(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2008/0100773 A1
`Hwang et al.
`(43) Pub. Date:
`May 1, 2008
`
`US 20080 100773A1
`
`(54) BACKLIGHT, ALENS FOR A BACKLIGHT,
`AND A BACKLIGHT ASSEMBLY HAVING
`THE SAME
`
`(76) Inventors:
`
`Seong Yong Hwang, Seongnam-Si
`(KR); Se Ki Park, Suwon-Si
`(KR); Jin Sung Choi, Cheonan-Si
`(KR); Jin Soo Kim, Seoul (KR)
`Correspondence Address:
`E. CHAU & ASSOCIATES, LLC
`13O WOODBURY ROAD
`WOODBURY, NY 11797
`(21) Appl. No.:
`
`11/923,106
`
`(22) Filed:
`(30)
`
`Oct. 24, 2007
`Foreign Application Priority Data
`
`Oct. 31, 2006 (KR) ............................. 2006-O106462
`
`
`
`
`
`
`
`
`
`Publication Classification
`
`(51) Int. Cl.
`F2IV 23/02
`F2IS 8/00
`GO2F I/335
`F27. II/00
`
`(2006.01)
`(2006.01)
`(2006.01)
`(2006.01)
`
`(52) U.S. Cl. ........... 349/62; 362/235; 362/268; 362/361
`
`ABSTRACT
`(57)
`A lens for a backlight, including: a light transmissive body
`including outer and inner Surface areas, the outer Surface
`area having a convex surface and a concave Surface, the
`inner Surface area having a convex surface and a concave
`surface, wherein the convex surface of the outer surface area
`has a curvature different from a curvature of the convex
`Surface of the inner Surface area and the concave Surface of
`the outer surface area has a curvature different from a
`curvature of the concave surface of the inner Surface area.
`
`1 OO
`120 x 1000
`1 O
`
`2OO
`
`1
`
`LGI 1010
`
`

`

`Patent Application Publication May 1, 2008 Sheet 1 of 9
`
`US 2008/O100773 A1
`
`FIG. 1
`
`
`
`1 O
`
`1 O
`
`FIG 2
`
`
`
`T1
`
`2
`
`

`

`Patent Application Publication
`
`May 1, 2008 Sheet 2 of 9
`
`US 2008/O100773 A1
`
`11
`13
`P2
`Pl
`
`10
`
`2
`14
`
`FIG 3
`
`Light Source
`
`SS
`
`2CE-5
`
`8-5
`
`8-5
`14E-5
`2-5
`w
`
`3.
`
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`
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`
`:
`
`::::::::
`
`
`
`&: S& E:
`
`Distance mm
`
`3
`
`

`

`Patent Application Publication May 1, 2008 Sheet 3 of 9
`
`US 2008/O100773 A1
`
`FIG 5
`
`
`
`FIG. 6
`
`OO
`-N-
`2O 3O
`O
`---
`11 13 12 14 15
`
`O
`
`120
`
`4
`
`

`

`Patent Application Publication
`
`May 1, 2008 Sheet 4 of 9
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`US 2008/O100773 A1
`
`
`
`
`
`
`
`
`
`FIG 7
`
`FIG. 8
`
`O
`1 13 2 14 15
`
`120
`
`nX.
`
`47 4/4 Z/ / 4 / / /
`
`120
`
`O
`
`5
`
`

`

`Patent Application Publication May 1, 2008 Sheet 5 of 9
`
`US 2008/O100773 A1
`
`FIG 9
`
`
`
`6
`
`

`

`Patent Application Publication May 1, 2008 Sheet 6 of 9
`
`US 2008/O100773 A1
`
`a
`
`$3.
`
`1 OO
`
`O
`
`to
`
`200
`
`FIG. 12
`
`
`
`First SubStrate
`
`Second Substrate
`
`Third Substrate
`
`FOUrth Substrate
`
`Fifth SubStrate
`
`7
`
`

`

`Patent Application Publication May 1, 2008 Sheet 7 of 9
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`US 2008/O100773 A1
`
`
`
`8
`
`

`

`Patent Application Publication May 1, 2008 Sheet 8 of 9
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`US 2008/O100773 A1
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`FIG. 14
`
`
`
`9
`
`

`

`Patent Application Publication May 1, 2008 Sheet 9 of 9
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`US 2008/O100773 A1
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`
`
`2OOO
`
`3OO
`
`2OO
`
`10
`
`

