throbber
(11) Japanese Unexamined Patent Application Publication No.
`6-250178
`(43) Publication Date: September 9, 1994
`(21) Application No. 5-038216
`(22) Application Date: February 26, 1993
`(71) Applicant: Nihon Denyo Co., Ltd.
`(72) Inventor: Matsuoka et al.
`(74) Agent: Patent Attorney, Tani et al.
`
`(54) [Title of the Invention] SURFACE LIGHT SOURCE
`APPARATUS
`
`
`(57) [Abstract]
` [Object] An object is to obtain surface luminance with
`uniformity while retaining the optical intensity of a light
`source.
` [Construction] An elongated light source 12, which has a
`predetermined diameter D, is provided inside a housing 11,
`which has an opening 11A at its top. The opening 11A is
`covered by a prism lens sheet 13, over which a light-
`diffusing sheet 14 is provided. The distance from the
`elongated light source 12 to the prism lens film 13 is set
`to be a predetermined distance at which there is no gap
`between images that are formed by the elongated light source
`12 on the surface of the prism lens film 13.
`
`- 1 -
`
`Page 1 of 19
`
`TOYOTA EXHIBIT 1022
`
`

`

`[Claims]
`[Claim 1] A surface light source apparatus, comprising:
`
`a housing that has an opening at its top;
`
`at least one elongated light source that is provided
`inside the housing and has a predetermined diameter; and
`
`a prism lens film by which the opening is covered,
`
`wherein a distance from the elongated light source to
`the prism lens film is set to be a predetermined distance at
`which there is no gap between images that are formed by the
`elongated light source on the prism lens film.
`[Claim 2] The surface light source apparatus according to
`Claim 1,
`
`wherein the prism lens film is made up of plural prism
`lens films; and
`
`wherein the plural prism lens films are provided at the
`predetermined distance at which there is no gap between
`images that are formed by the elongated light source on the
`outermost one of the plural prism lens films.
`[Claim 3] The surface light source apparatus according to
`Claim 1,
`
`wherein the housing has reflection surfaces as inner
`surfaces of a light-source housing space, in which the
`elongated light source is housed;
`
`wherein the reflection surfaces include a first
`reflection surface, which is parallel to the prism lens film,
`
`- 2 -
`
`Page 2 of 19
`
`

`

`and second reflection surfaces, which are provided
`respectively at two sides next to the elongated light
`source;
`
`wherein each of the second reflection surfaces is
`located at a distance from the elongated light source, said
`distance being twice as large as the diameter of the
`elongated light source, or less than twice; and
`
`wherein each of the second reflection surfaces is
`inclined at a predetermined angle with respect to the first
`reflection surface.
`[Claim 4] The surface light source apparatus according to
`Claim 1,
`
`wherein the elongated light source is made up of plural
`elongated light sources; and
`
`wherein the plural elongated light sources are arranged
`at pitch that is twice as large as the diameter of the
`elongated light source, or less than twice.
`[Claim 5] The surface light source apparatus according to
`any of Claims 1 to 4, further comprising a diffusion film
`provided over a front surface of the prism lens film.
`[Detailed Description of the Invention]
`[0001]
`[Field of Industrial Application] The present invention
`relates to a surface light source apparatus. More
`particularly, the invention relates to a direct-under-type
`
`- 3 -
`
`Page 3 of 19
`
`

`

`surface light source apparatus that is mounted behind a non-
`self-luminous display device such as a liquid crystal
`display device in portable electronic equipment such as a
`liquid crystal television, a word processor, a person
`computer, etc., and is used as a light source for
`backlighting such a non-self-luminous display device.
`[0002]
`[Description of the Related Art] As a structure of such a
`direct-under-type surface light source apparatus, for
`example, the following structure is known in the art (refer
`to Japanese Examined Patent Application Publication No. 59-
`008809). An elongated light source such as a fluorescent
`lamp is provided inside a housing that has an opening. A
`diffusion plate is provided at the opening. For the purpose
`of overcoming the lack of optical uniformity, a light
`control film (LCF) is interposed between the lamp and the
`diffusion plate.
`[0003]
`[Problems to be Solved by the Invention] In general, it is
`required that such a surface light source apparatus should
`have uniform illumination luminance throughout the entire
`surface irrespective of a distance from a light source, and,
`in addition, it is required that the original intensity of
`light emitted from the light source should be retained
`without any substantial loss. Moreover, in order to satisfy
`
`- 4 -
`
`Page 4 of 19
`
`

