throbber
(11) Japanese Unexamined Patent Application Publication No.
`3-189679
`(43) Publication Date: August 19, 1991
`(21) Application No. 1-328228
`(22) Application Date: December 20, 1989
`(71) Applicant: Shin-Etsu Polymer Co., Ltd.
`(72) Inventor: SUZUKI et al.
`(74) Agent: Patent Attorney, Minoru YAKUSHI
`
`SPECIFICATION
`
`1.
`2.
`
`Title of the Invention: SURFACE LIGHT SOURCE DEVICE
`Claims
`(1) A surface light source device comprising a light
`diffusion layer, a transparent light guide layer, and a
`reflective layer, which are successively stacked in a
`direction of a line of sight, the transparent light guide
`layer having an embossed pattern on at least one surface
`thereof, the embossed pattern including discontinuously
`arranged oblique surfaces, at least one or more of which are
`disposed in each cell of a grid with a pitch in a range of
`0.1 to 1.0 mm, wherein a light source and a light-source
`reflective layer are arranged on an edge of the transparent
`light guide layer.
`(2) A surface light source device comprising a light
`
`- 1 -
`
`VIZIO EX. 1008
`K.J. Pretech Ex. 1008
`
`VIIO EX. 1008
`K.J. Pretech Ex. 1008
`
`Pretech_000481
`
`

`
`diffusion layer, a transparent light guide layer, and a
`reflective layer, which are successively stacked in a
`direction of a line of sight, wherein a light source and a
`light-source reflective layer are arranged on at least one
`edge of the transparent light guide layer, the transparent
`light guide layer having an embossed pattern on at least one
`surface thereof, the embossed pattern including a
`quadrangular-pyramid-shaped projection or recess in each
`cell of a grid with a pitch in a range of 0.1 to 1.0 mm, the
`quadrangular-pyramid-shaped projections or recesses having
`oblique surfaces at an angle in a range of 20° to 80°.
`
`(3) The surface light source device according to Claim
`1 or 2, wherein the embossed pattern is such that the
`projection area of the cells of the grid increases as a
`perpendicular distance from the light source increases.
`3. Detailed Description of the Invention
`[Industrial Field of Application]
`
`The present invention relates to surface light source
`devices used for illumination or the like, and more
`particularly, to illumination devices used as surface light
`sources for uniformly illuminating a relatively large area
`by using light from a point light source or a linear light
`source. For example, the present invention relates to
`surface light source devices used as an illumination panel
`for an advertisement display or the like or a backlight of a
`
`- 2 -
`
`Pretech_000482
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`

`
`transmissive liquid crystal display apparatus, and more
`particularly, to a high-brightness surface light source
`device having a uniform brightness distribution.
`[Description of the Related Art]
`
`In general, in the case where fluorescent lamps are
`used for indoor illumination or to illuminate, for example,
`an outdoor advertising board during the night, several
`fluorescent lamps are arranged next to each other and a
`light-diffusing plate-shaped object, such as a milk-white
`plate, is disposed above the fluorescent lamps, so that
`light emitted from the linear light sources is converted
`into pseudo-surface light source. In this method according
`to the related art, because light flux that is emitted from
`each fluorescent lamp uniformly over the entire
`circumference is roughly spread along a plane at a certain
`position, the brightness distribution along a planer region
`in which the light diffusing plate is arranged may include
`unattractive non-uniform portions. These portions visually
`show the outlines or the like of the fluorescent lamps, and
`may degrade the appearance of the illuminating device. To
`prevent this, it is necessary to place the light diffusing
`plate at a position far from the fluorescent lamps, and this
`is a disadvantage from the viewpoint of space requirements
`or the like.
`
`Recently, there has been an increasing demand for a
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`- 3 -
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`Pretech_000483
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`

