ISO/FDIS 9050

Glass in building — Determination of luminous and solar characteristics of glazing

ISO 9050:2003 specifies methods of determining light and energy transmittance of solar radiation for glazing in buildings. These characteristic data can serve as a basis for light, heating and ventilation calculations of rooms and can permit comparison between different types of glazing. ISO 9050:2003 is applicable both to conventional glazing units and to absorbing or reflecting solar-control glazing, used as glazed apertures. The appropriate formulae for single, double and triple glazing are given. Furthermore, the general calculation procedures for units consisting of more than components are established. ISO 9050:2003 is applicable to all transparent materials. One exception is the treatment of the secondary heat transfer factor and the total solar energy factor for those materials that show significant transmittance in the wavelength region of ambient temperature radiation (5 microns to 50 microns), such as certain plastic sheets.

Titre manque

General Information

• Status: Not Published
• ICS: 81.040.20 - Glass in building
• Technical Committee: ISO/TC 160 - Glass in building
• Current Stage: 5020 - FDIS ballot initiated: 2 months. Proof sent to secretariat
• Start Date: 06-May-2026
• Completion Date: 06-May-2026

Relations

• Revises: ISO 9050:2003 - Glass in building — Determination of light transmittance, solar direct transmittance, total solar energy transmittance, ultraviolet transmittance and related glazing factors
• Effective Date: 09-Dec-2023

Overview

ISO/FDIS 9050:2026, Glass in building - Determination of luminous and solar characteristics of glazing, is an international standard developed by ISO/TC 160, Glass in Building. This standard establishes reliable methods for determining the light and energy transmittance of solar radiation through transparent building materials such as glazing. The resulting data enables designers, engineers, and specifiers to compare glazing products and to calculate the impact of various glazing types on lighting, heating, and ventilation requirements. ISO 9050:2026 applies to all transparent materials used in buildings, including conventional, absorbing, solar-control, and building-integrated photovoltaic (BIPV) glazing, with detailed calculation methods for single, double, and triple glazing units.

---

Key Topics

• Luminous (Light) Transmission and Reflectance
  The standard specifies procedures for measuring how much visible light is transmitted and reflected by glazing-from both natural daylight (illuminant D65) and artificial sources.

• Solar Energy Transmittance and Absorptance
  Methods are provided to determine the amount of solar energy that passes through or is absorbed by glazing, critical for assessing solar heat gain in buildings.

• Shading Coefficient
  Calculation of the shading coefficient, which is the ratio of total solar energy transmitted by a glazing to that of standard clear glass, enables direct comparison of solar control properties.

• Ultraviolet (UV) Transmittance and Damage Factors
  ISO 9050 outlines how to determine glazing's UV transmittance and associated CIE and skin damage factors, supporting considerations required for protecting interiors from fading and UV exposure.

• Spectral Properties and Multi-layer Glazing
  The standard details formulae for spectral transmittance and reflectance for single, double, and triple glazing. It also includes matrix calculation methods for more complex multi-layer systems.

• Special Glazing Types
  Specific procedures are included for laminated glass, screen-printed glass, and BIPV glazing, enabling accurate characterization of modern, high-performance products.

---

Applications

ISO/FDIS 9050:2026 finds practical application in multiple fields within the building and construction industries:

• Building Design & Daylighting Analysis
  Architects and lighting engineers use luminous transmittance data to model indoor illumination and enhance occupant comfort.

• Energy Performance Evaluation
  HVAC designers rely on total solar energy transmittance (g-value) to optimize energy consumption for heating, cooling, and ventilation.

• Glazing Comparison and Specification
  The standard allows contractors and building professionals to objectively compare solar-control, low-e, and standard glazing for new constructions and renovations.

• Sustainability and Certification
  Accurate energy and light transmittance data supports green building certification and compliance with energy codes.

• Specialty and Safety Glazing
  The UV transmittance and damage factors assist in specifying glazing for sensitive environments, such as museums or hospitals, where light and UV mitigation are priorities.

• Building-Integrated Photovoltaics (BIPV)
  The inclusion of BIPV methods aids designers in quantifying both energy production and daylighting effects of photovoltaic glazing.

---

Related Standards

• ISO 10291: Glass in building - Determination of steady-state U values (thermal transmittance) of multiple glazing - Guarded hot plate method
• ISO 10292: Glass in building - Calculation of steady-state U values (thermal transmittance) of multiple glazing
• ISO 10293: Glass in building - Determination of steady-state U values (thermal transmittance) of multiple glazing - Heat flow meter method
• ISO 20589: Glass in building - Determination of the emissivity

These related ISO standards support a complete analysis of glazing energy performance, from solar transmittance to thermal insulation properties, enabling comprehensive building envelope assessments.

---

Leveraging ISO/FDIS 9050:2026 is essential for stakeholders aiming to optimize building energy efficiency, daylight comfort, and occupant protection in modern construction projects. Integrating standardized glazing measurements ensures performance, compliance, and competitive market positioning.

Standards Content (Sample)

FINAL DRAFT
International
Standard
ISO/TC 160
Glass in building — Determination
Secretariat: BSI
of luminous and solar
Voting begins on:
characteristics of glazing
2026-05-06
Voting terminates on:
2026-07-01
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 SUPPOR TING DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
FINAL DRAFT
International
Standard
ISO/TC 160
Glass in building — Determination
Secretariat: BSI
of luminous and solar
Voting begins on:
characteristics of glazing
Voting terminates on:
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 SUPPOR TING DOCUMENTATION.
© ISO 2026
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 3
5 Determination of characteristics . 5
5.1 General .5
5.2 Insulating glass unit optical calculation .5
5.3 Light transmittance and reflectance .9
5.4 Solar direct transmittance, reflectance and absorptance .9
5.5 Total solar energy transmittance .10
5.5.1 Calculation .10
5.5.2 Division of incident solar radiant flux .10
5.5.3 Secondary heat transfer factor towards the inside . . 12
5.6 Shading coefficient .16
5.7 UV transmittance .16
5.8 CIE damage factor .16
5.9 Skin damage factor .17
5.10 Colour rendering .17
6 Expression of results .20
7 Test report .20
Annex A (normative) Procedures for calculation of the spectral characteristics of glass plates
with a different thickness, colour or both .34
Annex B (informative) Procedure for calculation of the spectral characteristics of laminated
glass .39
Annex C (informative) Procedure for calculation of the spectral characteristics of screen
printed glass .60
Annex D (informative) Matrix method for non-scattering incoherent optical systems – Total
solar energy transmittance for multi-pane glazing units . 61
Annex E (informative) Modifications to the formulae to permit calculation and declaration of
the luminous and solar properties of BIPV glazing .83
Annex F (informative) Example of calculation of colour rendering index in transmission .91
Bibliography .94

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 of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO’s adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 160, Glass in building.
[16]
This third edition cancels and replaces the second edition (ISO 9050:2003 ), which has been technically
revised.
The main changes are as follows:
— changes to the calculation of the internal heat transfer coefficient;
— clarification provided that UV transmittance is determined only for the total range and not split into UVA
and UVB;
— modification to normalized relative spectral distribution of global solar radiation based on 10 nm
wavelength intervals;
— a procedure is provided for the calculation of the spectral properties of laminated glass;
— guidance is given on how to determine the spectral characteristics of screen printed glass;
— introduction of a matrix method for non-scattering incoherent optical systems, including multiple layers;
— modifications to the formulae to permit calculation and declaration of the luminous and solar properties
of BIPV glazing;
— examples of calculation of colour rendering index have been given.
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
While this document presents the formulae for the exact calculations of the spectral characteristics of
glazing, it does not consider the uncertainty of the measurements necessary to determine the spectral
parameters that are used in the calculations. It should be noted that, for simple glazing systems where few
measurements are required, the uncertainty of the results will be satisfactory if correct measurements
procedures have been followed. When the glazing systems become complex and a large number of
measurements is required to determine the spectral parameters, the uncertainty is cumulative with the
number of measurements and should be considered in the final results.
In this document, the term “interface” is considered a surface characterized by its transmission and
reflections of light intensities. That is, the interaction with light is incoherent, all phase information being
lost. In the case of thin films (not described in this document), interfaces are characterized by transmission
and reflections of light amplitudes, i.e. the interaction with light is coherent and phase information is
available. Finally, for clarity, a coated interface can be described as having one or more thin films, but the
entire stack of thin films is characterized by its resulting transmission and reflection of light intensities.
In Annex B, the procedure for the calculation of spectral characteristics of laminated glass makes specific
reference to coated glass. The same procedure can be adopted for filmed glass (e.g. adhesive backed
polymeric film applied to glass).

v
FINAL DRAFT International Standard ISO/FDIS 9050:2026(en)
Glass in building — Determination of luminous and solar
characteristics of glazing
1 Scope
This document specifies methods of determining the luminous and solar characteristics of glazing in
buildings. These characteristics can serve as a basis for lighting, heating and cooling calculations of rooms
and permit comparison between different types of glazing.
This document applies both to conventional glazing and to absorbing or reflecting solar-control glazing, used
as vertical or horizontal glazed apertures. The appropriate formulae for single, double and triple glazing are
given. A matrix method is provided as an alternative calculation method.
This document introduces a method to determine the luminous and solar properties of building-integrated
photovoltaic (BIPV) glazing.
This document is accordingly applicable to all transparent materials except those which show significant
transmission in the wavelength region 5 µm to 50 µm of ambient temperature radiation, such as certain
plastic materials.
Materials with light-scattering properties for incident radiation are dealt with as conventional transparent
materials subject to certain conditions (see 5.3).
Angular light and solar properties of glass in building are excluded from this document. However, research
work in this area is summarised in References [1],[2] and [3].
Guidance on the measurement of luminous and spectral properties of glass can be found in Reference [4].
Vacuum insulating glass (VIG) is excluded from the scope of this document. For determination of the g value
[5]
of VIG, refer to ISO 19916-1 .
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 10291, Glass in building — Determination of steady-state U values (thermal transmittance) of multiple
glazing — Guarded hot plate method
ISO 10292, Glass in building — Calculation of steady-state U values (thermal transmittance) of multiple glazing
ISO 10293, Glass in building — Determination of steady-state U values (thermal transmittance) of multiple
glazing — Heat flow meter method
ISO 20589, Glass in building — Determination of the emissivity
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 https:// www .iso .org/ obp

