Display lighting unit - Part 2-5: Measurement method for optical quantities of non-planar light sources

IEC 62595-2-5:2021 specifies the measurement methods for measuring the optical characteristics of convex and concave cylindrical light sources. These non-planar light sources (NPLSs) can have either a continuous, distinct, segmented or block-wised light radiating surface, for example OLED panels, integrated LEDs, integrated mini-LEDs, micro-LEDs, laser diodes, each being either monochromatic or polychromatic.

General Information

Status
Published
Publication Date
20-May-2021
Technical Committee
Current Stage
PPUB - Publication issued
Completion Date
21-May-2021
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IEC 62595-2-5
Edition 1.0 2021-05
INTERNATIONAL
STANDARD
colour
inside
Display lighting unit –
Part 2-5: Measurement method for optical quantities of non-planar light sources
IEC 62595-2-5:2021-05(en)
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---------------------- Page: 2 ----------------------
IEC 62595-2-5
Edition 1.0 2021-05
INTERNATIONAL
STANDARD
colour
inside
Display lighting unit –
Part 2-5: Measurement method for optical quantities of non-planar light sources
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 31.120; 31.260 ISBN 978-2-8322-9771-1

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC 62595-2-5:2021 © IEC 2021
CONTENTS

FOREWORD ........................................................................................................................... 5

INTRODUCTION ..................................................................................................................... 7

1 Scope .............................................................................................................................. 8

2 Normative references ...................................................................................................... 8

3 Terms, definitions, abbreviated terms and letter symbols ................................................. 9

3.1 Terms and definitions.............................................................................................. 9

3.2 Abbreviated terms ................................................................................................... 9

3.3 Letter symbols (quantity symbols/unit symbols)..................................................... 10

4 Measurement devices .................................................................................................... 11

4.1 General ................................................................................................................. 11

4.2 Spot-type light measuring device .......................................................................... 11

4.3 Spectroradiometer (spectral radiance-meter) ........................................................ 12

4.4 Electrical measurement devices ............................................................................ 12

4.4.1 Current meter ................................................................................................ 12

4.4.2 Voltage meter ................................................................................................ 13

4.5 Luminous flux measurement devices ..................................................................... 13

4.5.1 General ......................................................................................................... 13

4.5.2 Luminous flux ................................................................................................ 13

4.5.3 Sample stage ................................................................................................ 15

5 General measuring conditions ....................................................................................... 15

5.1 Standard conditions .............................................................................................. 15

5.2 Darkroom conditions ............................................................................................. 16

5.3 Measurement setup .............................................................................................. 16

5.4 Setting the electrical characteristics of measurement devices ............................... 16

5.4.1 Conditions ..................................................................................................... 16

5.4.2 Current .......................................................................................................... 16

5.4.3 Voltage .......................................................................................................... 16

5.4.4 Power ............................................................................................................ 16

5.4.5 Warm-up time ................................................................................................ 17

6 Optical measurement methods ...................................................................................... 17

6.1 General ................................................................................................................. 17

6.2 Conditions ............................................................................................................ 17

6.3 Perceptual visual quality ....................................................................................... 17

6.3.1 General ......................................................................................................... 17

6.3.2 Procedures .................................................................................................... 17

6.4 Lateral and directional scanning configuration ...................................................... 18

6.4.1 General ......................................................................................................... 18

6.4.2 Lateral scanning configuration ....................................................................... 18

6.4.3 Directional scanning configuration ................................................................. 20

6.5 Depth-of-field and depth-of-focus in measurement ................................................ 22

6.5.1 General ......................................................................................................... 22

6.5.2 Front and rear depth-of-field (DoF) ................................................................ 22

6.5.3 Front and rear depth-of-focus (dof) ................................................................ 23

6.6 Measurement procedures...................................................................................... 23

6.6.1 General ......................................................................................................... 23

6.6.2 Cylindrical LS mounting for lateral measurements ......................................... 23

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IEC 62595-2-5:2021 © IEC 2021 – 3 –