`
`relatively small surface light source having a uniform
`brightness distribution for use as a backlight of a liquid
`crystal television set, a portable personal computer, or a
`liquid crystal display.
`
`To comply with such a demand, electroluminescence (EL)
`devices and direct backlights, in which fluorescent lamps
`are arranged directly below and the brightness distribution
`is adjusted with a light shielding filter or the like, have
`been developed. However, these devices have poor durability
`and do not provide sufficiently satisfactory diffused
`illumination. Accordingly, Japanese Unexamined Patent
`Application Publication No. 51-88042, for example, has
`proposed a technology for achieving diffused illumination of
`a plane by using a single transparent light guide plate and
`guiding light from a side edge of the transparent light
`guide plate. This technology has already been put into
`practical use in some applications.
`[Problems to be Solved by the Invention]
`
`However, in the case where a single transparent light
`guide plate is used in the structure of the related art,
`since the transparent light guide plate itself has a low
`light diffusion coefficient and the brightness provided
`thereby is low, it is necessary to form a hairline-patterned
`rough surface on a back surface or print an appropriate
`pattern on the back surface by using reflective paint so
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`- 4 -
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`Pretech_000484
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`

`
`that light can be efficiently scattered and the brightness
`can be increased. These methods of improvement have
`limitations, and satisfactory results cannot be obtained
`even though cumbersome processes are required. Also, it is
`necessary to increase the thickness of the transparent light
`guide layer by a considerably large amount to achieve the
`surface brightness required of the surface light source
`device, and there is a problem in that requirements for
`reduction in size and weight of the device cannot be
`satisfied.
`
`The present invention has been made to solve the above-
`described problems of the related art, and an object of the
`present invention is to provide an inexpensive surface light
`source device which includes an extremely thin transparent
`light guide layer but emits light with a brightness that is
`equivalent to or higher than that of light emitted by a
`structure of the related art, which can be reduced in size
`and weight, and which has a simple structure that can be
`easily manufactured.
`[Means for Solving the Problems]
`
`According to the present invention, a surface light
`source device is characterized by including a light
`diffusion layer, a transparent light guide layer, and a
`reflective layer, which are successively stacked in a
`direction of a line of sight, the transparent light guide
`
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`Pretech_000485
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`

`
`layer having an embossed pattern on at least one surface
`thereof, the embossed pattern including discontinuously
`arranged oblique surfaces, at least one or more of which are
`disposed in each cell of a grid with a pitch in a range of
`0.1 to 1.0 mm. A light source and a light-source reflective
`layer are arranged on at least one edge of the transparent
`light guide layer. The embossed pattern may be such that
`the projection area of the cells of the grid gradually
`increases along with the distance from the light source as
`necessary.
`[Operation]
`
`In the surface light source device according to the
`present invention, to increase the reflection and diffusion
`efficiencies and surface brightness, an embossed pattern is
`formed on at least one surface of the transparent light
`guide layer, the embossed pattern including discontinuously
`arranged oblique surfaces, at least one or more of which are
`disposed in each cell of a grid with a pitch in the range of
`0.1 to 1.0 mm. Therefore, light that enters the transparent
`light guide layer through a light incident surface reaches
`an oblique surface or a side in each cell of the grid. The
`light travels through the transparent light guide layer
`while being efficiently scattered by being transmitted
`through or repeatedly totally reflected by an air or
`adhesive layer depending on the incident angle thereof, the
`
`- 6 -
`
`Pretech_000486
`
`

`
`air or adhesive layer being disposed between the transparent
`light guide layer and the reflective layer or between the
`transparent light guide layer and the light diffusion layer
`and having a refractive index smaller than that of the
`transparent light guide layer. As a result, a high-
`brightness surface light source including a relatively thin
`light guide layer can be provided. When the pattern is
`formed such that the projection area of the cells of the
`grid gradually increases along with the distance from the
`light source, the brightness distribution along an effective
`light emitting surface can be adjusted, so that a uniform
`surface light source can be provided.
`[Embodiment]
`
`An embodiment of the present invention will be
`described with reference to Figs. 1 and 2. A light
`diffusion layer 1 is arranged so as to extend over the
`entire area between tubular light sources 4, 4, and a
`transparent light guide layer 2 and a reflective layer 3 are
`successively stacked below the light diffusion layer 1.
`
`The light diffusion layer 1 receives light emitted from
`the transparent light guide layer 2 and uniformly diffuses
`the light over the entire area. Since a white surface light
`source is required as a backlight for a liquid crystal panel
`or the like, a milk-white sheet or plate composed of an
`acrylic resin or a polycarbonate resin containing an
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`Pretech_000487
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`

