Display lighting unit - Part 2-3: Electro-optical measuring methods for LED frontlight unit

IEC 62595-2-3:2018(E) specifies the standard measurement conditions and measuring methods for determining electrical, optical, and electro-optical properties of LED frontlight units (FLUs) for reflective displays.

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Status
Published
Publication Date
07-Feb-2018
Technical Committee
Current Stage
PPUB - Publication issued
Start Date
08-Feb-2018
Completion Date
08-Feb-2018
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IEC 62595-2-3
Edition 1.0 2018-02
INTERNATIONAL
STANDARD
Display lighting unit –
Part 2-3: Electro-optical measuring methods for LED frontlight unit
IEC 62595-2-3:2018-02(en)
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IEC 62595-2-3
Edition 1.0 2018-02
INTERNATIONAL
STANDARD
Display lighting unit –
Part 2-3: Electro-optical measuring methods for LED frontlight unit
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 31.120; 31.260 ISBN 978-2-8322-5360-1

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

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC 62595-2-3:2018 © IEC 2018
CONTENTS

FOREWORD ........................................................................................................................... 4

1 Scope .............................................................................................................................. 6

2 Normative references ...................................................................................................... 6

3 Terms, definitions, abbreviated terms and letter symbols ................................................. 6

3.1 Terms and definitions .............................................................................................. 6

3.2 Abbreviated terms ................................................................................................... 8

3.3 Letter symbols (quantity symbols / unit symbols)..................................................... 9

4 Measuring devices ......................................................................................................... 10

4.1 General ................................................................................................................. 10

4.2 Light measuring device (LMD) ............................................................................... 10

4.2.1 Luminance meter ........................................................................................... 10

4.2.2 Spectroradiometer (spectral radiance-meter) ................................................. 10

4.2.3 Conoscopic system ........................................................................................ 10

4.2.4 Image sensor ................................................................................................. 10

4.3 Other devices ....................................................................................................... 10

4.3.1 Sample stage ................................................................................................ 10

4.3.2 Light absorber ............................................................................................... 11

5 General measuring conditions ....................................................................................... 11

5.1 Standard conditions .............................................................................................. 11

5.2 Measurement setup .............................................................................................. 11

5.3 Warm-up time ....................................................................................................... 12

6 Electrical measurement methods ................................................................................... 12

6.1 Conditions ............................................................................................................ 12

6.2 Current ................................................................................................................. 12

6.3 Voltage ................................................................................................................. 12

6.4 Power consumption ............................................................................................... 12

7 Optical measurement methods ...................................................................................... 13

7.1 General ................................................................................................................. 13

7.2 Dark room conditions ............................................................................................ 13

7.2.1 General ......................................................................................................... 13

7.2.2 Measurement items under the external lighting condition ............................... 13

7.2.3 Measurement items under the internal lighting condition ................................ 13

7.3 Conditions ............................................................................................................ 13

7.4 Luminance ............................................................................................................ 14

7.4.1 General ......................................................................................................... 14

7.4.2 Procedures .................................................................................................... 14

7.5 Angular luminance distribution (ALD) .................................................................... 15

7.6 Luminance uniformity or non-uniformity ................................................................. 15

7.7 Spectral power distribution .................................................................................... 16

7.8 Chromaticity .......................................................................................................... 16

7.9 Colour uniformity .................................................................................................. 16

7.10 Angular luminance uniformity ................................................................................ 16

7.11 Angular colour uniformity ...................................................................................... 16

7.12 FLU polarization characteristic measurement ........................................................ 16

7.13 Normal- or inverted-state FLU characteristics ....................................................... 17

7.14 Optical noise measuring ........................................................................................ 17

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IEC 62595-2-3:2018 © IEC 2018 – 3 –

7.15 Cosmetic quality or perceptual visual quality ......................................................... 17

Annex A (informative) Optical structure of an FLU................................................................ 19

Annex B (informative) Normal-state FLU and inverted-state FLU ......................................... 20

Annex C (informative) Angular measurement system ........................................................... 21

Annex D (informative) Measurement parameters for BRDF and BTDF.................................. 22

D.1 BRDF .................................................................................................................... 22

D.2 BTDF .................................................................................................................... 22

Annex E (informative) Determining the polarization state of reflected light on the front

surface of an FLU or transmitted light through the FLU .................................................. 24

Annex F (informative) Optical transfer function (OTF) of an FLU .......................................... 25