`

`US 2008/O 100773 A1
`
`May 1, 2008
`
`BACKLIGHT, A LENS FOR A BACKLIGHT,
`AND A BACKLIGHT ASSEMBLY HAVING
`THE SAME
`
`CROSS-REFERENCE TO RELATED PATENT
`APPLICATION
`0001. This application claims priority to Korean Patent
`Application No. 2006-0106462, filed on Oct. 31, 2006, in
`the Korean Intellectual Property Office, the disclosure of
`which is incorporated by reference herein in its entirety.
`
`BACKGROUND OF THE INVENTION
`0002 1. Technical Field
`0003. The present invention relates backlights, and more
`particularly, to a lens for a backlight capable of uniform
`illuminance distribution, a backlight capable of preventing a
`light leakage phenomenon, and a backlight assembly having
`the same.
`0004 2. Discussion of the Related Art
`0005. A liquid crystal display device displays an image
`by using a separate light Source. In other words, the liquid
`crystal display device does not emit light by itself. There
`fore, the liquid crystal display device includes a lighting unit
`Such as a backlight.
`0006. A cold cathode fluorescent lamp (CCFL) has been
`used as a conventional light source for the backlight. In
`some applications, the CCFL has been replaced with a light
`emitting diode (LED) element having features Such as
`elongated life, low power consumption, light weight, and
`slim size.
`0007. A backlight may include a plurality of LED ele
`ments disposed as a Surface light source on a plane for
`Supplying light to a flat panel liquid crystal display device.
`In this configuration, the light emitted to an overhead area of
`the LED element (e.g., directly upward) has a greatest
`intensity; however, the intensity of the light gradually
`decreases from the overhead area to a peripheral area of the
`LED element. In other words, an illuminance distribution on
`a horizontal plane spaced a predetermined distance apart
`from the LED element exhibits a substantial Gaussian
`distribution, thus the light emitted from the LED element is
`not uniformly distributed over a wide area.
`0008. When such an LED element is used as a surface
`light source of the backlight, the LED elements should be
`arranged at Small intervals. However, this increases the
`number of LED elements disposed on a plane and, in turn,
`the manufacturing cost of the backlight. Further, the light
`emitted from the LED element spreads to the overhead and
`peripheral areas of the LED element. Thus, for example,
`when some of the LED elements in the backlight are driven
`to locally Supply light to an area of a liquid crystal display
`device, the light spreads to the overhead and peripheral areas
`of the LED element, thereby causing a light leakage phe
`OO.
`0009. Accordingly, there exists a need for a backlight that
`includes a plurality of LED elements that provides uniform
`luminance distribution and that prevents a light leakage
`phenomenon.
`
`SUMMARY OF THE INVENTION
`0010. According to an exemplary embodiment of the
`present invention, there is provided a lens for a backlight,
`comprising a light transmissive body including outer and
`
`inner Surface areas, the outer Surface area having a convex
`Surface and a concave Surface, the inner Surface area having
`a convex surface and a concave Surface, wherein the convex
`surface of the outer surface area has a curvature different
`from a curvature of the convex surface of the inner surface
`area and the concave surface of the outer Surface area has a
`curvature different from a curvature of the concave surface
`of the inner Surface area.
`0011. The curvature of the convex surface of the inner
`Surface area is greater than the curvature of the convex
`surface of the outer surface area, and the curvature of the
`concave surface of the inner Surface area is Smaller than the
`curvature of the concave surface of the outer Surface area.
`0012. The convex surface of the outer surface area is
`disposed in a central area of the light transmissive body and
`has a first curvature; the concave Surface of the outer Surface
`area has a second curvature and extends from an end of the
`convex surface of the outer Surface area to an edge of the
`light transmissive body; the convex surface of the inner
`Surface area is disposed in the central area of the light
`transmissive body and has a third curvature greater than the
`first curvature; and the concave Surface of the inner Surface
`area has a fourth curvature Smaller than the second curvature
`and extends from an end of the convex surface of the inner
`surface area to the edge of the light transmissive body. The
`third curvature is about 1.5 times to about 10 times greater
`than the first curvature and the second curvature is about 1.5
`times to about 5 times greater than the fourth curvature.
`0013. According to an exemplary embodiment of the
`present invention, there is provided a backlight comprising
`a substrate; a plurality of light emitting diode (LED) ele
`ments mounted on the Substrate; and a plurality of lenses,
`each lens disposed over an LED element of the plurality of
`LED elements, each lens including a light transmissive body
`having outer and inner Surface areas, the outer Surface area
`having a convex surface and a concave surface, the inner
`Surface area having a convex surface and a concave Surface,
`wherein the convex surface of the outer surface area has a
`curvature different from a curvature of the convex surface of
`the inner Surface area and the concave surface of the outer
`surface area has a curvature different from a curvature of the
`concave surface of the inner Surface area.
`0014. The convex surface of the outer surface area is
`disposed in a central area of the light transmissive body and
`has a first curvature; the concave Surface of the outer Surface
`area has a second curvature and extends from an end of the
`convex surface of the outer Surface area to an edge of the
`light transmissive body; the convex surface of the inner
`Surface area is disposed in a central area of the light
`transmissive body and has a third curvature greater than the
`first curvature; and the concave Surface of the inner Surface
`area has a fourth curvature Smaller than the second curvature
`and extends from an end of the convex surface of the inner
`surface area to the edge of the light transmissive body. The
`LED element is disposed under the concave surface of the
`inner Surface area.
`00.15 Each lens further comprises a protruding member
`disposed in a lower peripheral area of the light transmissive
`body. Each lens further comprises a fixing means for fixing
`the light transmissive body to the substrate.
`(0016. When a full width at a half maximum (FWHM) of
`an illuminance distribution of each lens is 1, an interval
`between adjacent LED elements of the plurality of LED
`elements can be about 0.8 to about 1.2.
`
`11
`
`