`
`appropriate light diffusing agent is generally used.
`
`In this case, depending on the type and amount of the
`light diffusing agent contained, there is a risk that the
`diffusing effect or the surface brightness will be reduced
`due to small transmittance. Therefore, it is desirable to
`select a diffusing agent that is suitable for the
`characteristics the device is required to have.
`
`Examples of the transparent light guide layer 2 were
`produced by forming an embossed pattern 21 on both sides of
`acrylic resin plates (Acrylite (trade name), produced by
`Mitsubishi Rayon Co., Ltd.) having a size of 260  170  4
`mm (thickness) or 5 mm over the entire area thereof.
`Referring to Fig. 2A, the embossed pattern 21 was a pattern
`of quadrangular-pyramid-shaped recesses formed at a pitch of
`0.5 mm and having oblique surfaces at an angle of 45°.
`
`When the pitch of the pattern was 0.1 mm or less, the
`depth of the recesses was reduced, and the reflection and
`diffusion efficiencies were reduced accordingly. Therefore,
`sufficient brightness was not obtained, as shown in Table 1.
`
`When the pitch was 1 mm or more, the number of oblique
`surfaces was reduced. Also in this case, as shown in Table
`1, the brightness was reduced. In addition, when the pitch
`is large, there is a risk that the pattern will be visible
`through a light adjusting layer and the light diffusion
`layer, and the visual uniformity will be degraded.
`
`- 8 -
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`Pretech_000488
`
`

`
`Therefore, the pitch is preferably in the range of 0.1 to
`1.0 mm, and more preferably, in the range of 0.4 to 0.6 mm.
`
`With regard to the angle of the oblique surfaces, as
`shown in Table 1, the reflection and diffusion efficiencies
`were low and sufficient brightness was not obtained when the
`angle was 18° or 85°. Therefore, the angle is preferably in
`the range of 20° to 80°, and more preferably, in the range
`of 40° to 60°.
`
`
`
`Example
`
`2
`1
`5
`4
`Quadrangular Quadrangular
`
`Pyramid
`Pyramid
`0.5
`0.5
`
`45
`
`45
`
`Table 1
`Comparative Example
`6
`5
`3
`4
`2
`4
`4
`4
`4
`5
`Quadrangular Quadrangular Hairline Quadrangular Quadrangular
`
`
`
`Pyramid
`Pyramid
`Pyramid
`Pyramid
`0.5
`0.05
`2
`0.5
`0.5
`
`Light Guide Layer
`Thickness (mm)
`Type
`Pitch
`(mm)
`
`Embossed Angle of
`Pattern
`Oblique
`Surfaces
`(°)
`Surface
`Both Sides Both Sides Single Side Both Sides Both Sides
`-
`Direction Single Side Both Sides
`400
`470
`400
`420
`440
`150
`* Brightness (nit)
`600
`650
`*Brightness in a central region of the light emission surface, where the distance from the light source is maximum and the brightness
`is minimum.
`
`The material of the transparent light guide layer 2 is
`not particularly limited, and may be, for example, glass, a
`thermosetting resin such as an epoxy resin or a silicone
`resin, or a thermoplastic resin such as an acrylic resin, a
`polycarbonate resin, or a polyolefin resin such as
`polypropylene or polyethylene. From the viewpoint of
`transmittance, workability, and heat resistance, an acrylic
`resin, a polycarbonate resin, a silicone rubber, or a
`polymer thereof is preferably used.
`
`1
`4
`
`No
`
`-
`
`-
`
`45
`
`45
`
`45
`
`18
`
`85
`
`- 9 -
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`Pretech_000489
`
`

