prEN ISO 9488

Solar energy - Vocabulary (ISO/DIS 9488:2020)

Sonnenenergie - Vokabular (ISO/DIS 9488:2020)

Diese Internationale Norm definiert grundlegende Begriffe im Bereich der Sonnenenergie.

Énergie solaire - Vocabulaire (ISO/DIS 9488:2020)

Sončna energija - Slovar (ISO/DIS 9488:2020)

General Information

• Status: Not Published
• ICS: 01.040.27 - Energy and heat transfer engineering (Vocabularies)
• ICS: 01.040.71 - Chemical technology (Vocabularies)
• ICS: 27.160 - Solar energy engineering
• Technical Committee: CEN/TC 312 - Thermal solar systems and components
• Current Stage: 4599 - Dispatch of FV draft to CMC - Finalization for Vote
• Due Date: 27-Jul-2021
• Completion Date: 27-Jul-2021
• Ref Project: oSIST prEN ISO 9488:2020 - Solar energy - Vocabulary (ISO/DIS 9488:2020)

RELATIONS

• Revised: EN ISO 9488:1999 - Solar energy - Vocabulary (ISO 9488:1999)
• Effective Date: 21-Nov-2017

Standards Content (sample)

SLOVENSKI STANDARD
oSIST prEN ISO 9488:2020
01-september-2020
Sončna energija - Slovar (ISO/DIS 9488:2020)
Solar energy - Vocabulary (ISO/DIS 9488:2020)
Sonnenenergie - Vokabular (ISO/DIS 9488:2020)
Énergie solaire - Vocabulaire (ISO/DIS 9488:2020)
Ta slovenski standard je istoveten z: prEN ISO 9488
ICS:
01.040.27 Prenos energije in toplote Energy and heat transfer
(Slovarji) engineering (Vocabularies)
27.160 Sončna energija Solar energy engineering
oSIST prEN ISO 9488:2020 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST prEN ISO 9488:2020
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oSIST prEN ISO 9488:2020
DRAFT INTERNATIONAL STANDARD
ISO/DIS 9488
ISO/TC 180 Secretariat: SA
Voting begins on: Voting terminates on:
2020-07-08 2020-09-30
Solar energy — Vocabulary
Énergie solaire — Vocabulaire
ICS: 27.160; 01.040.27
THIS DOCUMENT IS A DRAFT CIRCULATED
This document is circulated as received from the committee secretariat.
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
ISO/CEN PARALLEL PROCESSING
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 9488:2020(E)
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. ISO 2020
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oSIST prEN ISO 9488:2020
ISO/DIS 9488:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

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.
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Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

3.1 Terms for solar geometry .............................................................................................................................................................. 1

3.2 Radiation terms and quantities ................................................................................................................................................ 3

3.3 Radiation measurement .................................................................................................................................................................. 9

3.4 Radiation properties and processes ..................................................................................................................................10

3.5 Indoor and outdoor climates ...................................................................................................................................................11

3.6 Collector types ......................................................................................................................................................................................11

3.7 Collector components and related quantities ...........................................................................................................13

3.8 Types of solar heating systems ..............................................................................................................................................20

3.9 System components and related quantities (other than collectors) .....................................................21

3.10 Non-solar-specific terms .............................................................................................................................................................23

Bibliography .............................................................................................................................................................................................................................25

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Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation 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 180, Solar energy.

This second edition cancels and replaces the first edition (ISO 9488:1999), which has been technically

revised.
The main changes compared to the previous edition are as follows:
— update of definitions

— addition of several new terms, according to the development of new standards for solar thermal

technology in the past two decades.

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 2020 – All rights reserved
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DRAFT INTERNATIONAL STANDARD ISO/DIS 9488:2020(E)
Solar energy — Vocabulary
1 Scope
This International Standard defines basic terms relating to solar energy.
2 Normative references
There are no normative references in this document.
3 Terms and definitions

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1 Terms for solar geometry
3.1.1
aphelion
point in the Earth's orbit at which it is furthest from the sun

Note 1 to entry: At the aphelion, the Earth is approximately 152 X 10 km from the Sun.

3.1.2
perihelion
point in the Earth's orbit at which it is closest to the sun

Note 1 to entry: At the perihelion, the Earth is approximately 147 x 10 km from the sun.

