INTERNATIONAL ISO

STANDARD 16474-4

First edition
2013-11-15

Paints and varnishes — Methods of

exposure to laboratory light sources —
Part 4:
Open-flame carbon-arc lamps
Peintures et vernis — Méthodes d’exposition à des sources lumineuses
de laboratoire —
Partie 4: Lampes à arc au carbone

Reference number
ISO 16474-4:2013(E)

© ISO 2013
ISO 16474-4:2013(E)


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 ISO 16474-4:2013(E)


Contents Page

Foreword......................................................................................................................................................................................................................................... iv
Introduction...................................................................................................................................................................................................................................v
1 Scope.................................................................................................................................................................................................................................. 1
2 Normative references....................................................................................................................................................................................... 1
3 Terms and definitions...................................................................................................................................................................................... 1
4 Principle......................................................................................................................................................................................................................... 2
5 Apparatus...................................................................................................................................................................................................................... 2
5.1 Laboratory light source.................................................................................................................................................................... 2
5.2 Test chamber............................................................................................................................................................................................. 6
5.3 Radiometer.................................................................................................................................................................................................. 6
5.4 Black-standard/black-panel thermometer...................................................................................................................... 6
5.5 Wetting and humidity-control equipment....................................................................................................................... 6
5.6 Specimen holders.................................................................................................................................................................................. 7
5.7 Apparatus to assess changes in properties..................................................................................................................... 7
6 Test specimens........................................................................................................................................................................................................ 7
7 Exposure conditions.......................................................................................................................................................................................... 7
7.1 Temperature............................................................................................................................................................................................... 7
7.2 Relative humidity of chamber air............................................................................................................................................ 8
7.3 Spray cycle................................................................................................................................................................................................... 8
8 Procedure..................................................................................................................................................................................................................... 8
8.1 General............................................................................................................................................................................................................ 8
8.2 Mounting the test specimens....................................................................................................................................................... 8
8.3 Exposure........................................................................................................................................................................................................ 8
8.4 Duration of test........................................................................................................................................................................................ 9
8.5 Measurement of radiant exposure.......................................................................................................................................... 9
8.6 Determination of changes in properties after exposure...................................................................................... 9
9 Test report.................................................................................................................................................................................................................... 9
Bibliography.............................................................................................................................................................................................................................. 10

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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 35, Paints and varnishes, Subcommittee SC 9,
General test methods for paints and varnishes.
ISO 16474 consists of the following parts, under the general title Paints and varnishes — Methods of
exposure to laboratory light sources:
— Part 1: General guidance
— Part 2: Xenon-arc lamps
— Part 3: Fluorescent UV lamps
— Part 4: Open-flame carbon-arc lamps

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Introduction
Coatings of paints, varnishes and similar materials (subsequently referred to simply as coatings) are
exposed to laboratory light sources, in order to simulate in the laboratory the ageing processes which
occur during natural weathering or behind window glass.

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INTERNATIONAL STANDARD ISO 16474-4:2013(E)

Paints and varnishes — Methods of exposure to laboratory

light sources —
Part 4:
Open-flame carbon-arc lamps

1 Scope
This part of ISO 16474 specifies methods for exposing specimens to open-flame carbon-arc lamps in
the presence of moisture to reproduce the weathering effects that occur when materials are exposed in
actual end-use environments to daylight or to daylight filtered through window glass.
The specimens are exposed to filtered open-flame carbon-arc light under controlled conditions
(temperature, humidity and/or wetting). Different types of filters are used to simulate either direct
exposure to the environment or exposure through window glass.
Specimen preparation and evaluation of the results are covered in other International Standards for
specific materials.
General guidance is given in ISO 16474-1.
NOTE Open-flame carbon-arc exposures for plastics are described in ISO 4892-4.