`
`The embossed pattern may be formed on the transparent
`
`light guide layer 2 by any method, and may be easily formed
`by, for example, performing a mechanical process directly on
`the transparent light guide layer 2. Alternatively, when
`the transparent light guide layer 2 is composed of a
`thermoplastic resin, the embossed pattern may be easily
`formed by performing a thermal pressing process for
`transferring a pattern formed on a separate component, such
`as a roll-shaped or plate-shaped steel member, in advance or
`performing injection molding or casting using a mold having
`the pattern.
`
`The reflective layer 3 may be composed of, for example,
`an evaporated aluminum sheet or a synthetic resin plate made
`of, for example, a PET acrylic material or ABS containing a
`diffusing agent. In the examples, a "Tetryte" (trade name,
`produced by Tokyo Oike Sangyo Co., Ltd) sheet obtained by
`evaporating silver onto a PET base and then performing a
`top-coating process was used.
`
`Reference numeral 4 denotes light sources, and two
`three-wavelength cold-cathode tubes (produced by Stanley
`Electric Co., Ltd.) having a tube diameter of 6 mm, an
`effective light emission length of 260 mm, a tube current of
`5 mA, and a tube brightness of 7000 nit, were arranged in
`the longitudinal direction so as to face each other.
`Reference numeral 5 denotes light-source reflective layers
`
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`Pretech_000490
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`

`
`provided to reduce loss of light emitted by the light
`sources 4 and direct the light so that the light was
`effectively guided to the incident end surfaces of the
`transparent light guide layer 2. The material of the light-
`source reflective layers was the same as that of the
`reflective layer 3.
`
`The layers may be stacked together in such a manner
`that outer peripheral regions around an illumination surface
`serve as bonding regions in which the layers are bonded
`together by pieces of double-sided adhesive tape or an
`adhesive, welded together, or fixed to each other by, for
`example, being fitted to a form frame or other frames. In
`addition, to reduce loss of light, a reflective sheet (not
`shown) that is similar to the reflective layer 3 is
`preferably bonded to side portions where the light sources 4
`are not provided. In any case, the components are
`preferably integrally bonded or assembled together.
`
`In the surface light source device according to the
`present embodiment, the light sources were turned on through
`an inverter at a power supply voltage of 12 V. As a result,
`as shown in Table 1, the surface brightness was 650 nit when
`the thickness was 5 mm, and 600 nit when the thickness was 4
`mm.
`As Comparative Example 1, a 4-mm-thick flat acrylic
`
`plate (not processed) was used in place of the transparent
`
`- 11 -
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`Pretech_000491
`
`

`
`light guide layer 2. In this case, the brightness was 150
`nit. As Comparative Example 2, a 5-mm-thick acrylic plate
`having a hairline pattern formed on both sides thereof, the
`hairline pattern having a pitch of 0.5 mm and including
`oblique surfaces at an angle of 45°, was used as a
`transparent light guide layer. In this case, the brightness
`was 400 nit. Thus, it was found that, with the embossed
`pattern including quadrangular-pyramid-shaped elements
`arranged in a grid according to the present invention, the
`diffusion efficiency and the surface brightness can be
`increased compared to those achieved by the hairline pattern
`according to the related art, and a higher brightness can be
`achieved by a thinner light guide layer compared to those of
`the related art.
`
`As is clear from Comparative Examples 3, 4, 5, and 6,
`when the embossed pattern was formed on 4-mm-thick acrylic
`plates such that the angle of oblique surfaces was 45° and
`the pitch was 0.05 or 2 mm, and such that the pitch was 0.5
`mm and the angle of oblique surfaces was 18° or 85°, the
`brightnesses were 470 nit, 400 nit, 420 nit, and 440 nit.
`Thus, the light diffusion efficiency was low and sufficient
`reflecting and diffusing effect was not obtained by the
`embossed pattern including the quadrangular-pyramid-shaped
`elements.
`Here, the embossed pattern 21 may be a pattern of
`
`
`- 12 -
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`Pretech_000492
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`

`
`quadrangular-pyramid-shaped projections, as illustrated in
`Fig. 3, or a pattern of elements having the shape of a
`triangular pyramid or other pyramids, a conical shape, or a
`truncated pyramidal or conical shape. Alternatively, the
`embossed pattern 21 may be a pattern including mountain-
`shaped or valley-shaped elements, each including one or two
`oblique surfaces, or a pattern including oblique surfaces
`that are discontinuously arranged so that the combination
`thereof including vertical surfaces does not form a hairline
`pattern. Moreover, it is not necessary to form the embossed
`pattern 21 on both sides, and the embossed pattern 21 may
`instead be formed only one of the front and back surfaces.
`
`In this case, the angle  of the oblique surfaces is
`selected from the range of 20° to 80°. Also, the grid is
`not limited to those having rectangular cells, and a grid
`having polygonal cells, such as triangular cells, may be
`formed as appropriate in accordance with the combination of
`the oblique surfaces.
`
`Figs. 4 to 6 show other examples of embossed patterns
`formed on the transparent light guide layer 2. Fig. 4 shows
`an example in which four oblique surfaces oriented in
`respective directions are at different angles. Similar to
`the above-described examples, the quadrangular-pyramid-
`shaped elements may either be projections, whose apices
`project outward, or recesses. Alternatively, these
`
`- 13 -
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`Pretech_000493
`
`

