JPH0581877U - Surface lighting device - Google Patents

Abstract

(57) [Abstract] [Purpose] Surface illumination for enhancing the brightness of the surface near the second, third and fourth side surfaces facing or orthogonal to the first side surface of a light guide plate provided with a light emitting diode and performing uniform illumination. Provide a device. The present invention provides a light guide plate and a light emitting diode disposed on a first side surface of the light guide plate in order to solve the above problems. And the second, third, which is opposite or orthogonal to the first side surface,
The second, third, and fourth side surfaces are inclined so that the length of one side on the back surface side of the light guide plate becomes shorter than the length of one side on the front surface side facing the back surface side so that total reflection is performed on the fourth side surface. It is a thing.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a surface lighting device used for flat panel display, especially for liquid crystal display.

[0002]

[Prior Art]

 In recent years, many surface illuminating devices used for flat display and the like have been proposed. Among them, the apparatus filed by the applicant of the present application in Japanese Patent Application No. 3-107041 is shown in a sectional view of FIG. In this figure, the light guide plate 31 has a recess 33 formed in the first side surface 32. In the substrate 34, conductive layers 36a, 36b, 36c are formed on a resin layer 35, and a light emitting diode 37 is fixed. A reflection frame 38 is provided so as to cover the substrate 34, and these constitute a surface lighting device 39. A liquid crystal display 40 and a circuit board 41 are provided above and below the light guide plate 31.

[0003]

[Problems to be solved by the device]

 However, in the above-mentioned device, there is a drawback in that the illumination on the liquid crystal display 40 becomes non-uniform. Particularly, the surface 43 near the second side surface 42 of the light guide plate 31 is dark. This is because the light 44, 45 emitted from the light emitting diode 37 is substantially orthogonal to the second side surface 42, and most of it is emitted as transmitted light outside the device. Therefore, the present invention solves the above-mentioned deficiencies, that is, to provide a surface lighting device that enhances the brightness of the surface near each side surface and performs uniform lighting.

[0004]

[Means for Solving the Problems]

 In order to solve the above problems, the present invention provides a light guide plate and a light emitting diode disposed on the first side surface of the light guide plate. The length of one side on the back surface side of the light guide plate is made shorter than the length of one side on the front surface side facing the first side surface so that the light is totally reflected by the second, third, and fourth side surfaces facing or orthogonal to the first side surface. The second, third, and fourth side surfaces are inclined in such a direction.

[0005]

[Action]

 In the present invention, as described above, the second, third and fourth side surfaces are inclined in the direction in which the length of one side on the back surface side of the light guide plate becomes shorter than the length of one side on the front surface side. Therefore, the light emitted from the light emitting diode is totally reflected by the second, third, and fourth side surfaces, and the reflected light enhances the brightness of the surface near each side surface.

[0006]

【Example】

 An embodiment of the present invention will be described below with reference to FIGS. 1 (a) and 1 (b). FIG. 1A is a sectional view of a surface lighting device according to this embodiment, and FIG. 1B is an exploded perspective view of the device. In these figures, the light guide plate 1 is made of, for example, a resin having a length of 20 to 100 mm, a width of 10 to 30 mm, a thickness of about 1.5 to 8 mm, and a refractive index of 1.2 to 1.6, such as acrylic resin. , Is in the shape of a truncated pyramid. A recess 3 is formed on the first side surface 2 of the light guide plate 1. The light guide plate 1 preferably has a reflection plate at the bottom, a plurality of transparent plates laminated on the reflection plate, and a diffusion plate provided thereon. And this transparent plate is the acrylic plate on which the white paint is printed in spots. The first side surface 2 is formed so as to be substantially perpendicular to the front surface 4 and the back surface 5.

The second side surface 6 facing the first side surface 2 is formed to be inclined in a direction in which the length A of one side on the back surface side is shorter than the length B of one side on the front surface side. The inclination angle φ of the second side surface 6 is determined according to the refractive index and size of the light guide plate 1 (thickness and length B of one side on the front surface side) so as to totally reflect. Also, the third and fourth side surfaces 7 and 8 located substantially orthogonal to the first side surface 2 are also inclined in a direction in which the length C of one side on the back surface side becomes shorter than the length D of one side on the front surface side. Is formed. Two cylindrical pins 9 are formed on the first side surface 2.

In the substrate 10, the power supply terminal 12 and the conductive layers 13A and 14 are printed and printed on the resin layer 11 made of, for example, glass epoxy resin, and the white coated portion 15 is formed on the surface excluding the periphery of the conductive layer 13A. It is a long one. The substrate 10 has two through holes 16 having a diameter of about 1.5 mm and a thickness of about 0.5 mm. A light emitting diode 18 is fixed on the conductive layer 13A of the substrate 10 via a conductive adhesive 17 such as silver paste. The light emitting diode 18 is made of, for example, gallium phosphide, emits green light having a wavelength of about 580 nm, and has a size of a substantially cubic shape with one side of about 300 μm. The light emitting diodes 18 are fixed in line along the longitudinal direction of the substrate 10 on the surface of the substrate 10 with a pitch of 1.5 to 5 mm. A thin metal wire 19 is provided between the light emitting diode 18 and the conductive layer 13B (not shown). Since the two pins 9 of the light guide plate 1 are inserted and welded into the through holes 16 of the substrate 10 so that the light emitting diode 18 is located in the concave portion 3 of the light guide plate 1, the surface of the substrate 10 and the light guide plate 1 are welded. The first side surface 2 of the abuts. The surface lighting device 20 is configured by these components. The liquid crystal display 21 and the circuit board 22 are arranged above and below the light guide plate 1, respectively.