— IEC Electropedia: available at https:// www .electropedia .org/
3.1
light transmittance
fraction of the incident light that is transmitted by the glass
3.2
light reflectance
fraction of the incident light that is reflected by the glass
3.3
total solar energy transmittance
fraction of the incident solar radiation that is transmitted by the glass, including secondary heat transfer
following absorption
3.4
solar direct transmittance
fraction of incident solar radiation that is directly transmitted by the glass
3.5
solar direct reflectance
fraction of the incident solar radiation that is reflected by the glass
3.6
ultraviolet transmittance
fraction of the incident UV component of the solar radiation that is transmitted by the glass
3.7
colour rendering index in transmission
change in colour of an object as a result of the light being transmitted by the glass
3.8
shading coefficient
ratio of the total solar energy transmittance of the glass to the total solar energy transmittance of clear float
glass
3.9
PV module
planar photovoltaic module
planar device designed to convert solar radiation into electricity by the photovoltaic (PV) effect
Note 1 to entry: The glazing configuration of a planar PV module may be, but is not restricted to, a coated or uncoated
pane of glass, a coated polymer film, a glass-polymer laminate or a glass-polymer-glass laminate. For the sake of
brevity, the term planar PV module is understood to mean a planar PV module in Annex E.
3.10
building-integrated photovoltaic glazing
BIPV glazing
architectural glazing that incorporates a planar photovoltaic (PV) module (3.9) as one of its panes
Note 1 to entry: In this context, architectural glazing refers to glazed apertures in buildings.
3.11
optically homogeneous
attribute of glazing with optical properties, which, when determined using a spectrophotometer, are
independent of the position selected for measurement
Note 1 to entry: Many thin-film planar photovoltaic (PV) modules (3.9) are examples of optically homogeneous glazing.

3.12
optically inhomogeneous
attribute of glazing with optical properties, which, when determined using a spectrophotometer, vary
significantly (i.e. by an amount greater than measurement tolerances) on the position selected for
measurement
Note 1 to entry: Typically, this refers to areas on a scale of cm that have a visibly different appearance, e.g. crystalline
photovoltaic (PV) cells surrounded by a transparent embedding material.
3.13
open circuit
OC
electrical state of a photovoltaic (PV) device in which the output electric current is zero
Note 1 to entry: Adapted from IEC TS 61836:2016, 3.4.57.
3.14
maximum power point
MPP
point on a PV device’s current-voltage characteristic where the product of electric current and voltage yields
the maximum electrical power under specified operating conditions
[SOURCE: IEC TS 61836:2016, 3.4.43.3]
3.15
standard test conditions
STC
reference values of in-plane irradiance G 1000Wm/ , photovoltaic cell junction temperature

I,ref
(25 °C), and a reference spectral irradiance distribution calculated for air mass = 1,5 to be used during the
testing of any photovoltaic device
[SOURCE: IEC TS 61836:2016, 3.4.87]
3.16
conversion efficiency
ratio of electric power generated by a photovoltaic (PV) device per unit area to its incident irradiance
[SOURCE: IEC TS 61836:2016, 3.1.17]
3.17
interface
surface characterized by its transmission and reflections of light intensities
3.18
coated interface
interface that has one or more thin films, with the entire stack of thin films being characterized by its
resulting transmission and reflection of light intensities
4 Symbols
D65 standard illuminant D65
UV ultraviolet radiation
τ ultraviolet transmittance
UV
 spectral transmittance

spectral reflectance


τ light transmittance
V
light reflectance
ρ
v
solar direct transmittance
τ
e
ρ solar direct reflectance
e
g
total solar energy transmittance
general colour rendering index in transmission
R
a
relative spectral distribution of illuminant D65
D
λ
V  spectral luminous efficiency

α solar direct absorptance
e
incident solar radiant flux
Φ
e
secondary internal heat transfer factor
q
i
q secondary external heat transfer factor
e
proportion of total absorbed solar radiation that is extracted from the PV cell-covered area of
α
elec
a BIPV glazing unit as electricity
relative spectral distribution of solar radiation
S
λ
h external heat transfer coefficient
e
h internal heat transfer coefficient
i
ε
corrected emissivity
Λ
thermal conductance
λ
wavelength

wavelength interval
relative spectral distribution of UV in solar radiation
U
λ
SC shading coefficient
τ CIE damage factor
df
F skin damage factor
sd
spectral normalised radiant flow
I 

η photovoltaic conversion efficiency of a planar PV module
mod
A
surface area
r
reflectance on interface
CR coverage ratio
power conversion efficiency of a hypothetical planar PV module with 100 % cell coverage
η
cell,mod
ratio
5 Determination of characteristics
5.1 General
The characteristics are determined for quasi-parallel, near normal radiation incidence (see Reference [4])
using the radiation distribution of illuminant D65 (see Table 1), solar radiation in accordance with Table 2,
ultraviolet (UV) radiation in accordance with Table 3, CIE damage function in accordance with Table 4 and
skin damage function in accordance with Table 5.
The characteristics are as follows:
— the spectral transmittance  and the spectral reflectance  in the wavelength range from
 
300 nm to 2 500 nm;
— the light transmittance τ and the light reflectance ρ for illuminant D65;
v v
— the solar direct transmittance τ and the solar direct reflectance ρ ;
e e
— the total solar energy transmittance g;
— the UV-transmittance τ ;
UV
— the general colour rendering index in transmission R ;
a
— the total shading coefficient, SC:
— CIE damage factor τ ;
df
— skin damage factor F .
sd
To characterize glazing, the principal parameters are τ and g; the other parameters are optional to provide
v
additional information.
If the value of a given characteristic is to be calculated for different glass thicknesses (in the case of uncoated
glass) or for the same coating applied to different substrates, it shall be obtained by calculation in accordance
with Annex A.
A procedure for the calculation of the spectral characteristics of laminated glass is given in Annex B.
Guidelines on determining the spectral characteristics of screen-printed glass are given in Annex C.
A modified matrix method is provided as an alternative calculation method in Annex D.
Modifications to the formulae to permit calculation and declaration of the luminous and solar properties of
BIPV glazing are given in Annex E.
The convention adopted in this document is for the incident radiation to be from left to right. The left side is
also referred to as outside or outdoors, whereas the right side is also referred to as inside or indoors.
The use of an integrating sphere is necessary when light scattering materials are tested. In this case the size
of the sphere and its aperture should be large enough to collect all possible scattered light and to obtain fair
average values when surface patterns are irregularly distributed.
5.2 Insulating glass unit optical calculation
In the case of an insulating glass unit, the spectral transmittance  , the spectral reflectance  and
 
T
th
the spectral absorptance  of the j pane in the glazing unit are calculated from the spectral

j
transmittances and reflectances of the individual components using Formulae (1) to (5):

For double glazing:
 
 
  (1)


1 
 
 
 
1 2
    (2)
 

1 
 
2 
 
 
2 1
   (3)
 

1 
 

  
  
T 12 1
   (4)
 

1 
 
 
 
T 12
  (5)


1 
 
where
is the spectral transmittance of the double glazing;


is the spectral reflectance of the double glazing for external incident radiation;


 is the spectral reflectance of the double glazing for internal incident radiation;


T
is the spectral absorptance of the first (outer) pane in the double glazing for external incident


radiation;
T
is the spectral absorptance of the second (inner) pane in the double glazing for external inci-


dent radiation;
is the spectral transmittance of the first (outer) pane;


is the spectral reflectance of the first (outer) pane, measured in the direction of incident ra-


diation;

is the spectral reflectance of the first (outer) pane, measured in the direction opposite to the


incident radiation;
is the spectral transmittance of the second pane;


is the spectral reflectance of the second pane, measured in the direction of the incident radiation;



is the spectral reflectance of the second pane, measured in the direction opposite to the in-


cident radiation;
is the spectral direct absorptance of the outer pane, measured in the direction of the incident


radiation, given by Formula (6):
 1   (6)
  
11 1
is the spectral direct absorptance of the outer pane, measured in the opposite direction to the



incident radiation, given by Formula (7):

 1   (7)
  
11 1
is the spectral direct absorptance of the second pane, measured in the direction of the incident


radiation, given by Formula (8):
 1   (8)
  
22 2
The above is illustrated in Figure 1.
Key
1 pane 1
2 cavity
3 pane 2
Figure 1 — Transmittance and reflectance in a double glazing insulating glass unit
For triple glazing, Formulae (9) to (14) apply.
  
