JP2007328173A - Surface light source device - Google Patents

Abstract

A surface light source device including a light reflection plate having an optimal mountain shape that minimizes luminance unevenness according to the light source height, light source pitch, and device depth of the surface light source device is provided.
A plurality of linear light sources 16 are arranged in parallel between a reflecting plate 12 and a diffusing plate 14 arranged in parallel to each other, and the reflecting plate has a mountain shape between adjacent linear light sources. In the surface light source device provided with the protruding mountain-shaped reflector 18, the peak angle θ at which the projection centrality calculated by the predetermined formulas (1) to (3) is minimized is used as the peak angle θ of the mountain-shaped reflector. Or it is set as the range of the summit angle +/- 5 degree which the projection center degree becomes the minimum.
[Selection] Figure 1

Description

  The present invention relates to a surface light source device used for, for example, a backlight of a liquid crystal display device or an illumination signboard, and more specifically to a surface light source device using a light reflecting plate having a mountain shape.

  Conventionally, as a surface light source device used for a backlight of a liquid crystal display device, an illumination signboard, or the like, there is one using a light reflecting plate made of a synthetic resin having a three-dimensional shape. As such a light reflecting plate, for example, a linear folding line composed of perforations, crease lines, half-cuts, etc. is formed on a foamed plastic film or sheet that reflects light, and this film or sheet is formed by the above folding line. There has been proposed a light reflection plate in which a mountain-shaped reflector is formed by bending along a line (see, for example, Patent Document 1).

  When producing a surface light source device using the light reflecting plate having the mountain shape, a plurality of linear light sources are arranged in parallel between the light reflecting plate and the diffusing plate, and a mountain is formed between adjacent linear light sources. Place the type reflector. In this surface light source device, in order to reduce luminance unevenness, a method of projecting light onto a light source intermediate portion on the front surface of the surface light source device by providing a mountain-shaped reflector between the light sources is used.

JP 2004-138715 A

  However, the light reflecting plate of Patent Document 1 does not have a clear mountain shape (peak height, peak angle) that minimizes luminance unevenness according to the design of the surface light source device (light source height, light source pitch, device depth). It was. Therefore, the light reflecting plate of Patent Document 1 can minimize the luminance unevenness of the surface light source device by providing a mountain-shaped reflector between the light sources, although the mountain shape has a certain effect in suppressing the luminance unevenness. It was unclear whether or not.

  The present invention has been made in view of the above-described circumstances, and includes a light reflector having an optimal mountain shape that minimizes luminance unevenness according to the light source height, light source pitch, and device depth of the surface light source device. An object of the present invention is to provide a surface light source device.

  As a result of intensive studies to achieve the above object, the present inventors have defined a “projection center”, which will be described later, as an index indicating the mountain shape of the light reflector, and determined the peak angle θ of the mountain reflector. It is found that, when the peak angle at which the projection centrality is minimized or a range close to the peak angle, the luminance unevenness can be minimized according to the light source height, light source pitch, and device depth of the surface light source device. It was.

The present invention has been made on the basis of the above knowledge, and a plurality of linear light sources are arranged in parallel between a reflecting plate and a diffusing plate arranged in parallel to each other, and between adjacent linear light sources. In the surface light source device provided with a mountain-shaped reflector protruding in a mountain shape from the reflector, the peak central angle θ of the mountain-shaped reflector is calculated by the following formulas (1) to (3) Provided is a surface light source device characterized by having a peak angle within a range of ± 5 ° in which the angle is minimized.
Projection centrality = (larger of L1 and L2) / (L0 / 2)
... Above (1) Formula L1 = H × tan θ / 2 + L3
= H × tan θ / 2 + K × tan (90−θ + E)
∵L3 = K × tanD
= K x tan (90-2A-E)
= K × tan (90−θ + E)
∵D = 90-2A-E
From ∵ E + A + 90 + (90−θ / 2) = 180, A = θ / 2−E
here,
E = tan ⁻¹ (h / (P / 2−H × tan θ / 2))
It is.
... or more (2) Formula L2 = (K−H) × tanG
= (K−H) × tan (θ / 2−B)
= (K−H) × tan (θ−90 + F)
From F + B + θ / 2 + 90 = 180, B = 90−F−θ / 2
here,
F = tan ⁻¹ ((H−h) / (P / 2))
It is.
... Equation (3) above
H: Vertical distance from the reflector surface to the top of the mountain-shaped reflector θ: Peak angle of the mountain-shaped reflector h: Vertical distance from the reflector surface to the center of the linear light source P: Centers of adjacent linear light sources Horizontal distance = L0
K: A vertical distance from the reflecting plate surface to the diffusion plate.