`

`US 2008/O 100773 A1
`
`May 1, 2008
`
`0017. The plurality of LED elements emit light on an
`element-by-element basis, or on a group-by-group basis
`when the plurality of LED elements are divided into at least
`two groups.
`0018. According to an exemplary embodiment of the
`present invention, there is provided a backlight comprising
`a substrate; a plurality of LED elements mounted on the
`substrate; and a lens disposed over the plurality of LED
`elements, the lens including a light transmissive body hav
`ing outer and inner Surface areas, the outer Surface area
`having a convex surface and a concave surface, the inner
`Surface area having a convex surface and a concave Surface,
`wherein the convex surface of the outer surface area has a
`curvature different from a curvature of the convex surface of
`the inner Surface area and the concave surface of the outer
`surface area has a curvature different from a curvature of the
`concave surface of the inner Surface area.
`0019. The convex surface of the outer surface area is
`disposed in a longitudinally extending central area of the
`light transmissive body and has a first curvature; the concave
`Surface of the outer Surface area has a second curvature and
`extends from an end of the convex surface of the outer
`Surface area to a longitudinally extending edge of the light
`transmissive body; the convex surface of the inner surface
`area is disposed in the longitudinally extending central area
`of the light transmissive body and has a third curvature
`greater than the first curvature; and the concave Surface of
`the inner surface area has a fourth curvature smaller than the
`second curvature and extends from an end of the convex
`Surface of the inner Surface area to the longitudinally extend
`ing edge of the light transmissive body. The light transmis
`sive body extends in a longitudinal direction.
`0020. The backlight further comprises a filler disposed
`between the lens and the plurality of LED elements.
`0021. According to an exemplary embodiment of the
`present invention, there is provided a backlight assembly
`comprising a light source unit including a Substrate; a
`plurality of LED elements disposed on the substrate to emit
`light; and a plurality of lenses, each lens disposed over an
`LED element of the plurality of LED elements, each lens
`including a light transmissive body having outer and inner
`Surface areas, the outer Surface area having a convex surface
`and a concave surface, the inner Surface area having a
`convex surface and a concave surface, wherein the convex
`surface of the outer surface area has a curvature different
`from a curvature of the convex surface of the inner surface
`area and the concave Surface of the outer Surface area has a
`curvature different from a curvature of the concave surface
`of the inner Surface area; and a receiving member for
`receiving the light source unit.
`0022. The convex surface of the outer surface area is
`disposed in a central area of the light transmissive body and
`has a first curvature; the concave surface of the outer Surface
`area has a second curvature and extends from an end of the
`convex surface of the outer Surface area to an edge of the
`light transmissive body; the convex surface of the inner
`Surface area is disposed in a central area of the light
`transmissive body and has a third curvature greater than the
`first curvature; and the concave Surface of the inner Surface
`area has a fourth curvature Smaller than the second curvature
`and extends from an end of the convex surface of the inner
`Surface area to the edge of the light transmissive body.
`0023 The plurality of LED elements emit light on an
`element-by-element basis, on a group-by-group basis when
`
`the plurality of LED elements are divided into at least two
`groups, or on a Substrate-by-Substrate basis when more than
`one substrate is included in the light source unit. The
`backlight assembly further comprises a light guide plate
`disposed adjacent to the light source unit.
`0024. According to an exemplary embodiment of the
`present invention, there is provided a liquid crystal display
`device comprising a liquid crystal display panel for display
`ing an image; and a backlight assembly for emitting light to
`the liquid crystal display panel, wherein the backlight
`assembly includes a plurality of LED elements for emitting
`light; and a plurality of lenses, each lens including a light
`transmissive body having outer and inner Surface areas, the
`outer Surface area having a convex surface and a concave
`Surface, the inner Surface area having a convex surface and
`a concave Surface, wherein the convex surface of the outer
`surface area has a curvature different from a curvature of the
`convex surface of the inner Surface area and the concave
`surface of the outer surface area has a curvature different
`from a curvature of the concave surface of the inner surface
`aca.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`0025. The above and other features of the present inven
`tion will become more apparent by describing in detail
`exemplary embodiments thereof with reference to the
`accompanying drawings, in which:
`0026 FIG. 1 is a perspective view of a lens for a
`backlight according to an exemplary embodiment of the
`present invention;
`0027 FIG. 2 is a sectional view illustrating the lens of
`FIG. 1;
`0028 FIG. 3 is a sectional view illustrating a light
`emitting characteristic of the lens of FIG. 1;
`0029 FIG. 4 is a simulation result graph illustrating an
`illuminance distribution of the lens of FIG. 1;
`0030 FIG. 5 is a perspective view schematically illus
`trating a backlight according to an exemplary embodiment
`of the present invention;
`0031
`FIG. 6 is a sectional view illustrating the backlight
`of FIG. 5;
`0032 FIG. 7 is a view illustrating an operation of the
`backlight of FIG. 5;
`0033 FIG. 8 is a sectional view illustrating a backlight
`according to an exemplary embodiment of the present
`invention;
`0034 FIG. 9 is a sectional view illustrating a backlight
`according to an exemplary embodiment of the present
`invention;
`0035 FIG. 10 is a perspective view schematically illus
`trating a backlight according to an exemplary embodiment
`of the present invention;
`0036 FIG. 11 is an exploded perspective view schemati
`cally illustrating a backlight assembly according to an
`exemplary embodiment of the present invention;
`0037 FIG. 12 is a illustrates sequential driving of the
`backlight assembly of FIG. 11 as compared to that of a
`conventional backlight assembly:
`0038 FIG. 13 is an exploded perspective view schemati
`cally illustrating a backlight assembly according to an
`exemplary embodiment of the present invention;
`0039 FIG. 14 is an exploded view schematically illus
`trating a backlight assembly according to an exemplary
`embodiment of the present invention; and
`
`12
`
`