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 4582, Plastics — Determination of changes in colour and variations in properties after exposure to
daylight under glass, natural weathering or laboratory light sources
ISO 4618, Paints and varnishes — Terms and definitions
ISO 9370, Plastics — Instrumental determination of radiant exposure in weathering tests — General
guidance and basic test method
ISO 16474-1, Paints and varnishes — Methods of exposure to laboratory light sources — Part 1: General guidance

3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 4618 and the following apply.
3.1
radiant exposure
H
amount of radiant energy to which a test panel has been exposed

∫
Note 1 to entry: Radiant exposure is given by the equation H = E ⋅ dt

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where

H is the radiant exposure, in joules per square metre;

E is the irradiance, in watts per square metre;

t is the exposure time, in seconds

Note 2 to entry: If the irradiance E is constant throughout the whole exposure time, the radiant exposure H is
given simply by the product of E and t.

4 Principle

4.1 Specimens of the materials to be tested are exposed to glass-filtered open-flame carbon-arc light, to
heat, to relative humidity and to water (see 4.3) under controlled environmental conditions.

4.2 The exposure conditions may be varied by selection of

a) the light filter(s);

b) the temperature during light exposure;
c) the relative humidity of the chamber air during light and dark exposures, when test conditions
requiring control of humidity are used;
d) the type of wetting (see 4.3);
e) the water temperature and wetting cycle;
f) the timing of the light/dark cycle.

4.3 Wetting is usually produced by spraying the test specimens with demineralised/ deionized water
or by condensation of water vapour onto the surfaces of the specimens.

4.4 The procedure may include measurements of the irradiance and radiant exposure in the plane of
the specimens.

4.5 It is recommended that a similar material of known performance (a control) be exposed

simultaneously with the test specimens to provide a standard for comparative purposes.

4.6 Intercomparison of results obtained from the test specimens exposed in different types of apparatus
should not be made unless an appropriate statistical relationship has been established between the
apparatuses for the particular material to be tested.

5 Apparatus

5.1 Laboratory light source

5.1.1 General

Open-flame carbon-arc light sources typically use one, three or four pairs of carbon rods which contain
a mixture of rare-earth metal salts and have a surface coating of a metal such as copper. An electric
current is passed between the carbon rods which burn, giving off ultraviolet, visible and infrared
radiation. The pairs of carbon rods are burned in sequence, with one pair burning at any one time.
Use the carbon rods recommended by the manufacturer of the apparatus. The radiation reaching the
specimens passes through glass filters. Three types of glass filter are used in practice. Tables 1 and 2

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show the typical relative spectral power distribution for open-flame carbon-arc lamps with daylight
and window-glass filters, respectively. When extended-UV filters are used, the relative spectral power
distribution shall meet the requirements of Table 3.
NOTE Solar spectral irradiance for a number of different atmospheric conditions is described in CIE No. 85.
The benchmark daylight used in this part of ISO 16474 is that defined in CIE No. 85:1989, Table 4.

5.1.2 Spectral irradiance of open-flame carbon-arc lamps with daylight filters (Type 1)

The data in Table 1 are typical of an open-flame carbon-arc lamp with glass filters used to simulate
daylight (see CIE No. 85:1989, Table 4).

5.1.3 Spectral irradiance of open-flame carbon-arc lamps with window glass filters (Type 2)

The data in Table 2 are typical of an open-flame carbon-arc lamp with window-glass filters.

5.1.4 Spectral irradiance of open-flame carbon-arc lamps with extended-UV filters (Type 3)

The data in Table 3 are typical of an open-flame carbon-arc lamp with extended-UV filters. A typical
example of a suitable type 3 filter is that commonly known as Corex 70581).

