance . 4
5.2 Temperature . 5
5.3 Humidity . 6
5.4 Maximum allowable deviations . 6
5.5 Other requirements for the exposure device . 6
5.6 Air quality in the test environment . 7
6 Test specimens . 7
6.1 Form, shape and preparation . 7
6.2 Specimen selection, preparation, mounting, and conditioning . 7
7 Test conditions and procedure .8
7.1 Allowable deviations from the set points . 8
7.2 Duration of exposure . 9
8 Test report . 9
8.1 General reporting requirements . 9
8.2 Light stability reporting requirements . 9
Annex A (informative) Evaluation of light stability reciprocity behaviour .11
Annex B (informative) Example of Chamber Uniformity Verification Method .13
Bibliography .15
iii
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ISO/DIS 18937-1:2022(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 42, Photography.
This new multi-part edition cancels and replaces ISO 18937:2020 (Ed. 2). This revision of the existing
ISO 18937 standard separates the standard into three separate parts in a similar way to two other
artificial exposure testing series, ISO 4892 (plastics, in TC61), and ISO 16474 (paints and varnishes,
in TC35). This part 1 focuses on general guidance, which includes aspects of the testing that applies
to all of the other specific parts, including minimum performance requirements of the instruments
used, details of control systems, calibration requirements, test specimen development, and reporting
requirements. Part 2 focuses on exposures using xenon-arc lamps. Part 3 focuses on exposures using
LED lamps. Specific testing requirements based on simulation to the defined use cases and capabilities
of the instruments are included in the Part 2 and Part 3 documents.
A list of all parts in the ISO 18937 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.
iv
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ISO/DIS 18937-1:2022(E)
Introduction
This document addresses the methods for measuring the indoor light stability of reflection prints,
and transparent or translucent films, both colour and monochrome.[5],[12-17],[18-24] Outdoor light
stability is addressed in ISO 18930, with additional background referenced in ISO TR 18945.[2],[3]
The length of time that such photographs are to be kept can vary from a few days to many hundreds of
years and the importance of image stability can be correspondingly small or great. Often the ultimate
use of a particular photograph may not be known at the outset. If display is part of the intended use,
knowledge of the lightfastness level of colour photographs is important to manufacturers to improve
print materials and to many users to match their display longevity expectations for any given use
profile, especially since stability requirements may vary depending upon the application.
The images of most modern analogue and digitally-printed colour photographs are made up of cyan,
magenta, yellow, red, green, blue, orange, black, grey, white or other colourants. Colour photographic
images typically fade during storage and display; they will usually also change in colour balance because
the various image colourants seldom fade at the same rate. In addition, a yellowish (or occasionally
other colour) stain may form and physical degradation may occur, such as embrittlement and cracking
of the support and image layers. The rate of fading and staining can vary appreciably and is governed
principally by the intrinsic stability of the colour photographic material and by the conditions under
which the photograph is stored and displayed. For silver halide prints, black & white or colour, the
quality of any chemical processing is another important factor. Post processing treatments and post-
production treatments, such as application of lacquers, plastic laminates, and retouching colours, also
may affect the stability of colour materials.
The light stability of colour photographs is influenced primarily by the intensity of the radiation/light
source, the duration of exposure to light, the relative spectral irradiance of the light source, and the
ambient temperature and humidity conditions. However, the normally slower dark fading and staining
reactions also proceed during display periods and will contribute to the total change in image quality.
Ultraviolet radiation is particularly harmful to some types of colour photographs and can cause rapid
fading as well as degradation of the underlying substrate. Information about the light stability of colour
photographs can be obtained from accelerated light stability tests. These require special test units
equipped with high-intensity light sources in which test strips can be exposed for days, weeks, months,
or even years, to produce the required amount of image fading (or staining). The temperature and
moisture content of the specimen prints should be directly or indirectly controlled throughout the test
period, and the types of light sources should be chosen to yield data that can be correlated satisfactorily
with those obtained under conditions of normal use.
Accelerated light stability tests for predicting the behaviour of photographic colour images under
normal display conditions may be complicated by “reciprocity failure." When applied to light-induced
fading and staining of colour images, reciprocity failure refers to the failure of a colourant to fade, or
to form stain, equally when irradiated with high-intensity versus low-intensity light, even though the
total light exposure (intensity × time) is kept constant through appropriate adjustments in exposure
duration. The extent of colourant fading and stain formation can be greater or smaller under accelerated
conditions, depending on the photochemical reactions involved in the colourant degradation, on
the kind of colourant dispersion, on the nature of the binder material, and on other variables. For
example, the supply of oxygen that can diffuse into a photograph’s image-containing layers from the
surrounding atmosphere may be restricted in an accelerated test (dry gelatine, for example, is an
excellent oxygen barrier). This may change the rate of colourant fading relative to the fading that would
occur under normal display conditions. The magnitude of reciprocity failure may also be influenced by
the temperature and moisture content of the test specimen prints. Furthermore, light fading may be
influenced by the pattern of irradiation — continuous versus intermittent — as well as by light/dark
cycling rates (see Annex A).