`

`US 2008/O 100773 A1
`
`May 1, 2008
`
`0040 FIG. 15 is an exploded perspective view schemati
`cally illustrating a liquid crystal display device according to
`an exemplary embodiment of the present invention.
`
`DETAILED DESCRIPTION OF EXEMPLARY
`EMBODIMENTS
`0041. The present invention will be described more fully
`hereinafter with reference to the accompanying drawings, in
`which exemplary embodiments of the invention are shown.
`This invention may, however, be embodied in many different
`forms and should not be construed as being limited to the
`embodiments set forth herein.
`0042 FIG. 1 is a perspective view of a lens for a
`backlight according to an exemplary embodiment of the
`present invention, and FIG. 2 is a sectional view illustrating
`the lens of FIG. 1. FIG. 3 is a sectional view illustrating a
`light emitting characteristic of the lens of FIG. 1. FIG. 4 is
`a simulation result graph illustrating an illuminance distri
`bution of the lens of FIG. 1.
`0043 Referring to FIGS. 1 and 2, the lens for a backlight
`according to this exemplary embodiment includes a light
`transmissive body 10 having inner and outer curved Sur
`faces.
`0044. In the body 10, the outer curved surface includes a
`convex surface 11 and a concave surface 12, and the inner
`curved surface includes a convex surface 13 and a concave
`surface 14. Specifically, the outer curved surface includes
`the outer convex surface 11 disposed in a central area of the
`body 10 and having a first curvature, and the outer concave
`Surface 12 having a second curvature and extending from an
`end of the outer convex surface 11 to an edge of the body 10.
`In addition, the inner curved surface includes the inner
`convex surface 13 disposed below the outer convex surface
`11 in the central area of the body 10 and having a third
`curvature greater than the first curvature, and the inner
`concave Surface 14 having a fourth curvature Smaller than
`the second curvature and extending from an end of the inner
`convex surface 13 to the edge of the body 10. The body 10
`further includes a vertical surface 15 for connecting between
`the end of the outer concave surface 12 and the end of the
`inner concave surface 14, as shown in FIGS. 1 and 2. The
`vertical surface 15 may be omitted, if necessary. A curved or
`slanted surface may be formed in place of the vertical
`Surface 15.
`0045. The body 10 is formed in a substantially semi
`elliptical spherical shape and provided with a cavity in its
`internal central portion. The semi-elliptical body 10 includes
`a concave edge area defined by the outer concave Surface 12.
`The cavity has a Substantially semi-elliptical spherical shape
`by means of the inner convex surface 13.
`0046) With the lens for a backlight having this structure,
`the illuminance of light concentrated on an overhead area of
`a light source of a backlight can be uniformly distributed
`over a wide overhead area. For example, in the lens for a
`backlight of this exemplary embodiment, the outer and inner
`concave Surfaces 12 and 14 disposed in the edge area of the
`body 10 allow light propagating in a lateral direction of the
`body 10 to be refracted in an upward direction. The outer
`and inner convex surfaces 11 and 13 in the central area of the
`body 10 allow light propagating in the upward direction of
`the body 10 to be refracted in the lateral direction.
`0047 Specifically, as shown in FIG. 3, light emitted to
`the inner convex surface 13 is refracted by the inner convex
`surface 13 to be distant from the central axis (indicated by
`
`a dotted line in FIG. 3) of the body 10, and light emitted to
`the outer convex surface 11 is refracted by the outer convex