  
12 3
  (9)

 2 
   
11      
      
12 23 2 13
   
2  2 2
 
  1      
      
1 22 31 2 33
 
    (10)
 
 2 
   
11       
      
12 23 2 1 33
   
2  2 2 
 
  1     
       
3 21 23 2 1
  
    (11)
 
 2 
   
11      
      
12 23 2 1 3
   
 2 
 
  1      
        
11 22 31 22 13
T  
   (12)
 
 2 
   
11       
      
12 23 22 13
   

 
 1      
       
12 23 12 2 33
T  
  (13)

 2 
   
11       
      
12 23 2 1 33
   
  
  
T 12 3
  (14)

 2 
   
11      
      
12 23 2 13
   
where
is the spectral transmittance of the triple glazing;


is the spectral reflectance of the triple glazing for external incident radiation;


is the spectral reflectance of the triple glazing for internal incident radiation;


T
is the spectral absorptance of the first (outer) pane in the triple glazing for external incident


radiation;
T
is the spectral absorptance of the second (middle) pane in the triple glazing for external incident


radiation;
T
is the spectral absorptance of the third (inner) pane in the triple glazing for external incident


radiation;
  
 ,  ,  ,  ,  ,  ,  ,  and  are explained in Formula (1)
        
1 1 1 2 2 2 1 1 2
to Formula (5);
is the spectral transmittance of the third pane;


is the spectral reflectance of the third pane, measured in the direction of the incident radiation;



is the spectral reflectance of the third pane, measured in the direction opposite to the incident


radiation;

is the spectral direct absorptance of the second pane, measured in the opposite direction to the


incident radiation, given by Formula (15):

 1   (15)
  
22 2
is the spectral direct absorptance of the third pane, measured in the direction of the incident


radiation, given by Formula (16):
 1   (16)
  
33 3
The above is illustrated in Figure 2.
Key
1 pane 1
2 cavity 1
3 pane 2
4 cavity 2
5 pane 3
Figure 2 — Transmittance and reflectance in a triple glazing insulating glass unit

For glazing with more than three components, formulae similar to Formula (1) to Formula (5) and
Formula (9) to Formula (14) are found to calculate  of such glazing from the spectral coefficients of the

individual components. As an example, glazing composed of five components may be treated as follows:
a) first consider the first three components as triple glazing and calculate the spectral characteristics of
this combination;
b) next, run the same procedure for the next two components as double glazing;
c) then calculate  for the five-component glazing, considering it as double glazing consisting of the

preceding triple and double glazing (or, alternatively, the methodology in Annex D can be followed).
NOTE Measurement of light scattering glass products is the subject of a round robin test programme under the
responsibility of International Commission on Glass, Technical Committee 10. The results of this programme are
expected to include suggestions for improvements in measurement and prediction techniques.
5.3 Light transmittance and reflectance
The light transmittance τ and reflectance ρ of the glazing are calculated using Formulae (17) and (18):
v v
780nm
DV  
 


380nm
  (17)
v
780nm
DV  



380nm
780nm
DV  
 


380nm
  (18)
v
780nm
DV  

 
380nm
where
D is the relative spectral distribution of illuminant D65 (see Reference [6]);
λ
 is the spectral transmittance of the glazing;

 is the spectral reflectance of the glazing;

V  is the spectral luminous efficiency for photopic vision defining the standard observer for

photometry (see Reference [6]);
 is the wavelength interval.
Table 1 indicates the values for DV  for wavelength intervals of 10 nm. The table has been drawn


up in such a way that DV  1 .


For calculating the internal light reflectance  is used instead of  in Formula (18).
 
5.4 Solar direct transmittance, reflectance and absorptance
The solar direct transmittance τ , the solar direct reflectance ρ and the solar direct absorptance α of
e e e, j
the glazing are calculated using Formulae (19), (20) and (21):
2500nm
S  

 
300nm
  (19)
e
2500nm
S 


300nm
2500nm
S  



300nm
  (20)
e
2500nm
S 


300nm
2500
nm
T
S  

  j
300nm
  (21)
e,j
2500nm
S 


300nm
where
S is the relative spectral distribution of the solar radiation (see Table 2);
λ
 is the spectral transmittance of the glazing;

 is the spectral reflectance of the glazing;

T
th
 is the spectral absorptance of the j pane from the outside in the glazing consisting of n glass

j
panes;
 is the wavelength interval.
In the case of multiple glazing, the spectral transmittance  , the spectral reflectance  and the
 
T
spectral absorptance  are calculated in accordance with 5.2.

j
The relative spectral distribution, S , used to calculate the solar direct transmittance is derived from
λ
[7]
CIE 85 . The corresponding values S  are given in Table 2. The table was drawn up in such a way that

S  1 .

1 [16]
NOTE 1 For measurements previously undertaken in accordance with ISO 9050:2003, Table 2, where there is
no transmittance or reflectance data at a given wavelength in Table 2 of this document, the missing values can be
obtained by linear interpolation.
NOTE 2 Contrary to real situations, it is always assumed, for simplification, that the spectral distribution of the
solar radiation (see Table 2) is not dependent upon atmospheric conditions (e.g. dust, mist, moisture content) and that
the solar radiation strikes the glazing as a collimated beam and at normal incidence. The resulting errors are very
small.
5.5 Total solar energy transmittance
5.5.1 Calculation
The total solar energy transmittance g is calculated, as given in Formula (22), as the sum of the solar direct
transmittance τ and the secondary heat transfer factor q of the glazing towards the inside (see 5.4 and
e i
5.5.3), the latter resulting from heat transfer by convection and longwave IR-radiation of that part of the
incident solar radiation which has been absorbed by the glazing:
gq (22)
ei
5.5.2 Division of incident solar radiant flux
The incident solar radiant flux Φ is divided into the following three parts (see Figure 3):
e
a) the transmitted part,   ;
ee
b) the reflected part,   ;
ee
c) the absorbed part,   ;
ee
where
is the solar direct transmittance (see 5.4);
τ
e
is the solar direct reflectance (see 5.4);
ρ
e
is the solar direct absorptance (see 5.4), given by Formula (23).
α
e
n
 (23)
ee, j

j1
Key
1 outer pane
2 inner pane
3 unit incident radiant flux
Figure 3 — Example of division of the incident radiant flux

The relation between the three characteristics is given by Formula (24):
 1 (24)
eee
The absorbed part   is subsequently split into two parts q Φ and q Φ which are energy transferred
ee ie ee
to the inside and outside respectively, as in Formula (25):
 qq (25)
ei e
where
q is the secondary heat transfer factor of the glazing towards the inside;
i
q is the secondary heat transfer factor of the glazing towards the outside.
e
5.5.3 Secondary heat transfer factor towards the inside
5.5.3.1 Boundary conditions
For the calculation of the secondary heat transfer factor towards the inside, q , the heat transfer coefficients
i
of the glazing towards the outside, h , and towards the inside, h are needed. These values mainly depend
e i
on the position of the glazing, wind velocity, inside and outside temperatures, and furthermore on the
temperature of the two external glazing surfaces.
As the purpose of this document is to provide basic information on the performance of glazing, conventional
conditions have been stated for simplicity:
a) position of the glazing: vertical;
b) outside surface: wind velocity: approximately 4 m/s, corrected emissivity = 0,837;
c) inside surface: natural convection, emissivity optional;
d) air spaces are unventilated.
Under these conventional, average conditions, h is 25 W/(m ∙K) and standard values for h shall be obtained
e i
using Formula (26):
hh h (26)
ir c
where
h is the internal radiative heat transfer coefficient;
r
h is the internal convective heat transfer coefficient.
c
For the purposes of this document, the internal radiative heat transfer coefficient for uncoated soda lime
glass surfaces is 4,8 W/(m ⋅K), rounded to one decimal place.

If the internal surface of the glass has a lower emissivity the internal radiative heat transfer coefficient is
given by Formula (27):
hT4   (27)
rs
where
ε is the corrected emissivity of the coated surface;
−8 2 4
σ is Stefan-Boltzmann’s constant, 5,67 × 10 W/(m ·K );
T is the mean temperature of the internal surface of the glass (K).
s
This is only applicable if there is no condensation on the coated surface. A procedure for determining the
corrected emissivity of a coating is given in ISO 20589.
A value of 293,15 K can be assumed for T in Formula (27),
s
The value of h is 2,5 W/(m ·K) for free convection for horizontal heat flow.
c
For vertical soda lime glass surfaces and free convection, Formula (28) applies:
h =4,8+2,5=7,3 (28)
i
which is standardized for the purposes of comparison of U values.
For uncoated soda lime silicate glass,  0,837 and h =7,3 W /m K

i
With reasonable confidence the same value can be used for uncoated borosilicate glass, alkaline earth
silicate glass, alumino silicate glass and glass ceramics.
The corrected emissivity shall be defined and measured in accordance with ISO 20589.
5.5.3.2 Single glazing
The secondary internal heat transfer factor, q , of single glazing is calculated using Formula (29):
i
h
i
q  (29)
ie
hh
ei
where
α is the solar direct absorptance in accordance with 5.4;
e
h and h are the heat transfer coefficients towards the outside and inside respectively in accordance
e i
with 5.5.3.1.
5.5.3.3 Double glazing
The secondary internal heat transfer factor, q , of double glazing is calculated using Formula (30):
i
  
ee,,12 e,2
  
h 
 
e
 
q  (30)
i
 
11 1

 
hh 
 
 ie 
where
h and h are the heat transfer coefficients towards the outside and inside respectively in accordance
e i
with 5.5.3.1;
α is the solar direct absorptance of the outer pane within the double glazing in accordance with
e,1
5.4;
α is the solar direct absorptance of the second pane within the double glazing in accordance with
e,2
5.4;
Λ is the thermal conductance between the outer surface and the innermost surface of the double
glazing (see Figure 4).
The thermal conductance Λ shall be determined by the calculation method in accordance with ISO 10292.
Where this is not possible, it shall be determined by measurement in accordance with ISO 10291 or
ISO 10293.
Key
1 pane 1
2 pane 2
3 outside
4 inside
Figure 4 — Illustration of the meaning of thermal conductance Λ