`

`a demand for compact low-cost equipment, easy manufacturing
`and excellent mount-ability are required.
`[0004]
`
`However, the performance of a prior-art apparatus
`described above is not satisfactory in terms of retaining
`the original intensity of light emitted from a light source,
`although its performance in terms of uniform illumination
`luminance is acceptable. This is because, in the above
`apparatus, the light control film is formed by printing a
`light-shielding pattern such as dots on a film surface, and
`a bright portion of light coming from the light source is
`shielded by means of the light-shielding pattern, thereby
`obtaining uniform illumination luminance.
`[0005]
`
`An object of the present invention is to solve the
`above problem of prior art and to provide a surface light
`source apparatus that makes it possible to obtain uniform
`surface luminance without a decrease in the luminous level
`of a light source, and offers excellent mount-ability.
`[0006]
`[Means for Solving the Problems] In order to achieve the
`above object, a surface light source apparatus according to
`the present invention comprises: a housing that has an
`opening at its top; at least one elongated light source that
`is provided inside the housing and has a predetermined
`
`- 5 -
`
`Page 5 of 19
`
`

`

`diameter; and a prism lens film by which the opening is
`covered, wherein a distance from the elongated light source
`to the prism lens film is set to be a predetermined distance
`at which there is no gap between images that are formed by
`the elongated light source on the prism lens film.
`[0007]
`[Operation] In a surface light source apparatus according
`to the present invention, when light is emitted from at
`least one light source, mainly, two elongated-light-source
`images are formed on a prism lens film. The distance
`between the elongated light source and the prism lens film
`is set to be a predetermined distance at which no gap is
`formed between the two light-source images. Therefore, it
`is possible to obtain surface brightness with uniform
`illumination while retaining the original intensity of light
`emitted from the light source without a decrease in it.
`[0008]
`[Embodiments] With reference to the accompanying drawings,
`exemplary embodiments of the present invention will now be
`explained.
`[0009]
`
`A first embodiment of the present invention is
`illustrated in Figs. 1 and 2. In these drawings, the
`reference numeral 10 denotes a surface light source
`apparatus that is provided behind the liquid crystal panel
`
`- 6 -
`
`Page 6 of 19
`
`

`

`of a liquid crystal display device. The surface light
`source apparatus 10 includes, as its main components, a
`housing 11, an elongated light source 12, and a prism lens
`film 13. Roughly speaking, the housing 11 has a shape of a
`rectangular parallelepiped with an opening 11A at its top.
`In the present embodiment, the elongated light source 12 is
`a linear or rod-like lamp that is provided inside the
`housing 11 and has a predetermined diameter D. The opening
`11A is covered by the prism lens film 13. If necessary, a
`light-diffusing sheet 14 is provided over the upper surface
`of the prism lens film 13.
`[0010]
`
`An edge-raised terrace region 11B is formed around the
`opening 11A at the top portion of the housing 11. A light-
`source housing space 11C, inside which the elongated light
`source 12 is housed, is formed in the housing 11. A bottom
`region 11D, which is parallel to the edge-raised terrace
`region 11B, is formed as the floor of the light-source
`housing space 11C. Two slope regions 11E, each of which is
`inclined at an angle of 45 with respect to the bottom
`region 11D and the edge-raised terrace region 11B, are
`formed as sloped wall surfaces of the light-source housing
`space 11C. At each of the two sides next to the elongated
`light source 12, the slope region 11E extends in its length
`direction in parallel to the elongated light source 12. A
`
`- 7 -
`
`Page 7 of 19
`
`