`surface 11 to be distant from the central axis of the body 10.
`These refractions are made at boundaries of the outer and
`inner convex surfaces 11 and 13. In this manner, the lights
`emitted to the inner and outer convex surfaces 11 and 13 are
`refracted at their boundaries and spread to be distant from
`the central axis of the body 10. In other words, the lights
`emitted to the central area of the body 10 can spread out in
`the lateral direction. In this case, the light spread can be
`adjusted by changing the first and third curvatures of the
`outer and inner convex surfaces 11 and 13. In other words,
`the illuminance distribution of the light from the light source
`concentrated on the central area can be widened by the outer
`and inner convex surfaces 11 and 13. Meanwhile, light
`emitted to the inner concave surface 14 is refracted by the
`inner concave surface 14 toward the central axis of the body
`10, and light emitted to the outer concave surface 12 is
`refracted by the outer concave surface 14 toward the central
`axis of the body 10. Accordingly, the light emitted to the
`outer and inner concave Surfaces 12 and 14 are refracted at
`their boundaries and concentrated in the central axis of the
`body 10. In other words, the light emitted to the edge area
`of the body 10 can be concentrated in the central area of the
`body 10. In this case, the light concentration can be adjusted
`by changing the second and fourth curvatures of the outer
`and inner concave Surfaces 12 and 14.
`0048. As described above, according to this exemplary
`embodiment, the light emitted to the edge area of the body
`10 is concentrated in the central area, and the light emitted
`to the central area is spread in the lateral direction, thus
`obtaining uniform illuminance distribution over a wide
`overhead area. In addition, the light can be prevented from
`spreading to a peripheral area of the lens.
`0049. Abacklight having the lens according to this exem
`plary embodiment can have a Substantially rectangular illu
`minance distribution as shown in FIG. 4. Here, the graph of
`FIG. 4 shows a simulation result illustrating the illuminance
`distribution on a plane spaced about 40 mm apart from the
`lens for a backlight, which is disposed under a lower end of
`the central axis of the lens (e.g., the center of the body 10).
`It can be seen from FIG. 4 that the illuminance distribution
`is substantially uniform within a radius of about 60 mm from
`the center of the body 10 (e.g., light source), but the light
`illuminance is Suddenly reduced in a radius ranging from
`about 60 mm to about 80 mm. It can also be seen that no
`light is substantially output in a radius over 80 mm. If a full
`width at half maximum (FWHM) that is a peak width at a
`point corresponding to one half of an illuminance peak
`height is defined as a light diffusion distance, the lens for a
`backlight according to this exemplary embodiment has a
`light diffusion distance of about 140 mm.
`0050. Accordingly, it can be seen from the graph of FIG.
`4 that the light concentrated on the central overhead area of
`the light source is spread in the lateral direction of the
`overhead area of the light source by the lens of this exem
`plary embodiment, and the light spreading in the lateral
`direction of the light source is concentrated on the overhead
`area of the light source by the lens. In this manner, the use
`of the lens of this exemplary embodiment can prevent the
`light from spreading in the lateral direction of the light
`Source and make the illuminance distribution uniform in a
`wide overhead area of the light source.
`
`13
`
`