3.1.3
solar declination

angle subtended between the Earth-sun line and the plane of the equator (north positive)

Note 1 to entry: The solar declination is zero on equinox dates, varying between +23.45 ° (June 22) and -23.45 °

(December 22).
3.1.4
solar azimuth angle
solar azimuth

projected angle between a straight line from the apparent position of the sun to the point of observation

and due north, measured clockwise, using the projections on the local horizontal plane

Note 1 to entry: This is the same definition as the one of the geographical azimuth. It is valid over the whole globe.

3.1.5
zenith
point vertically above the observer
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3.1.6
solar zenith angle
angular distance of the sun from the vertical
3.1.7
solar altitude angle
solar elevation angle
complement of the solar zenith angle
h = 90° - θ
3.1.8
solar hour angle

angle between the sun projection on the equatorial plane at a given time and the sun projection on the

same plane at solar noon

Note 1 to entry: The solar hour angle changes by approximately 360° within 24 h (approximately 15° per hour).

This angle is negative for morning hours and positive for afternoon hours, i.e. ω (in degrees) ≈ 15 (Hr-12) where

Hr is the solar time in hours.
3.1.9
solar noon
local time of day at which the sun crosses the observer's meridian.
3.1.10
solar time

hour of the day as determined by the apparent angular motion of the sun across the sky, with solar noon

as the reference point for 12:00 h

Note 1 to entry: Solar time = standard time + 4 (L - L ) + E, where L is the longitude of the standard meridian

st loc st

for the local time zone, L is the longitude of the location in question and E is the equation of time, which takes

loc

into account the perturbations in the Earth's rate of rotation around the sun that affect the time at which the sun

crosses the observer's meridian. The correction 4 (L - L ) + E is expressed in minutes. An additional correction

st loc
is needed if the standard time is a daylight saving time.
3.1.11
angle of incidence
incidence angle

angle between the line joining the centre of the solar disc to a point on an irradiated surface and the

outward normal to the irradiated surface
3.1.12
solar tracker
sun tracker

power-driven or manually operated movable support which may be employed to keep a device oriented

with respect to the sun
3.1.13
equatorial tracker
sun-following device having an axis of rotation parallel to the Earth's axis

Note 1 to entry: The parameters of motion are the hour angle and the declination of the sun.

3.1.14
altazimuth tracker

sun-following device which uses the solar elevation angle and the azimuth angle of the sun as

coordinates of movement
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3.1.15
sun-path diagram

graphic representation of solar altitude versus solar azimuth, showing the position of the Sun as a

function of time for various dates of the year

Note 1 to entry: If solar time is used, the diagram is valid for all locations of the same latitude.

3.1.16
heliodon

solar-angle simulator for conducting shading assessments on buildings or collector arrays, usually

having a model table which tilts for the latitude and rotates for the hour of day, and a lamp to represent

the sun, mounted at some distance away on a vertical rail, allowing adjustment for declination

3.1.17
solarscope

device similar to a heliodon, but having a fixed horizontal model table and a light source movable to any

solar altitude and azimuth
3.2 Radiation terms and quantities
3.2.1
radiation
transfer of energy in the form of electromagnetic waves
[SOURCE: WMO R0260]

Note 1 to entry: Radiation can also be used to refer to multiple quantities used to describe the process called

radiation. For example, radiation could mean energy or irradiance.
[SOURCE: WMO CIMO Guide, 2017]
3.2.2
radiant energy
quantity of energy transferred by radiation
[SOURCE: WMO R0200]
3.2.3
radiant flux
radiation flux
flux of radiation [SOURCE: WMO R0230]
power emitted, transferred or received in the form of radiation
[SOURCE: ISO 31-6]
3.2.4
radiance

radiant power emitted, transmitted, reflected or received by a given surface, per unit solid angle per

unit projected area.
−2 −1

Note 1 to entry: Radiance is expressed in watts per square metre per steradian (W·m ·sr ).

3.2.5
irradiance

Quotient of the radiant flux incident on the surface and the area of that surface, or the rate at which

radiant energy is incident on a surface, per unit area of that surface
Note 1 to entry: Irradiance is expressed in watts per square metre (W∙m ).
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3.2.6
irradiation
DEPRECATED: insolation

incident energy per unit area of a surface, found by integration of irradiance over a specified time

interval.
3.2.7
radiant exitance

at a point on a surface, the radiant flux leaving the element of the surface, divided by the area of

that element
[SOURCE: ISO 31-6]
Note 1 to entry: Formerly called radiant emittance.

Note 2 to entry: The radiant energy may leave the surface by emission, reflection and/or transmission.