5.5.3.4 Triple glazing
The secondary internal heat transfer factor of triple glazing, q , is calculated using Formula (31):
i
   
ee,,3 32ee,,32ee,,1
   
 h
 
23 12 e
 
q  (31)
i
 
11 1 1
 
 
hh  
 
 ie 112 23 
where
α is the solar direct absorptance of the outer pane within the triple glazing in accordance with
e,1
5.4;
α is the solar direct absorptance of the second pane within the triple glazing in accordance with
e,2
5.4;
α is the solar direct absorptance of the third pane within the triple glazing in accordance with
e,3
5.4;
h and h are the heat transfer coefficients towards the outside and inside respectively in accordance
e i
with 5.5.3.1;
Λ is the thermal conductance between the outer surface of the first pane and the centre of the
second pane (see Figure 5);
Λ is the thermal conductance between the centre of the second pane and the innermost surface
of the third pane (see Figure 5).
The thermal conductances Λ and Λ are determined in accordance with 5.5.3.3.
12 23
Key
1 pane 1
2 pane 2
3 pane 3
4 outside
5 inside
Figure 5 — Illustration of the meaning of the thermal conductances Λ and Λ
12 23
5.5.3.5 Quadruple glazing
The secondary internal heat transfer factor of quadruple glazing can be determined by reference to the g
value calculation in Annex D.
5.6 Shading coefficient
The shading coefficient, SC, is given as the total solar energy transmittance of the glazing, divided by the
total solar energy transmittance of 3 mm or 4 mm clear float.
NOTE 1 In some countries, SC can be specifically referred to as total shading coefficient.
NOTE 2 The value of the total solar energy transmittance of a clear float glass of 3 mm to 4 mm nominal thickness is
traditionally assumed as 0,87.
The value that is actually used as the total solar energy transmittance for the clear float glass pane should
be stated.
5.7 UV transmittance
A standard relative spectral distribution for the UV part of the global solar radiation, U , is given (see,
λ
Reference [8]). Table 3 gives the values of U  for wavelength intervals of 5 nm in the UV range. The

table has been drawn up with relative values in such a way that U   1 for the total UV range.

The UV-transmittance τ is calculated using Formula (32):
uv
380nm
U  



300nm
  (32)
uv
380nm
U 


300nm
where
 is the spectral direct transmittance of the glazing (see 5.2);

U is the relative distribution of the UV part of global solar radiation;
λ
 is the wavelength interval.
NOTE If statements are made about the UV transmission of glazing, in most cases it is sufficient to give τ , the
uv
transmittance for the total UV radiation contained in global solar radiation.
5.8 CIE damage factor
The CIE damage factor τ (see Reference [9]) is calculated according to Formulae (33) and (34):
df
600�nm
 CS 

 
300�nm
  (33)
df
600�nm
CS 


300�nm
0,012
Ce (with λ in nm) (34)

where
S is the relative spectral distribution of solar radiation;
λ
τ (λ) is the spectral transmittance of the glazing (see 3.3);
Δλ and the integration procedure are the same as in 3.3 except that the data points shall be chosen
at the wavelengths given in Table 4.

Table 4 gives the values of C S Δλ. This table has been drawn up with relative values in such a way that ΣC
λ λ λ
S Δλ = 1 for the range from 300 nm to 600 nm.
λ
This average extends over the UV and part of the visible portions of the solar spectrum, which can contribute
to the solar radiation damage of materials.
5.9 Skin damage factor
The skin damage factor F (see Reference [10]) is calculated according to Formula (35):
sd
400nm
 ES 

 
300nm
F  (35)
sd
400nm
ES 
 
300nm
where
S is the relative spectral distribution of solar radiation;
λ
E is the CIE erythemal effectiveness spectrum;
λ
τ (λ) is the spectral transmittance of the glazing (see 3.3);
Δλ and the integration procedure are the same as in 3.3 except that the data points shall be chosen
at the wavelengths given in Table 5.
Table 5 gives the values of E S Δλ. This table has been drawn up with relative values in such a way that ΣE
λ λ λ
S Δλ = 1 for the range from 300 nm to 400 nm.
λ
This average extends over the UV and part of the visible portions of the solar spectrum, which can contribute
to the solar radiation damage of skin.
5.10 Colour rendering
The colour rendering properties of glazing in transmission are expressed by the general colour rendering
index in transmission R . This index enables to express synthetically a quantitative evaluation of the
a
differences in colour between eight test colours lighted directly by the reference illuminant D65 and by the
same illuminant transmitted through the glazing (see Reference [11]).
The test colours are defined by their spectral reflectance  ( i from 1 to 8), reported in Table 6

i
(see R
...

ISO/DIS FDIS 9050:2026(en)
ISO/TC 160/WG 8
Secretariat: BSI
Date: 2026-01-2304-21
Glass in building — Determination of luminous and solar
characteristics of glazing
FDIS stage
ISO #####-#:####(X/FDIS 9050:2026(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
EmailE-mail: [e-mail]
Website: www.iso.org
Published in Switzerland
© ISO #### 2026 – All rights reserved
ii
ISO/DIS FDIS 9050:20252026(en)
Contents
Foreword . iv
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols . 4
5 Determination of characteristics . 5
5.1 General . 5
5.2 Insulating glass unit optical calculation . 6
5.3 Light transmittance and reflectance . 10
5.4 Solar direct transmittance, reflectance and absorptance . 12
5.5 Total solar energy transmittance . 13
5.6 Shading coefficient . 19
5.7 UV transmittance . 20
5.8 CIE damage factor . 20
5.9 Skin damage factor . 21
5.10 Colour rendering . 23
6 Expression of results . 26
7 Test report . 26
Annex A (normative) Procedures for calculation of the spectral characteristics of glass plates
with a different thickness, colour or both . 42
Annex B (informative) Procedure for calculation of the spectral characteristics of laminated
glass . 47
Annex C (informative) Procedure for calculation of the spectral characteristics of screen
printed glass . 75
Annex D (informative) Matrix method for non-scattering incoherent optical systems – Total
solar energy transmittance for multi-pane glazing units . 76
Annex E (informative) Modifications to the formulae to permit calculation and declaration of
the luminous and solar properties of BIPV glazing . 103
Annex F (informative) Example of calculation of colour rendering index in transmission . 113
Bibliography . 116

iii
ISO #####-#:####(X/FDIS 9050:2026(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).
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 of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO’s adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 160, Glass in building.
[16][16]
This third edition cancels and replaces the second edition (ISO 9050:2003 ),), which has been technically
revised.
The main changes are as follows:
— — changes to the calculation of the internal heat transfer coefficient;
— — clarification provided that UV transmittance is determined only for the total range and not split into
UVA and UVB;
— — modification to normalized relative spectral distribution of global solar radiation based on 10 nm
wavelength intervals;
—
— — a procedure is provided for the calculation of the spectral properties of laminated glass;
— — guidance is given on how to determine the spectral characteristics of screen printed glass.— ;
— introduction of a matrix method for non-scattering incoherent optical systems, including multiple layers;
— — modifications to the formulae to permit calculation and declaration of the luminous and solar
properties of BIPV glazing.;
— — examples of calculation of colour rendering index hashave been given.
© ISO #### 2026 – All rights reserved
iv
ISO/DIS FDIS 9050:20252026(en)
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 #####-#:####(X/FDIS 9050:2026(en)
Introduction
While this document presents the formulae for the exact calculations of the spectral characteristics of glazing,
it does not consider the uncertainty of the measurements necessary to determine the spectral parameters that
are used in the calculations. It should be noted that, for simple glazing systems where few measurements are
required, the uncertainty of the results will be satisfactory if correct measurements procedures have been
followed. When the glazing systems become complex and a large number of measurements areis required to
determine the spectral parameters, the uncertainty is cumulative with the number of measurements and
should be considered in the final results.
TheIn this document, the term “interface used in this International Standard,” is considered to be a surface
characterized by its transmission and reflections of light intensities. That is, the interaction with light is
incoherent, all phase information being lost. In the case of thin films (not described in this International
Standarddocument), interfaces are characterized by transmission and reflections of light amplitudes, i.e. the
interaction with light is coherent and phase information is available. Finally, for clarity, a coated interface can
be described as having one or more thin films, but the entire stack of thin films is characterized by its resulting
transmission and reflection of light intensities.
In Annex BAnnex B,, the procedure for the calculation of spectral characteristics of laminated glass makes
specific reference to coated glass. The same procedure can be adopted for filmed glass (e.g. adhesive backed
polymeric film applied to glass).
© ISO #### 2026 – All rights reserved
vi
DRAFT International Standard ISO/DIS 9050:2025(en)

Glass in building — Determination of luminous and solar
characteristics of glazing
1 Scope
This document specifies methods of determining the luminous and solar characteristics of glazing in buildings.
These characteristics can serve as a basis for lighting, heating and cooling calculations of rooms and permit
comparison between different types of glazing.
This document applies both to conventional glazing and to absorbing or reflecting solar-control glazing, used
as vertical or horizontal glazed apertures. The appropriate formulae for single, double and triple glazing are
given. A matrix method is provided as an alternative calculation method.
This document introduces a method to determine the luminous and solar properties of building-integrated
photovoltaic (BIPV) glazing.
This document is accordingly applicable to all transparent materials except those which show significant
transmission in the wavelength region 5 µm to 50 µm of ambient temperature radiation, such as certain plastic
materials.
Materials with light-scattering properties for incident radiation are dealt with as conventional transparent
materials subject to certain conditions (see 5.35.3).).
Angular light and solar properties of glass in building are excluded from this document. However, research
[1] [2] [3]
work in this area is summarised in References 1 , ,2and 3 .
[4]
Guidance on the measurement of luminous and spectral properties of glass can be found in Reference [4] .
Vacuum insulating glass (VIG) is excluded from the scope of this document. For determination of the g value
[5][5]
of VIG, refer to ISO 19916--1 .
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 10291, Glass in building — Determination of steady-state U values (thermal transmittance) of multiple
glazing — Guarded hot plate method
ISO 10292, Glass in building — Calculation of steady-state U values (thermal transmittance) of multiple glazing
ISO 10293, Glass in building — Determination of steady-state U values (thermal transmittance) of multiple
glazing — Heat flow meter method
ISO 20589, Glass in building — Determination of the emissivity

