ISO 20589:2025
(Main)Glass in building — Determination of the emissivity
Glass in building — Determination of the emissivity
This document specifies a procedure for determining the emissivity at room temperature of the surfaces of glass and coated glass. The emissivity is necessary for taking into account heat transfer by radiation from surfaces at the standard temperature of 283 K in the determination of the U value and of the total solar transmittance of glazing according to REF [5] \r \h ISO 9050[5] 08D0C9EA79F9BACE118C8200AA004BA90B0200000008000000040000005B0035005D000000 , REF [6] \r \h ISO 10291[6] 08D0C9EA79F9BACE118C8200AA004BA90B0200000008000000040000005B0036005D000000 , REF [7] \r \h ISO 10292[7] 08D0C9EA79F9BACE118C8200AA004BA90B0200000008000000040000005B0037005D000000 , and REF [8] \r \h ISO 10293[8] 08D0C9EA79F9BACE118C8200AA004BA90B0200000008000000040000005B0038005D000000 . The procedure, being based on spectrophotometric specular reflectance measurements at near normal incidence on materials that are non-transparent in the infrared region, is not applicable to glazing components with at least one of the following characteristics: a) with rough or structured surfaces where the incident radiation is diffusely reflected; b) with curved surfaces where the incident radiation is regularly reflected at angles unsuitable to reach the detector while using specular reflectance accessories; c) infrared transparent. However, it can be applied with caution to any glazing component provided its surfaces are flat and non-diffusing (see non-diffusing glazing component) and it is non-transparent in the infrared region (see glazing component non-transparent in the infrared region). Although transmittance measurements are included in this document, they are only necessary to check if the specimen is non-transparent in the infrared region in the context of this document (see glazing component non-transparent in the infrared region). If the specimen is transparent in the infrared region, this document is not applicable.
Titre manque
General Information
Buy Standard
Standards Content (Sample)
International
Standard
ISO 20589
First edition
Glass in building — Determination
2025-08
of the emissivity
Reference number
© ISO 2025
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
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 2
5 Brief outline of the procedure to determine corrected emissivity . 3
6 Spectral normal reflectance measurements and calculations . 3
6.1 Specimen preparation .3
6.2 Spectral normal reflectance measurements .4
6.2.1 General .4
6.2.2 Test apparatus .4
6.2.3 Measurement .4
6.2.4 Accuracy .5
6.3 Interpolation.5
6.4 Determination of normal reflectance .5
6.4.1 General .5
6.4.2 Calculation method .5
6.4.3 Noise criterion .5
7 Calculation of total normal emissivity and corrected emissivity . 6
7.1 Total normal emissivity . .6
7.2 Corrected emissivity .6
8 Test report . 6
Annex A (normative) Table for determining total normal reflectance . 8
Annex B (informative) Procedures to improve the accuracy of spectral normal reflectance
measurements . 9
Annex C (informative) Transmittance and diffuse reflectance measurements and calculation
of total normal transmittance .11
Annex D (informative) Determination of absolute reflectance by comparing the energy of the
beam reflected from the specimen to that of the incident beam .12
Bibliography .16
iii
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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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 World Trade Organization (WTO) principles in the
Technical Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html.
This document was prepared by the European Committee for Standardization (CEN) (as EN 12898:2019)
and was adopted, without modification other than those given below by Technical Committee ISO/TC 160,
Glass in building.
— informative parts of the Scope have been moved to the Introduction;
— “this European Standard” was changed to “this document”;
— references to EN standards have been changed to references to the corresponding ISO standards;
— clarifications have been made to Figure D.1, Figure D.2, Figure D.3 and Figure D.4, and their keys;
— the term “sample” has been changed to “specimen”.