3.2.8
ultraviolet radiation
electromagnetic radiation of wavelength in the range of 10 nm to 400 nm

Note 1 to entry: UVA radiation has a wave-length range of 315 nm to 400 nm; UVB radiation has a wavelength

range of 280 nm to 315 nm; UVC radiation (wavelength range 280 nm to X-rays) cannot be detected by solar

energy technologies.
3.2.9
visible radiation
light
electromagnetic radiation of wavelengths causing visual sensations for humans

Note 1 to entry: Visible radiation is generally accepted to be within the wavelength band of 380 nm to 780 nm

3.2.10
infrared radiation

electromagnetic radiation of wavelengths longer than those of visible radiation and shorter than

about 1 mm
3.2.11
shortwave radiation
radiation of wavelength shorter than 3 μm but longer than 280 nm
3.2.12
longwave radiation

radiation of wavelength greater than 3 μm, typically originating from sources at terrestrial

temperatures

Note 1 to entry: Examples of sources of longwave radiation are clouds, atmosphere, ground and terrestrial

objects.
Note 2 to entry: Sometimes is called thermal radiation.
3.2.13
solar radiation
DEPRECATED: shortwave radiation
DEPRECATED: insolation
radiation emitted by the sun
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3.2.14
solar energy
energy emitted by the sun in the form of electromagnetic energy

Note 1 to entry: Solar energy is primarily in the wavelength region from 0,3 μm to 3,0 μm.

Note 2 to entry: Solar energy is generally understood to mean any energy made available by the capture and

conversion of solar radiation.
3.2.15
solar flux
radiant flux originating from the sun
3.2.16
solar spectrum

distribution by wavelength (or frequency) of electromagnetic radiation emitted from the sun

3.2.17
direct radiation
direct solar radiation
beam radiation
beam solar radiation

radiation incident on a given plane, and originating from a small solid angle centred on the sun's disk

Note 1 to entry: In general, direct solar radiation is measured by instruments with field-of-view angles of up to

6°. Therefore, a part of the scattered radiation around the sun's disk (circumsolar radiation) is included, as the

solar disk itself has a field-of-view angle of about 0,5°.
Note 2 to entry: Direct radiation is usually measured at normal incidence.

Note 3 to entry: Approximately from 97 to 99% of the direct solar radiation received at the ground is contained

within the wavelength range from 0,3 μm to 3 μm [SOURCE: Reference [1] ].

Note 4 to entry: Further details on circumsolar radiation and its role for direct radiation are provided in circumsolar

radiation, circumsolar irradiance, circumsolar contribution, sunshape and direct solar irradiance.

3.2.18
circumsolar radiation

radiation scattered by the atmosphere so that it appears to originate from an area of the sky immediately

adjacent to the sun
Note 1 to entry: Circumsolar radiation causes the solar aureole.

Note 2 to entry: Further details on circumsolar radiation and its role for direct radiation are provided in circumsolar

irradiance, circumsolar contribution, sunshape and direct solar irradiance
3.2.19
circumsolar irradiance

quotient of the radiant flux of the circumsolar radiation on a given plane receiver surface to the area of

that surface

Note 1 to entry: If the receiver plane is perpendicular to the axis of the solid angle, the circumsolar irradiance is

called circumsolar normal irradiance. Circumsolar irradiance is usually measured at normal incidence.

3.2.20
circumsolar contribution

contribution of a specific portion of the circumsolar normal irradiance to the direct normal irradiance.

The circumsolar contribution refers to a specific ring-shaped angular region described by an inner and

the outer angular distance from the centre of the sun.

Note 1 to entry: If the inner angle describing this angular region is the half-angle of the sun disk the circumsolar

contribution is also called circumsolar ratio.
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Note 2 to entry: Depending on the circumsolar irradiance measurement instrument or the solar technology

involved, different wavelength ranges are included. In order to describe circumsolar irradiance correctly, the

wavelength range or the spectral response of the instrument or the involved technology has to be specified.

3.2.21
sunshape

azimuthal average radiance profile as a function of the angular distance from the centre of the sun,

normalized to 1 at the centre of the sun and considering the wavelength range of shortwave radiation.

3.2.22
hemispherical radiation
hemispherical solar radiation
solar radiation received by a plane surface from a solid angle of 2π sr

Note 1 to entry: The tilt angle and the azimuth of the surface should be specified, e.g. horizontal.

Note 2 to entry: Hemispherical solar radiation is composed of direct solar radiation and diffuse solar radiation

(solar energy scattered in the atmosphere as well as solar radiation reflected by the ground).

Note 3 to entry: Solar engineers commonly use the term global radiation in place of hemispherical radiation. This

use is a source of confusion if the referenced surface is not horizontal (see global radiation).