F.1 Optical transfer function evaluation chart .............................................................. 25

F.2 Example of optical transfer function ...................................................................... 25

Annex G (informative) Sources of optical noise in a normal-state FLU with a reflective

display ........................................................................................................................... 27

Annex H (informative) Formulation of contrast ratio for a reflective display with an

integrated FLU ............................................................................................................... 28

H.1 Contrast ratio for a reflective display without FLU integration ............................... 28

H.2 Contrast ratio for a reflective display with FLU integration .................................... 28

Annex I (informative) Example of optical noise of an FLU .................................................... 29

Bibliography .......................................................................................................................... 30

Figure 1 – Example of light absorber (optical trap) ................................................................ 11

Figure 2 – Example of measurement setup for a LED FLU .................................................... 12

Figure 3 – Illustration of zenith angle θ and azimuth angle ϕ (normal-state FLU) ................... 14

Figure 4 – Polar coordinate system for frontlight unit measurement ...................................... 15

Figure 5 – Example of light polarizing characteristics of an FLU in inverted state .................. 17

Figure A.1 – Direct edge-lit FLU and indirect edge-lit FLU.................................................... 19

Figure B.1 – Normal-state FLU ............................................................................................. 20

Figure B.2 – Inverted-state FLU ............................................................................................ 20

Figure C.1 –Standard goniometric system ............................................................................. 21

Figure C.2 – Conoscopic system ........................................................................................... 21

Figure D.1 – System for measuring the BRDF ....................................................................... 22

Figure D.2 – Measuring the BRDF of an LGP for an FLU ...................................................... 22

Figure D.3 – System for measuring the BTDF ....................................................................... 23

Figure E.1 – Geometry of a reflected or transmitted polarized light ....................................... 24

Figure F.1 – Printed charts on photographic paper for measuring the OTF of the FLU .......... 25

Figure F.2 – Example of OTF ................................................................................................ 26

Figure G.1 – Light rays of an FLU with a reflective LC display .............................................. 27

Figure G.2 – Sources of noises in a normal-state FLU with a reflective display ..................... 27

Figure I.1 – Optical signal and noise in a normal-state FLU .................................................. 29

Table 1 – Letter symbols (quantity symbols / unit symbols) ..................................................... 9

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– 4 – IEC 62595-2-3:2018 © IEC 2018
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DISPLAY LIGHTING UNIT –
Part 2-3: Electro-optical measuring methods for LED frontlight unit
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

international co-operation on all questions concerning standardization in the electrical and electronic fields. To

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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.

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 62595-2-3 has been prepared by IEC technical committee TC 110:

Electronic display devices.
The text of this International Standard is based on the following documents:
CDV Report on voting
110/891/CDV 110/933A/RVC

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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IEC 62595-2-3:2018 © IEC 2018 – 5 –

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.
A bilingual version of this publication may be issued at a later date.
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– 6 – IEC 62595-2-3:2018 © IEC 2018
DISPLAY LIGHTING UNIT –
Part 2-3: Electro-optical measuring methods for LED frontlight unit
1 Scope

This part of IEC 62595 specifies the standard measurement conditions and measuring

methods for determining electrical, optical, and electro-optical properties of LED frontlight

units (FLUs) for reflective displays.
NOTE: See 3.1.1 for a definition of reflective display.
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 62595-1-2, Display lighting unit – Part 1-2: Terminology and letter symbols

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

backlight unit

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

with integrated lighting units
3 Terms, definitions, abbreviated terms and letter symbols

For the purposes of this document, the terms, definitions, abbreviated terms and letter

symbols given in IEC 62595-1-2 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
3.1 Terms and definitions
3.1.1
reflective display

display whose function is based on the light reflection of a reflective layer in its structure

EXAMPLE A reflective LCD, an electronic paper display, a micro electro-mechanical system (MEMS) and a micro

electro-opto-mechanical system (MEOMS) display device. See IEC 62679-3-3.
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IEC 62595-2-3:2018 © IEC 2018 – 7 –
3.1.2
normal state
normal-state FLU

state of an FLU in which the light emerges from its front surface that faces toward the

reflective display

Note 1 to entry: For an example, see Annex A, Annex B, Figure A.1 and Figure B.1, [1] to [8] .