Next, an optical path in the surface lighting device according to the embodiment of the present invention will be described with reference to FIG. In this figure, the inclination angle φ for total reflection of the second side surface 6 is obtained. The point where the second side surface 6 and the back surface 5 intersect is E, the perpendicular is F, the arbitrary point on the second side 6 is G, and the perpendicular is H. Letting θ and θ ₁ be the incident angles of the outgoing lights 23 and 24 at the points E and G, and α be the angle at which the outgoing lights 23 and 24 intersect, θ ₁ = θ + α α> 0, so θ <θ ₁ That is, θ has the smallest incident angle in the light reflected by the second side surface 6. Therefore, when the refractive index of the light guide plate 1 is n, the condition for total reflection is sin θ ≧ 1 / n. Here, if the angle at which the emitted light 23 and the back surface intersect is β, then θ + β + φ = π / 2, θ = π / 2− (β + φ), and by substituting this into the above-mentioned conditional expression for total reflection, the following equation is obtained. Be done.

[0010]

[Equation 1]

From the above equation, the following equation is obtained. cos (β + φ) ≧ 1 / n, and as a result, the following equation is obtained.

[0012]

[Equation 2]

Next, assuming that the thickness of the light guide plate 1 is I and the height of the light emitting diode 18 is approximately the middle height of the light guide plate 1, tan β = I / 2A. If A and B are sufficiently larger than I, then tan β≈β≈I / 2A≈I / 2B. By substituting this into the above-mentioned formula 2, the following formula is obtained.

[0014]

[Equation 3]

Therefore, the inclination angle φ is obtained by substituting the following specific numerical values. Substituting n = 1.4, I = 5 mm, and B = 100 mm, the right-hand side of Equation 3 = 0.752-5 / 200 = 0.75 radians = 42 ° 58 ', and thus has the above-mentioned refractive index and size. When the light guide plate 1 is used, if the inclination angle φ of the second side surface 6 is smaller than 42 ° 58 ', total reflection occurs. Therefore, the total reflection increases the brightness on the surface J near the second side surface 6.

In the vicinity of the second side surface 2, the light K that enters the liquid crystal display 21 directly from the light emitting diode 18 through the front surface 4 of the light guide plate and the light K reflected by the back surface 5 of the light guide plate and then passes through the front surface 4. There is light L incident on the liquid crystal display 21. Therefore, the brightness is high on the surface M near the second side surface 2. However, in the vicinity of the center of the light guide plate 1, since the light that directly reaches the front surface 4 from the light emitting diode 18 and the light that reflects from the back surface 5 and reaches the front surface 4 have a large incident angle, they are totally reflected on the front surface 4 and externally reflected. It is hard to come to. Therefore, the brightness tends to be low near the center N of the surface 4 of the light guide plate 1. In order to deal with this, it is preferable to form the spots of the transparent plate constituting the light guide plate 1 roughly near the first side surface 2 and the second side surface 6 and densely near the center. Dense reflection near the center causes a lot of irregular reflection, and the brightness increases near the center N near the center of the surface of the light guide plate, and uniform illumination is obtained as a whole.

Further, referring again to FIG. 1B, by inclining the third and fourth side faces 7 and 8 inward with respect to the back surface 5, total reflection is performed on the third and fourth side faces 7 and 8. .. Therefore, the brightness is increased on the surfaces P and Q near these side surfaces. In the above description, the second side surface 6 or the third side surface 7 or the fourth side surface 8 is treated as a flat surface (straight line when viewed in a sectional view), but in the present invention, it may be a curved surface. It does not matter as long as it has a shape of total reflection.

[0018]

[Effect of the device]

 In the present invention, as described above, the second side surface facing the first side surface provided with the light emitting diode is inclined so that the length of one side on the back side of the light guide plate is shorter than the length of one side on the front side. Let Therefore, the light emitted from the light emitting diode is totally reflected by the second side surface, and the reflected light enhances the brightness of the surface near the second side surface. If the reflecting member is provided on the second side surface, the device becomes larger and the cost increases accordingly. However, since the present invention only inclines the second side surface, the device remains small and the cost does not increase. .. In the present invention, the third and fourth side surfaces, which are substantially orthogonal to the first side surface, are also inclined in a direction in which the length of one side on the back surface side becomes shorter than the length of one side on the front surface side. Therefore, the brightness is enhanced on the surfaces near these side surfaces, and good uniform illumination is obtained as a whole.

More preferably, in the present invention, the spots of the transparent plate forming the light guide plate are formed roughly near the first side surface and the second side surface and densely near the center. Dense reflection near the center causes a large amount of diffuse reflection, which increases light diffusion and thus increases the brightness near the center of the surface of the light guide plate. As described above, on the surfaces near the second, third, and fourth side surfaces of the light guide plate, the brightness is increased by total reflection, and on the surface near the center, the brightness is increased by light diffusion, so that overall better quality is obtained. Uniform illumination is obtained.

[Brief description of drawings]

FIG. 1A is a sectional view of a surface lighting device according to an embodiment of the present invention, and FIG. 1B is an exploded perspective view of the surface lighting device.

FIG. 2 is a drawing showing an optical path in a surface lighting device according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view of a conventional surface lighting device.

[Explanation of symbols]

 1 Light guide plate 2 1st side surface 4 Surface 5 Back surface 6 2nd side surface A, C 1 side length on the back side B, D 1 side length on the front side 18 Light emitting diode

Claims (1)

[Scope of utility model registration request] 1. A light guide plate, and a light emitting diode arranged on a first side face of the light guide plate. The second, third, and fourth side faces are opposed to or substantially orthogonal to the first side face. The second, third, and fourth side surfaces are inclined so that the length of one side on the back surface side of the light guide plate becomes shorter than the length of one side on the front surface side facing the light guide plate so as to be reflected. Surface lighting device characterized by.