`

`US 2008/O 100773 A1
`
`May 1, 2008
`
`0051. The curvatures of the outer and inner convex
`surfaces 11 and 13 and the outer and inner concave surfaces
`12 and 14 of the lens can be changed to adjust the illumi
`nance distribution. In this exemplary embodiment, the third
`curvature of the inner convex surface 13 is greater than the
`first curvature of the outer convex surface 11, and the second
`curvature of the outer concave Surface 12 is greater than the
`fourth curvature of the inner concave surface 14, thereby
`obtaining the Substantially rectangular illuminance distribu
`tion as described above. In this exemplary embodiment, the
`curvatures of the curved Surfaces can be changed to adjust
`the side slopes of the graph of FIG. 4.
`0052 For example, the third curvature of the inner con
`vex surface 13 is about 1.5 times to about 10 times greater
`than the first curvature of the outer convex surface 11. For
`example, the third curvature of the inner convex surface 13
`is greater than that of the other curved surfaces. The third
`curvature can be about 2 times to about 5 times greater than
`the first curvature. In this case, a magnification of the third
`curvature and the first curvature can be changed to adjust a
`width of the area having the uniform illuminance distribu
`tion. The use of the inner convex surface 13 having the third
`curvature greater than the first curvature can allow light
`emitted to the central overhead area of the lens to widely
`spread in the lateral direction. In addition, the use of the
`outer convex surface 11 having the first curvature can allow
`the light illuminance to be uniformly distributed. In this
`case, when the magnification of the third curvature is Smaller
`than that that of its magnification range, the light does not
`spread widely and uniformly, thus concentrating the light
`illuminance distribution on the central area. When the mag
`nification of the third curvature is greater than that of its
`magnification range, the light in the central area spreads too
`widely, thus degrading the light illuminance distribution in
`the central area.
`0053 For example, the second curvature of the outer
`concave surface 12 is about 1.5 times to about 5 times
`greater than the fourth curvature of the inner concave
`Surface 14. In this case, the inner concave Surface 14 having
`the fourth curvature that is relatively small refracts the light
`emitted in the lateral direction of the lens or toward the edge
`area of the body 10 to the direction of the outer curved
`Surface. The outer concave Surface 12 having the second
`curvature greater than the fourth curvature can concentrate
`the light emitted in the lateral direction of the lens or toward
`the edge area of the body 10 in the central area. Accordingly,
`the light illuminance distribution can be uniform in the
`overhead area of the light source, and the light spread (or
`leakage) to the edge area of the lens can be prevented. Here,
`when a magnification of the second curvature is Smaller than
`that of its magnification range, the light may spread to the
`edge area of the lens. In addition, when it is greater than that
`of its magnification range, the illuminance distribution may
`not be uniform.
`0054. In the lens for a backlight of this exemplary
`embodiment, the body 10 is formed in a bell shape, as shown
`in FIG. 1. For example, the body 10 has one section formed
`in a Substantially hysteresis loop shape with respect to the
`center of the body 10, as shown in FIG. 2. The hysteresis
`loop shape section has two inflection points P1 and P2. In
`this case, the convex surfaces 11 and 13 are located over the
`inflection points P1 and P2 and the concave surfaces 12 and
`14 are located under the inflection points P1 and P2. The first
`inflection point P1 is located at a boundary between the outer
`
`convex surface 11 and the outer concave surface 12, and the
`second inflection point P2 is located at a boundary between
`the inner convex surface 13 and the inner concave surface
`14. When a total height T1 of the body 10 is 1, a height T2
`of the first inflection point P1 from the top of the body 10 can
`range from about 0.1 of T1 to about 0.5 of T1. A height T3
`of the second inflection point P2 from the top of the body 10
`can range from about 0.5 of T1 to about 0.9 of T1. Further,
`when a maximum width T4 of the body 10 is 1, a maximum
`interval T5 between the first two opposite inflection points
`P1 can range from about 0.5 of T4 to about 0.9 of T4. A
`maximum interval T2 between the second two opposite
`inflection points P2 can range from about 0.2 of T4 to about
`0.6 of T4. The heights and intervals of the first and second
`inflection points P1 and P2 may be changed to adjust the
`illuminance distribution of the light emitted via the lens.
`This is because the heights and intervals of the first and
`second inflection points P1 and P2 depend on the curvatures
`of the curved surfaces.
`0055. The lens for a backlight of this exemplary embodi
`ment may further include a protruding member 20 disposed
`in a lower peripheral area of the body 10. For example, the
`protruding member 20 is formed in a substantially circular
`strip, and the light source of the backlight is located in an
`internal space defined by the protruding member 20. In other
`words, a light emitting diode (LED) element for emitting
`white light is located in a central space defined by the
`protruding member 20.
`0056. The lens for a backlight may further include a
`plurality offixing protrusions 30 protruding from the bottom
`area of the protruding member 20. The use of the fixing
`protrusions 30 allows the lens for a backlight of this exem
`plary embodiment to be fixed over the light source. The
`fixing protrusions of a cylindrical shape are shown in FIGS.
`1 and 2. The protrusions are not limited thereto and may be
`formed, for example, in a hook shape. The fixing protrusions
`30 may be omitted, if necessary. For example, the fixing
`protrusions 30 may be omitted if the protruding member 20
`is directly attached to the light Source using an adhesive
`member.
`0057 The foregoing description has illustrated that one
`convex surface and one concave surface having a different
`curvature are provided in each of the inner and outer sides
`of the body of the lens. However, the embodiments of the
`present invention are not limited thereto. For example, a
`plurality of convex surfaces and a plurality of concave
`Surfaces can be provided in each of the inner and outer sides
`of the body of the lens according to this exemplary embodi
`ment. In other words, a plurality of convex surfaces and a
`plurality of concave surfaces may be provided in each of the
`outer and inner surface areas of the body to have different
`curvatures. In this case, the number of the convex surfaces
`may differ from that of the concave surfaces. Further, the
`plurality of convex and concave surfaces may be disposed
`differently depending on certain features of the lens. In other
`words, the convex surfaces may be located in a portion of the
`edge area of the body as well as the central area thereof, and
`the concave surfaces may be located in a portion of the
`central area of the body.
`0.058 A backlight for a backlight assembly including a
`lens for a backlight according to an exemplary embodiment
`of the present invention will now be described.
`0059 FIG. 5 is a perspective view schematically illus
`trating a backlight according to an exemplary embodiment
`
`14
`
`

