ISO 18937:2014
(Main)Imaging materials — Photographic reflection prints — Methods for measuring indoor light stability
Imaging materials — Photographic reflection prints — Methods for measuring indoor light stability
ISO 18937:2014 describes test equipment and procedures for measuring the light stability of images of colour photographic reflection prints designed for display in, for example, houses, apartments, other dwelling places, offices and commercial display, when subjected to certain illuminants at specified temperatures and relative humidities. It also addresses colour photographic reflection prints designed for display in galleries and museums. Indoor illumination conditions described in ISO 18937:2014 include a) simulated indoor daylight typical home display, b) simulated direct sunlight in-window display, c) fluorescent illumination using "cool white", and d) other types of illumination sources, such as other fluorescent lamps, tungsten halogen, LED, OLED and metal halide lamps. ISO 18937:2014 is applicable to reflection colour prints made with colour hardcopy materials. Included are inkjet prints, thermal dye diffusion transfer ("dye-sub") prints, liquid- and dry-toner electrophotographic prints, prints made with traditional chromogenic ("silver-halide") photographic colour materials and, in general, all types of colour prints made with direct analog and digital print processes. The recommended evaluation methods can also be applied to black-and-white photographic prints.
Matéruaux pour l'image — Tirages photographiques par réflexion — Méthodes de mesure de la stabilité de la lumière en intérieur
General Information
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 18937
First edition
2014-02-01
Imaging materials — Photographic
reflection prints — Methods for
measuring indoor light stability
Matéruaux pour l’image — Tirages photographiques par réflexion —
Méthodes de mesure de la stabilité de la lumière en intérieur
Reference number
ISO 18937:2014(E)
©
ISO 2014
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ISO 18937:2014(E)
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ISO 18937:2014(E)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Requirements . 3
5 Test methods — General. 3
5.1 Safety precautions . 3
5.2 Acceleration and reciprocity issues . 3
5.3 Catalytic fade issues . 4
5.4 Light intensity control . 4
5.5 Spectral power distribution . 4
5.6 Humidity control . 4
5.7 Temperature control . 5
5.8 Air quality in the test environment . 7
5.9 Duration of exposures. 8
6 Test equipment. 8
6.1 Light source measurements . 8
6.2 Light exposure equipment . 9
6.3 Specifications for optical filters . 9
6.4 Chamber fade uniformity .11
7 Illumination specifications .13
7.1 General .13
7.2 Simulated indoor daylight typical home display .14
7.3 Simulated direct sunlight indoor in-window display .15
7.4 Fluorescent illumination using “cool white” fluorescent lamps .16
7.5 Other light sources.18
8 Sample preparation .19
8.1 Samples .19
8.2 Sample preparation .19
9 Measurements and calculations .20
9.1 Holding and measurement conditions .20
9.2 Attributes to be measured .21
9.3 Calculations and computations .22
10 Test report .24
Annex A (informative) Evaluation of light stability reciprocity behaviour .26
Annex B (informative) Method for interpolation
.28
Annex C (informative) Procedure to calibrate the temperature relationship between the test
sample prints and the control set point of the black panel or white panel used to control
temperature in a light stability testchamber or test room .29
Annex D (informative) Relative spectral transmittance of filters .36
Annex E (informative) Examples of light exposure equipment .40
Annex F (informative) Example of filter configuration .42
Annex G (informative) Spectral irradiance for simulated indoor daylight .45
Annex H (informative) Relative spectral power distribution for F-6 cool white fluorescent lamps 47
Annex I (informative) Example chamber fade uniformity test target .49
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ISO 18937:2014(E)
Bibliography .50
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ISO 18937:2014(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. 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. 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 on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers
to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 42, Photography.
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ISO 18937:2014(E)
Introduction
This International Standard addresses the methods and procedures for measuring the indoor light
[6][8][9][18] [23][30]
stability of reflection colour photographs. −
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 might not be known at the outset. Knowledge of the useful life of colour
photographs is important to many users, especially since stability requirements can vary depending
upon the application.
The images of most modern analog and digitally-printed colour photographs are made up of cyan,
magenta, yellow, red, green, blue, orange, black, gray, 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 can form and physical degradation might 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. The quality of any chemical processing is another
important factor. Post-processing treatments and, in the case of digitally generated photographs, post-
production treatments, such as application of lacquers, plastic laminates, and retouching colours, also
can affect the stability of colour materials.
The light stability of colour photographs is influenced primarily by the intensity of the illumination, the
duration of exposure to light, the spectral distribution of the illumination, 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 plastic layers such as the pigmented polyethylene layer of RC (resin-coated) paper
supports.