Table 1 — Typical ultraviolet spectral power distribution for open-flame carbon-arc lamps with
daylight filters (type 1)a,b
Typical distribution for open-
Spectral passband flame carbon-arc lamp with CIE No. 85:1989, Table 4d,e
daylight filtersc
(λ = wavelength in nm) % %
λ < 290 0,05
290 ≤ λ ≤ 320 2,9 5,4
320 < λ ≤ 360 20,5 38,2
360 < λ ≤ 400 76,6 56,4
a This table gives the irradiance in the given passband, expressed as a percentage of the total irradiance between 290 nm
and 400 nm. To determine the relative spectral power distribution of an open-flame carbon-arc lamp through a specific
daylight filter or set of filters, the spectral power distribution shall be measured from 250 nm to 400 nm. Typically, this is
done in 2 nm increments. The total irradiance in each passband is then summed and divided by the total irradiance between
290 nm and 400 nm.
b The table gives typical data for an open-flame carbon-arc lamp with borosilicate-glass daylight filters. There is currently
not enough data available to develop a specification for the open-flame carbon-arc lamp with a daylight filter.
c For any individual spectral power distribution, the calculated percentages for the passbands in this table will sum to
100 %.
d The data from CIE No. 85:1989, Table 4, is the global solar irradiance on a horizontal surface for an air mass of 1,0, an
ozone column of 0,34 cm at STP, 1,42 cm of precipitable water vapour and a spectral optical depth of aerosol extinction of 0,1
at 500 nm. These data are provided for comparison purposes only.
e For the solar spectrum represented by CIE No. 85:1989, Table 4, the UV irradiance (290 nm to 400 nm) is 11 % and the
visible irradiance (400 nm to 800 nm) is 89 %, expressed as a percentage of the total irradiance between 290 nm to 800 nm.

1) Corex 7058 is an example of a suitable product available commercially. This information is given for the
convenience of users of this part of ISO 16474 and does not constitute an endorsement by ISO of this product.

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Table 2 — Typical ultraviolet spectral power distribution for open-flame carbon-arc lamps with
window-glass filters (type 2)a,b
Typical distribution for open- CIE No. 85:1989, Table 4,
Spectral passband flame carbon-arc lamp with plus effect of window
window-glass filtersc glassd,e
(λ = wavelength in nm) % %
λ < 300 0,0
300 ≤ λ ≤ 320 0,3 ≤1
320 < λ ≤ 360 18,7 33,1
360 < λ ≤ 400 81,0 66,0
a This table gives the typical irradiance in the given passband, expressed as a percentage of the total irradiance between
290 nm and 400 nm. To determine the irradiance in each passband for an open-flame carbon-arc lamp with a specific set of
window-glass filters, the spectral power distribution shall be measured from 250 nm to 400 nm. Typically, this is done in
2 nm increments. The total irradiance in each passband is then summed and divided by the total irradiance between 290 nm
and 400 nm.
b The table gives typical data for an open-flame carbon-arc lamp with window-glass filters. There is currently not enough
data available to develop a specification for the spectral power distribution.
c For any individual spectral power distribution, the calculated percentages for the passbands in this table will sum to
100 %. Contact the manufacturer of the carbon-arc apparatus for the spectral power distribution data for the particular
carbon arcs and window-glass filters used.
d The data from CIE No. 85:1989, Table 4, plus the effect of window glass was determined by multiplying the CIE
No. 85:1989, Table 4, data by the transmission typical for window glass used in the USA and Europe. These data are provided
for comparison purposes only.
e For the CIE No. 85:1989, Table 4 plus window glass data, the UV irradiance between 300 nm and 400 nm ranges from
7,7 % to 10,6 % and the visible radiation ranges from 89,4 % to 92,3 %, expressed as a percentage of the total irradiance
between 300 nm and 800 nm.

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Table 3 — Ultraviolet spectral power distribution for open-flame carbon-arc lamps