6.6.3 Lateral luminance .......................................................................................... 24

6.6.4 Lateral luminance uniformity .......................................................................... 24

6.6.5 Lateral chromaticity and chromaticity variation ............................................... 25

6.6.6 Directional luminance .................................................................................... 25

6.6.7 Directional luminance variations .................................................................... 26

6.6.8 Directional chromaticity and chromaticity variation ......................................... 26

6.6.9 Luminous flux ................................................................................................ 27

7 Precautions ................................................................................................................... 30

7.1 Remarks ............................................................................................................... 30

7.2 Further remarks .................................................................................................... 31

7.2.1 General ......................................................................................................... 31

7.2.2 Report ........................................................................................................... 31

Annex A (informative) Measurement field on the curved light source .................................... 32

A.1 General ................................................................................................................. 32

A.2 NPLS curvature and measurement field ................................................................ 32

A.3 MFs on planar, convex and concave cylindrical LSs .............................................. 33

Annex B (informative) Planar light source measurement ...................................................... 35

B.1 General ................................................................................................................. 35

B.2 Luminance meter and measurement field .............................................................. 35

Annex C (informative) Contours of light measurement fields on plane, cylindrical

convex, and concave light sources ........................................................................................ 36

C.1 General ................................................................................................................. 36

C.2 MF contour on a non-tilt and tilt planar DUT .......................................................... 36

C.3 Projection of an MF contour on the outer surface of a cylindrical DUT ................... 37

Annex D (informative) LMD aperture and inclination angle on a cylindrical light source ........ 41

D.1 General ................................................................................................................. 41

D.2 Inclination angle.................................................................................................... 41

D.3 Inclination angle variation ..................................................................................... 42

D.4 Depth-of-field ........................................................................................................ 43

D.5 Measurement field size on the cylindrical light source ........................................... 45

Bibliography .......................................................................................................................... 50

Figure 1 – Cartesian and spherical coordinate systems for NPLS measurement ................... 11

Figure 2 – Example of LMD with the observation area surrounding the measurement field .... 12

Figure 3 – Current and voltage measurements using an ammeter between points C and

D and a voltage meter between points A and B ..................................................................... 13

Figure 4 – Geometry of 4π-sphere measurement ................................................................... 14

Figure 5 – Measuring points on convex and concave DUTs based on the setups of

Figure 4 ................................................................................................................................ 15

Figure 6 – Example of a mirror type goniometric system ....................................................... 15

Figure 7 – Planar LS and cylindrical LS (NPLS) in lateral scanning measurement

arrangements ....................................................................................................................... 19

Figure 8 – Planar LS and cylindrical LS (NPLS) in a directional scanning arrangement ......... 21

Figure 9 – Pictorial illustration of depth-of-field, depth-of-focus and circle of confusion

for an LMD ............................................................................................................................ 22

Figure 10 – Rear depth-of-field in the measurement setup of a cylindrical light source .......... 23

Figure A.1 – Schematic diagram of the optical characteristics measurement of planar,

convex and concave cylindrical light source .......................................................................... 32

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– 4 – IEC 62595-2-5:2021 © IEC 2021

Figure C.1 – Geometry of intersections of a cone and a plane in non-tilt and tilt

conditions ............................................................................................................................. 36

Figure C.2 – Expanded plane of a cone and intersection lines with tilt and non-tilt

planes (see Figure C.1) ........................................................................................................ 37

Figure C.3 – Simulated intersections of three planar light sources with a cone

(measurement field angle, i.e., a solid angle) ........................................................................ 37

Figure C.4 – Geometry for calculating the intersection of a cone (measurement field

angle; solid angle) and a cylinder (light source) .................................................................... 38

Figure C.5 – Intersection of a cone and a cylindrical DUT ..................................................... 38

Figure C.6 – Measurement of a convex cylindrical LS and the possible cases, and
illustration of the effect of the measurement field angle cone and the angle of

inclination of the measurement direction ............................................................................... 40

