IEC 62977-2-2:2020

IEC 62977-2-2 ®
Edition 1.0 2020-09
INTERNATIONAL
STANDARD
colour
inside
Electronic displays –
Part 2-2: Measurements of optical characteristics – Ambient performance
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IEC 62977-2-2 ®
Edition 1.0 2020-09
INTERNATIONAL
STANDARD
colour
inside
Electronic displays –
Part 2-2: Measurements of optical characteristics – Ambient performance

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 31.120; 31.260 ISBN 978-2-8322-8816-0

– 2 – IEC 62977-2-2:2020 © IEC 2020
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 9
2 Normative references . 9
3 Terms, definitions, abbreviated terms and symbols . 9
3.1 Terms and definitions . 9
3.2 Abbreviated terms . 10
3.3 Symbols . 10
4 Standard measuring conditions . 11
4.1 Standard measuring environmental conditions . 11
4.2 Viewing direction and light source coordinate system . 12
4.3 Standard lighting conditions . 12
4.3.1 General . 12
4.3.2 Standard measuring darkroom conditions . 13
4.3.3 Standard ambient illumination . 13
4.3.4 Standard illumination geometries . 14
4.4 Standard setup conditions . 20
4.4.1 General . 20
4.4.2 Adjustment of display . 20
4.4.3 Starting conditions of measurements . 21
4.4.4 General conditions of measuring equipment . 21
4.5 Reflection standards . 22
4.5.1 General . 22
4.5.2 Diffuse reflectance standard . 22
4.6 Locations of measurement field. 23
5 Darkroom luminance and spectra. 23
5.1 General . 23
5.2 Test pattern . 23
5.2.1 General . 23
5.2.2 Simple box test patterns . 23
5.2.3 Multi-colour test pattern . 24
5.2.4 Measuring conditions . 25
5.2.5 Measuring method . 25
6 Reflection measurements . 26
6.1 General . 26
6.2 Measuring conditions . 26
6.3 Measuring the hemispherical diffuse reflectance . 27
6.4 Measuring the reflectance factor for a directed light source. 28
7 Ambient optical performance . 30
7.1 General . 30
7.2 Ambient contrast ratio . 30
7.2.1 General . 30
7.2.2 Measuring conditions . 30
7.2.3 Measuring method . 30
7.3 Ambient display colour . 31

7.3.1 General . 31
7.3.2 Measuring conditions . 31
7.3.3 Measuring method . 31
7.4 Ambient colour gamut volume . 33
7.4.1 General . 33
7.4.2 Measuring conditions . 34
7.4.3 Measuring method . 34
Annex A (normative) RGB boundary colours for CIELAB gamut volume measurements . 37
A.1 General . 37
A.2 Equally-spaced 98 boundary colours on the RGB cube . 37
A.3 Recommended 602 boundary colours on the RGB cube . 40
Annex B (informative) Calculation method for CIELAB gamut volume. 54
B.1 Purpose . 54
B.2 Procedure for calculating the colour gamut volume . 54
B.3 Number of sampled colours . 55
B.4 RGB cube surface subdivision method for CIELAB gamut volume calculation . 55
B.4.1 General . 55
B.4.2 Assumption . 55
B.4.3 Uniform RGB grid algorithm . 55
B.4.4 Software example execution . 57
Bibliography . 67

Figure 1 – Representation of the viewing direction (direction of measurement) and
coordinate system used for light source configuration . 12
Figure 2 – Illustrated examples for directional illumination . 15
Figure 3 – Example of the measuring setup using directional illumination where
θ = 40° and θ = 30° . 16
S R
Figure 4 – Example of ring light illumination measuring setup where θ ± ∆ = 35 ± 5
S
and θ = 20° . 17
R
Figure 5 – Detailed schematic of ring light characteristics . 18
Figure 6 – Example of measurement geometries for hemispherical illumination using
an integrating sphere (left) or sampling sphere (right) . 19
Figure 7 – Layout diagram of measurement setup . 22
Figure 8 – Example of centre box test patterns using the standard 4 % and
10 % area boxes . 24
Figure 9 – Standard medium APL RGBCMYWx test pattern used for centre luminance
and spectra measurements with 25 % APL . 25
Figure 10 – Example of the range in colours produced by a display . 36
Figure B.1 – Analysis flow chart for calculating the CIELAB gamut volume . 54
Figure B.2 – Example of tessellation using 5 × 5 grid of surface colours on the
RGB cube . 57
Figure B.3 – Example of tessellation for the RGB cube using a 3 × 3 grid . 59
Figure B.4 – Example of tessellation for the CIELAB gamut volume using a 3 × 3 grid . 59