`

`US 2008/O 100773 A1
`
`May 1, 2008
`
`of the present invention, and FIG. 6 is a sectional view
`illustrating the backlight of FIG. 5. FIG. 7 is a view
`illustrating an operation of the backlight of FIG. 5. FIG. 8 is
`a sectional view illustrating a backlight according to an
`exemplary embodiment of the present invention. FIG. 9 is a
`sectional view illustrating a backlight according to an exem
`plary embodiment of the present invention.
`0060 Referring to FIGS. 5 to 9, the backlight according
`to this exemplary embodiment includes a substrate 110, a
`plurality of LED elements 120 mounted on the substrate 110.
`and a plurality of lenses 100 respectively provided over the
`LED elements 120. Each of the lenses 100 includes a light
`transmissive body 10. The body 10 includes an outer convex
`surface 11 disposed in a central area of the body 10 and
`having a first curvature, an outer concave surface 12 having
`a second curvature and extending from an end of the outer
`convex surface 11 to an edge of the body 10, an inner convex
`Surface 13 disposed in the central area and having a third
`curvature greater than the first curvature, an inner concave
`Surface 14 having a fourth curvature Smaller than the second
`curvature and extending from an end of the inner convex
`surface 13 to the edge of the body 10, and a vertical surface
`15 for connecting between the end of the outer concave
`surface 12 and the end of the inner concave surface 1