3.1.3
inverted state
inverted-state FLU
FLU with an illuminating surface toward a viewer
Note 1 to entry: For an example, see Figure B.2.
3.1.4
optical trap

optical device that is used in FLU measurements for trapping or absorbing the emergent light

from the opposite surface of the FLU under measurement device, whether the FLU is in a

normal state or in inverted state
Note 1 to entry: For examples, see Figure 1.
3.1.5
optical absorbing sheet
optical absorbing plate

plane sheet or plate that is used beneath an FLU under measurement to absorb the emergent

light
3.1.6
BRDF
bi-directional reflectance distribution function

variation of reflected luminance (L (θ ,φ θ ,φ ,λ )) due to the change of non-polarized

vR r r; i i i
illumination (E (θ ,φ ,λ )) of an infinitesimal uniform area on an FLU
v i i i

Note 1 to entry: See Annex C and Annex D. In case of an equal reflection factor of the FLU surface, the BRDF is

a space invariant characteristic, and the eigen value of the FLU is expressed in solid angle (Ω) unit, i.e., in terms of

steradian.
3.1.7
BTDF
bi-directional transmittance distribution function

variation of transmitted luminance (L (θ ,φ θ ,φ ,λ )) due to non-polarized illuminating

vT r r; i i i
variation (E (θ ,φ ,λ )) of an infinitesimal area on an FLU
v i i i

Note 1 to entry: See Annex C and Annex D. In case of an equal transmittance factor on each point of the FLU

surface, the BTDF is a space invariant characteristic, and the eigen value of the BRDF of the FLU is expressed in

solid angle (Ω) unit, i.e., in terms of steradian.
3.1.8
BPDF
bi-directional polarization distribution function

variation of luminance with polarization of the reflected light (L (θ ,φ θ ,φ ,λ )) due to a

vP r r; i i i

change of non-polarized illumination (E (θ ,φ ,λ )) of an infinitesimal uniform area on an FLU

v i i i

Note 1 to entry: See Annex C, Annex D and Annex E. In case of an equal reflection factor on each point of the

FLU surface, the BPDF is a space invariant characteristic, and the eigen value of the BTDF of the FLU is

expressed in solid angle (Ω) unit, i.e., in terms of steradian.
___________
Numbers in square brackets refer to the Bibliography.
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– 8 – IEC 62595-2-3:2018 © IEC 2018
3.1.9
OTF
optical transfer function

contrast of transmitted line pairs through an FLU versus line pairs periodicities and

orientations
Note 1 to entry: See Annex F.
3.1.10
optical transfer function evaluation chart
OTF evaluation chart

printed charts of straight black and white line pairs with different widths (line pairs per

millimeter) and periodicities for use beneath a normal-state FLU to measure and plot the

observed light intensity versus line pairs per millimeter

Note 1 to entry: An example of the resolution test chart can be obtained based on ISO 12233 [9].

Note 2 to entry: See Annex F.
3.1.11
optical signal-to-noise ratio
optical SNR

ratio of the luminance of the illuminating directed light, L (x ,y , θ ,φ), toward the

v,signal i i j j

reflective display in a predefined direction in the spherical coordinate system, (θ, φ), and the

(x ,y ,θ ,φ ), i.e. besides the directed illuminating light, expressed
luminance of noise, L
v,noise i i j j
L (x , y ,θ ,φ)
v,signal i i j j
SNR= (1)
L (x , y ,θ ,φ)
v,noise i i j j
3.1.12
aliasing interference fringe
moiré pattern

periodic interference pattern that appears between the spatial distribution of the sub-micro or

micro-optical structures on the front surface (non-illuminating surface) of a normal-state FLU

and the spatial pixel structure of the reflective display
Note 1 to entry: See [1] to [8].
3.1.13
visual inspection

act of checking defects such as distraction of the transparency caused by flaws in the

LGP/LGF of the non-lit FLU or scratches on either side of an FLU that can been seen under

high white illumination by turning over in various directions
3.1.14
perceptual visual quality
cosmetic quality

image fidelity performance of the lit FLU when the images of the reflective display are viewed

through the FLU

Note 1 to entry: It is also the performance of a normal-state FLU in an integration or in combination with a