That is, in the present invention, the peak angle θ of the mountain-shaped reflector is set in the following range.
[Crest angle at which the projection centrality is minimized −5 ° ≦ Crest angle θ ≦ Crest angle at the minimum projection centrality + 5 °]

  In the present invention, it is particularly preferable to minimize the luminance unevenness, and the peak angle θ of the peak-shaped reflector is the peak angle at which the projection centrality calculated by the equations (1) to (3) is minimized. That is.

  According to the present invention, luminance unevenness can be minimized according to the light source height, light source pitch, and device depth of the surface light source device.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following examples. FIG. 1 is a diagram schematically showing an embodiment of a surface light source device according to the present invention. In the surface light source device 10 of this example, a plurality of linear light sources (cold cathode ray tubes) 16 are arranged in parallel and at equal intervals between a reflector 12 and a diffuser 14 arranged in parallel to each other. In addition, a mountain-shaped reflector 18 protruding in a mountain shape from the reflecting plate 12 is provided between the adjacent linear light sources 16. The mountain-shaped reflector 18 may be formed integrally with the reflector 12, mechanically joined to the reflector 12, or fixed to the reflector 12 with an adhesive or the like. Further, the reflection by the reflector 12 and the mountain-shaped reflector 18 is preferably specular reflection.

  In the surface light source device of the present invention, the peak angle θ of the peak-shaped reflector is the peak angle at which the projection centrality calculated by the above formulas (1) to (3) is minimized. Here, the degree of projection center will be described. FIG. 2 is a diagram showing the concept of projection centrality. The projection center degrees are L1 (range from the top of the mountain reflector to the light source side) and L2 (mountain reflector) in the range in which the reflected light of the mountain reflector is projected onto the diffuser (mountain reflected light projection range). Is a value obtained by dividing the larger value in the range from just above (to the side opposite to the light source) by half the light source pitch L0 / 2. The projection centrality obtained by the equation (1) is an index indicating how much light reflected by the slope of the mountain-shaped reflector is collected in the light source intermediate portion (near the top of the mountain-shaped reflector). When the projection centrality is minimum, the reflected light from the slope of the mountain-shaped reflector is most concentrated on the intermediate portion of the linear light source, and the luminance unevenness approaches the minimum. However, even if the peak angle θ of the peak-shaped reflector is in the range of the peak angle ± 5 ° at which the projection centrality is minimized, it is possible to obtain a small luminance unevenness that is almost equivalent.

  In the present invention, the peak height is H, the peak angle of the peak-shaped reflector is θ, and the surface light source device parameter is h, the light source pitch is P, and the surface light source device depth is the peak shape parameter. When L is K, L1 and L2 are calculated by the equations (2) and (3). That is, L1 and L2 can be obtained from parameters H, θ, h, P, and K. The parameter of the surface light source device is a fixed value, and when H is fixed and θ is a variable and the projection centrality is calculated by equation (1), the projection centrality has a minimum value, and the apex angle θ at that time is obtained. be able to. In addition, L1, L2, L3, H, θ, h, P, K, A, B, D, E, F, and G in each of the above formulas are shown in FIG.

  In the present invention, the material for forming the reflector and the mountain-shaped reflector is not limited, but a foamed sheet having a diffuse reflectance of 95% or more can be suitably used. Particularly preferred is a thermoplastic resin film or sheet having fine bubbles or pores having an average bubble diameter of not less than the wavelength of light and not more than 50 μm inside. Examples of the material of the thermoplastic resin film or sheet include, for example, general-purpose resins such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, polychlorinated biphenyl, polyethylene terephthalate, and polyvinyl alcohol, polycarbonate, polybutylene terephthalate, polyethylene naphthalate, and polyamide. , Polyacetal, polyphenylene ether, ultrahigh molecular weight polyethylene, polysulfone, polyethersulfone, polyphenylene sulfide, polyarylate, polyamideimide, polyetherimide, polyetheretherketone, polyimide, polytetrafluoroethylene, liquid crystal polymer, fluororesin, etc. Examples include engineering plastics, copolymers or mixtures thereof. Among these, polyester, polyphenylene sulfide, polypropylene, and cyclopolyolefin are preferable because of their good heat resistance and impact resistance. In addition, antioxidants, ultraviolet inhibitors, lubricants, pigments, reinforcing agents, and the like can be appropriately added to the thermoplastic resin. Moreover, you may form by apply | coating the coating layer containing these additives.