`

`mirror-surface sheet 15, which is a sheet formed by vapor
`deposition of silver, aluminum, or the like, is bonded to
`the surface of each of the bottom region 11D and the two
`slope regions 11E. The bottom region 11D with the mirror-
`surface sheet 15 thereon functions as a first reflection
`surface 15A. Each of the two slope regions 11E with the
`mirror-surface sheet 15 thereon functions as a second
`reflection surface 15B.
`[0011]
`
`The prism lens film 13 is bonded to the edge-raised
`terrace region 11B of the housing 11 by means of a double-
`sided tape or the like, with its prism face up as
`illustrated in Fig. 2. For example, a prism lens film that
`has a thickness t of 230 m, a vertex array pitch p of 31 m,
`and an angle of inclination "a" of each prism of 100 can be
`used as the film 13.
`[0012]
`
`The light-diffusing sheet 14 is bonded to the prism
`lens film 13 also by means of a double-sided tape or the
`like. The light-diffusing sheet 14 is made of, for example,
`a polyester film or a polycarbonate film. In order to apply
`uniform illumination light to a liquid crystal panel, light-
`diffusing particles are mixed in the light-diffusing sheet
`14, or, the light-diffusing sheet 14 has a roughened surface.
`[0013]
`
`- 8 -
`
`Page 8 of 19
`
`

`

`The elongated light source 12 is, for example, a
`
`fluorescent tube that has a diameter D. A distance H from
`the elongated light source 12 to the prism lens film 13 is
`set at a predetermined distance described later. A distance
`from the center of the elongated light source 12 to the
`center of the second reflection surface 15B is set at a
`predetermined distance described later.
`[0014]
`
`As illustrated in Fig. 4, there is a predetermined
`relationship between the distance H from the elongated light
`source 12 to the prism lens film 13 and a distance L between
`two images (LS-I, LS-II) formed by the elongated light
`source 12 on the surface of the prism lens film 13, wherein
`the thickness t of the prism lens film 13, the angle of
`inclination "a" of each prism of the prism lens film 13, and
`the vertex array pitch p of the prism lens film 13 are
`parameters that define said relationship.
`[0015]
`
`Let us assume for the purpose of explanation that
`plural elongated light sources are arranged at 2D intervals,
`which is twice as large as the diameter D of each of the
`plural elongated light sources. Since the illustrated
`relationship holds, under this assumption of 2D light-source
`array, if the distance from the elongated light source(s) 12
`to the prism lens film 13 is set at H0, which is a distance
`
`- 9 -
`
`Page 9 of 19
`
`

`

`at which the two images LS-I and LS-II do not overlap each
`other, or in other words, at which L = 0 holds, it follows
`that the images of the elongated light sources 12 are
`arranged densely without overlapping one another and without
`any gap therebetween on the surface of the prism lens film
`13. Therefore, it is possible to obtain uniform
`illumination luminance with high brightness.
`[0016]
`
`The present invention is based on the principle
`described above. In the first embodiment, the distance from
`the elongated light source 12 to the prism lens film 13 is
`set at H0. In addition, instead of arranging plural
`elongated light sources, the second reflection surfaces 15B
`are utilized for obtaining light whose amount is equivalent
`to that of three elongated light sources by means of a
`single elongated light source 12 only.
`[0017]
`
`In order to satisfy the relationship described above,
`each of the second reflection surfaces 15B is formed at a
`position where the distance from the center of the second
`reflection surface 15B to the center of the elongated light
`source 12 is twice as large as the diameter D of the
`elongated light source 12.
`[0018]
`
`In the present embodiment, which includes the structure
`
`- 10 -
`
`Page 10 of 19
`
`

`

`described above, when light is emitted from the elongated
`light source 12, the two direct images LS-I and LS-II are
`formed next to each other without overlapping each other and
`without any gap therebetween on the surface of the prism
`lens film 13, which is provided at a predetermined distance
`of H0 from the elongated light source 12, as illustrated in
`Fig. 3(B). In addition, to the left/right of these direct
`images, two images LM-1 and LM-II are formed by reflection
`from the second reflection surface 15B next to each other
`without overlapping each other and without any gap
`therebetween on the surface of the prism lens film 13. In
`the illustrated structure, as mentioned above, it is
`possible to use virtual three light sources by means of,
`actually, a single elongated light source only, which is
`very efficient.
`[0019]
`
`The inventors of this patent application conducted an
`experiment on the structure of the present embodiment under
`the following conditions: a cold cathode fluorescent tube
`that has a diameter of 3.2 mm (D = 3.2) and a length of 24
`mm was used as the elongated light source 12; the size of
`the opening 11A in a direction orthogonal to the elongated
`light source 12 is approximately 20 mm; an electric current
`of 3 mA was applied. Illumination luminance of 5,000 NIT
`was obtained. In-plane brightness distribution on the
`
`- 11 -
`
`Page 11 of 19
`
`