Under preparation. Stage at the time of publication: ISO/PRF 20589:2025.
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 https://www.iso.org/obp
— — IEC Electropedia: available at https://www.electropedia.org/
3.1 3.1
light transmittance
fraction of the incident light that is transmitted by the glass
3.2 3.2
light reflectance
fraction of the incident light that is reflected by the glass
3.3 3.3
total solar energy transmittance
fraction of the incident solar radiation that is transmitted by the glass, including secondary heat transfer
following absorption
3.4 3.4
solar direct transmittance
fraction of incident solar radiation that is directly transmitted by the glass
3.5 3.5
solar direct reflectance
fraction of the incident solar radiation that is reflected by the glass
3.6 3.6
ultraviolet transmittance
fraction of the incident UV component of the solar radiation that is transmitted by the glass
3.7 3.7
colour rendering index in transmission
change in colour of an object as a result of the light being transmitted by the glass
3.8 3.8
shading coefficient
ratio of the total solar energy transmittance of the glass to the total solar energy transmittance of clear float
glass
3.9 3.9
PV module
planar photovoltaic module
planar device designed to convert solar radiation into electricity by the photovoltaic (PV) effect
Note 1 to entry: The glazing configuration of a planar PV module may be, but is not restricted to, a coated or uncoated
pane of glass, a coated polymer film, a glass-polymer laminate or a glass-polymer-glass laminate. For the sake of brevity,
the term planar PV module is understood to mean a planar PV module in Annex EAnnex E.
© ISO #### 2026 – All rights reserved
ISO/DIS FDIS 9050:20252026(en)
3.10 3.10
building-integrated photovoltaic glazing
BIPV glazing
architectural glazing that incorporates a planar photovoltaic (PV) module (3.9) as one of its panes
Note 1 to entry: In this context, architectural glazing refers to glazed apertures in buildings.
3.11 3.11
optically homogeneous
attribute of glazing with optical properties, which, when determined using a spectrophotometer, are
independent of the position selected for measurement
Note 1 to entry: Many thin-film planar photovoltaic (PV) modules (3.9) are examples of optically homogeneous glazing.
3.12 3.12
optically inhomogeneous
attribute of glazing with optical properties, which, when determined using a spectrophotometer in accordance
with this International Standard, vary significantly (i.e. by an amount greater than measurement tolerances)
on the position selected for measurement
Note 1 to entry: Typically, this refers to areas on a scale of cm that have a visibly different appearance, e.g. crystalline
photovoltaic (PV) cells surrounded by a transparent embedding material.
3.13 3.13
open circuit
OC
with reference to a PV device, an electrical state of a photovoltaic (PV) device in which the output electric
current is zero
Note 1 to entry: Adapted from 3.4.57 of IEC TS 61836):2016, 3.4.57.
3.14 3.14
maximum power point
MPP
point on a PV device’s current-voltage characteristic where the product of electric current and voltage yields
the maximum electrical power under specified operating conditions
[SOURCE: IEC TS 61836:2016, 3.4.43.3]
3.15 3.15
standard test conditions
STC
reference values of in-plane irradiance ,(𝐺𝐺 = 1 000 W/m ), photovoltaic cell junction temperature (25 °C),
I,ref
and a reference spectral irradiance distribution calculated for air mass = 1,5 to be used during the testing of
any photovoltaic device
[SOURCE: IEC TS 61836:2016, 3.4.87]
3.16 3.16
conversion efficiency
ratio of electric power generated by a photovoltaic (PV) device per unit area to its incident irradiance
[SOURCE: IEC TS 61836:2016, 3.1.17]
3.17
interface
The term interface used in this International Standard, is considered to be a surface characterized by its
transmission and reflections of light intensities
3.18
coated interface
a coated interface can be described as havingthat has one or more thin films, butwith the entire stack of thin
films isbeing characterized by its resulting transmission and reflection of light intensities

4 Symbols
D65 standard illuminant D65
UV ultraviolet radiation
𝜏𝜏 ultraviolet transmittance
UV
𝜏𝜏(𝜆𝜆) spectral transmittance
𝜌𝜌(𝜆𝜆) spectral reflectance
𝜏𝜏 light transmittance
V
𝜌𝜌 light reflectance
v
𝜏𝜏 solar direct transmittance
e
𝜌𝜌 solar direct reflectance
e
𝑔𝑔 total solar energy transmittance
𝑅𝑅 general colour rendering index in transmission
a
𝐷𝐷 relative spectral distribution of illuminant D65
𝜆𝜆
𝑉𝑉(𝜆𝜆) spectral luminous efficiency
𝛼𝛼 solar direct absorptance
e
𝛷𝛷 incident solar radiant flux
e
𝑞𝑞 secondary internal heat transfer factor
i
𝑞𝑞 secondary external heat transfer factor
e
proportion of total absorbed solar radiation that is extracted from the PV cell-covered area of a BIPV
𝛼𝛼
elec
glazing unit as electricity
𝑆𝑆 relative spectral distribution of solar radiation
𝜆𝜆
ℎ external heat transfer coefficient
e
ℎ internal heat transfer coefficient
i
𝜀𝜀 corrected emissivity
𝛬𝛬 thermal conductance
𝜆𝜆 wavelength
Δ𝜆𝜆 wavelength interval
𝑈𝑈 relative spectral distribution of UV in solar radiation
𝜆𝜆
SC shading coefficient
τ CIE damage factor
df
F skin damage factor
sd
© ISO #### 2026 – All rights reserved
ISO/DIS FDIS 9050:20252026(en)
D65 standard illuminant D65
𝐼𝐼(𝜆𝜆) spectral normalised radiant flow
𝜂𝜂 photovoltaic conversion efficiency of a Planarplanar PV module
mod
𝐴𝐴 surface area
𝑟𝑟 reflectance on interface
CR coverage ratio
𝜂𝜂
power conversion efficiency of a hypothetical Planarplanar PV module with 100 % cell coverage ratio
cell,mod
5 Determination of characteristics
5.1 General
The characteristics are determined for quasi-parallel, near normal radiation incidence (see Reference [4] [4]))
using the radiation distribution of illuminant D65 (see Table 1Table 1),), solar radiation in accordance with
Table 2Table 2,, ultraviolet (UV) radiation in accordance with Table 3Table 3,, CIE damage function in
accordance with Table 4Table 4 and skin damage function in accordance with Table 5Table 5.
The characteristics are as follows:
— — the spectral transmittance 𝜏𝜏(𝜆𝜆) and the spectral reflectance 𝜌𝜌(𝜆𝜆) in the wavelength range from 300 nm
to 2 500 nm;
— — the light transmittance 𝜏𝜏 and the light reflectance 𝜌𝜌 for illuminant D65;
v v
— — the solar direct transmittance 𝜏𝜏 and the solar direct reflectance ;𝜌𝜌 ;
e e
— — the total solar energy transmittance g;
— — the UV-transmittance ;𝜏𝜏 ;
UV
— — the general colour rendering index in transmission ;𝑅𝑅 ;
a
— — the total shading coefficient, SC;:
— CIE damage factor τ ;
df
— skin damage factor F .
sd
To characterize glazing, the principal parameters are 𝜏𝜏 and ;g; the other parameters are optional to provide
v
additional information.
If the value of a given characteristic is to be calculated for different glass thicknesses (in the case of uncoated
glass) or for the same coating applied to different substrates, it shall be obtained by calculation (in accordance
with Annex AAnnex A).
A procedure for the calculation of the spectral characteristics of laminated glass is given in Annex BAnnex B.
Guidelines on determining the spectral characteristics of screen-printed glass are given in Annex CAnnex C.
A modified matrix method is provided as an alternative calculation method in Annex DAnnex D.
Modifications to the formulae to permit calculation and declaration of the luminous and solar properties of
BIPV glazing are given in Annex EAnnex E.
The convention adopted in this document is for the incident radiation to be from left to right. The left side is
also referred to as outside or outdoors, whereas the right side is also referred to as inside or indoors.
The use of an integrating sphere is necessary when light scattering materials are tested. In this case the size
of the sphere and its aperture should be large enough to collect all possible scattered light and to obtain fair
average values when surface patterns are irregularly distributed.
5.2 Insulating glass unit optical calculation
In the case of aninsulatingan insulating glass unit, the spectral transmittance ,𝜏𝜏(𝜆𝜆), the spectral reflectance
𝑇𝑇
th
𝜌𝜌(𝜆𝜆) and the spectral absorptance 𝛼𝛼 (𝜆𝜆) of the j pane in the glazing unit are calculated from the spectral
𝑗𝑗
transmittances and reflectances of the individual components using Formulae (1)Formulae (1) to (5)(5)::
For double glazing:
(1)
(2)
(3)
(4)
(5)
𝜏𝜏 (𝜆𝜆)⋅𝜏𝜏 (𝜆𝜆)
1 2
𝜏𝜏(𝜆𝜆) =
′
1−𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)
(1)
𝜏𝜏 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)
1 2
𝜌𝜌(𝜆𝜆) =𝜌𝜌 (𝜆𝜆) + (2)
′
1−𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)
2 ′
𝜏𝜏 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)
2 1
𝜌𝜌′(𝜆𝜆) =𝜌𝜌′ (𝜆𝜆) + (3)
2 ′
1−𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)
′
𝜏𝜏 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)⋅𝛼𝛼 (𝜆𝜆)
1 2 1
𝑇𝑇
𝛼𝛼 (𝜆𝜆) =𝛼𝛼 (𝜆𝜆) +
1 1
′
1−𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)
(4)
𝜏𝜏 (𝜆𝜆)⋅𝛼𝛼 (𝜆𝜆)
1 2
𝑇𝑇
𝛼𝛼 (𝜆𝜆) =
′
1−𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)
(5)
where
𝜏𝜏(𝜆𝜆) is the spectral transmittance of the double glazing;
𝜌𝜌(𝜆𝜆) is the spectral reflectance of the double glazing for external incident radiation;
′
𝜌𝜌 (𝜆𝜆) is the spectral reflectance of the double glazing for internal incident radiation;
𝑇𝑇
𝛼𝛼 (𝜆𝜆) is the spectral absorptance of the first (outer) pane in the double glazing for external
incident radiation;
𝑇𝑇
is the spectral absorptance of the second (inner) pane in the double glazing for external
𝛼𝛼 (𝜆𝜆)
incident radiation;
𝜏𝜏 (𝜆𝜆) is the spectral transmittance of the first (outer) pane;
© ISO #### 2026 – All rights reserved
ISO/DIS FDIS 9050:20252026(en)
𝜌𝜌 (𝜆𝜆) is the spectral reflectance of the first (outer) pane, measured in the direction of incident
radiation;
′
𝜌𝜌 (𝜆𝜆) is the spectral reflectance of the first (outer) pane, measured in the direction opposite to the
incident radiation;
𝜏𝜏 (𝜆𝜆) is the spectral transmittance of the second pane;
𝜌𝜌 (𝜆𝜆) is the spectral reflectance of the second pane, measured in the direction of the incident
radiation;
′
𝜌𝜌 (𝜆𝜆) is the spectral reflectance of the second pane, measured in the direction opposite to the
incident radiation;
𝛼𝛼 (𝜆𝜆) is the spectral direct absorptance of the outer pane, measured in the direction of the incident
radiation, given by Formula (6)Formula (6)::
𝛼𝛼 (𝜆𝜆) = 1−𝜏𝜏 (𝜆𝜆)−𝜌𝜌 (𝜆𝜆) (6)
1 1 1
′
𝛼𝛼 (𝜆𝜆) is the spectral direct absorptance of the outer pane, measured in the opposite direction to the
incident radiation, given by Formula (7)Formula (7)::
(7)
′ ′
𝛼𝛼 (𝜆𝜆) = 1−𝜏𝜏 (𝜆𝜆)−𝜌𝜌 (𝜆𝜆) (7)
1 1 1
𝛼𝛼 (𝜆𝜆) is the spectral direct absorptance of the second pane, measured in the direction of the incident
radiation, given by Formula (8)Formula (8)::
𝛼𝛼 (𝜆𝜆) = 1−𝜏𝜏 (𝜆𝜆)−𝜌𝜌 (𝜆𝜆) (8)
2 2 2
The above is illustrated in Figure 1Figure 1.