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
Introduction
This document is based on the use of reflectance measurements using double beam dispersive infrared
spectrometers capable of measuring over almost the entire spectral range of a black body standard reference
[1]
temperature and determining the emissivity by the 30 ordinate method. It also takes account of Fourier
Transform Infrared (FTIR) spectrophotometers where the spectral range is limited. It describes a method
th
whereby spectrophotometers can be used to determine emissivity if they are able to measure up to the 24
ordinate point and if they satisfy a noise criterion for this spectral range. It allows the inclusion of data from
th th
the 25 ordinate point up to the 30 ordinate point.
As FTIR spectrophotometers are single beam instruments as opposed to dispersive spectrophotometers
which are double beam instruments (and thus able to correct for instrument drift), a procedure was
[2]
developed by the European funded project, THERMES, to correct for drift. This procedure is described in
[3] [4]
and . Other categories of ordinate errors using FTIR spectrophotometers are discussed in .
v
International Standard ISO 20589:2025(en)
Glass in building — Determination of the emissivity
1 Scope
This document specifies a procedure for determining the emissivity at room temperature of the surfaces of
glass and coated glass.
The emissivity is necessary for taking into account heat transfer by radiation from surfaces at the standard
temperature of 283 K in the determination of the U value and of the total solar transmittance of glazing
[5] [6] [7] [8]
according to ISO 9050 , ISO 10291 , ISO 10292 , and ISO 10293 .
The procedure, being based on spectrophotometric specular reflectance measurements at near normal
incidence on materials that are non-transparent in the infrared region, is not applicable to glazing
components with at least one of the following characteristics:
a) with rough or structured surfaces where the incident radiation is diffusely reflected;
b) with curved surfaces where the incident radiation is regularly reflected at angles unsuitable to reach
the detector while using specular reflectance accessories;
c) infrared transparent.
However, it can be applied with caution to any glazing component provided its surfaces are flat and non-
diffusing (see non-diffusing glazing component) and it is non-transparent in the infrared region (see glazing
component non-transparent in the infrared region).
Although transmittance measurements are included in this document, they are only necessary to check if the
specimen is non-transparent in the infrared region in the context of this document (see glazing component
non-transparent in the infrared region). If the specimen is transparent in the infrared region, this document
is not applicable.
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 10292, Glass in building — Calculation of steady-state U values (thermal transmittance) of multiple glazing
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at http:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
infrared
5 µm to 50 µm spectral range
3.2
emissivity
ratio of the energy emitted by a given surface at a given temperature to that of a perfect emitter (black body
with normal and corrected emissivity = 1,0) at the same temperature
Note 1 to entry: Two different definitions of emissivity should theoretically be used to describe radiation exchange
between:
a) glass surfaces facing each other in multiple glazing (effective emissivity);
b) a glass surface facing a room (hemispherical emissivity).
[9]
However, in practice numerical differences were found to be negligibly small. Thus, corrected emissivity is used to
describe both types of heat exchange with a close approximation.
3.3
specular reflectance
regular reflectance
reflectance according to the laws of geometrical optics, without the diffuse component
Note 1 to entry: The measurement arrangement should be such that the instrument beam reaches the detector after
being specularly reflected on the surface of the specimen (reference mirror) at an angle of incidence ≤ 10°.
3.4
diffuse reflectance
refle
...
International
Standard
ISO 20589
First edition
Glass in building — Determination
of the emissivity
PROOF/ÉPREUVE
Reference number
© ISO 2025
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
PROOF/ÉPREUVE
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviations . 2
5 Brief outline of the procedure to determine corrected emissivity . 3
6 Spectral normal reflectance measurements and calculations . 3
6.1 Specimen preparation .3
6.2 Spectral normal reflectance measurements .4
6.2.1 General .4
6.2.2 Test apparatus .4
6.2.3 Measurement .4
6.2.4 Accuracy .5
6.3 Interpolation.5
6.4 Determination of normal reflectance .5
6.4.1 General .5
6.4.2 Calculation method .5
6.4.3 Noise criterion .5
7 Calculation of total normal emissivity and corrected emissivity . 6
7.1 Total normal emissivity . .6
7.2 Corrected emissivity .6
8 Test report . 6
Annex A (normative) Table for determining total normal reflectance . 8
Annex B (informative) Procedures to improve the accuracy of spectral normal reflectance
measurements . 9
Annex C (informative) Transmittance and diffuse reflectance measurements and calculation
of total normal transmittance .11
Annex D (informative) Determination of absolute reflectance by comparing the energy of the
beam reflected from the specimen to that of the incident beam .12
Bibliography .16
PROOF/ÉPREUVE
iii
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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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 World Trade Organization (WTO) principles in the
Technical Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html.