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DRAFT INTERNATIONAL STANDARD ISO/DIS 18937-1:2022(E)
Imaging materials — Photographic reflection prints —
Methods for measuring indoor light stability — Part 1:
General guidance —
Part 1:
General guidance
1 Scope
This part of ISO 18937 provides information and general guidance about the methods for measuring
the indoor light stability of reflection prints, both colour and monochrome, transparent or translucent
films, and photographic prints for backlit displays. This part is relevant to the selection and operation
of the methods of exposure to radiation and environmental stress factors described in detail in
subsequent parts. It also describes general performance requirements for devices used for exposing
printed material to laboratory light sources. Information regarding performance requirements is for
producers of artificial accelerated lightfastness devices.
NOTE In this part of ISO 18937, the term “light source” refers to radiation sources that emit UV radiation,
visible radiation, infrared radiation, or any combination of these types of radiation.
This document does not include test procedures for determining the effects of light exposure on the
physical stability of images, supports, or binder materials. However, it is recognized that in some
instances, physical degradation such as support embrittlement, image layer cracking, or delamination
of an image layer from its support, rather than the stability of the image itself, will determine the useful
life of a print material.
Print image stability results determined for one printer model, software settings, colorant, and media
combination may not be applicable to another combination.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 2471, Paper and board — Determination of opacity (paper backing) — Diffuse reflectance method
ISO 9370, Plastics — Instrumental determination of radiant exposure in weathering tests — General
guidance and basic test method
ISO 11664-1, Colorimetry – Part 1: CIE standard colorimetric observers
ISO 18913, Imaging materials — Permanence — Vocabulary
ISO 18941, Imaging materials — Colour reflection prints — Test method for ozone gas fading stability
ISO 18944, Imaging materials — Reflection colour photographic prints — Test print construction and
measurement
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 18913 apply.
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ISO/DIS 18937-1:2022(E)
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Principle
4.1 General
4.1.1 Specimens of the samples to be tested are exposed to laboratory light sources under controlled
environmental conditions. The methods described include the requirements for the measurement of
the irradiance (or illuminance) and radiation exposure in the plane of the specimen, the temperature of
specified black panel sensors, the chamber air temperature, and the relative humidity.
4.1.2 The test methods in this series can be useful as stand-alone methods for comparing the stability
of image materials with respect to one specific failure mode. Data from the test methods in this series
can be used in stand-alone reporting of the absolute or comparative stability of image materials with
respect to the specific failure mode described in this document, when reported in accordance with the
reporting requirements of this document.
4.2 Significance
4.2.1 When conducting exposures in devices that use laboratory light sources, it is important to
consider how well the accelerated-test conditions simulate the actual-use environment with respect
to the light spectrum for the sample being tested. In addition, it is essential to consider the effects
of variability in both the accelerated test and actual exposures when setting up experiments and
interpreting results from those exposures.
4.2.2 Even though it is very tempting, it is invalid to assign to all materials a “general acceleration
factor” relating “x” hours, megajoules, or klx-hours of radiant exposure in an artificial accelerated
exposure to “y” months or years of actual exposure. Such general acceleration factors are invalid for the
following reasons.
a) Acceleration factors are material-dependent and can be significantly different for each material
and for different formulations of the same material in both actual-use and artificial accelerated
exposures.
b) Acceleration factors calculated based on the ratio of irradiance between a laboratory light source
and filtered daylight or other illuminations representative for specific indoor use profiles (even
when identical passbands are used) do not take into consideration the effects of temperature,
moisture, and differences in relative spectral irradiance between the laboratory light source and
solar radiation.
NOTE Acceleration factors determined for a specific formulation of a material may be valid, but only if
they are based on data from a sufficient number of tests in the end-use environment and artificial accelerated
exposures so that results used to relate times to failure in each exposure can be analysed using statistical
methods.
4.2.3 There are a number of factors that may decrease the degree of correlation between accelerated
tests using laboratory light sources and exposures in end-use conditions:
a) the differences in the relative spectral irradiance of the laboratory light source and that
representative for the indoor use case,
b) the irradiance/illuminance levels higher than those experienced in actual-use conditions,
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ISO/DIS 18937-1:2022(E)
c) the exposure cycles that use continuous exposure to radiation from a laboratory light source
without any dark periods,
d) the specimen temperatures different than those in actual conditions,
e) the exposure conditions that produce unrealistic temperature differences between light- and dark-
coloured specimens,
f) the unrealistic levels of moisture in the accelerated test compared with actual-use conditions
4.3 Use of accelerated tests with laboratory light sources
4.3.1 Results from artificial accelerated exposures conducted in accordance with any of the parts of
this document are best used to compare the relative performance of materials. Comparisons between
materials when tested in different exposure devices must consider variables inherent to the design of
those devices. Results can be expressed by comparing the exposure time or radiant exposure necessary
to reduce the level of a characteristic property to some specified level. A common application of this is
a test conducted to establish that the level of quality of different batches does not vary from that of a
control of known performance.
4.3.2 It is strongly recommended that at least one control be exposed with each test for the purpose
of comparing the performance of the test materials to that of the control.