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 desired amount of
image fading (or staining). The temperature of the sample prints and their moisture content needs to be
controlled throughout the test period, and the types of light sources need to 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 might 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, which can diffuse into a photograph’s image-containing layers from the surrounding
atmosphere, can be restricted in an accelerated test (dry gelatine, for example, is an excellent oxygen
barrier). This can change the rate of colourant fading relative to the fading that would occur under normal
display conditions. The magnitude of reciprocity failure can also be influenced by the temperature and
moisture content of the test sample prints. Furthermore, light fading can 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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INTERNATIONAL STANDARD ISO 18937:2014(E)
Imaging materials — Photographic reflection prints —
Methods for measuring indoor light stability
1 Scope
This International Standard describes test equipment and procedures for measuring the light stability of
images of colour photographic reflection prints designed for display in, for example, houses, apartments,
other dwelling places, offices and commercial display, when subjected to certain illuminants at specified
temperatures and relative humidities. This International Standard also addresses colour photographic
reflection prints designed for display in galleries and museums.
Indoor illumination conditions described in this International Standard include a) simulated indoor
daylight typical home display, b) simulated direct sunlight in-window display, c) fluorescent illumination
using “cool white”, and d) other types of illumination sources, such as other fluorescent lamps, tungsten
halogen, LED, OLED and metal halide lamps.
This International Standard is applicable to reflection colour prints made with colour hardcopy materials.
Included are inkjet prints, thermal dye diffusion transfer (“dye-sub”) prints, liquid- and dry-toner
electrophotographic prints, prints made with traditional chromogenic (“silver-halide”) photographic
colour materials and, in general, all types of colour prints made with direct analog and digital print
processes. The recommended evaluation methods can also be applied to black-and-white photographic
prints.
This International Standard 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, colourant and media
combination might not be applicable to image prints produced through another printer model, software
settings, colourant and media combination.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 5-3, Photography and graphic technology — Density measurements — Part 3: Spectral conditions
ISO 5-4, Photography and graphic technology — Density measurements — Part 4: Geometric conditions for
reflection density
ISO 2471, Paper and board — Determination of opacity (paper backing) — Diffuse reflectance method
ISO 4892-1, Plastics — Methods of exposure to laboratory light sources — Part 1: General guidance
ISO 4892-2, Plastics — Methods of exposure to laboratory light sources — Part 2: Xenon-arc lamps
ISO 9370, Plastics — Instrumental determination of radiant exposure in weathering tests — General
guidance and basic test method
ISO 11664-4, Colorimetry — Part 4: CIE 1976 L*a*b* Colour space
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ISO 18937:2014(E)
ISO 13655, Graphic technology — Spectral measurement and colorimetric computation for graphic arts
images
ISO 18913, Imaging materials — Permanence — Vocabulary
ISO/TR 18931, Imaging materials — Recommendations for humidity measurement and control
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
CIE S 023/E:2013, Characterization of the Performance of Illuminance Meters and Luminance Meters
ASTM G113, Standard Terminology Relating to Natural and Artificial Weathering Tests of Nonmetallic
Materials
ASTM G151, Standard Practice for Exposing Nonmetallic Materials in Accelerated Test Devices that Use
Laboratory Light Sources
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 18913 and the following apply.
NOTE In any case where the terms and definitions are duplicated with ISO 18913, the following terms
and definitions take precedence for the use of this International Standard.
3.1
operational control point
set point for equilibrium conditions measured at one or more sensor locations in an exposure device
[SOURCE: ASTM G 113-09, 3.2]
3.2
operational fluctuations
positive and negative deviations from the setting of the sensor at the operational control set point during
equilibrium conditions in a laboratory accelerated weathering device
[SOURCE: ASTM G 113-09, 3.3]
Note 1 to entry: Operational fluctuations are the result of unavoidable machine variables and do not include
measurement uncertainty. Operational fluctuations apply only at the location of the control sensor and do not
imply uniformity of conditions throughout the test chamber.
3.3
operational uniformity
range around the operational control point for measured parameters within the intended exposure area
within the limits of the intended operational range
[SOURCE: ASTM G 113-09, 3.6]
Note 1 to entry: Operational uniformity evaluates the measured parameters throughout the volume of a test
chamber so that regions of the test chamber volume can be determined to comply within the required stated
limits of the measured parameter operating aim.
3.4
uncertainty of measurement
parameter, associated with the result of a measurement, that characterizes the dispersion of the values
that could be reasonably attributed to the measurement
Note 1 to entry: The parameter might be, for example, a standard deviation (or a given multiple of it), or the half-
width of an interval having a stated confidence level.
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ISO 18937:2014(E)
Note 2 to entry: Uncertainty of measurement comprises, in general, many components. Some of these components
may be evaluated from statistical distribution of the results of a series of measurements and can be characterized
by experimental standard deviations. The other components, which can also be characterized by standard
deviations, are evaluated from assumed probability distributions based on experience or other information.