`
`projections and recesses may be partially mixed. However,
`preferably, quadrangular-pyramid-shaped elements are
`recesses.
`
`Fig. 5 shows an example in which the pitch is gradually
`changed. Fig. 6 shows an example in which the arrangement
`of the quadrangular-pyramid-shaped elements is changed by
`arranging the cells of the grid in a staggered pattern. As
`illustrated in Fig. 7, a triangular-pyramid-shaped element
`may be arranged in each cell of the grid. Alternatively, as
`illustrated in Figs. 8 and 9, the embossed pattern 21 may be
`formed such that one or two oblique surfaces are arranged in
`each cell of the grid.
`
`The surface of the above-described transparent light
`guide layer 2 on which the embossed pattern is formed is at
`the back side and faces the reflective layer 3. The space
`between the transparent light guide layer 2 and the
`reflective layer 3 may be filled with an adhesive.
`Alternatively, an air layer may be provided between the
`transparent light guide layer 2 and the reflective layer 3.
`Embossed patterns having different pitches may be formed on
`the front and back surfaces of the transparent light guide
`layer 2.
`
`As a result of various studies regarding the embossed
`pattern 21 on the transparent light guide layer 2, it was
`found that when the embossed pattern is formed such that the
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`Pretech_000494
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`

`
`projection area of the embossed elements gradually increases
`along with the distance from each light source, as
`illustrated in Fig. 10, a surface light source device having
`a uniform brightness distribution over an effective light
`emitting area can be obtained.
`
`The area of each embossed element does not exceed the
`area of each cell of the grid at a predetermined pitch in
`the range of 0.1 to 1.0 mm. However, the area of each
`embossed element is preferably as large as possible to
`increase the brightness. The minimum value of the area of
`each embossed element is not limited in any way.
`
`The change rate at which the area of the embossed
`elements is changed between the maximum value and the
`minimum value may be determined arbitrarily. Here, the
`illuminance at a certain point is inversely proportional to
`the square of the distance between that point and a light
`source. In addition, the intensity of light degreases in a
`transparent medium. On the basis of these facts and the
`result of various experiments, it was found that
`satisfactory brightness distribution can be obtained when,
`assuming that the embossed elements are square shaped as
`illustrated in Fig. 10, the length Y of each side for the
`distance X from the light source is set so as to satisfy an
`exponential-logarithmic equation Y = a + blnX (1) (where a
`and b are values determined by a light diffusion layer, a
`
`- 15 -
`
`Pretech_000495
`
`

`
`reflective layer, a light source, a light-source reflective
`layer, a pitch, and the maximum and minimum areas of the
`embossed elements), that is, so that the area of the
`embossed elements is Y2 = (a + blnX)2. Therefore, the
`embossed pattern is preferably formed so as to satisfy this
`equation.
`
`In Example 3, a transparent light guide layer 2 was
`produced by forming an embossed pattern 21 on one side of an
`acrylic resin plate (Acrylite (trade name), produced by
`Mitsubishi Rayon Co., Ltd.) having a size of 260  170  5
`mm (thickness) over the entire area thereof. Referring to
`Fig. 10, the embossed pattern 21 included quadrangular-
`pyramid-shaped recesses which were arranged in a vertically
`symmetrical manner at a pitch of 0.5 mm and which had
`oblique surfaces at an angle of 45°. The length of each
`side of the embossed elements En at the largest
`perpendicular distance from the light sources at both edges
`was set to a maximum length 0.380 mm, and the length of each
`side of the embossed elements E1 closest to the light source
`regions was set to 0.210 mm. The length of each side of the
`embossed elements En-1 to E2 between them was set so as to
`satisfy Y = 0.184 + 0.144lnX. A light diffusion layer 1, a
`reflective layer 3, light sources 4, and light-source
`reflective layers 5 were similar to those in the above-
`described examples. The two light sources were turned on
`
`- 16 -
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`Pretech_000496
`
`