  More specifically, as an example of the foamed sheet, a polyester-based sheet in which an extruded sheet of thermoplastic polyester is impregnated with carbon dioxide gas under high pressure and then heated and foamed has an internal cell diameter of 50 μm or less. A foam sheet (for example, MCPET (registered trademark) manufactured by Furukawa Electric Co., Ltd.) can be used. Since this polyester foam sheet has a high diffuse reflectance, uniform brightness can be obtained. In addition, a cyclopolyolefin foamed sheet having an internal cell diameter of 50 μm or less can be used.

  Another preferred example of the material forming the reflector and the mountain-shaped reflector is a film or sheet of a thermoplastic resin containing a filler, in which a large number of voids are formed with the filler as a core. Is mentioned. In this case, in the film or sheet, the thermoplastic resin film or sheet containing the filler is formed by forming an unstretched film or sheet containing the filler and stretching the unstretched film or sheet. A porous stretched film or sheet in which a large number of voids are formed as nuclei is preferable.

  In this invention, it is preferable that the thickness of the foam sheet which forms a reflecting plate and a mountain-shaped reflector is 200-2000 micrometers. It is preferable that the thickness of the foamed sheet is in the range of 200 to 2000 μm because of rigidity. Moreover, it is preferable that the specific gravity of the said foam sheet is 0.1-0.7. Furthermore, the reflector and the mountain-shaped reflector in the present invention may be formed by appropriately attaching the above-described film or sheet to a metal plate.

  In the present invention, as the linear light source, for example, a straight fluorescent lamp or a cold cathode tube can be used.

  In the present invention, the diffusion plate can be appropriately selected and used.

  Next, although the Example of the surface light source device which concerns on this invention is shown, this invention is not limited to the following example. FIG. 3 shows a calculation example of the projection center degree of the surface light source device, and FIG. 4 shows an actual correlation between the projection center degree and luminance unevenness in the surface light source device manufactured based on the calculation of FIG. As shown in FIGS. 3 and 4, the luminance unevenness of the surface light source device is minimized in the vicinity of the peak angle where the projection centrality is minimized. That is, in the calculation example of FIG. 3, the central degree of projection is the minimum near the peak angle of 112 °. Further, in the actual luminance evaluation result of FIG. 4, the luminance unevenness is the smallest around the peak angle of 112 °.

It is a figure which shows typically one Embodiment of the surface light source device which concerns on this invention. It is a figure which shows the idea of a projection center degree. It is a graph which shows the example of calculation of the projection center degree of a surface light source device. It is a graph which shows the actual correlation with the projection center degree and brightness nonuniformity in the surface light source device produced based on the calculation of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Surface light source device 12 Reflector 14 Diffusion plate 16 Linear light source 18 Mountain-shaped reflector

Claims (4)

A plurality of linear light sources are arranged in parallel between a reflecting plate and a diffusing plate arranged in parallel to each other, and a mountain-shaped reflector that protrudes from the reflecting plate in a mountain shape between adjacent linear light sources In the surface light source device provided with the above, the peak angle θ of the peak-shaped reflector is in the range of the peak angle ± 5 ° at which the projection centrality calculated by the following formulas (1) to (3) is minimized. A surface light source device.
Projection centrality = (larger of L1 and L2) / (L0 / 2)
... Above (1) Formula L1 = H × tan θ / 2 + L3
= H × tan θ / 2 + K × tan (90−θ + E)
here,
E = tan ⁻¹ (h / (P / 2−H × tan θ / 2))
It is.
... or more (2) Formula L2 = (K−H) × tanG
= (K−H) × tan (θ / 2−B)
= (K−H) × tan (θ−90 + F)
here,
F = tan ⁻¹ ((H−h) / (P / 2))
It is.
... Equation (3) above
H: Vertical distance from the reflector surface to the top of the mountain-shaped reflector θ: Peak angle of the mountain-shaped reflector h: Vertical distance from the reflector surface to the center of the linear light source P: Centers of adjacent linear light sources Horizontal distance = L0
K: A vertical distance from the reflecting plate surface to the diffusion plate.   2. The surface light source device according to claim 1, wherein the peak angle θ of the peak-shaped reflector is a peak angle at which the projection centrality calculated by the formulas (1) to (3) is minimized.   The surface light source device according to claim 1, wherein the reflection plate and the mountain-shaped partition plate are made of a foam sheet having a diffuse reflectance of 95% or more.   4. The surface light source device according to claim 3, wherein the foamed sheet is made of a thermoplastic resin having fine bubbles or pores having an average bubble diameter of not less than the wavelength of light and not more than 50 μm.

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