Table 1 – Measurement structure from optical quantities to evaluation and to results
(top down) . 8
Table 2 – Summary of symbols . 11
Table 3 – Eigenvalues M and M for CIE daylight Illuminants D50, D65, and D75 . 28
1 2
– 4 – IEC 62977-2-2:2020 © IEC 2020
Table A.1 – Equally-spaced 98 RGB boundary colours used for CIELAB gamut volume
measurements . 38
Table A.2 – Recommended RGB boundary colours used for CIELAB colour gamut

volume measurements . 41
Table B.1 – Example RGB boundary colours used to demonstrate how the CIELAB
colour gamut volume can be calculated . 58

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRONIC DISPLAYS –
Part 2-2: Measurements of optical characteristics –
Ambient performance
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
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patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 62977-2-2 has been prepared by IEC technical committee 110:
Electronic displays.
The text of this International Standard is based on the following documents:
FDIS Report on voting
110/1213/FDIS 110/1232/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 62977 series, published under the general title Electronic displays,
can be found on the IEC website.

– 6 – IEC 62977-2-2:2020 © IEC 2020
Future standards in this series will carry the new general title as cited above. Titles of existing
standards in this series will be updated at the time of the next edition.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
INTRODUCTION
This document describes the common optical measurement methods applicable in the field of
electronic display devices, which overlap with some of the parts of existing documents
developed inside TC 110 (IEC 61747-6-2 [17] , IEC 62341-6-2 [18], IEC 61988-2-2 [19],
IEC 62715-5-1 [20], IEC 62679-3-1 [21]), that describe the optical measurement methods of
the individual technologies, such as LCD, OLED, PDP and others. This document on common
optical measurement methods is intended to be used as the reference document in future
documents and in revisions of existing documents (e.g. IEC 61747-6-2 [17], IEC 62341-6-2
[18], IEC 61988-2-2 [19], IEC 62715-5-1 [20], IEC 62679-3-1 [21]). The existing standards
documents will be revised in their maintenance time and they will refer to this document to the
largest extent.
All documents in IEC TC 110 that are concerned with the measurement of optical properties
of electronic display devices under ambient illumination refer to a set of methods and
procedures that are similar to each other, or sometimes even identical. This document is
intended to identify these methods and to describe them, together with suitable precautions
and diagnostics, as a reference for forthcoming documents to make the work of the involved
experts more efficient and to avoid duplication of efforts.
Introduction of the common optical measurement methods (COMMs) is also related to a
structure where each kind of optical measurement finds its unambiguous position for
identification of similarities to other methods or for clarification of distinctions. This structural
classification together with a general taxonomy is supposed to make the process of
documents production easier, faster and thus more effective.
The above characteristics are summarized in Table 1. The display characteristics that are
addressed in this part of IEC 62977 are indicated by a check mark √ in the table.
_____________
Numbers in square brackets refer to the Bibliography.

– 8 – IEC 62977-2-2:2020 © IEC 2020
Table 1 – Measurement structure from optical quantities
to evaluation and to results (top down)
Test pattern,
Illumination Temperature,
Variables Time Location Direction electrical driving,
conditions humidity
input signal
(x, y) (θ, φ)
Data
sampling Fast Slow Slow Slow Slow √
condition
Evaluation
Results Transitions Temporal Lateral Directional Static pattern, √ Darkroom, √ Standard
from one stability uniformity uniformity environment √
Characteristic Indoor,
optical state (uniformity)
function (electro-
to another
Outdoor
optic transfer
state (for
function, EOTF)
example from
test-pattern-1
Characteristic
to test-
values (e.g.
pattern-2)
threshold,
saturation)
Evaluation Turn-on, Luminance, √
1st order turn-off,
Contrast, √
delay
chromaticity, √
(latency)
time periods,
Threshold,
temporal
saturation values,
modulations
steepness of
transitions, etc.
Evaluation Flicker EOTF from which
2nd order prediction,
the exponent γ is
moving
evaluated
picture
Chromaticity/ colour
response
gamut area,
time, etc.
Colour gamut
volume, √
ELECTRONIC DISPLAYS –
Part 2-2: Measurements of optical characteristics –
Ambient performance
1 Scope
This part of IEC 62977 specifies standard measurement conditions and measuring methods
for determining the optical characteristics of electronic displays under indoor and outdoor
illumination conditions. Standard illumination geometries are specified and the reflection
properties of flat screens are determined under those conditions. Reference illumination
levels and spectra are used to estimate the photometric and colorimetric characteristics of
electronic displays under the same conditions. These methods apply to emissive,
transmissive, and reflective displays, or combinations thereof, that render real 2D images on
a flat screen.
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.
IEC 60050-845, International Electrotechnical Vocabulary (IEV) – Part 845: Lighting
IEC 61966-2-1, Multimedia systems and equipment – Colour measurement and management
– Part 2-1: Colour management – Default RGB colour space – sRGB
ISO/CIE 11664-1, Colorimetry – Part 1: CIE standard colorimetric observers
ISO/CIE 11664-4, Colorimetry – Part 4: CIE 1976 L*a*b* colour space
ISO 15076-1:2010, Image technology colour management – Architecture, profile format and
data structure – Part 1: Based on ICC.1:2010
CIE 15, Colorimetry
CIE 168, Criteria for the evaluation of extended-gamut colour encoding
3 Terms, definitions, abbreviated terms and symbols
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-845 and the
following apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp

– 10 – IEC 62977-2-2:2020 © IEC 2020
3.1.1
signal pixel
smallest encoded picture element in the input image
Note 1 to entry: Signal pixel is defined as the unit of signal resolution.
3.1.2
pre-gamma average picture level
average input level of all signal pixels relative to an equivalent white pixel driven by a digital
RGB input
Note 1 to entry: Unless otherwise stated, the pre-gamma average picture level (APL) will simply be referred to as
average picture level in this document.
Note 2 to entry: The APL will normally be expressed as a percentage, where a full white screen at maximum drive
level would be 100 % APL.
Note 3 to entry: The pre-gamma APL is also called gamma-corrected APL in IEC 62087-2 [14]. In addition, it is
noted that the tone rendering curve may not have a power law function with a well-defined exponent (gamma).
3.1.3
APL loading
influence of average picture level on display performance, for example luminance
3.2 Abbreviated terms
APL pre-gamma average picture level
CCT correlated colour temperature
CIE Commission Internationale de L’Eclairage (International Commission on
Illumination)
CIELAB CIE 1976 (L*a*b*) colour space
DUT device under test
EOTF electro-optic transfer function
FWHM full-width-at-half-maximum
ILU integrated lighting unit (e.g. an edge-lit front guide plate)
LCD liquid crystal display
LED light emitting diode
LMD light measuring device
OLED organic light emitting diode
RGB red, green, and blue
SDR standard dynamic range
sRGB standard RGB colour space defined in IEC 61966-2-1

3.3 Symbols
A list of symbols used in this document is given in Table 2.

Table 2 – Summary of symbols
Symbol Units Definition
E lx illuminance
-2 -1
E(λ) W∙m ∙nm spectral irradiance
-2 -1
E (λ) W∙m ∙nm spectral irradiance from a directed light source at normal incidence
dir
spectral irradiance of a CIE standard illuminant from a directed light
-2 -1
E (λ) W∙m ∙nm
CIE,dir
source at normal incidence
-2 -1
W∙m ∙nm spectral irradiance from a hemispherical diffuse light source
E (λ)
hemi
spectral irradiance of a CIE standard illuminant from a
-2 -1
E (λ) W∙m ∙nm
CIE,hemi
hemispherical diffuse light source
R  luminous reflectance factor for a rendered display colour Q
Q
R (λ) spectral reflectance factor for a rendered display colour Q
Q
luminous reflectance or diffuse reflectance for a rendered display
ρ
Q
colour Q
spectral reflectance for a rendered display colour Q
ρ (λ)
Q
−2
L cd⋅m darkroom luminance for a rendered display colour Q
Q
−1 −2 −1
L (λ) W⋅sr ⋅m ⋅nm darkroom spectral radiance for a rendered display colour Q
Q
ambient spectral radiance, including reflected and darkroom emitted
−1 −2 −1
L (λ) W⋅sr ⋅m ⋅nm
,
Q amb
light, for a rendered display colour Q
reflected spectral radiance when the reflection coefficients are
−1 −2 −1
L (λ) W⋅sr ⋅m ⋅nm
Refl
independent of the rendered display colour Q
CIE tristimulus values of the rendered display colour Q in a
−2
X , Y , and Z cd⋅m for Y
Q Q Q Q
darkroom
X , Y equivalent CIE tristimulus values, including reflected and darkroom
−2
Q,amb Q,amb,
cd⋅m for Y
Q,amb
and Z emitted light, for a rendered display colour Q
Q,amb
CIE 1931 chromaticity coordinates of the rendered display colour Q
x , y
Q Q
in a darkroom
equivalent CIE 1931 chromaticity coordinates, including reflected
x , y
Q,amb Q,amb
and darkroom emitted light, for a rendered display colour Q