`
`through an inverter at a power supply voltage of 12 V. As a
`result, as shown in Table 2, a surface light source whose
`brightness is as high as 700 nit and which has a very
`uniform brightness distribution along an effective light
`emitting surface was obtained.
`Table 2
`Comparative
`Example
`7
`4
`Quadrangular
`Pyramid
`0.5
`
`
`
`Example
`
`3
`4
`Quadrangular
`Pyramid
`0.5
`
`4
`4
`Quadrangular
`Pyramid
`0.5
`
`45
`
`45
`
`45
`
`Single Side
`
`Single Side
`
`Single Side
`
`0.188
`0.044
`
`700
`3
`
`
`
`0.008
`0.044
`
`450
`4
`
`
`
`(Uniform
`Pattern)
`
`600
`35
`
`Embossed
`Pattern
`
`Light Guide Layer
`Thickness (mm)
`Type
`Pitch (mm)
`Angle of
`Oblique
`Surfaces (°)
`Surface
`Direction
`Logarithmic
`Equation *
`a =
`b =
`Brightness (%)
`** Brightness Variation (nit)
`Brightness Distribution
`Region
`* Y = a + blnX
`
`** Light Source Variation =
`
`min)
`(max
`
`max
`
`
`
`
`
`(%)100
`
`
`
`As Comparative Example 7, a pattern of quadrangular-
`
`pyramid-shaped recesses arranged at a pitch of 0.5 mm and
`having oblique surfaces at an angle of 45° was formed over
`the entire area of an acrylic plate similar to the above-
`described acrylic plate. The brightness and brightness
`distribution of Comparative Example 7 were compared with
`those of Example 3. As a result, the brightness variation
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`- 17 -
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`Pretech_000497
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`

`
`of Comparative Example 7 was as large as 35%, and the
`brightness thereof was 600 nit. In contrast, in Example 3,
`in which the embossed elements were formed such that the
`projection area thereof varied, the optical path in the
`transparent light guide layer was controlled by the embossed
`pattern, and a large amount of light in regions near the
`light sources was guided through the light guide layer to a
`central region in which the amount of light was small. As a
`result, the brightness distribution was corrected over the
`entire area of the light emitting surface, and was made
`uniform. In addition, loss of light in the regions near the
`light sources was reduced, and high brightness was obtained.
`
`As Example 4, a and b in Equation (1) were set to a =
`0.008 and b = 0.044, respectively, and the length of each
`side of the largest embossed elements was set to 0.200 mm (X
`= 80). In this case, although the brightness distribution
`was uniform, since the total projection area of the embossed
`elements in the entire area of the light emitting surface
`was small, the amount of light emitted from the light
`emitting surface was reduced. Therefore, the brightness was
`450 nit, and was not very high.
`
`Therefore, the area of each embossed element is
`preferably increased to increase the brightness. Also, the
`brightness suitable for the use of the device can be
`obtained by appropriately setting the area of each embossed
`
`- 18 -
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`Pretech_000498
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`

`
`element.
`
`The embossed pattern is not limited to the square
`pyramid pattern as illustrated in Fig. 10, and may instead
`be a pattern of other pyramidal shapes, as illustrated in
`Fig. 12. Alternatively, two or more of such shapes may be
`employed in combination.
`
`In addition, it is not necessary that the projection
`area of the embossed elements be gradually changed. For
`example, as illustrated in Fig. 13, the embossed elements
`may be grouped into blocks, each including several embossed
`elements, and the projection area of the embossed elements
`may be changed in units of blocks within a range in which
`the brightness distribution is not affected.
`In this case, the angle  of the oblique surfaces of
`
`the embossed elements is selected from the range of 20° to
`80°. In the case where only one light source is provided, a
`pattern illustrated in Fig. 11 may be employed.
`
`The region in which the pattern is formed is not
`limited to the entire area of the light emitting surface,
`and the pattern may instead be formed only in a region where
`the function of a light source is to be provided.
`
`Fig. 14 illustrates an example in which embossed
`elements having oblique surfaces at different angles are
`alternately arranged and all of the embossed elements have
`the same depth. Fig. 15 illustrates an example in which the
`
`- 19 -
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`Pretech_000499
`
`

