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SEMI D35-1103 E © SEMI 2003 12 R3-3.4 On the other hand, when the tem p erature is high, the mercury molecule densit y goes up dramatically, reabsorption of ultrav iolet rays by mercury itself takes place, the amount of …
SEMI D35-1103
E
© SEMI 2003 11
RELATED INFORMATION 3
PRECAUTIONS AGAINST MEASURING METHOD OF COLD
FLUORESCENT LAMP
NOTICE: This related information is not an official part of SEMI D35 and was derived from Japan Backlight TF.
R3-1 Introduction
R3-1.1 The cold fluorescent lamp (CCFL) is turned on
usually by using a compact DC/AC convertible power
supply called inverter. The CCFL has been developed
with top priorities such as a narrow diameter, space-
saving shape and high brightness for its application and
so the inverter has been requested to have a low profile
space-saving shape with high efficiency as well.
R3-1.2 Understanding these requirements are satisfied
and the characteristics such as high voltage, high
frequency and micro current are compassable as trade-
off in the CCFL, we should handle it with care.
R3-2 Stray Capacitance and Leakage Current
R3-2.1 Stray Capacitance
R3-2.1.1 The stray capacitance is defined as a
characteristic that behaves as if it had the electrostatic
capacity that system does not provide and its volume is
too unstable to be measured quantitatively
(unintentional electrostatic capacity element). If a
formula for electrostatic capacity between two parallel
copper wires is put into an equation, it will be nearly
expressed as follows;
C = Q/V = (0)/(log ((da)/a) ------ (1)
where
C: electrostatic capacity (stray capacitance)
d: distance between wires
a: diameter of wire
R3-2.1.2 According to the above-mentioned equation
(1), it is understood that the stray capacitance does not
affect the frequency but is inversely proportional to
logarithm of the distance between wires. (This means
that the closer the distance between high potentials
becomes, the more the stray capacitance increases, and
the longer the wire becomes, the stray capacitance
increases as well.)
R3-2.2 Leakage Current
R3-2.2.1 The leakage current is the inverter secondary
current that flows to the above-mentioned stray
capacitance. (It equal to the inverter secondary current
except for that of CCFL.) Suppose “C” is the stray
capacitance around CCFL and “I” is the current that
flows to “C” and sinusoidal AC voltage is applied, the
bellow-equation is obtained.
I = ·C·V = 2f·C·V ------ (2)
where
I: leakage current (true AC current)
f: AC frequency
C: stray capacitance (electrostatic capacity)
V: tube voltage (true AC voltage)
R3-2.2.2 According to the above-mentioned equation
(2), the leakage current increases proportionally to the
increase of the frequency, stray capacitance, or
potential difference.
R3-2.2.3 Since the stray capacitance and leakage
current increase or decrease by each parameter such as
the length of high voltage wire, distance between the
wire and the conductor of ground, lighting frequency
and potential difference, it is recommended that
measuring conditions should be specified and
standardized as much as possible.
R3-3 Temperature Characteristics
R3-3.1 The CCFL is quite sensitive to mercury
temperature characteristics because its fluorescent
substance emits light receiving ultraviolet rays from
mercury particles as activation energy.
R3-3.2 If the temperature of mercury particles is
regarded as the same as the CCFL wall temperature
when lighting, and suppose the tube temperature is
25°C at 0°C of ambient temperature against wall
temperature at 50°C, approximately 1/10 of saturated
steam pressure difference will take place and actual
luminance of the tube will be approximately 1/2. On
the contrary for the high temperature side, suppose the
wall temperature is 100°C against the ambient
temperature 70°C the steam pressure difference which
is greater by 20 times will take place and the actual tube
luminance is approximately 2/3.
R3-3.3 In this manner, the temperature and tube
luminance have peak characteristics within a certain
temperature range because the partial pressures of Ar,
Ne and Hg have the optimum density against the
lighting tube current. When the temperature is low, the
luminance decreases due to the lack of absolute amount
of ultraviolet rays caused by insufficient mercury
molecules.
SEMI D35-1103
E
© SEMI 2003 12
R3-3.4 On the other hand, when the temperature is
high, the mercury molecule density goes up
dramatically, reabsorption of ultraviolet rays by
mercury itself takes place, the amount of ultraviolet
rays that reach the fluorescent substance decreases and
so the luminance decreases accordingly. The further
attention necessary is that the mass (thickness) of glass
tube is made as thin as possible because the CCFL has
been developed with such top priority as to have the
narrow diameter, space-saving shape and high
luminance. For this reason, the heat capacity is very
small, which means the inside mercury molecule
temperature will be affected greatly by heat transfer
caused by interference with surrounding members and
cooling effect of convective wind to the glass.
R3-3.5 Since the luminance varies due to the impact to
the glass temperature by each parameter such as the
interference of surrounding members, contact of other
materials and cooling effect of convective wind, it is
recommended that measuring conditions should be
specified and standardized as much as possible.