Note 4 to entry: Approximately 97 % to 99 % of the hemispherical solar radiation incident at the Earth's surface

is contained within the wavelength range from 0,3 μm to 3 μm [SOURCE: Reference [1]].

3.2.23
global radiation
global solar radiation
hemispherical solar radiation received by a horizontal plane

Note 1 to entry: Approximately 97 % to 99 % of the global solar radiation incident at the Earth’s surface is

contained within the wavelength range from 0,3 μm to 3 μm [SOURCE: Reference [1]].

Note 2 to entry: Solar engineers commonly use the term global radiation in place of hemispherical radiation. This

use is a source of confusion if the referenced surface is not horizontal (see hemispherical radiation).

3.2.24
diffuse radiation
diffuse solar radiation
hemispherical solar radiation minus direct solar radiation

Note 1 to entry: For the purposes of solar energy technology, diffuse radiation includes solar radiation scattered

in the atmosphere as well as solar radiation reflected by the ground, depending on the tilt angle of the receiver

surface.

Note 2 to entry: The tilt angle and the azimuth of the receiver surface should be specified, e.g. horizontal.

3.2.25
atmospheric radiation
DEPRECATED: shortwave sky radiation
longwave radiation emitted by and propagated through the atmosphere
[SOURCE: WMO A2940]
3.2.26
extraterrestrial solar radiation
solar radiation received at the limit of the Earth's atmosphere
[SOURCE: WMO E1370]
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3.2.27
solar constant

solar irradiance outside the Earth's atmosphere on a plane normal to the direction of this radiation,

when the Earth is at its mean distance from the sun (149,5 x 10 km)
-2 -2

Note 1 to entry: Historically the solar constant is considered to be 1 367 W∙m ± 7 W∙m [SOURCE: Reference

[2].]. The new value of 1361.1 W∙m , from the most recent determination of the solar constant, is currently

under consideration [SOURCE: Reference [3].].
3.2.28
direct solar irradiance

quotient of the radiant flux on a given plane receiver surface received from a small solid angle centred

on the sun's disk to the area of that surface

Note 1 to entry: If the plane is perpendicular to the axis of the solid angle, direct normal solar irradiance G is

received.

Note 2 to entry: Direct solar irradiance is expressed in watts per square metre (W∙m ).

Note 3 to entry: Approximately 97% to 99% of the direct solar radiation received at ground level is contained

within the wavelength range from 0,3 µm to 3 µm [SOURCE: Reference [1].]. Depending on the direct irradiance

measurement instrument or the solar technology involved, different wavelength ranges are included. In order

to describe direct irradiance correctly, the wavelength range or the spectral response of the instrument or the

involved technology has to be specified.

Note 4 to entry: In general, direct normal solar irradiance is measured by instruments with field-of-view angles

of up to 6°. The currently recommended instrument design uses 5° field-of-view [SOURCE: WMO CIMO guide

2017]. A part of the scattered radiation around the Sun's disk (circumsolar radiation) is included, as the solar disk

itself has a field-of-view angle of about 0,5°.

Note 5 to entry: In order to describe direct normal solar irradiance accurately, it is necessary to specify how

circumsolar radiation is included in it using the following terms. B is the experimental direct normal irradiance.

BP= ()ξϕ,,Ld()ξϕ coss()ξξin() ξdϕ.
n ∫∫
0 0
where
-2 -1

L(ξ,φ) is the broadband sky radiance - usually expressed in W· m sr - for an element of sky

whose angular position is defined by the angular distance ξ from the centre of the sun disk

and the azimuth angle φ in the sun disk and the circumsolar region;

P(ξ,φ) is the penumbra function of the measurement device that is sometimes also called “accept-

ance function”;

α is the greatest angular distance from the sun disk centre for which radiation is measured

by the instrument.
ideal ideal

In atmospheric radiation transfer models, another parameter is often used: B (α ). B (α ) is the direct

n l n l

normal irradiance up to the angular limit α which in this case mostly corresponds to the sun disk half-angle

ideal

(∼0,27°). B (α ) is calculated as B , the penumbra function being set equal to 1 [see also SOURCE: Reference

n l n
ideal

[4].]. In concentrating solar power plant models B (α ) or B might be used depending on the sunshape data

n l n

applied in the model. The angular limit α also has to fit to the applied sunshape data.