NOTE A control would be a material of similar composition and construction to the test material. An
example would be when a formulation different from one currently being manufactured for commercial use is
being evaluated. In this case, the control would be the material made with the original, or current, formulation.
4.3.3 In some specification tests, properties of test specimens are evaluated after a specific exposure
time or radiant exposure using a test cycle with a prescribed set of conditions. Results from any
accelerated exposure test conducted in accordance with any of the parts of this document should not be
used to make a “pass/fail” decision for materials, based on the level of a specific property after a specific
exposure time or radiant exposure, unless the combined reproducibility of the effects of a particular
exposure cycle and property measurement method has been established.
4.4 Other limitations
4.4.1 Conversion of data obtained from these methods for the purpose of making public statements
regarding product life shall be in accordance with the applicable documents for specification of print
life.
4.4.2 No accelerated laboratory exposure test can be specified as a total simulation of actual use
conditions. Results obtained from laboratory accelerated exposures can be considered as representative
of actual use exposures only when the correlation has been established for the specific materials being
tested and when the type of degradation is the same. Even if results from a specific exposure test
conducted in accordance with any of the parts of this document are found to be useful for comparing
the relative durability of materials exposed in a particular environment, it cannot be assumed that they
will be useful for determining the relative durability of the same materials in a different environment.
4.4.3 Print image stability results from the test methods in those documents, especially in terms
of the amount of acceleration and/or correlation to end-use service life, that are determined for one
printer model, software settings, colorant, and media combination should not be applied to another
printer model, software settings, colorant, and media combination.
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ISO/DIS 18937-1:2022(E)
4.5 Safety cautions
In light stability tests, a high irradiance level is used, often with significant UV content. Special care
shall be taken to avoid eye injury or skin erythema. Precautions should be taken to ensure that the light
source cannot inadvertently be viewed without suitable eye and skin protection.
5 Requirements for laboratory exposure devices
5.1 Irradiance
5.1.1 Laboratory light sources are used to provide irradiance for the test specimens. In ISO 18937-2, a
xenon-arc lamp for use with dedicated optical UV filters is specified and in ISO 18937-3 an LED lamp is
specified.
5.1.2 The exposure device shall provide holders or space appropriate for placement of specimens and
any designated sensing devices in positions that allow uniform irradiance from the radiation source.
5.1.3 Exposure devices shall be designed such that the irradiance at any location in the area used for
specimen exposures is at least 80 % of the maximum irradiance measured in this area. Procedures for
measuring irradiance uniformity by the device manufacturers are given in Annex B.
NOTE The irradiance (illuminance) uniformity in exposure devices depends on several factors, such as the
configuration of the lamp with respect to the exposed samples. In addition, irradiance uniformity can be affected
by the type of specimen and the number of specimens being exposed.
5.1.4 If the minimum irradiance at any position in the specimen exposure area is between 80 % and
90 % of the maximum irradiance, specimens shall be periodically repositioned to reduce the variability
in radiant exposure. The repositioning procedure and schedule shall be agreed upon by all interested
parties.
NOTE There are several possible procedures, including random positioning of replicate specimens, that can
be used to reduce the variability in exposure stresses experienced by specimens during exposure. Consult the
device manufacturer for guidance.
5.1.5 If the irradiance at any position in the area used for specimen exposure is at least 90 % of the
maximum irradiance, it is not necessary to use periodic repositioning of the specimens during exposure
to ensure uniform radiant exposure. While periodic repositioning of the specimens is not necessary in
this case, it is nevertheless good practice in order to assure that the variability in exposure stresses
experienced during the exposure period is kept to the minimum.
NOTE 1 Depending on the specific sensitivity of the material to the exposure stress factors, periodic
repositioning of the specimens is good practice to minimize variability of material degradation in replicate
specimens. Minimizing variability in exposure stress levels is especially important when the test involves
relative comparison of prints made with different printing methods or with different colourant/substrate
material combinations.
NOTE 2 Random placement of replicate specimens is also good practice to reduce the effect of any variability
in the conditions within the exposure area.
5.1.6 Follow the device manufacturer’s instructions for lamp and filter replacement and for any pre-
ageing of lamps and/or filters.
5.1.7 General
5.1.7.1 A radiometer for measuring irradiance in a specific wavelength range or a narrow passband
that complies with the requirements outlined in ISO 9370 shall be used to measure the irradiance, E, or
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ISO/DIS 18937-1:2022(E)
spectral irradiance, E , and the radiant exposure, H, or spectral radiant exposure, H , in the plane of the
λ λ
specimen surface.
5.1.7.2 Alternatively, a radiometer for measuring illuminance that has a spectral response
corresponding to the photopic standard luminous efficiency V(λ), which is identical to the colour-
matching function y(λ) specified in ISO 11664-1 shall be used to measure the irradiance (illuminance).
In this case, the irradiance (illuminance) is reported in lux and the radiant exposure is reported in luxˑh.
5.1.7.3 The radiometer shall be mounted so that it receives the same radiation as the specimen
surface. If it is not positioned in the specimen plane, it shall have a sufficiently wide field of view and
be calibrated for irradiance at the specimen distance. The radiometer
...
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