IEC 62595-2:2012
(Main)LCD backlight unit - Part 2: Electro-optical measurement methods of LED backlight unit
LCD backlight unit - Part 2: Electro-optical measurement methods of LED backlight unit
IEC 62595-2:2012 specifies the standard measurement conditions and measuring methods for determining electrical, optical, and electro-optical parameters of LED backlight units for liquid crystal displays.
NOTE: Other backlights (Cold Cathode Fluorescent Lamps (CCFLs), External Electrode Fluorescent Lamps (EEFLs), Hot Cathode Fluorescent Lamps (HCFLs), Carbon Nano Tube (CNT), etc.) are excluded from this standard.
Ecran LCD à rétro-éclairage - Partie 2: Méthodes de mesures électro-optiques d'un écran à rétro-éclairage à DEL
La CEI 62595-2:2012 spécifie les conditions de mesure et des méthodes de mesure normalisées en vue de déterminer des paramètres électriques, optiques et électro-optiques d'écrans à rétro-éclairage à DEL pour afficheurs à cristaux liquides.
NOTE: D'autres rétro-éclairages (les lampes fluorescentes à cathode froide (CCFL), les lampes fluorescentes à électrode externe (EEFL), les lampes fluorescentes à cathode chaude (HCFL), les nanotubes de carbone (CNT), etc.) sont exclus de la présente norme.
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Standards Content (Sample)
IEC 62595-2
®
Edition 1.0 2012-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
LCD backlight unit –
Part 2: Electro-optical measurement methods of LED backlight unit
Écran LCD à rétro-éclairage –
Partie 2: Méthodes de mesures électro-optiques d'un écran à rétro-éclairage à
DEL
IEC 62595-2:2012
---------------------- Page: 1 ----------------------
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IEC 62595-2
®
Edition 1.0 2012-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
LCD backlight unit –
Part 2: Electro-optical measurement methods of LED backlight unit
Écran LCD à rétro-éclairage –
Partie 2: Méthodes de mesures électro-optiques d'un écran à rétro-éclairage à
DEL
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX P
ICS 31.120; 31.260 ISBN 978-2-83220-344-6
Warning! Make sure that you obtained this publication from an authorized distributor.
Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.
® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – 62595-2 © IEC:2012
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 General measurement conditions . 5
4.1 Standard atmospheric conditions for LED BLU . 5
4.2 Measuring setup . 5
4.3 Warm-up time . 6
5 Measurement methods . 7
5.1 Electrical measurement methods . 7
5.1.1 Conditions . 7
5.1.2 Current . 7
5.1.3 Voltage . 7
5.1.4 Power consumption . 7
5.2 Optical measurement methods . 8
5.2.1 Conditions . 8
5.2.2 Luminance . 8
5.2.3 Luminance uniformity. 8
5.2.4 Spectral power distribution . 10
5.2.5 Chromaticity . 10
5.2.6 Colour uniformity . 10
5.2.7 Correlated colour temperature . 11
5.2.8 Angular luminance uniformity . 11
5.2.9 Angular colour uniformity . 11
5.2.10 Measurement methods of block-wise BLU. 12
Annex A (informative) Practical measurement methods of block-wise BLU . 14
Bibliography . 16
Figure 1 – Example of measuring setup for LED BLU . 6
Figure 2 – Example of warm-up characteristic of BLU . 7
Figure 3 – Definition of zenith angle θ and azimuth angle ϕ. . 8
Figure 4 – Examples of measurement point layout . 10
Figure 5 – Angular luminance uniformity measurement . 11
Figure 6 – Example of test pattern (8 × 10 segments) for block-wise BLU . 12
Figure 7 – Example of incoherent point spread function . 12
Figure 8 – Example of test pattern of incoherent point spread function . 13
Figure 9 – Example of test pattern of crosstalk . 13
Figure A.1 – Measurement of average slope of incoherent point spread function . 14
Figure A.2 – Black box pattern for crosstalk measurement using LCD . 15
Figure A.3 – Example of crosstalk measurement results using LCD . 15
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62595-2 © IEC:2012 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
LCD BACKLIGHT UNIT –
Part 2: Electro-optical measurement methods of LED backlight 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
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
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Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
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with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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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 has been prepared by IEC Technical Committee 110:
Electronic display devices.
The text of this standard is based on the following documents:
FDIS Report on voting
110/384/FDIS 110/406/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication 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 LCD backlight unit,
can be found on the IEC website.