This document was prepared by the European Committee for Standardization (CEN) (as EN 12898:2019)
and was adopted, without modification other than those given below by Technical Committee ISO/TC 160,
Glass in building.
— informative parts of the Scope have been moved to the Introduction;
— “this European Standard” was changed to “this document”;
— references to EN standards have been changed to references to the corresponding ISO standards;
— clarifications have been made to Figure D.1, Figure D.2, Figure D.3 and Figure D.4, and their keys;
— the term “sample” has been changed to “specimen”.
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.
PROOF/ÉPREUVE
iv
Introduction
This document is based on the use of reflectance measurements using double beam dispersive infrared
spectrometers capable of measuring over almost the entire spectral range of a black body standard reference
[1]
temperature and determining the emissivity by the 30 ordinate method. It also takes account of Fourier
Transform Infrared (FTIR) spectrophotometers where the spectral range is limited. It describes a method
th
whereby spectrophotometers can be used to determine emissivity if they are able to measure up to the 24
ordinate point and if they satisfy a noise criterion for this spectral range. It allows the inclusion of data from
th th
the 25 ordinate point up to the 30 ordinate point.
As FTIR spectrophotometers are single beam instruments as opposed to dispersive spectrophotometers
which are double beam instruments (and thus able to correct for instrument drift), a procedure was
[2]
developed by the European funded project, THERMES, to correct for drift. This procedure is described in
[3] [4]
and . Other categories of ordinate errors using FTIR spectrophotometers are discussed in .
PROOF/ÉPREUVE
v
International Standard ISO 20589:2025(en)
Glass in building — Determination of the emissivity
1 Scope
This document specifies a procedure for determining the emissivity at room temperature of the surfaces of
glass and coated glass.
The emissivity is necessary for taking into account heat transfer by radiation from surfaces at the standard
temperature of 283 K in the determination of the U value and of the total solar transmittance of glazing
[5] [6] [7] [8]
according to ISO 9050 , ISO 10291 , ISO 10292 , and ISO 10293 .
The procedure, being based on spectrophotometric specular reflectance measurements at near normal
incidence on materials that are non-transparent in the infrared region, is not applicable to glazing
components with at least one of the following characteristics:
a) with rough or structured surfaces where the incident radiation is diffusely reflected;
b) with curved surfaces where the incident radiation is regularly reflected at angles unsuitable to reach
the detector while using specular reflectance accessories;
c) infrared transparent.
However, it can be applied with caution to any glazing component provided its surfaces are flat and non-
diffusing (see non-diffusing glazing component) and it is non-transparent in the infrared region (see glazing
component non-transparent in the infrared region).
Although transmittance measurements are included in this document, they are only necessary to check if the
specimen is non-transparent in the infrared region in the context of this document (see glazing component
non-transparent in the infrared region). If the specimen is transparent in the infrared region, this document
is not applicable.
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 10292, Glass in building — Calculation of steady-state U values (thermal transmittance) of multiple glazing
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at http:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
infrared
5 µm to 50 µm spectral range
PROOF/ÉPREUVE
3.2
emissivity
ratio of the energy emitted by a given surface at a given temperature to that of a perfect emitter (black body
with normal and corrected emissivity = 1,0) at the same temperature
Note 1 to entry: Two different definitions of emissivity should theoretically be used to describe radiation exchange
between:
a) glass surfaces facing each other in multiple glazing (effective emissivity);
b) a glass surface facing a room (hemispherical emissivity).