Key
1 pane 1
2 cavity
3 pane 2
1 pane 1
2 cavity
3 pane 2
Figure 1— Transmittance and reflectance in a double glazing insulating glass unit
For triple glazing, Formulae (9)Formulae (9) to (14)(14) apply.
(9)
(10)
(11)
(12)
(13)
(14)
𝜏𝜏 (𝜆𝜆)⋅𝜏𝜏 (𝜆𝜆)⋅𝜏𝜏 (𝜆𝜆)
1 2 3
𝜏𝜏(𝜆𝜆) = (9)
′ ′ 2 ′
[1−𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)]⋅[1−𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)]−𝜏𝜏 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)
1 2 2 3 2 1 3
2 ′ 2 2
𝜏𝜏 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)⋅ [1−𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)] +𝜏𝜏 (𝜆𝜆)⋅𝜏𝜏 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)
1 2 2 3 1 2 3
𝜌𝜌(𝜆𝜆) =𝜌𝜌 (𝜆𝜆) +
′ ′ 2 ′
[1−𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)]⋅ [1−𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)]−𝜏𝜏 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)
2 3 3
1 2 2 1
(10)
2 ′ ′ 2 2 ′
𝜏𝜏 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)⋅[1−𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)]+𝜏𝜏 (𝜆𝜆)⋅𝜏𝜏 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)
3 2 1 2 3 2 1
′ ′
𝜌𝜌 (𝜆𝜆) =𝜌𝜌 (𝜆𝜆) + (11)
′ ′ 2 ′
[1−𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)]⋅[1−𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)]−𝜏𝜏 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)
2 3 3
1 2 2 1
′ ′ 2 ′
𝜏𝜏 (𝜆𝜆)⋅𝛼𝛼 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)⋅[1−𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)]+𝜏𝜏 (𝜆𝜆)⋅𝜏𝜏 (𝜆𝜆)⋅𝛼𝛼 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)
1 1 2 2 3 1 2 1 3
𝑇𝑇
𝛼𝛼 (𝜆𝜆) =𝛼𝛼 (𝜆𝜆) + (12)
1 1
′ ′ 2 ′
[1−𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)]⋅[1−𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)]−𝜏𝜏 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)
2 3 3
1 2 2 1
′ ′
𝜏𝜏 (𝜆𝜆)⋅𝛼𝛼 (𝜆𝜆)⋅[1−𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)]+𝜏𝜏 (𝜆𝜆)⋅𝜏𝜏 (𝜆𝜆)⋅𝛼𝛼 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)
1 2 2 3 1 2 2 3
𝑇𝑇
𝛼𝛼 (𝜆𝜆) = (13)
2 ′ ′ 2 ′
[1−𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)]⋅[1−𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)]−𝜏𝜏 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)
2 3 3
1 2 2 1
𝜏𝜏 (𝜆𝜆)⋅𝜏𝜏 (𝜆𝜆)⋅𝛼𝛼 (𝜆𝜆)
1 2 3
𝑇𝑇
𝛼𝛼 (𝜆𝜆) =
′ ′ 2 ′
[1−𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)]⋅ [1−𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)]−𝜏𝜏 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)⋅𝜌𝜌 (𝜆𝜆)
2 3 3
1 2 2 1
(14)
where
𝜏𝜏(𝜆𝜆) is the spectral transmittance of the triple glazing;
𝜌𝜌(𝜆𝜆) is the spectral reflectance of the triple glazing for external incident radiation;
′
𝜌𝜌 (𝜆𝜆) is the spectral reflectance of the triple glazing for internal incident radiation;
𝑇𝑇
𝛼𝛼 (𝜆𝜆) is the spectral absorptance of the first (outer) pane in the triple glazing for external incident
radiation;
𝑇𝑇
is the spectral absorptance of the second (middle) pane in the triple glazing for external
𝛼𝛼 (𝜆𝜆)
incident radiation;
𝑇𝑇
is the spectral absorptance of the third (inner) pane in the triple glazing for external incident
𝛼𝛼 (𝜆𝜆)
radiation;
© ISO #### 2026 – All rights reserved
ISO/DIS FDIS 9050:20252026(en)
′ ′ ′
, , , , , , , 𝜏𝜏 (𝜆𝜆), 𝜌𝜌 (𝜆𝜆), 𝜌𝜌 (𝜆𝜆), 𝜏𝜏 (𝜆𝜆), 𝜌𝜌 (𝜆𝜆), 𝜌𝜌 (𝜆𝜆), 𝛼𝛼 (𝜆𝜆), 𝛼𝛼 (𝜆𝜆) and 𝛼𝛼 (𝜆𝜆) are explained in
1 1 2 2 1 2
1 2 1
Formula (1)Formula (1) to Formula (5)Formula (5);;
𝜏𝜏 (𝜆𝜆) is the spectral transmittance of the third pane;
𝜌𝜌 (𝜆𝜆) is the spectral reflectance of the third pane, measured in the direction of the incident radiation;
′
𝜌𝜌 (𝜆𝜆) is the spectral reflectance of the third pane, measured in the direction opposite to the incident
radiation;
′
𝛼𝛼 (𝜆𝜆) is the spectral direct absorptance of the second pane, measured in the opposite direction to the
incident radiation, given by Formula (15)Formula (15)::
′ ′
𝛼𝛼 (𝜆𝜆) = 1−𝜏𝜏 (𝜆𝜆)−𝜌𝜌 (𝜆𝜆) (15)
2 2 2
𝛼𝛼 (𝜆𝜆) is the spectral direct absorptance of the third pane, measured in the direction of the incident
radiation, given by Formula (16)Formula (16)::
𝛼𝛼 (𝜆𝜆) = 1−𝜏𝜏 (𝜆𝜆)−𝜌𝜌 (𝜆𝜆) (16)
3 3 3
The above is illustrated in Figure 2Figure 2.