`

`light-diffusing sheet 14 was 82%.
`[0020]
`
`In a case where the distance from the center of the
`second reflection surface 15B to the center of the elongated
`light source 12 is twice as large as the diameter D of the
`elongated light source 12 and, in addition, where the
`distance from the elongated light source 12 to the prism
`lens film 13 is set at H0, as described above, images formed
`on the surface of the prism lens film 13 are arranged
`without overlapping one another and without any gap
`therebetween, resulting in uniform brightness distribution.
`If the distance mentioned above is greater than 2D, or is
`greater than the predetermined value H0, it is not possible
`to obtain uniform brightness distribution because of a gap
`between adjacent images on the prism lens film 13.
`Conversely, if the distance mentioned above is less than 2D,
`or is less than the predetermined value H0, there are image
`overlaps on the prism lens film 13. However, the inventors
`confirmed as the results of the experiment that brightness
`distribution is not significantly affected if the image
`overlaps are slight.
`[0021]
`
`The overlap experiment was conducted under the same
`conditions as those described above except that the distance
`from the center of the second reflection surface 15B to the
`
`- 12 -
`
`Page 12 of 19
`
`

`

`center of the elongated light source 12 was set to be less
`than 2D to form image overlaps, with a reduction in the size
`of the opening 11A to approximately 15 mm. In-plane
`brightness distribution of 80% and illumination luminance of
`5,000 NIT were obtained.
`[0022]
`
`As can be concluded from the above results, the slope
`angle of each of the second reflection surfaces 15B
`mentioned earlier is not limited to 45, and can be modified
`in accordance with the above distance adjustment as long as
`no gap is formed between adjacent images on the prism lens
`film 13.
`[0023]
`
`Next, with reference to Fig. 5, a second embodiment of
`the present invention will now be explained. In the
`foregoing embodiment, a single linear elongated light source
`12 is used. In the present embodiment, a W-shaped elongated
`light source 121 is used, which is equivalent to the use of
`four linear elongated light sources. (In the present
`embodiment, the pitch of the linear portion of the W-shaped
`elongated light source 121 is 6D, where D denotes diameter.)
`Therefore, the basic unit structure of the present
`embodiment is the same as that of the first embodiment. The
`same reference numerals are assigned to the same functional
`portions/components as those of the first embodiment to
`
`- 13 -
`
`Page 13 of 19
`
`

`

`avoid redundant explanation.
`[0024]
`
`The present invention is effective for enlarging a
`lighting surface. The inventors of this patent application
`conducted an experiment on the structure of the present
`embodiment under the following conditions: a W-shaped cold
`cathode fluorescent tube that has a diameter of 4.8 mm (D =
`4.8) and a linear-portion length of 110 mm was used as the
`elongated light source 12; the size of the opening 11A in a
`direction orthogonal to the elongated light source 121 is
`approximately 80 mm; an electric current of 5 mA was applied.
`Illumination luminance of 7,000 NIT was obtained. In-plane
`brightness distribution of 80% was obtained.
`[0025]
`
`Next, with reference to Figs. 6 and 7, a third
`embodiment of the present invention will now be explained.
`[0026]
`
`In the first and second embodiments described above,
`reflection surfaces are used for virtually increasing the
`number of elongated light source(s). In contrast, in the
`present embodiment, the number of prism lens film(s) is
`increased to obtain the same or similar effects.
`[0027]
`
`With reference to Fig. 6, the structure of the present
`embodiment will now be explained, wherein the same reference
`
`- 14 -
`
`Page 14 of 19
`
`

`

`numerals are assigned to the same functional
`portions/components as those of the foregoing embodiments.
`The reference numeral 11 denotes a housing that has a
`rectangular light-source housing space 11C0 without any
`sloped wall surface for reflection. A first prism lens film
`131 is bonded to the edge-raised terrace region 11B around
`the opening 11A by means of a double-sided tape or the like.
`In addition, a second prism lens film 132 is bonded by means
`of a double-sided tape or the like at the predetermined
`distance H0 mentioned above therefrom due to the presence of
`spacers 16 sandwiched therebetween.
`[0028]
`
`A U-shaped elongated light source 122 is used as the
`elongated light source. However, the U shape is not
`essential. What is essential is that the distance H between
`the elongated light source 122 and the first prism lens film
`131 is set to be a predetermined distance HD.
`[0029]
`
`As described earlier, there is a predetermined
`relationship illustrated in Fig. 4 between the distance H
`from the elongated light source to the prism lens film and a
`distance L between two images (LS-I, LS-II) formed on the
`surface of the prism lens film.
`[0030]
`
`In the present embodiment, the distance H is set to be
`
`- 15 -
`
`Page 15 of 19
`
`