[9]
However, in practice numerical differences were found to be negligibly small. Thus, corrected emissivity is used to
describe both types of heat exchange with a close approximation.
3.3
specular reflectance
regular reflectance
reflectance according to the laws of geometrical optics, without the diffuse component
Note 1 to entry: The measurement arrangement should be such that the instrument beam reaches the detector after
being specularly reflected on the surface of the specimen (reference mirror) at an
...
ISO/DISPRF 20589
ISO/TC 160
Secretariat: BSI
Date: 2024-10-112025-07-01
Glass in building — Determination of the emissivity
DIS stage
Warning for WD’s and CD’s
This document is not an ISO International Standard. It is distributed for review and comment. It is subject to change
without notice and may not be referred to as an International Standard.
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.
PROOF
ISO/DISPRF 20589:2025(en)
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
E-mail: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO/DISPRF 20589:2025(en)
Contents
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviations . 2
5 Brief outline of the procedure to determine corrected emissivity . 3
6 Spectral normal reflectance measurements and calculations . 3
6.1 Specimen preparation . 3
6.2 Spectral normal reflectance measurements . 4
6.3 Interpolation . 5
6.4 Determination of normal reflectance . 5
7 Calculation of total normal emissivity and corrected emissivity . 6
7.1 Total normal emissivity . 6
7.2 Corrected emissivity . 7
8 Test report . 7
Annex A (normative) Table for determining total normal reflectance . 9
Annex B (informative) Procedures to improve the accuracy of spectral normal reflectance
measurements . 10
Annex C (informative) Transmittance and diffuse reflectance measurements and calculation of
total normal transmittance . 12
Annex D (informative) Determination of absolute reflectance by comparing the energy of the
beam reflected from the specimen to that of the incident beam . 13
Bibliography . 19
iii
ISO/DISPRF 20589:2025(en)
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 drawnISO draws attention to the possibility that some of the elementsimplementation of this
document may beinvolve the subjectuse of (a) patent(s). ISO takes no position concerning the evidence,
validity or applicability of any claimed patent rights in respect thereof. As of the date of publication of this
document, ISO had not received notice of (a) patent(s) which may be required to implement this document.
However, implementers are cautioned that this may not represent the latest information, which may be
obtained from the patent database available at www.iso.org/patents. 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 ).
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 World Trade Organization (WTO) principles in the Technical
Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html.
This document was prepared by the European Committee for Standardization (CEN) (as EN 12898:2019) and
was adopted, without modification other than those given below by Technical Committee ISO/TC 160, Glass
in Buildingbuilding.
— informative parts of the Scope have been moved to the Introduction;
— “this European Standard” was changed to “this document”;
— references to EN standards have been changed to references to the corresponding ISO standards;
— clarifications have been made to Figure D.1, Figure D.2, Figure D.3 and Figure D.4, and their keys;
— the term “sample” has been changed to “specimen”.
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
ISO/DISPRF 20589:2025(en)
Introduction
This document is based on the use of reflectance measurements using double beam dispersive infrared
spectrometers capable of measuring over almost the entire spectral range of a black body standard reference
[1]
temperature and determining the emissivity by the 30 ordinate method. and it It also takes account of
Fourier Transform Infrared (FTIR) spectrophotometers where the spectral range is limited. It describes a
method whereby spectrophotometers can be used to determine emissivity if they are able to measure up to
th
the 24 ordinate point and if they satisfy a noise criterion for this spectral range. It allows the inclusion of data
th th
from the 25 ordinate point up to the 30 ordinate point.
As FTIR spectrophotometers are single beam instruments as opposed to dispersive spectrophotometers
which are double beam instruments (and thus able to correct for instrument drift), a procedure was developed
[2] [3]
by the European funded project, THERMES, to correct for drift. This procedure is described in and . Other
[4]
categories of ordinate errors using FTIR spectrophotometers are discussed in .