`
`angle of oblique surfaces increases as the distance from the
`light source decreases. Fig. 16 illustrates an example in
`which projecting embossed elements are mixed. Fig. 17
`illustrates an example in which the embossed elements are
`arranged in a staggered pattern. Fig. 18 illustrates an
`example in which triangular-pyramid-shaped elements are
`arranged as elements having pyramidal shapes other than
`quadrangular pyramid. Fig. 19 illustrates an example in
`which the pitch of the embossed elements is gradually
`changed. Fig. 20 illustrates an example in which various
`pyramid-shaped elements are mixed. All or some of these
`examples may also be employed in combination.
`[Advantages of the Invention]
`
`According to the present invention, the transparent
`light guide layer has an embossed pattern on at least one
`surface thereof, the embossed pattern including
`discontinuously arranged oblique surfaces, at least one or
`more of which are disposed in each cell of a grid with a
`pitch in the range of 0.1 to 1.0 mm. Therefore, light that
`enters the transparent light guide plate through a light
`incident surface reaches an oblique surface or a side in
`each quadrangular-pyramid-shaped element. Then, the light
`travels through the light guide plate while being
`efficiently scattered by being transmitted through or
`repeatedly totally reflected by an air layer or an adhesive
`
`- 20 -
`
`Pretech_000500
`
`

`
`layer depending on the incident angle thereof, the air layer
`or the adhesive layer being disposed between the light guide
`plate and a reflective plate or between the light guide
`plate and a light diffusion plate and having a refractive
`index smaller than that of the light guide plate. When the
`embossed elements are formed such that the projection area
`thereof gradually increases along with the distance from the
`light source, the brightness distribution along the
`effective light emitting surface can be made uniform without
`using an additional member for light adjustment. As a
`result, the function of a surface light source can be
`provided, and the size and weight of the entire device can
`be reduced.
`4. Brief Description of the Drawings
`
`Fig. 1 illustrates a surface light source device
`according to an embodiment of the present invention, wherein
`Fig. 1A is a perspective view illustrating the assembly and
`Fig. 1B is a vertical sectional view. Figs. 2A and 2B are
`an enlarged plan view and a sectional view, respectively, of
`a transparent light guide plate. Figs. 3A and 3B are an
`enlarged plan view and a sectional view, respectively, of a
`transparent light guide plate according to another example.
`Figs. 4 to 7 are enlarged plan views of transparent light
`guide plates according to other examples. Fig. 8A is an
`enlarged plan view illustrating an example in which a single
`
`- 21 -
`
`Pretech_000501
`
`

`
`oblique surface is disposed in each cell of a grid. Fig. 8B
`is a vertical sectional view of Fig. 8A taken along line I-I.
`Fig. 9A is an enlarged plan view illustrating an example in
`which two oblique surfaces are disposed in each cell of a
`grid. Fig. 9B is a vertical sectional view of Fig. 9A taken
`along line II-II. Fig. 10 is an overall view of a pattern
`in which the projection area of embossed elements is changed
`in the case where two light sources are used. Fig. 11A is
`an enlarged plan view of the pattern in the case where a
`single light source is used. Fig. 11B is a vertical
`sectional view of Fig. 11A. Fig. 12A is an enlarged plan
`view of the pattern according to another example. Fig. 12B
`is a vertical sectional view of Fig. 12A. Fig. 13A is an
`enlarged plan view illustrating the case in which the
`embossed elements are grouped into blocks and the projection
`area thereof is changed in units of blocks. Fig. 13B is a
`vertical sectional view of Fig. 13A. Parts (A) and (B) of
`Figs. 14 to 16 are plan views and vertical sectional views
`of parts of other examples. Figs. 17 to 20 are partial plan
`views of transparent light guide plates according to other
`examples.
`
`1: light diffusion layer, 2: transparent light guide
`layer, 3: reflective layer, 4: light source, 5: light-source
`reflective layer.
`
`
`- 22 -
`
`Pretech_000502

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