with extended-UV filters (type 3)a,b
Spectral passband Minimumc Maximumc CIE No. 85:1989, Table 4d,e
(λ = wavelength in nm) % % %
λ < 290 4,9
290 ≤ λ ≤ 320 2,3 6,7 5,4
320 < λ ≤ 360 16,4 24,3 38,2
360 < λ ≤ 400 68,1 80,1 56,4
a This table gives the irradiance in the given passband, expressed as a percentage of the total irradiance between
250 nm and 400 nm. To determine whether a specific filter or set of filters for an open-flame carbon-arc lamp meets the
requirements of this table, the spectral power distribution shall be measured from 250 nm to 400 nm. Typically, this is done
in 2 nm increments. The total irradiance in each wavelength passband is then summed and divided by the total irradiance
from 250 nm to 400 nm.
b The minimum and maximum limits in this table are based on 24 spectral power distribution measurements with
open-flame carbon-arc lamps with filters from different production lots and of various ages, used in accordance with the
recommendations of the manufacturer. The minimum and maximum limits are at least three sigma from the mean for all the
measurements. Open-flame carbon-arc lamps emit significant amounts of short-wavelength UV radiation between 250 nm
and 280 nm. The intensity of this short-wavelength UV radiation varies with the age and initial transmission properties of
the extended-UV filters used, as well as the composition of the carbon rods. The composition of the carbon rods can vary
between production lots and between manufacturers.
c The minimum and maximum columns will not necessarily sum to 100 % because they represent the minima and
maxima for the measurement data used. For any individual spectral power distribution, the percentages calculated for
the passbands in this table will sum to 100 %. For any individual open-flame carbon-arc lamp with extended-UV filters,
the calculated percentage in each passband shall fall within the minimum and maximum limits given. Test results can be
expected to differ if obtained using open-flame carbon-arc apparatuses in which the spectral power distributions differed
by as much as that allowed by the tolerances. Contact the manufacturer of the carbon-arc apparatus for specific spectral
power distribution data for the carbon-arc lamp and filters used.
d The data from CIE No. 85:1989, Table 4, is the global solar irradiance on a horizontal surface for an air mass of 1,0, an
ozone column of 0,34 cm at STP, 1,42 cm of precipitable water vapour and a spectral optical depth of aerosol extinction of 0,1
at 500 nm. These data are provided for comparison purposes only.
e For the solar spectrum represented by CIE No. 85:1989, Table 4, the UV irradiance (290 nm to 400 nm) is 11 % and
the visible irradiance (400 nm to 800 nm) is 89 %, expressed as a percentage of the total irradiance between 290 nm and
800 nm.

5.1.5 Factors which can affect the spectral power distribution of open-flame carbon-arc lamps

The following factors can affect the spectral power distribution:

a) differences in the composition and thickness of the filters can have large effects on the amount of
short-wavelength UV radiation transmitted;
b) accumulation of dirt or other residues on the filter can affect the filter transmission properties;
c) differences in the composition of the metallic salts used in the carbon rods can affect the spectral
power distribution.

5.1.6 Irradiance uniformity

The irradiance at any position in the area used for specimen exposure shall be at least 80 % of the
maximum irradiance. Requirements for periodic repositioning of specimens when this requirement is
not met are described in ISO 16474-1.
For some materials of high reflectivity, or/and high sensitivity to irradiance and temperature, periodic
repositioning of specimens is recommended to ensure uniformity of exposures, even when the irradiance
uniformity in the exposure area is within the limits so that repositioning is not required.

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5.2 Test chamber

The test chamber contains a specimen frame, with provision for passing air over the specimens for
temperature control.
The frame rotates about the central axis of the carbon-arc holder. A typical frame diameter is 96 cm.
Other frame diameters may be used if mutually agreed upon by all interested parties. The test specimens
shall be mounted directly on the frame or mounted in holders attached to the frame. The frame may be
vertical or inclined.
The upper and lower carbon rods, as well as the filters, shall be installed in accordance with the
instructions of the manufacturer of the apparatus.
The apparatus shall be fitted with equipment for programming exposure cycles within the operational
limits of the apparatus.

5.3 Radiometer
The radiometer used shall comply with the requirements outlined in ISO 16474-1 and ISO 9370.

5.4 Black-standard/black-panel thermometer

The black-standard or black-panel thermometer used shall comply with the requirements for these
devices given in ISO 16474-1.
NOTE Typically, this device is controlled by black-panel temperature only.