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.
v
ISO/DISPRF 20589:2025(en)
Glass in building — Determination of the emissivity
1 Scope
This document specifies a procedure for determining the emissivity at room temperature of the surfaces of
glass and coated glass.
The emissivity is necessary for taking into account heat transfer by radiation from surfaces at the standard
temperature of 283 K in the determination of the U value and of the total solar transmittance of glazing
[5] [6] [7] [8]
according to ISO 9050 , ISO 10291 , ISO 10292 , and ISO 10293 [6] to [9].
The procedure, being based on spectrophotometric regularspecular reflectance measurements at near normal
incidence on materials that are non-transparent in the infrared region, is not applicable to glazing components
with at least one of the following characteristics:
a) with rough or structured surfaces where the incident radiation is diffusely reflected;
b) with curved surfaces where the incident radiation is regularly reflected at angles unsuitable to reach the
detector while using regularspecular reflectance accessories;
c) infrared transparent.
However, it can be applied with caution to any glazing component provided its surfaces are flat and non-
diffusing (see non-diffusing glazing component) and it is non-transparent in the infrared region (see glazing
component non-transparent in the infrared region).
Although transmittance measurements are included in this document, they are only necessary to check if the
specimen is non-transparent in the infrared region in the context of this document (see glazing component
non-transparent in the infrared region). If the specimen is transparent in the infrared region, this document
is not applicable.
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 10292, Glass in building — Calculation of steady-state U values (thermal transmittance) of multiple glazing
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminologicalterminology databases for use in standardization at the following
addresses:
— ISO Online browsing platform: available at http://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at http://www.iso.org/obp
ISO/DISPRF 20589:2025(en)
3.23.1
infrared
5 µm to 50 µm spectral range
3.33.2
emissivity
ratio of the energy emitted by a given surface at a given temperature to that of a perfect emitter (black body
with normal and corrected emissivity = 1,0) at the same temperature
Note 1 to entry: Two different definitions of emissivity should theoretically be used to describe radiation exchange
between:
a) glass surfaces facing each other in multiple glazing (effective emissivity);
b) a glass surface facing a room (hemispherical emissivity).
[9]
However, in practice numerical differences were found to be negligibly small (see ). Thus, corrected emissivity is used
to describe both types of heat exchange with a close approximation.
3.43.3
specular reflectance
regular reflectance
reflectance according to the laws of geometrical optics, without the diffuse component
Note 1 to entry: The measurement arrangement should be such that the instrument beam reaches the detector after
being specularly reflected on the surface of the specimen (reference mirror) at an angle of incidence ≤ 10°.
3.53.4
diffuse reflectance
reflectance not containing any regular component, due to rough surfaces and/or transparent materials
containing inhomogeneous particles
3.63.5
total reflectance
sum of specular reflectance (3.3regular) and diffuse reflectance (3.4)
3.73.6
non-diffusing glazing component
glazing component with a diffuse reflectance (3.4) ≤ 0,05, measured at the near infrared (3.1) wavelength of
2 µm (see )
Note 1 to entry: The purpose of this measurement is to ensure that the specimen is non-diffusing in the measurement
range. Most integrating spheres sold with visible/near infrared spectrophotometers have a port designed to measure
diffuse reflectance. Diffuse reflectance measurements in the infrared range are difficult to perform.
Note 2 to entry: See Annex C.
3.83.7
glazing component non-transparent in the infrared region
glazing component with a total normal transmittance ≤ 0,05 at 283 K, measured spectrophotometrically
4 Abbreviations
For the purposes of this document, the following abbreviations apply.
ε total corrected emissivity at 283 K
ISO/DISPRF 20589:2025(en)
ε total normal emissivity at 283 K
n
E reading of the spectrophotometer with the specimen placed on the specimen support of the
reflectance accessory
E the instrument reading without placing anything on the specimen support
E the instrument reading with the reference mirror replacing the specimen
st
R total normal reflectance at 283
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.