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The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication 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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62595-2 © IEC:2012 – 5 –
LCD BACKLIGHT UNIT –
Part 2: Electro-optical measurement methods of LED backlight unit
1 Scope
This part of IEC 62595 series specifies the standard measurement conditions and measuring
methods for determining electrical, optical, and electro-optical parameters of LED backlight
units for liquid crystal displays.
NOTE Other backlights (Cold Cathode Fluorescent Lamps (CCFLs), External Electrode Fluorescent Lamps
(EEFLs), Hot Cathode Fluorescent Lamps (HCFLs), Carbon Nano Tube (CNT), etc.) are excluded from this
standard.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60050 (all parts), International Electrotechnical Vocabulary (available at
http://www.electropedia.org)
IEC 61747-6, Liquid crystal and solid-state display devices – Part 6: Measuring methods for
liquid crystal modules – Transmissive type
IEC 62595-1-2, LCD Backlight unit – Part 1-2: Terminology and letter symbols
CIE publication 15:2004, Colorimetry
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 62595-1-2 apply.
4 General measurement conditions
4.1 Standard atmospheric conditions for LED BLU
Unless otherwise specified, all tests and measurements for LED backlight unit shall be carried
out after sufficient warm-up time for illumination sources and devices under test (see 4.3),
under the standard environmental conditions, at a temperature of 25 °C ± 3 °C, at a relative
humidity of 25 % to 85 %, and at an atmospheric pressure of 86 kPa to 106 kPa. When
different environmental conditions are used, they shall be noted in the detail specification (see
IEC 61747-6).
4.2 Measuring setup
DUT, LMD, power source, driving and control devices for LED, and electrical measuring
devices should be arranged appropriately for electro-optical measurements for LED BLU.
An example of measuring setup is shown in Figure 1.
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– 6 – 62595-2 © IEC:2012
LMD
Power supply
Backlight unit
Stage
IEC 1673/12
LMD
Power supply
Backlight unit
Stage
Dimming control
IEC 1674/12
Power consumption of LED BLU Power consumption of LED
P = V × I P = V × I
BLU BLU BLU LED LED LED
LED
I I
BLU
DC LED LED
converter
power array’s
and
controller
V
BLU
V
LED
IEC 1675/12
Power source Power meter SMPS DUT
IEC 1676/12
Key
LMD light measuring device
SMPS switching-mode power supply
DUT device under test
Figure 1 – Example of measuring setup for LED BLU
4.3 Warm-up time
Transient measurement shall be carried out and recorded until the fluctuations of luminance
measured at the centre point of the BLU become less than the range specified in IEC 61747-6.
As in Figure 2, luminance of LED backlights is affected by transient temperature behaviour of
LED output. It takes a certain time for LEDs until their junction temperature reach the steady
state. All measuring conditions shall be kept constant over the time range of recording.
Transient measurement of chromaticity should be carried out in the same manner as in the
above.
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62595-2 © IEC:2012 – 7 –
1,5
1,0
0,5
0
0 10 20 30 40 50 60
Time (min)
IEC 1677/12
Figure 2 – Example of warm-up characteristic of BLU
5 Measurement methods
5.1 Electrical measurement methods
5.1.1 Conditions
BLU shall be placed in the measurement arrangement and it shall be assured that all required
conditions are fulfilled.
After applying the initial electrical driving conditions (i.e. analogue input voltage(s) or digital
input signals) of the BLU and waiting during the warm-up time specified in 4.3 in order to
reach the steady state, the measurement of the electrical quantities of interest should be
started.
5.1.2 Current
The measurement of input current is performed under standard measuring conditions using
current meter shown in Figure 1.
5.1.3 Voltage
The measurement of input voltage is performed under standard measuring conditions using
voltage meter shown in Figure 1.
5.1.4 Power consumption
Basically, the measurement of power consumption should be carried out under the standard
measuring conditions in 4.1, using a power meter.
Relative luminance
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5.2 Optical measurement methods
5.2.1 Conditions
LED BLU to be measured should be placed in the measurement arrangement and it shall be
assured that all required conditions are fulfilled.
After applying the initial electrical driving conditions to the BLU and after waiting during the
warm-up time specified in 4.3 in order to reach the steady state, the measurement of the
optical quantities of interest shall be started.