5.5 Wetting and humidity-control equipment

5.5.1 General

Specimens may be exposed to moisture in the form of water spray or condensation. If condensation
or other methods are used to expose the test specimens to moisture, details of the procedures and
exposure conditions used shall be included in the exposure report.
NOTE The relative humidity of the air can have a significant influence on the photodegradation of coatings.

5.5.2 Relative-humidity control equipment

For exposures where relative-humidity control is required, the location of the sensors used to measure
the humidity shall be as specified in ISO 16474-1.

5.5.3 Spray system

The test chamber shall be equipped with a means of directing an intermittent water spray onto the fronts
or backs of the test specimens under specified conditions. The spray shall be uniformly distributed
over the test specimens. The spray system shall be made from corrosion-resistant materials that do not
contaminate the water employed.
The water sprayed onto the test specimen surfaces shall have a conductivity below 5 μS/cm, contain less
than 1 μg/g dissolved solids content and leave no observable stains or deposits on the test specimens.
Care shall be taken to keep silica levels below 0,2 μg/g. A combination of deionization and reverse
osmosis may be used to produce water of the desired quality.
A spray system designed to cool the test specimen by spraying the back surface of the test specimen
or the test specimen backing might be required when the exposure programme specifies periods of
condensation.

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5.6 Specimen holders

Specimen holders may be in the form of an open frame, leaving the backs of the test specimens exposed,
or they may provide the test specimens with a solid backing. They shall be made from inert materials
that will not affect the results of the exposure, for example non-oxidizing alloys of aluminium or stainless
steel. Brass, steel or copper shall not be used in the vicinity of the test specimens. The backing used
might affect the results, as might any space between the backing and the test specimen, particularly
with transparent test specimens, and shall be agreed on between the interested parties.

5.7 Apparatus to assess changes in properties

The apparatus required by the International Standards relating to the determination of the properties
chosen for monitoring (see also ISO 4582) shall be used.

6 Test specimens
Refer to ISO 16474-1.

7 Exposure conditions

7.1 Temperature

7.1.1 Black-standard/black-panel temperature

For referee purposes, it is recommended that black-standard temperatures be used. However, for normal
work, black-panel thermometers are widely used for open-flame carbon-arc lamp apparatus. In the case
of the black-panel temperature, (63 ± 3) °C is typically used.
NOTE 1 Allowance will have to be made for the fact that the two types of thermometer indicate different
temperatures, due to their different thermal conductivities (see ISO 16474-1). If a black-panel thermometer is
used, the temperature indicated will be 3 °C to 12 °C lower than that indicated by a black-standard thermometer
under typical exposure conditions.

If a black-panel thermometer is used, then the panel material, the type of temperature sensor and the
way in which the sensor is mounted on the panel shall be included in the exposure report.
Other temperatures may be used when agreed on by the interested parties, but shall be stated in the
exposure report.
NOTE 2 If higher temperatures are used for special exposures, the tendency for specimens to undergo thermal
degradation will increase and this might affect the results of such exposures.

If water spray is used, the temperature requirements apply to the end of the dry period. If the thermometer
does not reach a steady-state during the dry period after the short water-spray part of the cycle, check
and report if the specified temperature is reached during a longer dry period without water spray.
NOTE 3 During the water spray part of the cycle the black-standard or black-panel temperature is close to the
water temperature.

NOTE 4 The additional measurement of a white-standard/white-panel temperature with a

white-standard/white-panel thermometer according to ISO 16474-1 gives important information on the range of
surface temperatures of differently coloured test specimens.

7.1.2 Chamber air temperature

If required, the chamber air temperature may also be controlled. If so, use (40 ± 3) °C unless
otherwise specified.

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7.2 Relative humidity of chamber air

Unless otherwise specified, the relative humidity shall be set at 50 % and maintained at ± 10 %.
NOTE The relative humidity of the air as measured in the test chamber is not necessarily equivalent to the
moisture content of the air very close to the test specimen surface owing to the differences in temperature of test
specimens of different colours and thicknesses.