Figure D.1 – Measurement of a cylindrical light source for a non-zero aperture LMD

and fixed measurement field (b) ............................................................................................ 41

Figure D.2 – Variation of inclination angle, θ , with D for each cylindrical LS of

D LMD

radius R ................................................................................................................................ 42

Figure D.3 – Variation of rear DoF with D (for measurement field angles of 2°, 1°,

LMD

0,2°, 0,1°) for zero aperture LMD .......................................................................................... 43

Figure D.4 – Rear DoF variations with measurement distance D , for light source
LMD

R in Annex A ....................................................................................................................... 45

Figure D.5 – Variation of measurement field with D for cylindrical light sources of

LMD

radii R = 20 mm, 35 mm, 50 mm, and measurement field angles of β = 2°, 1°, 0,2°, 0,1° ....... 47

Figure D.6 – Difference in variation of MF with D for radii R = 20 mm, 35 mm, 50 mm .... 49

LMD

Table 1 – Letter symbols (quantity symbols/unit symbols) ..................................................... 10

Table B.1 – Example of a measurement result ...................................................................... 35

Table D.1 – Variation of inclination angles with half of the MF size; b/2 ................................. 43

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IEC 62595-2-5:2021 © IEC 2021 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DISPLAY LIGHTING UNIT –
Part 2-5: Measurement method for optical quantities
of non-planar light sources
FOREWORD

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indispensable for the correct application of this publication.

9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent

rights. IEC shall not be held responsible for identifying any or all such patent rights.

International Standard IEC 62595-2-5 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
110/1296/FDIS 110/1320/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 62595 series, published under the general title Display lighting unit,

can be found on the IEC website.
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– 6 – IEC 62595-2-5:2021 © IEC 2021

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.
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IEC 62595-2-5:2021 © IEC 2021 – 7 –
INTRODUCTION

The recent introduction of curved OLED TVs, and the expected rapid spread of flexible displays

in portable devices, highlights the necessity of new measurement methods. In recent years

flexible displays have been integrated into products such as cellular phones and wearable

devices [1] to [5] . Development and integration of flexible displays have increased the

application of curved devices, for example distinct or curved-back large-size wall displays,

foldable signage displays, and commercial wearable or handheld devices. The measurement of

optical characteristics of displays with radii larger than 35 mm has been documented.

Recently flexible light sources (LSs) have been used for general lighting applications and as

light source for flexible non-emissive displays. Since bending a planar lighting unit alters the

optical properties of the unit, assessment of the optical performance of the lighting units in a

curved state, i.e., concave or convex condition, is indispensable for manufacturing companies.

A light source can be a planar or non-planar (continuous multiple curvatures), i.e., convex (outer

light emitting surface of a curvature), or concave light source (inner light emitting surface of a

curvature). When a light source is bent the LS is under strain, i.e., tension or depression, the

optical characteristics differ from that of a planar LS. A non-planar LS may have local curvatures

on its surface with different surface normal from position to position. Such an LS can be a

semiconductor light-emitting diode (LED, OLED, polymer LED (PLED)) or a phosphor excited

type using a pump source. An LS can have a narrow-band radiation or more than one narrow

band emission.

Issues concerning flexible light sources with surface curvatures, which are different from those

issues concerning displays (e.g., resolution, contrast, lateral and directional characteristics or

directions of viewing), hitherto have not been documented.

Since the characteristics of a non-planar light source (NPLS) change with the decreasing radius

of the curvature, the optical characteristics of LS such as lateral and directional luminance and

luminance variations, lateral and directional chromaticity distributions and their variations,

luminous intensity distribution, and luminous flux, will be measured and evaluated.

This document establishes the measurement methods for cylindrical light sources that can be

a base for the study of non-planar LS, which is assumed to be an integration of small areas.

The fundamental element of such a surface can be a convex or a concave curvature with a first

order of radius, i.e., a cylindrical shape, which is worth considering in this document.