4 Standard measuring conditions
4.1 Standard measuring environmental conditions
Measurements shall be carried out under the following standard environmental conditions:
– temperature: 25 °C ± 3 °C,
– relative humidity: 25 % to 85 %,
– atmospheric pressure: 86 kPa to 106 kPa.

When different environmental conditions are used, they shall be noted in the report.

– 12 – IEC 62977-2-2:2020 © IEC 2020
4.2 Viewing direction and light source coordinate system
The viewing direction is the direction under which the observer looks at the point of interest
on the display under test (DUT). During the measurement, the light measuring device (LMD)
simulates the observer, by aiming the LMD at the point of interest on the DUT from the
viewing direction. The viewing direction is defined by two angles: the angle of inclination θ
(relative to the surface normal of the DUT) and the angle of rotation φ (also called azimuth
angle) as illustrated in Figure 1. Although the azimuth angle is measured in the counter-
clockwise direction, it is related to the directions on a clock face as follows: φ = 0° is the
3-o'clock direction ("right"), φ = 90° the 12-o'clock direction ("top"), φ = 180° the 9-o'clock
direction ("left") and φ = 270° the 6-o'clock direction ("bottom"). The same coordinate system
can be used to specify the positioning of the light sources used to represent the ambient
lighting environment.
NOTE This coordination is defined by the angle of inclination and the angle of rotation (azimuth angle)
in a polar coordinate system.
Figure 1 – Representation of the viewing direction (direction of measurement)
and coordinate system used for light source configuration
4.3 Standard lighting conditions
4.3.1 General
A light source is chosen to provide as broad, stable, and smooth a spectrum as possible in
order to reliably measure the spectral reflectance and reflection coefficients of the display
surface specific to the geometry of the light source. This document then applies the reflection
coefficients to simulate the display performance under the same geometric conditions using
an illuminant, that is, a model or measured light source with an illumination level and/or
spectrum that could be different from the light source used in the measurement.
An illuminant can be used to represent the use of a display that is viewed indoors (e.g. office),
or in direct daylight (outdoors). These environments generally contain a combination of
directed and uniform hemispherical diffuse light sources. The visual performance of the
display can depend on the type of illumination and measurement geometry. Subclause 4.3
specifies the detailed conditions of the light sources for reflectance measurements under
otherwise darkroom conditions.
A warm-up time can be necessary. The light source signal shall remain stable to within ±0,5 %
standard deviation within a single measurement, and ±2 % for longer (>30 min)
measurements.
4.3.2 Standard measuring darkroom conditions
The influence of unwanted background illumination shall be minimized, typically by
illuminating the display in a darkroom. Unwanted background illumination is mainly a
consideration for directed light sources, which is often solved by using light sources with
spectral irradiance values that are substantially larger than the background. The darkroom
spectral radiance contribution from the background illumination, that is, the measured spectral
th
radiance reflected off the DUT, shall be not more than 1/10 of the spectral radiance from the
device black state with the illumination source on. If this condition is not satisfied, then
background subtraction is required and it shall be noted in the report. In addition, if the
th
sensitivity of the LMD is more than 1/100 of the spectral radiance from the device black
state, then the spectral radiance sensitivity limit of the LMD shall be noted in the report.
4.3.3 Standard ambient illumination
The following illumination conditions are specified for the optical measurements of displays
under ambient illumination. The ambient illumination shall simulate indoor or outdoor
illumination conditions. A combination of a hemispherical diffuse and directed source
geometry is generally used to simulate either ambient indoor illumination or outdoor daylight
illumination under a clear sky [1] ,[2]. Uniform hemispherical diffuse illumination will be used
to simulate the background lighting in a room with the directed light source such as an occluded
luminaire in a room, or the hemispherical skylight incident on the display, with the sun occluded.
A directed light source in a darkroom will simulate the effect of directional illumination on a
display by a luminaire in a room, or from direct sunlight.
The following reference illumination conditions shall be used to simulate indoor and outdoor
display viewing environments. Additional conditions can also be used, depending on the use
case.
a) Indoor room illumination conditions:
• Uniform hemispherical diffuse illumination – Use a light source closely approximating
CIE Standard Illuminant A, CIE Standard Illuminant D65, or CIE Standard Illuminant
D50 as defined in CIE 15. For spectral measurements, a spectrally smooth broadband
light source (such as an approximation to CIE Standard Illuminant A) shall be used. A
measurement of the spectral reflectance factor using a broad light source (such as
