ISO/TS 18950:2021

TECHNICAL ISO/TS
SPECIFICATION 18950
First edition
2021-11
Imaging materials — Photographic
prints — Effect of light sources
on degradation under museum
conditions
Matériaux pour l'image — Épreuves photographiques — Effet des
sources de lumière sur la dégradation dans des conditions de musée
Reference number
© ISO 2021
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions, and abbreviated terms . 1
4 Use profile . 2
4.1 General . 2
4.2 Stress factors in museum use profile . 2
5 Test method . 3
5.1 General . 3
5.2 Sample specimen preparation . 3
5.2.1 Outline . 3
5.2.2 Contemporary materials . 4
5.2.3 Historic materials . 4
5.2.4 Selection of suitable test patches on historic materials . 4
5.2.5 Reference sample specimens . 5
5.2.6 Backing of the specimens . 5
5.2.7 Dummy sample . 5
5.3 Light exposure . 5
5.3.1 Outline . 5
5.3.2 Light intensity tolerances and long-term drift . 6
5.3.3 Specifications for filtered Xenon arc lamp to simulate indoor daylight . 6
5.3.4 Specifications for incandescent light . 7
5.3.5 Specifications for LED light . 7
5.4 Specifications for additional filters . 8
5.4.1 General . 8
5.4.2 UV Filter specifications for museum lighting . 8
6 Measurement .9
6.1 General . 9
6.2 Measurement conditions . 9
6.3 Calculation of colour difference . 9
6.4 Test procedure . 9
7 Evaluation .10
7.1 General . 10
7.2 Comparing light sources . 10
8 Test report .10
Annex A (informative) Translation of the test results into safe display duration .12
Annex B (informative) Examples of a relative spectral irradiance of white LEDs .14
Bibliography .15
iii
Foreword
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iv
Introduction
One of the typical uses of prints in museums is their display in a permanent or temporary exhibition
under ambient light or artificial illumination. In general, prints may fade due to various environmental
stresses, such as light, heat, humidity, pollutants, or biological attack, and the combination of these
factors. A museum can fully or partially control and suppress most of those factors. However, light is
[1]
necessary for display and will cause some degradation over time .
This document will provide guidance on how to assess light exposure-related damage to analogue and
digital photographic prints under museum display conditions for particular print materials sets. The
choice of the light source with the lowest damage potential depends on the specific material types in
the mix and the spectral irradiance of the light source.
The document can be of benefit to curators, conservators and lighting designers to select the display
lighting with the lowest possible damage potential to an exhibition. It can serve the manufacturers for
lighting materials to develop particular solutions for the museum.
Depending on the use case, material type and conditions, a two-tier evaluation may be possible.
Tier I evaluation is useful for comparison of different light sources, namely, to identify the light source
that will result in smallest image fading (∆E) under a given exposure level (lx-h).
Tier II evaluation is useful to estimate appropriate illumination levels (lx) to reach intended display
duration, if the following conditions are met (see Annex A for detailed discussion):
a) the museum is able to display the work with a light source having the same relative spectral
irradiance (RSI) as the one used for the testing; and
b) a set of representative test samples is available that have the same types of colourant and substrate
material as the display work, and
c) the assumption of linearity of image fading in response to different levels of light intensities
(reciprocity) is verified, for which test results under different combinations of illumination
intensity (lx) and duration (hours) are compared.
A test method of light stability for simulated daylight in indoor display is described in ISO 18937. Future
ISO 18937-1 is a description of a general test method and future ISO 18937-2 is a test method with
xenon light but which does not cover the particular museum display use case. Therefore, the covered
range of environmental conditions and wavelength of light is broader than what is required for this
document. It would be difficult to translate the test results following ISO 18937-1 into a specification
for museum print display requiring practically no degradation.
[2]
This document follows the recommendations of ISO/TS 21139-1:2019, Clause 4 for the definition of
a museum use profile and specifications, although the museums use case is not in the scope of ISO/
TS 21139-1.
v
TECHNICAL SPECIFICATION ISO/TS 18950:2021(E)
Imaging materials — Photographic prints — Effect of light
sources on degradation under museum conditions
1 Scope
The test method in this document is intended to be used to characterize and compare the degradation
of a set of print materials under exposure to particular light sources, eventually including optical filter
combinations, under museum environmental conditions. The document covers typical types of indoor
light sources commonly found in a museum including indoor daylight, LED, and incandescent light.
This document is applicable to analogue and digital reflection photographic prints.
NOTE Examples of photographic prints covered by this document are prints made with digital printing
technologies such as inkjet, electrophotography, and thermal dye transfer, as well as prints made on silver halide
colour paper but not prints made on black and white silver halide paper.
2 Normative referenc
...