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3.2.29
hemispherical irradiance
hemispherical solar irradiance
DEPRECATED: incident solar radiation intensity
DEPRECATED: instantaneous insolation
DEPRECATED: insolation
DEPRECATED: incident radiant flux density
hem

quotient of the radiant flux on a given plane receiver surface received from a solid angle of 2π sr to the

area of that surface

Note 1 to entry: The tilt angle and the azimuth of the surface should be specified, e.g. horizontal.

Note 2 to entry: Hemispherical irradiance is expressed in watts per square metre (W∙m ).

Note 3 to entry: Examples for hemispherical irradiance are global irradiance and the irradiance received in the

plane of solar collector [Plane of Array (POA) irradiance], also called "global tilted irradiance".

3.2.30
global irradiance
global solar irradiance
hemispherical solar irradiance on a horizontal plane G

Note 1 to entry: Global irradiance is expressed in watts per square metre (W∙m ).

Note 2 to entry: Global irradiance always refers to a horizontal plane. Global irradiance should not be confused

with global tilted irradiance (see hemispherical irradiance, Note 3 to entry).
3.2.31
diffuse solar irradiance
irradiance of diffuse solar radiation on a given plane receiver surface

Note 1 to entry: The tilt angle and the azimuth of the receiving surface should be specified, e.g. horizontal.

Note 2 to entry: Diffuse solar irradiance is expressed in watts per square metre (W∙m ).

3.2.32
spectral solar irradiance
solar irradiance per unit wavelength interval at a given wavelength
-2 -1

Note 1 to entry: Spectral solar irradiance is expressed in watts per square metre per micrometre (W∙m ∙μm ).

3.2.33
isorad

curve, drawn on a map, indicating sites of equal solar irradiation during a given interval of time

3.2.34
isohel

curve, drawn on a map, indicating sites of equal sunshine duration during a given interval of time

3.2.35
sky temperature

equivalent blackbody radiation temperature of the atmospheric longwave radiation received at a

horizontal surface
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3.3 Radiation measurement
3.3.1
World Radiometric Reference
WRR
measurement standard defining the SI unit of total irradiance

Note 1 to entry: See the WMO Guide to Meteorological Instruments and Methods of Observation, 2017, subclause

7.1.2.2 .

Note 2 to entry: The WRR was adopted by the WMO and has been in effect since 1 July 1980.

Note 3 to entry: In order to ensure its long-term stability, the WRR is maintained by a group (known as the World

Standard Group) of at least four pyrheliometers of different design which are under the auspices of the WMO

World Radiation Centre at Davos, in Switzerland.
3.3.2
radiometer
instrument used for measuring radiation

Note 1 to entry: Depending on the construction of the instrument, the readout of the instrument will give either

irradiance or irradiation.
3.3.3
pyrradiometer

radiometer for measuring the overall radiation including shortwave and longwave radiations on a plane

surface from a solid angle of 2π sr

Note 1 to entry: Depending on the construction of the instrument, the readout of the instrument will give either

irradiance or irradiation.
3.3.4
pyranometer

radiometer designed for measuring the solar irradiance on a plane receiver surface

3.3.5
pyrheliometer
DEPRECATED: actinometer

radiometer using a collimated detector for measuring the direct solar irradiance under normal

incidence

Note 1 to entry: Its spectral response should be approximately constant in the wavelength range of 0,3 μm to 3

μm and the acceptance angle is recommended to be 5° [SOURCE: WMO CIMO guide, 2017].

3.3.6
field-of-view angle

full angle of the geometrical cone which is defined by the centre of the pyrheliometer

receiver surface and the border of its aperture
3.3.7
pyrgeometer
radiometer for measuring the longwave irradiance on a plane receiver surface

Note 1 to entry: This spectral range is similar to that of atmospheric longwave radiation and is only nominal. The

spectral response of a pyrgeometer depends largely on the material used for the dome(s) protecting its receiving

surface.
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3.3.8
diffusometer

radiometer designed for measuring the diffuse solar radiation, consisting usually of a pyranometer and

a shading structure which can be a shading ball, a shading disk, a shading ring, a rotating shadowband

or a shading mask.
Note 1 to entry: For details, see ISO 9060 and ISO 9846.
3.4 Radiation properties and processes
3.4.1
absorptance
absorption factor

ratio of the radiant flux absorbed by an element of a surface to that of the incident radiation

Note 1 to entry: The absorptance may apply to either a single wavelength or a wavelength range.

3.4.2
emittance

ratio of radiant exitance of a body to that of a full radiator (blackbody) at the same temperature[SOURCE:

ISO 13731:2001].
Note 1 to
...