Tem p. vs M ercury vapor
0.0001
0.001
0.01
0.1
1
10
100
1000
0 100 200 300 400
Temp. (
℃
)
Vaper pressure
（
mmHg
）
Ambient Tem p. v s L u m inance
0
20
40
60
80
100
120
-40 -20 0 20 40 60 80 100
Ambient Tem p. (℃ )
Lum inance variation
(% )
Luminance(100% at 25
℃
）
Tem p. vs M ercury vapor
0.0001
0.001
0.01
0.1
1
10
100
1000
0 100 200 300 400
Temp. (
℃
)
Vaper pressure
（
mmHg
）
Ambient Tem p. v s L u m inance
0
20
40
60
80
100
120
-40 -20 0 20 40 60 80 100
Ambient Tem p. (℃ )
Lum inance variation
(% )
Luminance(100% at 25
℃
）
R3-4 Slide-up Speed
R3-4.1 The status where a main discharge starts is
measured for the measurement of stable discharge
voltage sliding gradually the voltage up from the
sufficiently low value. Since the starting point of main
discharge may vary by the slide-up speed, a special
attention should be paid.
R3-4.2 When the slide-up speed is so slow that the
ratio of partial pressure of Ar, Ne and Hg shifts to the
condition where lighting is easily performed because
the mercury vapor pressure increases by the heat
generation caused by half-lighting, the main discharge
may begin easily compared to the condition at low
CCFL temperature.
R3-4.3 Therefore, when measuring the CCFL, these
conditions should be specified and standardized as
much as possible.
R3-5 Use of Master CCFL
R3-5.1 When interrelating the spectroradiometer and
colorimeter, an actual CCFL is used often as a master
CCFL.
Precautions for such cases are
1) the registration date, production history, lighting
history and expiring date of the master CCFL
should be specified and attached to it, and
2) the master CCFL should be kept such that there
shall be no impact to reproduction of
measurement.
R3-5.2 Since this document is positioned as a related
document to standardized documents, the contents are
treated as “just for information”.
NOTICE: SEMI makes no warranties or
representations as to the suitability of the standards set
forth herein for any particular application. The
determination of the suitability of the standard is solely
the responsibility of the user. Users are cautioned to
refer to manufacturer's instructions, product labels,
product data sheets, and other relevant literature,
respecting any materials or equipment mentioned
herein. These standards are subject to change without
notice.
By publication of this standard, Semiconductor
Equipment and Materials International (SEMI) takes no
position respecting the validity of any patent rights or
copyrights asserted in connection with any items
mentioned in this standard. Users of this standard are
expressly advised that determination of any such patent
rights or copyrights, and the risk of infringement of
such rights are entirely their own responsibility.
Copyright by SEMI® (Semiconductor Equipment and Materials
International), 3081 Zanker Road, San Jose, CA 95134. Reproduction of
the contents in whole or in part is forbidden without express written
consent of SEMI.
SEMI D36-1103 © SEMI 2003 1
SEMI D36-1103
TERMINOLOGY FOR LCD BACKLIGHT UNIT
This standard was technically approved by the Global Flat Panel Display Committee and is the direct
responsibility of the Japanese Flat Panel Display Committee. Current edition approved by the Japanese
Regional Standards Committee on August 8, 2003. Initially available at www.semi.org October 2003; to be
published July 2003.
1 Purpose
1.1 These terms and definitions describe various
components and characteristics of backlight unit used
for light source of liquid crystal display. This standard
will be helpful to unify terminologies used for backlight
unit, which will improve manufacturing efficiency
resulting in reduction of manufacturing cost and time.
2 Scope
2.1 This standard is applicable to backlight unit. This
standard includes the terminologies of components used
in Backlight unit, inspection and measurement used in
backlight unit field as well as panel and instrumentation
field. The other area is not dealt with other SEMI
standard document.
NOTICE: This standard does not purport to address
safety issues, if any, associated with its use. It is the
responsibility of the users of this standard to establish
appropriate safety and health practices and determine
the applicability of regulatory or other limitations prior
to use.
3 Limitations
3.1 In this standard, our target is only backlight unit
and general purpose for terminology. Hence a special
language used for critical purpose is not mentioned. For
example, we do not define special languages depending
to personal emotion and a detail or small components
depending on special or general purpose.
3.2 The definition of lamp components follows the
language used in lighting company or other optics
related standardization.
4 Referenced Standards
4.1 CIE Standards
1
CIE 1931 — color space, CIE 1976 UCS
NOTICE: Unless otherwise indicated, all documents
cited shall be the latest published versions.
1 CIE International Commission on Illumination, Kegelgasse 27, A-
1030 Vienna, Austria
5 Terminology
5.1 General Terminology
5.1.1 Definition of Backlight Unit
5.1.1.1 Backlight unit (BLU) is a kind of light source
positioned at the backside of liquid crystal panel. Since
LCD is non-emissive display device it needs essentially
light source.
5.1.2 Structure of BLU
5.1.2.1 As an initial light source cold cathode
fluorescence lamp (CCFL) is used at bottom and/or
topside of BLU. The light emitted from CCFL is
entered into light guide plate (LGP). Here light is
spread out two-dimensional light by scattering sites at
the back surface LGP or inside of LGP. Two-
dimensional light is sometimes diffused by diffusion
sheet or conversed by prism sheet respectively. And
final light comes into human eyes.
g
e
d
c
b
f
a
Figure 1
General structure of BLU; From a) to g), each
components are indicate CCFL, reflection sheet,
light guide plate, diffusion sheet, two prism sheets,
protection sheet and panel respectively.
5.2 Components — The following measurement items
are recommended for BLU but these items depend on
user requirements if they are specified.
5.2.1 cold cathode fluorescence lamp — the positive
column or cathode discharge lamp of the glow
discharge. Namely, the ultraviolet by the releasing of
the second electron of cathode stimulates the phosphor,
so the lamp radiates the visible ray.