Basically, the measurement of this standard should be carried out at various angles between
DUT and LMD. A polar coordinate system (θ,ϕ), with the zenith denoted by θ and the azimuth
denoted by ϕ should be considered (see Figure 3).
z
LMD
θ
y
φ x
12:00
3:00
6:00
9:00
IEC 1678/12
Figure 3 – Definition of zenith angle θ and azimuth angle ϕ.
5.2.2 Luminance
The measurements should be carried out in the dark room under the standard measuring
conditions and for the design viewing directions.
a) Position the DUT.
b) Adjust the LMD to the specified viewing direction, according to angles θ and ϕ.
c) Supply the value of the input signals to the DUT. Then measure the DUT at position p to
i
obtain the luminance L (θ,ϕ). (In case of i = 0, the position implies the centre of the
vi
active area of the BLU.)
The LMD should be carefully checked before measurements, considering the following
checkpoints:
• 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-effects;
• linearity of detection and data-conversion.
NOTE CIE publication 69:1987 is available for reference of LMD evaluation procedures.
5.2.3 Luminance uniformity
Luminance uniformity, U, is a calculated value of how well the luminance remains constant
over the surface of the active area and it is a closely related to luminance measurement itself.
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62595-2 © IEC:2012 – 9 –
The luminance uniformity measurement is sensitive to testing positions. Typical layouts of
measurement points over the BLU surface are shown in Figure 4.
Luminance uniformity, U is calculated using one of the following four formulas which are
popularly used industry-wide.
L
vm
U=
L
vM
L
vM
U=
L
vm
L − L
vM vm
U=
L
vM
L − L
vM vm
U=
L
va
where
L is the maximum luminance value of all measurement points in Figure 4;
vM
L is the minimum luminance; and
vm
L is the average luminance calculated as:
va
N
L
vi
L =
va ∑
N
i=1
where
N is the number of measurement points; and
L is luminance of an arbitrary point.
vi
Typical measurement procedures of luminance uniformity U are as follows. At first, specified
input current and voltage are supplied to the BLU to be measured. Secondly, luminance is
measured at each point of the BLU (5, 9, 13 or 25 points). Basically, this measurement is
carried out usually at normal angle, however, the other angles can be also considered for
certain purposes.
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– 10 – 62595-2 © IEC:2012
H/10 H/10
H/4 H/4
H/10 H/10
H/4 H/4 H/4
H/4
H/4 H/4
H
H
IEC 1679/12 IEC 1680/12
(a) Layout of 25 points (b) Layout of 13 points
H/4 H/4
H/4 H/4
H
H
IEC 1681/12 IEC 1682/12
(c) Layout of 9 points (d) Layout of 5 points
Figure 4 – Examples of measurement point layout
5.2.4 Spectral power distribution
A spectral power distribution S(λ) is measured using a spectrometer or an equivalent optical
instrument. The measuring procedures are basically in accordance with 5.2.2 and 5.2.3.
5.2.5 Chromaticity
CIE 1931 chromaticity coordinates (IEC 60050-845:1987,845-03-28), x, y, z on the BLU
surface of the active area are obtained using the tristimulus values, X, Y, Z calculated from
measured spectral power distribution S(λ) given in 5.2.4 (see IEC 62595-1-2). Basically, this
measurement is carried out usually at normal angle, however, the other angles can be also
considered for certain purposes.
5.2.6 Colour uniformity
Colour uniformity, Δu’v’ should be basically evaluated using CIE 1976 chromaticity(IEC
60050-845:1987,845-03-53) differences between the centre and the other points on the BLU
surface, using the following equation.
2 2 1/2
Δu’v’ = Max [ { (u’ – u’ ) + (v’ – v’ ) } ] i = 1,2,3,.
i centre i centre
where
u’ = 4x / (-2x + 12y +3);
v’ = 9y / (-2x +12y +3);
V/10 V/10
V/4 V/4
V/4 V/4 V/4 V/4
V
V
V/10 V/10
V/4 V/4 V/4 V/4 V/4 V/4
V
V
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62595-2 © IEC:2012 – 11 –
x, y, z are CIE 1931 chromaticity coordinates.
The same measurement points shown in Figure 4 should be used.
5.2.7 Correlated colour temperature
Correlated colour temperature (CCT) is defined in IEC 60050-845:1987,845-03-50. The
calculation method from the measured data based upon the chromaticity coordinates is based
on CIE 15:2004.
1
NOTE Robertson’s procedure is available for an actual computing program.