`

`the predetermined distance HD, at which the distance between
`the two images LS-I and LS-II is equal to the diameter D of
`the elongated light source 122.
`[0031]
`
`Because of the structure described above, as
`illustrated in Fig. 7, the two images LS-I and LS-II of the
`elongated light source 122 are formed at a distance D from
`each other on the surface of the first prism lens film 131.
`Next, on the surface of the second prism lens film 132,
`which is provided at the predetermined distance H0 from the
`first prism lens film 131, two images LS-I-I and LS-I-II are
`formed from the image LS-I next to each other without
`overlapping each other and without any gap therebetween, and
`two images LS-II-I and LS-II-II are formed from the image
`LS-II next to each other without overlapping each other and
`without any gap therebetween.
`[0032]
`
`The present embodiment is equivalent to virtual
`arrangement of two linear elongated light sources. After
`all, surface illumination that is eight times as wide as the
`diameter D of the elongated light source 122 is obtained on
`the surface of the second prism lens film 132.
`[0033]
`
`The inventors of this patent application conducted an
`experiment on the structure of the present embodiment under
`
`- 16 -
`
`Page 16 of 19
`
`

`

`the following conditions: a U-shaped cold cathode
`fluorescent tube that has a diameter of 4.8 mm (D = 4.8) and
`a linear-portion length of 110 mm was used as the elongated
`light source 12; the size of the opening 11A in a direction
`orthogonal to the elongated light source 122 is
`approximately 40 mm; an electric current of 5 mA was applied.
`Illumination luminance of 5,000 NIT in candela per square
`meter (In-plane brightness distribution: 80%) was obtained.
`[0034]
`
`Needless to say, the foregoing embodiments are non-
`limiting examples and may be combined in various ways. For
`example, though not illustrated in the drawings, plural
`linear elongated light sources may be arranged next to one
`another non-virtually, and a prism lens film may be provided
`at the predetermined distance H0 therefrom. Such a
`structure can be recognized as one that embodies the basic
`principle on which the invention is based.
`[0035]
`
`As a matter of course, the elongated light source is
`not limited to a cold cathode light source. A hot cathode
`fluorescent tube, neon tube, or the like may be used. The
`size of the prism lens film is not limited to specific
`values of the foregoing examples. Any same functional
`component, irrespective of its name, can be used as the
`prism lens film.
`
`- 17 -
`
`Page 17 of 19
`
`

`

`[0036]
`[Advantages] As clear from the above explanation, with a
`surface light source apparatus according to the present
`invention, it is possible to obtain uniform surface
`brightness without any substantial loss in the optical
`intensity of a light source.
`[Brief Description of the Drawings]
`[Fig. 1] Fig. 1 depicts a first embodiment of the invention,
`wherein (A) is a plan view, (B) is a side view, and (C) is a
`sectional view taken along the line A-A in (A);
`[Fig. 2] Fig. 2 is an exploded perspective view of the
`first embodiment of the invention;
`[Fig. 3] Fig. 3 is a diagram for explaining the operation
`of the first embodiment of the invention;
`[Fig. 4] Fig. 4 is a graph for explaining the principle of
`the invention;
`[Fig. 5] Fig. 5 depicts a first embodiment of the invention,
`wherein (A) is a plan view, (B) is a side view, and (C) is a
`sectional view taken along the line B-B in (A);
`[Fig. 6] Fig. 6 depicts a third embodiment of the invention,
`wherein (A) is a plan view, (B) is a side view, and (C) is a
`sectional view taken along the line C-C in (A); and
`[Fig. 7] Fig. 7 is a diagram for explaining the operation
`of the third embodiment of the invention.
`[Reference Numerals]
`
`- 18 -
`
`Page 18 of 19
`
`

`

`10 surface light source apparatus
`11 housing
`12, 121, 122 elongated light source
`13 prism lens film
`14 light-diffusing sheet
`
`- 19 -
`
`Page 19 of 19
`
`

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