reflective display that indicates the no-distraction of a displayed image.
Note 2 to entry: See 7.15.
3.2 Abbreviated terms
ACU - angular colour uniformity
ALD - angular luminance distribution
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IEC 62595-2-3:2018 © IEC 2018 – 9 –
BPDF - bi-directional polarization distribution function
BRDF - bi-directional reflectance distribution function
BTDF - bi-directional transmittance distribution function
CCD – charge coupled device
CMOS - complementary metal oxide semiconductor
DUT - device under test
FLU - frontlight unit
FOS - front-of-screen
LCD - liquid crystal display
LED - light emitting diode
lp - line pairs
LGF - light-guide film
LGP - light-guide plate
LMD - light measuring device
OTF - optical transfer function
SLG - stick-light guide
3.3 Letter symbols (quantity symbols / unit symbols)
The letter symbols for FLUs are shown in Table 1.
Table 1 – Letter symbols (quantity symbols / unit symbols)
Arbitrary luminance of a point (x , y ) on an
i i
L (cd/m )
FLU
Maximum luminance on an FLU L (cd/m )
Minimum luminance on an FLU L (cd/m )
Average luminance on an FLU L (cd/m )
L (cd/m )
Centre luminance on FLU
Spatial luminance uniformity U (%)
Spatial luminance non-uniformity NU (%)
Angular luminance in an arbitrary direction L (x, y; θ,φ) (cd/m )
Solid angle
Ω (sr)
Colour uniformity
∆u’v’
(chromaticity difference)
Spectral power distribution of a display
S (λ)
FLU
lighting unit
Angular luminance distribution of transmitted
L (x ,y ,θ,φ) (cd/m )
vT i i
light at an arbitrary point (x ,y )
i i
Angular luminance distribution of reflected
L (x ,y ,θ,φ) (cd/m )
vR i i
light at an arbitrary point (x ,y )
i i
Angular luminance distribution of a polarized
L (x ,y ,θ,φ) (cd/m )
vP i i
light at an arbitrary point (x ,y )
i i
Angular colour uniformity ∆u’v’(θ,φ;x ,y ,)
i i
BRDF L (θ ,φ ;θ ,φ ,λ ) / E (θ ,φ ,λ ) (1/sr)
vR r r i i i v i i i
BTDF L (θ ,φ ;θ ,φ ,λ ) / E (θ ,φ ,λ ) (1/sr)
vT r r i i i v i i i
BPDF L (θ ,φ ;θ ,φ ,λ ) / E (θ ,φ ,λ ) (1/sr)
vP r r i i i v i i i
OTF C
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– 10 – IEC 62595-2-3:2018 © IEC 2018
4 Measuring devices
4.1 General

The following measuring devices shall be used in this document. The LMD shall be calibrated

with the appropriate photometric or spectrometric standards.
4.2 Light measuring device (LMD)
4.2.1 Luminance meter

The luminance meter (a spot meter or an imaging meter) shall be equivalent to the human eye.

The equipment shall be calibrated with the luminance standards, and should be carefully

checked before measurement, considering the following elements:
– sensitivity of the measured quantity to measuring light;

– errors caused by veiling glare and lens flare (i.e., stray light in optical system);

– timing of data-acquisition, low-pass filtering and aliasing interference fringe effects;

– linearity of detection and data-conversion.

NOTE: ISO/CIE 19476 [10] is available asreference for the LMD evaluation procedures.

4.2.2 Spectroradiometer (spectral radiance-meter)

The wavelength range shall be at least 380 nm to 780 nm and the spectral bandwidth shall be

5 nm or less. The wavelength accuracy shall be 0,3 nm or less. The equipment shall be

calibrated with the with the spectrometric standards. The performance should be carefully

checked before measurement, considering the same elements as in 4.2.1.
4.2.3 Conoscopic system

The conoscopic system is the angular optical distribution measurement system with Fourier

optics. The photometric values, such as luminance, which are obtained by the equipment

without any photometric standard calibration shall not be used. The relative values, such as

an angular optical distribution and colour uniformity, shall be applied.
4.2.4 Image sensor

The image sensor is constructed from a one-dimensional CCD (CMOS) line sensor or a

two-dimensional CCD (CMOS). The image sensor shall be applied for measuring the OTF

property of the DUT. The spatial resolution of the image sensor shall be at least twice as high

as that of the DUT.

NOTE Sampling frequency or resolution is double or more that of the chart under measurement to prevent the

aliasing interference fringe phenomenon or any countermeasure from eliminating aliasing interference fringe in the

measurement.
4.3 Other devices
4.3.1 Sample stage

The orthogonal three axes stage should be used to adjust the measurement points of the DUT.

The biaxial goniometer should be used to ad
...

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