Key
1 pane 1 4 cavity 2
2 cavity 1 5 pane 3
3 pane 2
Figure 1 pane 1
2 cavity 1
3 pane 2
4 cavity 2
5 pane 3
Figure 2— Transmittance and reflectance in a triple glazing insulating glass unit
For glazing with more than three components, formulae similar to Formula (1)Formula (1) to
Formula (5)Formula (5) and Formula (9)Formula (9) to Formula (14)Formula (14) are found to calculate
𝜏𝜏(𝜆𝜆) of such glazing from the spectral coefficients of the individual components. As an example, glazing
composed of five components may be treated as follows:
a) a) first consider the first three components as triple glazing and calculate the spectral
characteristics of this combination;
b) b) next, run the same procedure for the next two components as double glazing;
c) c) then calculate 𝜏𝜏(𝜆𝜆) for the five-component glazing, considering it as double glazing consisting
of the preceding triple and double glazing (or, alternatively, the methodology in Annex DAnnex D can be
followed).
NOTE Measurement of light scattering glass products is the subject of a round robin test programme under the
responsibility of International Commission on Glass, Technical Committee 10. The results of this programme are
expected to include suggestions for improvements in measurement and prediction techniques.
5.3 Light transmittance and reflectance
The light transmittance 𝜏𝜏 and reflectance 𝜌𝜌 of the glazing are calculated using Formulae (17)Formulae (17)
v v
and (18)(18)::
(17)
(18)
780nm
∑
𝐷𝐷 ⋅𝜏𝜏(𝜆𝜆)⋅𝑉𝑉(𝜆𝜆)⋅Δ𝜆𝜆
𝜆𝜆=380nm 𝜆𝜆
𝜏𝜏 = (17)
v 780nm
∑ 𝐷𝐷 ⋅𝑉𝑉(𝜆𝜆)⋅Δ𝜆𝜆
𝜆𝜆
𝜆𝜆=380nm
780nm
∑ 𝐷𝐷 ⋅𝜌𝜌(𝜆𝜆)⋅𝑉𝑉(𝜆𝜆)⋅Δ𝜆𝜆
𝜆𝜆
𝜆𝜆=380nm
𝜌𝜌 =
v
780nm
∑ 𝐷𝐷 ⋅𝑉𝑉(𝜆𝜆)⋅Δ𝜆𝜆
𝜆𝜆=380nm 𝜆𝜆
(18)
where
𝐷𝐷 is the relative spectral distribution of illuminant D65 (see Reference [6]);
𝜆𝜆
𝜏𝜏(𝜆𝜆) is the spectral transmittance of the glazing;
𝜌𝜌(𝜆𝜆) is the spectral reflectance of the glazing;
© ISO #### 2026 – All rights reserved
ISO/DIS FDIS 9050:20252026(en)
D is the relative spectral distribution of illuminant D65 (see [6]);

λ
𝑉𝑉(𝜆𝜆)
is
the
spe
ctra
l
lum
ino
us
effi
cien
cy
for
pho
topi
c
visi
on
defi
nin
g
the
sta
nda
rd
obs
erv
er
for
pho
tom
etry
(see
Ref
ere
nce
[6]
τλ is the spectral transmittance of the glazing;
( )
ρλ is the spectral reflectance of the glazing;
( )
V (λ ) is the spectral luminous efficiency for photopic vision defining the standard observer for
photometry (see [6]);
∆λ
is the wavelength interval.
Table 1);
Δ𝜆𝜆 is the wavelength interval.
Table 1 indicates the values for 𝐷𝐷 ⋅𝑉𝑉(𝜆𝜆)⋅Δ𝜆𝜆 for wavelength intervals of 10 nm. The table has been drawn up
𝜆𝜆
in such a way that .∑𝐷𝐷 ⋅𝑉𝑉(𝜆𝜆)⋅Δ𝜆𝜆 = 1.
𝜆𝜆
′
For calculating the internal light reflectance 𝜌𝜌 (𝜆𝜆) is used instead of 𝜌𝜌(𝜆𝜆) in Formula (18)Formula (18).
5.4 Solar direct transmittance, reflectance and absorptance
The solar direct transmittance ,𝜏𝜏 , the solar direct reflectance 𝜌𝜌 and the solar direct absorptance 𝛼𝛼 of the
e e e,𝑗𝑗
glazing isare calculated using Formulae (19)Formulae (19), (20), (20) and (21)(21)::
(19)
(20)
(21)
2500nm
∑ 𝑆𝑆 ⋅𝜏𝜏(𝜆𝜆)⋅Δ𝜆𝜆
𝜆𝜆=300nm 𝜆𝜆
𝜏𝜏 = (19)
e 2500nm
∑ 𝑆𝑆 ⋅Δ𝜆𝜆
𝜆𝜆
𝜆𝜆=300nm
2500nm
∑ 𝑆𝑆 ⋅𝜌𝜌(𝜆𝜆)⋅Δ𝜆𝜆
𝜆𝜆=300nm 𝜆𝜆
𝜌𝜌 = (20)
e 2500nm
∑ 𝑆𝑆 ⋅Δ𝜆𝜆
𝜆𝜆
𝜆𝜆=300nm
2500nm 𝑇𝑇
∑ 𝑆𝑆 ⋅𝛼𝛼 (𝜆𝜆)⋅Δ𝜆𝜆
𝜆𝜆
𝜆𝜆=300nm 𝑗𝑗
𝛼𝛼 = (21)
e,𝑗𝑗 2500nm
∑ 𝑆𝑆 ⋅Δ𝜆𝜆
𝜆𝜆
𝜆𝜆=300nm
where
𝑆𝑆 is the relative spectral distribution of the solar radiation (see Table 2
𝜆𝜆
S is the relative spectral distribution of the solar radiation (see Table 2);
λ
τλ( ) is the spectral transmittance of the glazing;
ρλ( ) is the spectral reflectance of the glazing;
th
T
is the spectral absorptance of the j pane from the outside in the glazing consisting of n
αλ( )
j
glass panes;
∆λ
is the wavelength interval.
);
𝜏𝜏(𝜆𝜆) is the spectral transmittance of the glazing;
𝜌𝜌(𝜆𝜆) is the spectral reflectance of the glazing;
𝑇𝑇
th
𝛼𝛼 (𝜆𝜆) is the spectral absorptance of the j pane from the outside in the glazing consisting of n glass
𝑗𝑗
panes;
Δ𝜆𝜆 is the wavelength interval.
In the case of multiple glazing, the spectral transmittance ,𝜏𝜏(𝜆𝜆), the spectral reflectance 𝜌𝜌(𝜆𝜆) and the spectral
𝑇𝑇
absorptance 𝛼𝛼 (𝜆𝜆) are calculated in accordance with 5.25.2.
𝑗𝑗
The relative spectral distribution, ,𝑆𝑆 , used to calculate the solar direct transmittance is derived from
𝜆𝜆
[7] [7]
CIE 85 . . The corresponding values 𝑆𝑆Δ𝜆𝜆 are given in Table 2Table 2. The table was drawn up in such a way
𝜆𝜆
that .∑𝑆𝑆Δ𝜆𝜆 = 1.
𝜆𝜆
1 [16] [16]
NOTE 1 For measurements previously undertaken in accordance with ISO 9050:2003, Table 2 ,, where there is
no transmittance or reflectance data at a given wavelength in Table 2Table 2 of this document, the missing values can be
obtained by linear interpolation.
© ISO #### 2026 – All rights reserved
ISO/DIS FDIS 9050:20252026(en)
NOTE 2 Contrary to real situations, it is always assumed, for simplification, that the spectral distribution of the solar
radiation (see Table 2Table 2)) is not dependent upon atmospheric conditions (e.g. dust, mist, moisture content) and that
the solar radiation strikes the glazing as a collimated beam and at normal incidence. The resulting errors are very small.
5.5 Total solar energy transmittance
5.5.1 Calculation
The total solar energy transmittance g is calculated, as given in Formula (22)Formula (22),, as the sum of the
solar direct transmittance 𝜏𝜏 and the secondary heat transfer factor 𝑞𝑞 of the glazing towards the inside (see
e i
5.45.4 and 5.5.35.5.3),), the latter resulting from heat transfer by convection and longwave IR-radiation of that
part of the incident solar radiation which has been absorbed by the glazing:
𝑔𝑔 =𝜏𝜏 +𝑞𝑞 (22)
e i
5.5.2 Division of incident solar radiant flux
The incident solar radiant flux 𝛷𝛷 is divided into the following three parts (see Figure 3Figure 3):):
e
a) a) the transmitted part, ;𝜏𝜏𝛷𝛷 ;
e e
b) b) the reflected part, ;𝜌𝜌𝛷𝛷 ;
e e
c) c) the absorbed part, ;𝛼𝛼𝛷𝛷 ;
e e
where
𝜏𝜏 is the solar direct transmittance (see 5.45.4););
e
𝜌𝜌 is the solar direct reflectance (see 5.45.4););
e
𝛼𝛼 is the solar direct absorptance (see 5.45.4),), given by Formula (23)Formula (23).
e
𝑛𝑛
𝛼𝛼 =∑ 𝛼𝛼 (23)
e 𝑗𝑗=1 e,𝑗𝑗
Key
1 outer pane
2 inner pane
3 unit incident radiant flux
1 outer pane
2 inner pane
3 unit incident radiant flux
Figure 3— Example of division of the incident radiant flux
The relation between the three characteristics is given by Formula (24)Formula (24)::
𝜏𝜏 +𝜌𝜌 +𝛼𝛼 = 1 (24)
e e e
The absorbed part 𝛼𝛼𝛷𝛷 is subsequently split into two parts 𝑞𝑞𝛷𝛷 and 𝑞𝑞𝛷𝛷 which are energy transferred to the
e e i e e e
inside and outside respectively, as in Formula (25)Formula (25)::
𝛼𝛼 =𝑞𝑞 +𝑞𝑞 (25)
e i e
where
is the secondary heat transfer factor of the glazing towards the inside;
q
i
q is the secondary heat transfer factor of the glazing towards the outside.