Illuminant A) enables the indoor photopic and colour metrics to be calculated later for
the desired reference spectra (for example CIE D65 Illuminant). The performance
metrics shall be calculated using 300 lx for an indoor reading environment [3]. The
actual hemispherical diffuse reflectance factor measurement can require higher
illumination levels for better measurement accuracy. The results are then scaled down
to the required illumination levels.
• Directional illumination – The same source spectra shall be used as with hemispherical
diffuse illumination. The indoor room photopic and colour metrics shall be calculated
using directional illumination of 200 lx incident on the display surface for an indoor
reading environment with the display in the vertical orientation. The actual reflectance
factor measurement can require higher illumination levels for better measurement
accuracy. The results are then scaled down to the required illumination levels. The directed
source shall be 45° above the surface normal (θ = 45°) and have an angular subtense
s
of no more than 5°. The angular subtense is defined as the full angle span of the light
source from the centre of the display’s measurement area.
• Other illumination levels may be used in addition to those defined above for calculating
the ambient contrast ratio under indoor illumination conditions. However,
approximately 60 % of the total illuminance should be hemispherical diffuse, and 40 %
directional illumination. Additional ratios of diffuse to directional illumination may also
be measured.
– 14 – IEC 62977-2-2:2020 © IEC 2020
b) Daylight illumination conditions:
• Uniform hemispherical diffuse illumination – Use a light source closely approximating
skylight with the spectral distribution of CIE Illuminant D75 [4]. Additional CIE daylight
illuminants (such as D65) may also be used, depending on the intended application.
For spectral measurements, the spectral reflectance factor measurements can be
made using a spectrally smooth broadband source (such as an approximation to CIE
Standard Illuminant A). Skylight photopic and colour metrics can be calculated later for
the CIE D75 Illuminant spectra. The skylight photopic and colour metrics shall be
calculated using 15 000 lx of hemispherical diffuse illumination (with specular included)
incident on a display surface in a vertical orientation [4],[5]. The actual hemispherical
diffuse reflectance factor measurement may be taken at lower illumination levels. The
results are then scaled up to the required illumination levels.
• Directional illumination – The directional light source shall approximate CIE daylight
Illuminant D50 [4]. Additional CIE daylight illuminants (such as D65) may also be used,
depending on the intended application. A spectrally smooth broadband source (such as
an approximation to CIE Standard Illuminant A) may be used for the reflectance factor
measurement. The sunlight photopic and colour metrics can be calculated later with
the D50 Illuminant spectra. The daylight contrast ratio or colour shall be calculated
using 65 000 lx for a directed source at an inclination angle of θ = 45° to the display
s
surface, and the LMD shall be aligned normal to the display surface (θ = 0) [4],[5].
d
The actual reflectance factor measurement may be taken at lower illumination levels.
The results are then scaled up to the required illumination levels. The contrast ratio
and colour are calculated for the scaled-up illuminance levels. The directed source
shall have an angular subtense of approximately 0,5°.
For daylight photopic and colour metric calculations from spectral reflectance factor
measurements, the relative spectral distributions of CIE Illuminants A, D50, D65 and D75
tabulated in CIE 15 shall be used. Additional CIE daylight illuminants shall be determined
using the appropriate eigenfunctions, as defined in CIE 15.
The UV region (< 380 nm) of the light source shall be cut off by a UV blocking filter. When
high light source illumination levels are used, an infrared-blocking filter is recommended to
minimize device heating.
If there is fluorescent light with a radiance larger than 1/100 that of the DUT black state
(including background reflected light) the spectral reflectance analysis should not be used. In
this case, the spectrum of the light sources should match the spectrum of the CIE illuminants,
and the photometric reflection coefficients shall be measured directly. These coefficients will
then include the contribution from the fluorescence. The presence of fluorescence can be
checked by turning the display off and shining a directional source (with a blue filter) on the
display at a 45° inclination angle and determining if a glow from the illumination area can be
observed.
4.3.4 Standard illumination geometries
4.3.4.1 General
The measurement geometry can have a significant effect on the measured reflection
properties of a display [6]. Three types of illumination geometries shall be used for
determining the performance of the display. Standard configurations for implementing these
illumination geometries are defined in 4.3.4. Additional illumination geometries may also be
used. The details of the illumination geometry used for a given measurement shall be reported.
Further guidance on the proper implementation of these illumination geometries is given in the
SID Information Display Measurements Standard [1].