7.3 Spray cycle

The spray cycle used shall be as agreed between the interested parties, but should preferably be one of
the following:
Spray cycle 1 duration of spraying period (front of the test specimens): (18,0 ± 0,5) min

dry interval between spraying periods: (102,0 ± 0,5) min

Spray cycle 2 duration of spraying period (front of the test specimens): (12,0 ± 0,5) min

dry interval between spraying periods: (48,0 ± 0,5) min

8 Procedure

8.1 General
It is recommended that at least three test specimens of each material evaluated be exposed in each run
to allow statistical evaluation of the results.

8.2 Mounting the test specimens

Attach the test specimens to the specimen holders in the equipment in such a manner that the test specimens
are not subject to any applied stress. Identify each test specimen by suitable indelible marking, avoiding
areas to be used for subsequent testing. As a check, a plan of the test specimen positions may be made.
If desired, in the case of specimens used to determine change in colour and appearance, a portion of each
test specimen may be shielded by an opaque cover throughout the exposure. This gives an unexposed
area adjacent to the exposed area for comparison. This is useful for checking the progress of the exposure,
but the data reported shall always be based on a comparison with file specimens stored in the dark.

8.3 Exposure
Before placing the test specimens in the test chamber, be sure that the apparatus is operating under the
desired conditions (see Clause 7). Programme the apparatus with the selected conditions to operate
continuously for the required number of cycles at the selected exposure conditions. Maintain these
conditions throughout the exposure, keeping any interruptions to service the apparatus and to inspect
the test specimens to a minimum.
Expose the test specimens and, if used, the irradiance-measuring instrument for the specified period.
Repositioning of the test specimens during exposure is desirable and might be necessary. Follow the
guidance in ISO 16474-1.
Replace filters after 2 000 h of use, or when pronounced discoloration or milkiness develops, whichever
occurs first. Clean the filters, at intervals recommended by the manufacturer, with a clean, dry, non-
abrasive cloth or towel, or with a solution of detergent in water followed by rinsing with clean water. It
is recommended that filters be replaced on a rotating schedule in order to provide more uniformity over

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long periods of exposure. In such cases, replace the filters sequentially, in pairs, every 500 h. Monitor the
age and position of the filter panes so that the oldest pair is removed each time.
If it is necessary to remove a test specimen for periodic inspection, take care not to touch the exposed
surface or alter it in any way. After inspection, return the test specimen to its holder or to its place in the
test chamber with its exposed surface oriented in the same direction as before.

8.4 Duration of test

8.4.1 Test until

a) either the surfaces of the test panels have been subjected to an agreed radiant exposure;
b) or an agreed or specified ageing criterion is satisfied.
In the latter case, remove and examine the test panels at various stages during the test period and
determine the end point by plotting an ageing curve.

8.4.2 No single test duration or test programme can be specified which would be suitable for all types
of coating. The total number of tests and the number of stages in each test shall be chosen as a function
of the requirements of the individual tests and shall be agreed between the interested parties for each
particular case. If not otherwise agreed, take two test panels for each assessment.

8.4.3 Testing of the test panels shall be carried out without interruption except for cleaning or
exchanging the carbon rods or the filter system or, when testing in stages, removal of the test panels.

8.4.4 If panels are evaluated for changes in gloss or colour, the panels shall be removed from the
weathering instrument at the end of the dry period.

8.5 Measurement of radiant exposure

If used, mount the radiometer so that it measures the irradiance at the exposed surface of the test specimen.
When radiant exposures are used, express the exposure interval in terms of incident radiant energy per
unit area of the exposure plane, in joules per square metre (J/m2) in the wavelength band selected.

8.6 Determination of changes in properties after exposure

These shall be determined as specified in ISO 4582.

9 Test report
Refer to ISO 16474-1.

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Bibliography

[1] CIE No. 85:1989, Solar spectral irradiance

[2] ISO 4892-4, Plastics — Methods of exposure to laboratory light sources — Part 4: Open-flame
carbon-arc lamps

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