5.2.8 Angular luminance uniformity
Angular performance of the LED BLU directly affects the whole display performances. The
luminance values at angles at (0°, 0°), (θ, 0°), (θ, 90°), (θ, 180°) and (θ, 270°) in the polar
coordinate system defined in 5.2.1 should be measured as in Figure 5. Measurement at
additional angles should be carried out if necessary.
The above measurements should be carried out at each point of the BLU shown in Figure 4 in
order to obtain angular luminance uniformity.
DUT
(θ, 90°)
(θ, 0°)
(0°, 0°)
(θ, 180°)
LMD
(θ, 270°)
IEC 1683/12
Figure 5 – Angular luminance uniformity measurement
5.2.9 Angular colour uniformity
Angular colour uniformity of BLU affects the whole display angular performance. The angles
can be selected in the same manner as the angular luminance uniformity given in 5.2.8. It
should be in accordance with 5.2.6 to obtain the chromaticity differences between the normal
angle and the other four angles.
—————————
1
See Bibliography
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5.2.10 Measurement methods of block-wise BLU
5.2.10.1 General
A block-wise BLU is used for LCD employing adaptive dimming technology. Each block must
be optimally controlled electrically and optically. A detail of the block segmentation is
determined depending upon the whole display design. The block-wise BLU should be
therefore measured block-by-block for the whole system employing the adaptive dimming
technology.
An example of block-wise checkerboard test pattern is shown in Figure 6.
IEC 1684/12
Figure 6 – Example of test pattern (8 × 10 segments) for block-wise BLU
5.2.10.2 Incoherent point spread function
When a single block turns on and the rest of the blocks turn off, incoherent point spread
function (I-PSF) is defined as a spatial luminance profile spreading outwards. An example of
I-PSF is shown in Figure 7. Based on I-PSF, image signals of LCD are controlled for
optimizing image quality.
IEC 1685/12
Figure 7 – Example of incoherent point spread function
In order to measure the I-PSF, a test pattern shown in Figure 8 should be used. The block of
the backlight unit for the measurement is turned on while all the other blocks are turned off.
The number of measurement points can be determined by manufacturers. Measurement point
size and field of view (FOV), which are determined by an aperture size of the LMD and
measurement distance from DUT to LMD, should be carefully selected. The measurement
point size should be same or smaller than the distance between measurement points, to avoid
overlap. The FOV of the LMD should be sufficiently smaller than the angle which is formed by
the minimum block of BLU and the measurement distance. All the measurement conditions
are followed by 5.2.2 (luminance measuring methods).
From a practical viewpoint, it is more convenient to use a single variable representing I-PSF
than I-PSF itself defined as a function consisting of continuously varying luminance values
(see A.1).
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62595-2 © IEC:2012 – 13 –
IEC 1686/12
Figure 8 – Example of test pattern of incoherent point spread function
5.2.10.3 Block-by-block uniformity
The block-wise checkerboard test pattern shown in Figure 6 or a single white test pattern in
Figure 8 should be used in order to evaluate block-by-block uniformity of I-PSF. Luminance,
colour, and I-PSF uniformity should be evaluated block-by-block. The uniformity values can be
calculated using similar formula shown in 5.2.3. Instead of the measurement points shown in
Figure 4, the centre point of each block should be used in this measurement.
5.2.10.4 Crosstalk
Crosstalk is the amount of light leaking from an on-block to adjacent blocks. It should be
measured using the block-wise checkerboard pattern shown in Figure 6 or a test pattern
shown in Figure 9.
IEC 1687/12
Figure 9 – Example of test pattern of crosstalk
5.2.10.5 Optical signal-to-noise ratio
Optical signal-to-noise (S/N) ratio is the ratio of luminous caused by an optical leakage from
an adjacent block to that of the block by itself. It should be measured using the block-wise
checkerboard pattern shown in Figure 6.
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Annex A
(informative)
Practical measurement methods of block-wise BLU
A.1 Measurement method of a single variable representing I-PSF
A single variable, average slope of I-PSF expressed as S is defined here for convenience
I-PSF
in practice. It is calculated using the luminance values near the turned-on BLU block as in the
following equation and Figure A.1. The number of measurement points, point size and FOV
are determined in the same manner as specified in 5.2.10.2.
n−1
(L − L )
p p
i i+1
∑
d
i=1
S =
I−PSF
n−1
where,
L is the luminance of the measuring point p ,
pi i
d is the distance between the measuring points.
W
W/2
p .p
n i
d
d Distance between measurement points
IE
...
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