4.3.4.2 Directional illumination
Directional illumination is obtained when a light source produces approximately parallel rays
incident on the DUT. The maximum deviation of the rays from the optical axis depends on the
diameter of both the source and measuring spot. The maximum angle of deviation from the
optical axis is given by
arctan r + [ ] (1)
( )
ms s
where r is the source radius, d is the distance to the measuring spot, and r is the
s ms
measuring spot radius. The illumination across the cross-section of the beam shall be uniform
to within 5 % ([L – L ] / L ). A source of light sufficiently distant from the DUT can
max min max
provide directional illumination (e.g. sun and moon). When simulating outdoor directional
ambient illumination like the sun and moon, the subtense of the source (as observed by the
DUT) should be ≤0,5°.
Directional illumination can be realized with at least three different types of sources when the
source dimensions are small enough compared to the distance between the source and the
measuring spot on the sample. These geometries are depicted in Figure 2:
– flat Lambertian source, for example the exit port of an integrating sphere (top, with light
source in grey),
– spherical isotropic source (e.g. incandescent bulb inside a diffusing glass-sphere) (middle,
with light source in grey),
– projection system with lenses or mirrors (bottom, with lens on the right).

Figure 2 – Illustrated examples for directional illumination
Directional illumination is implemented by using a light source with a small diameter
(compared to the distance to the measurement spot) aligned to form an inclination angle θ
S
with respect to the surface normal of the DUT. This directed light source produces an
illumination spot on the DUT. The LMD is placed at an inclination angle θ in the plane of the
R
incident light, and its measurement field centred within the illumination spot. The light source
and LMD can be adjusted over a range of inclination angles, but the LMD shall remain in the
plane of incidence (i.e. φ = φ + 180°). This configuration is shown in Figure 3 (left) with its
S R
representation in a polar coordinate system (right). The measurement field on the DUT is
defined by the DUT area element that is imaged on the detector in the LMD.

– 16 – IEC 62977-2-2:2020 © IEC 2020

Figure 3 – Example of the measuring setup using
directional illumination where θ = 40° and θ = 30°
S R
= 45° and θ = 0°. Alignment accuracy to within ±0,4° is
The standard conditions are θ
S R
recommended to keep alignment-related measurement error within ±5 %.
4.3.4.3 Ring light illumination
Ring light illumination can be considered a special case of directional illumination. It provides
directional illumination with rotational symmetry about the display’s surface normal and is
centred on the measurement spot. Ring light illumination can be realized in the following
ways:
– fiber-optic ring light,
– integrating sphere with a ring-shaped aperture (annulus),
– optical systems with lenses and mirrors, for example a concave ring mirror.
A ring-shaped light-source centred about the surface normal of the DUT illuminates the DUT
from an angle of inclination θ ± ∆ for all azimuthal angles φ = 0 to 360°. The LMD is aligned
S S
to form an angle θ < θ – ∆ with respect to the surface normal of the DUT. Figure 4 shows a
R S
side view of the measuring setup (left) and its representation in a polar coordinate system
(right). A more detailed illustration of the ring light characteristics is given in Figure 5. The
subtense of the ring light (2∆ in this case) shall be specified. The source and detector shall be
aligned to the defined geometry to within ±3°. The illumination of the measuring spot on the
DUT shall be uniform within 5 %. This setup is used with the light source fixed, and the LMD
can be adjusted within the limits of the ring light opening. The standard conditions are θ = 0°
R
and a source inclination angle of θ ± ∆ = 45° ± 3°.
S
Figure 4 – Example of ring light illumination
measuring setup where θ ± ∆ = 35 ± 5 and θ = 20°
S R
It is recommended that the ring light and LMD have an alignment accuracy of ±0,7° in order to
keep the alignment-related measurement error within ±5 %. When simulating outdoor
directional ambient illumination using the ring light, the subtense 2∆ of the source
(as observed by the DUT) should be ≤0,5°. A fiber-optic ring light is recommended in this case.

– 18 – IEC 62977-2-2:2020 © IEC 2020

Key:
Ring light subtense (2∆ K )
s, s
Ring light inclination (∆ , ∆ )
s
...