In addition, a curved light source is used in a variety of conditions. Therefore, the optical

measurements of an LS will be performed in a darkroom.

As in the measurement of planar LSs the following measurements are used for convex and

concave LS measurements: 1) a lateral scanning measurement and 2) a directional scanning

measurement. In the case of lateral scanning, the surface normal coincides with the optical axis

of the light measurement device. In the case of directional scanning the local surface normal

makes an angle with the optical axis of the measurement device.

Since the aperture of a light measurement device is not zero (non-zero aperture), there exist

an optimized measurement distance and angle (i.e., 0,1°, 0,2°, 1°, and 2°) for the

measurements. In the measurement of a cylindrical LS, a light measurement device which has

sufficient depth-of-field or depth-of-focus is selected, because the measurement field on the LS

has a three-dimensional geometry and is different from that of a plane.
____________
Numbers in square brackets refer to the Bibliography.
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– 8 – IEC 62595-2-5:2021 © IEC 2021
DISPLAY LIGHTING UNIT –
Part 2-5: Measurement method for optical quantities
of non-planar light sources
1 Scope

This part of IEC 62595 specifies the measurement methods for measuring the optical

characteristics of convex and concave cylindrical light sources. These non-planar light sources

(NPLSs) can have either a continuous, distinct, segmented or block-wised light radiating

surface, for example OLED panels, integrated LEDs, integrated mini-LEDs, micro-LEDs, laser

diodes, each being either monochromatic or polychromatic.
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 61747-6-2, Liquid crystal display devices – Part 6-2: Measuring methods for liquid crystal

display modules – Reflective type

IEC 62595-2-1, Display lighting unit – Part 2-1: Electro-optical measuring methods of LED

backlight unit

IEC 62595-2-3, Display lighting unit – Part 2-3: Electro-optical measuring methods for LED

frontlight unit

IEC 62679-3-3, Electronic paper displays – Part 3-3: Optical measuring methods for displays

with integrated lighting units

IEC 62922, Organic light emitting diode (OLED) panels for general lighting – Performance

requirements
ISO/CIE 11664-3, Colorimetry – Part 3: CIE tristimulus values

ISO/CIE 19476, Characterization of the performance of illuminance meters and luminance

meters
CIE S 017/E:2020, International Lighting Vocabulary
CIE 1931, Colour space
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IEC 62595-2-5:2021 © IEC 2021 – 9 –
3 Terms, definitions, abbreviated terms and letter symbols
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions 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
3.1.1
planar light source
light source with a nearly infinite radius of curvature
3.1.2
non-planar light source
light source having continuous multiple curvatures
3.1.3
convex light source
light source defined by the outer light emitting surface of a curvature
3.1.4
concave light source
light source defined by the inner light emitting surface of a curvature
3.1.5
flexible light source

light source capable of bending or being bent or to endure strain without being destroyed

3.1.6
single-curvature surface emission light source
cylindrical light source

light source that possesses one radius of curvature whether negative (concave) or positive

(convex), along its length, width or diagonal
3.1.7
multiple-curvature surface light source

light source that possesses multiple radii of curvatures whether negative (concave) or positive

(convex), along any dimension such as length, width or diagonal
3.1.8
phosphor converted emission light source

light source with a pump source that is used to excite a phosphor or any phosphor-like material

that radiates light of wavelengths longer than the pump source
3.2 Abbreviated terms
CCT Correlated colour temperature
COC Circle of confusion
DC Direct current
DoF Depth-of-field
dof Depth-of-focus
DUT Device under test
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– 10 – IEC 62595-2-5:2021 © IEC 2021
LED Light emitting diode
LMD Light measurement device
LS Light source
MF Masurement field
NPLS Non-planar light source
OLED Organic light emitting diode
PLS Panar light source
SLMD Spot-type light measuring device

NOTE The measurement field is an area on the DUT viewed through the LMD lens within a cone limited by the

measurement field angle.
3.3
...

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