e
𝑞𝑞 is the secondary heat transfer factor of the glazing towards the inside;
i
𝑞𝑞 is the secondary heat transfer factor of the glazing towards the outside.
e
5.5.3 Secondary heat transfer factor towards the inside
5.5.3.1 Boundary conditions
For the calculation of the secondary heat transfer factor towards the inside, ,𝑞𝑞 , the heat transfer coefficients
i
of the glazing towards the outside, ,ℎ , and towards the inside, ℎ are needed. These values mainly depend on
e i
© ISO #### 2026 – All rights reserved
ISO/DIS FDIS 9050:20252026(en)
the position of the glazing, wind velocity, inside and outside temperatures, and furthermore on the
temperature of the two external glazing surfaces.
As the purpose of this document is to provide basic information on the performance of glazing, conventional
conditions have been stated for simplicity:
a) a) position of the glazing: vertical;
b) b) outside surface: wind velocity: approximately 4 m/s, corrected emissivity = 0,837;
c) c) inside surface: natural convection, emissivity optional;
d) d) air spaces are unventilated.
Under these conventional, average conditions, ℎ is 25 W/(m .∙K) and standard values for ℎ shall be obtained
e i
using Formula (26)Formula (26)::
ℎ =ℎ +ℎ (26)
i r c
where
h is the internal radiative heat transfer coefficient;
r
h is the internal convective heat transfer coefficient.
c
ℎ is the internal radiative heat transfer coefficient;
r
ℎ is the internal convective heat transfer coefficient.
c
For the purposes of this document, the internal radiative heat transfer coefficient for uncoated soda lime glass
surfaces is 4,8 W/(m⋅K), rounded to one decimal place.
If the internal surface of the glass has a lower emissivity the internal radiative heat transfer coefficient is given
by Formula (27)Formula (27)::
ℎ = 4⋅𝜀𝜀⋅𝜎𝜎⋅𝑇𝑇 (27)
r s
where
ε
is the corrected emissivity of the coated surface;
−8 2 4
σ
is Stefan-Boltzmann’s constant, 5,67 × 10 W/(m ·K );
T is the mean temperature of the internal surface of the glass (K).
s
𝜀𝜀 is the corrected emissivity of the coated surface;
−8 2 4
𝜎𝜎 is Stefan-Boltzmann’s constant, 5,67 × 10 W/(m ·K );
𝑇𝑇 is the mean temperature of the internal surface of the glass (K).
s
This is only applicable if there is no condensation on the coated surface. A procedure for determining the
corrected emissivity of a coating is given in ISO 20589.
A value of 293,15 K can be assumed for T in Formula (27)Formula (27),,
s
The value of ℎ is 2,5 W/(m ·K) for free convection for horizontal heat flow.
c
For vertical soda lime glass surfaces and free convection, Formula (28)Formula (28) applies:
ℎ = 4,8 + 2,5 = 7,3 (28)
𝑖𝑖
which is standardized for the purposes of comparison of U values.
For uncoated soda lime silicate glass, 𝜀𝜀 = 0,837 and ℎ = 7,3𝑊𝑊/(𝑚𝑚 ⋅𝐾𝐾)
𝑖𝑖
With reasonable confidence the same value can be used for uncoated borosilicate glass, alkaline earth silicate
glass, alumino silicate glass and glass ceramics.
The corrected emissivity shall be defined and measured in accordance with ISO 20589.
5.5.3.2 Single glazing
The secondary internal heat transfer factor, ,𝑞𝑞 , of single glazing is calculated using
i
Formula (29)Formula (29)::
ℎ
i
𝑞𝑞 =𝛼𝛼 ⋅ (29)
i e
ℎ+ℎ
e i
where
𝛼𝛼 is the solar direct absorptance in accordance with 5.4;
e
ℎ and ℎ are the heat transfer coefficients towards the outside and inside respectively in accordance
e i
with 5.5.3.1
α is the solar direct absorptance in accordance with 5.4;
e
h and h are the heat transfer coefficients towards the outside and inside respectively in
e i
accordance with 5.5.3.1.
.
5.5.3.3 Double glazing
The secondary internal heat transfer factor, ,𝑞𝑞 , of double glazing is calculated using
i
Formula (30)Formula (30)::
(30)
𝛼𝛼 +𝛼𝛼 𝛼𝛼
e,1 e,2 e,2
[ + ]
ℎ 𝛬𝛬
e
𝑞𝑞 = (30)
i 1 1 1
[ + + ]
ℎ ℎ 𝛬𝛬
i e
where
ℎ and ℎ are the heat transfer coefficients towards the outside and inside respectively in accordance
e i
with 5.5.3.1;
𝛼𝛼 is the solar direct absorptance of the outer pane within the double glazing in accordance with
e,1
5.4;
𝛼𝛼 is the solar direct absorptance of the second pane within the double glazing in accordance with
e,2
5.4;
𝛬𝛬 is the thermal conductance between the outer surface and the innermost surface of the double
glazing (see Figure 4
h and h are the heat transfer coefficients towards the outside and inside respectively in
e i
accordance with 5.5.3.1;
© ISO #### 2026 – All rights reserved
ISO/DIS FDIS 9050:20252026(en)
α is the solar direct absorptance of the outer pane within the double glazing in accordance
e,1
with 5.4;
α is the solar direct absorptance of the second pane within the double glazing in
e,2
accordance with 5.4;
Λ
is the thermal conductance between the outer surface and the innermost surface of the
double glazing (see Figure 4).
).
The thermal conductance 𝛬𝛬 shall be determined by the calculation method in accordance with ISO 10292.
Where this is not possible, it shall be determined by measurement in accordance with ISO 10291 or ISO 10293.

Key
1 pane 1
2 pane 2
3 outside
4 inside
1 pane 1
2 pane 2
3 outside
4 inside
Figure 4— Illustration of the meaning of thermal conductance Λ
5.5.3.4 Triple glazing
The secondary internal heat transfer factor of triple glazing, ,𝑞𝑞 , is calculated using Formula (31)Formula (31)::
i
(31)
𝛼𝛼 𝛼𝛼 +𝛼𝛼 𝛼𝛼 +𝛼𝛼 +𝛼𝛼
e,3 e,3 e,2 e,3 e,2 e,1
[ + + ]
𝛬𝛬 𝛬𝛬 ℎ
23 12 e
𝑞𝑞 = (31)
1 1 1 1
i
[ + + + ]
ℎ ℎ 𝛬𝛬 𝛬𝛬
e 12 23
i
where
𝛼𝛼 is the solar direct absorptance of the outer pane within the triple glazing in accordance with
e,1
5.4;
𝛼𝛼 is the solar direct absorptance of the second pane within the triple glazing in accordance with
e,2
5.4;
𝛼𝛼 is the solar direct absorptance of the third pane within the triple glazing in accordance with
e,3
5.4;
ℎ and ℎ are the heat transfer coefficients towards the outside and inside respectively in accordance
e i
with 5.5.3.1;
𝛬𝛬 is the thermal conductance between the outer surface of the first pane and the centre of the
second pane (see Figure 5);
𝛬𝛬 is the thermal conductance between the centre of the second pane and the innermost surface
of the third pane (see Figure 5
is the solar direct absorptance of the outer pane within the triple glazing in accordance
α
e,1
with 5.4;
is the solar direct absorptance of the second pane within the triple glazing in accordance
α
e,2
with 5.4;
is the solar direct absorptance of the third pane within the triple glazing in accordance
α
e,3
with 5.4;
are the heat transfer coefficients towards the outside and inside respectively in
h and h
e i
accordance with 5.5.3.1;
is the thermal conductance between the outer surface of the first pane and the centre of
Λ
the second pane (see Figure 5);
Λ is the thermal conductance between the centre of the second pane and the innermost
surface of the third pane (see Figure 5).
).
The thermal conductances 𝛬𝛬 and 𝛬𝛬 are determined in accordance with 5.5.3.35.5.3.3.
12 23
© ISO #### 2026 – All rights reserved
ISO/DIS FDIS 9050:20252026(en)

Key
1 pane 1
2 pane 2
3 pane 3
4 outside
5 inside
1 pane 1
2 pane 2
3 pane 3
4 outside
5 inside
Figure 5— Illustration of the meaning of the thermal conductances Λ and Λ
12 23
5.5.3.5 Quadruple glazing
The secondary internal heat transfer factor of quadruple glazing can be determined by reference to the g value
calculation in Annex DAnnex D.
5.6 Shading coefficient
The shading coefficient, SC, is given as the total solar energy transmittance of the glazing, divided by the total
solar energy transmittance of 3 mm or 4 mm clear float.
NOTE 1 In some countries, SC can be specifically referred to as total shading coefficient.
NOTE 2 The value of the total solar energy transmittance of a clear float glass of 3 mm to 4 mm nominal thickness is
traditionally assumed as 0,87.
The value that is actually used as the total solar energy transmittance for the clear float glass pane should be
stated.
5.7 UV transmittance
A standard relative spectral distribution for the UV part of the global solar radiation, ,𝑈𝑈 , is given (see,
𝜆𝜆
Reference 8[8]). Table 3). Table 3 gives the values of 𝑈𝑈 ⋅𝛥𝛥𝜆𝜆 for wavelength intervals of 5 nm in the UV range.
𝜆𝜆
The table has been drawn up with relative values in such a way that ∑𝑈𝑈 ⋅𝛥𝛥𝜆𝜆 = 1 for the total UV range.
𝜆𝜆
The UV-transmittance 𝜏𝜏 is calculated using Formula (32)Formula (32)::
uv
(32)
...