Note 3 to entry: It is understood that the result of the measurement is the best estimate of the value of the
measurement, and that all components of uncertainty, including those arising from systematic effects, such as
components associated with corrections and reference standards, contribute to the dispersion.
[SOURCE: ASTM G 113 and ISO Guide 98-3:2008, 2.2.3]
4 Requirements
This International Standard specifies a set of recommended test methods with associated requirements
for permitted reporting. Data from these tests shall not be used to make life expectancy claims, such as
time-based print lifetime claims, either comparative or absolute. Conversion of data obtained from these
methods for the purpose of making public statements regarding product life shall be in accordance with
the applicable International Standards for specification of print life.
The test methods in this International Standard may be useful as stand-alone test methods for comparison
of the stability of image materials with respect to one specific failure mode. Data from the test methods
of this International Standard may be used in stand-alone reporting of the absolute or comparative
stability of image materials with respect to the specific failure mode dealt with in this International
Standard, when reported in compliance with the reporting requirements of this International Standard.
Caution shall be used when comparing test results for different materials. Comparisons shall be limited
to test cases using equipment with matching specifications and matching test conditions.
The test procedures contained within this standard allow for the use of a variety of light source and
filter combinations. Test results obtained using different test conditions, such as different light sources
and filters, shall not be compared. Materials under test can be expected to behave quite differently as a
result of different relative spectral power distributions of the flux incident on the specimen.
5 Test methods — General
5.1 Safety precautions
In light stability tests, high intensity illumination 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.
5.2 Acceleration and reciprocity issues
The sample prints to be tested are exposed to laboratory light sources under controlled environmental
conditions.
Commonly employed accelerated methods of testing light stability, for both photographic digital
hardcopy materials and for traditional analog photographic materials, are based on the concept that
increasing the light intensity should produce a proportional increase in the photochemical reactions that
occur during typical viewing or display conditions, without introducing any undesirable side effects.
However, because of “reciprocity failures” that might be present in high-intensity accelerated light
fading tests with imaging materials, this assumption may not always apply (i.e. a material might fade,
change colour balance, or stain a different amount when exposed to high-intensity illumination for a
short period than it does when exposed to lower-intensity illumination for a longer period, even though
the spectral distribution, the total light exposure [intensity × time], the temperature, and the relative
[12] [17][24]
humidity are the same in both cases.) −
In general, the closer accelerated test conditions are to actual use conditions, the more meaningful the
test results become.
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ISO 18937:2014(E)
For further discussion of approaches to evaluating reciprocity behaviour in the light-induced fading,
changes in colour balance, and stain formation in imaging materials, see Annex A.
5.3 Catalytic fade issues
Catalytic fade is the process by which a given colourant can fade faster (or slower) when in contact
with another colourant as a result of an image area containing more than just one of the colourants.
It can also occur when other components in the imaging system act as catalysts. Because this process
often involves photocatalysis, it can show a dependency on the nature of the light source as well as the
light absorption characteristics of the additional colourant, UV absorbing materials, intentionally-added
[31]
radical quenchers and other components.
Because of these complex interactions, catalytic fade and the resulting nonlinearities can confound
predictions of colour fading rates for real-world images.
5.4 Light intensity control
The light intensity shall be maintained and controlled throughout testing with an operational fluctuation
within ± 7 % of aim. The 24 h running average of the operational fluctuation, sampled at least every
15 min, shall be within ±4 % of aim. The running average shall not include the test condition transition
time which occurs when the test condition is initiated. This transition time shall be at most 1 h.
5.5 Spectral power distribution
This International Standard references the use of different light sources for accelerated tests with the
[25][26]
intention of reproducing as closely as possible different end-use lighting conditions. However,
no accelerated laboratory exposure test can be specified as a total simulation of actual use conditions.
Results obtained from these laboratory accelerated exposures may be considered as representative of
actual use exposures only when the degree of correlation has been established for the specific materials
being tested and when the type of degradation is the same. The relative durability of materials in actual
use conditions can be very different in different locations because of differences in radiant energy (both
in spectra power distribution and intensity), relative humidity, temperature, pollutants, such as ozone,
and other factors.
Light sources referenced in this International Standard include filtered xenon-arc, fluorescent, tungsten
halogen, LED or OLED (and others). Each of these can be useful to simulate the various existing lighting
conditions found in different environments. It shall be recognized that these different light sources emit
different spectral power distributions (SPDs). The combination of different SPDs from these light sources
and associated material sensitivities will significantly impact test results. As a result, test results of
replicate sample prints using different light sources shall not be compared to each other.
It is essential to consider the effects of variability in accelerated tests when conducting exposure
experiments and when interpreting the results from these tests. Sources of variability include sample-
to-sample, measurement instrument repeatability/reproducibility, and exposure zone uniformity. It is
recommended the user expose replicate sample prints to understand and mitigate the va
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