JPH11133208A - Optical element for converting surface light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface lighting device capable of converting light radiated from a point light source into a surface light source capable of uniformly irradiating a prescribed area with light without generating the uneveness of luminance while holding compact constitution. SOLUTION: A surface light source converting optical element 4 reflects incident light beams IL1 to ILn radiated from a point light source 1 for radiating light and emits the reflected light beams from the whole light emitting face 8 formed on the opposite side of the point light source side 1. Many prism parts P1 to Pn having a plane view circle as a whole and having prism incident faces I1 to In on the inner peripheral side and prism reflection faces R1 to Rn on the outer peripheral side are integrally formed on the point light source side of the element 4 by concentrical arrangement and the prism reflection faces R1 to Rn are formed so as to totally reflect incident light beams IL1 to ILn from the incident faces I1 to In to an almost fixed direction directed to the light emitting face 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element for converting a surface light source used for, for example, illuminating a display panel for a video camera or a backlight of a liquid crystal display, and a surface illuminating device using the same. is there.

[0002]

2. Description of the Related Art Conventionally, as a surface illuminating device used for such a purpose, as shown in FIG. 6, light emitted from a point light source 1 such as a light emitting diode is formed into a lens form by a light diffusing material. After the light is diffused by passing through the light diffusion plate 2, the light is converted into a surface light source, and then the entire display plate 3 on which necessary information is displayed in a film by characters or figures is illuminated.

[0003]

However, in the conventional surface illuminating device, the light component emitted in the direction of irradiating the display plate 3 is increased by diffusing the light emitted from the point light source 1 with the light diffusing plate 2. However, if the diffusion performance of the light diffusion plate 2 is improved for the purpose of increasing the vertical component ratio of light rays, the amount of light transmitted through the light diffusion plate 2 is extremely reduced, and the display panel 3
The total amount of light irradiating the light is significantly reduced. Furthermore, the incident light beams L1 and L2 from the point light source 1 to the light diffusing plate 2 are incident at a larger incident angle γ ₁ toward the peripheral end of the light diffusing plate 2, so that the reflected light component on the incident surface L ₂ ′ increases and decreases rapidly as the amount of light incident on the light diffusion plate 2 approaches the peripheral end. Therefore, the light emitted from the peripheral end of the light diffusion plate 2 is reduced, and the radiated light flux that can be effectively used for irradiating the display plate 3 is reduced. For example, as shown in FIG. 6, the incident light L2 incident on the peripheral end of the light diffusion plate 2 has a vertical component light L22 because the principal ray L21 cannot be refracted in a direction perpendicular to the display panel 3.
Is extremely reduced only by the amount of light diffused.

Therefore, in order to suppress a decrease in the amount of light at the peripheral end portion with respect to the amount of light at the central portion of the light diffusion plate 2, the light diffusion plate 2 having a long focal length is used to make the point light source 1 and the light diffusion plate 2 Although it is conceivable to set the interval to be large, the absolute value of the light amount decreases as the interval increases, and the entire device using the surface illumination device increases in size with an increase in unnecessary space, This leads to a reduction in the degree of freedom in equipment design. To solve this, a light diffusion plate having a short focal length and a large area is required, but it is difficult to realize.

For example, in order to realize a single lens having a short focal length, it is necessary to use a lens having a large curvature (that is, a small radius of curvature) on the lens surface.
Inevitably, there is a problem that the lens becomes small. In order to realize a lens with a short focal length, it is desirable that the lens is made of a material having a high refractive index. However, there is a limit as long as a resin is used as the lens material. To simply shorten the focal length, a configuration in which the principal point position is located outside the lens system, such as retrofocus, using a plurality of lenses can be considered. Not realistic in a system.

On the other hand, it is conceivable to use a Fresnel lens instead of the light diffusion plate 2. In this case, the response to the downsizing and thinning of the applied device is slightly improved, but the lens portion of the Fresnel lens has almost the same disadvantages as described above, and the light is incident on the vertical plane which is a weak point of the Fresnel lens. There is a problem that light rays such as light rays cannot be used as effective light rays.

Accordingly, the present invention provides an optical element for converting a surface light source into a surface light source capable of uniformly irradiating the radiated light of a point light source to a predetermined area without uneven brightness while maintaining a compact structure. And a surface illumination device using the same.

[0008]

In order to achieve the above object, a surface light source conversion element according to the present invention reflects incident light radiated from a point light source that emits light, and the point light source is defined as: The light is emitted from the entire light emitting surface on the opposite side,
On the surface on the side of the point light source, a large number of prism portions each having a circular shape in a plan view, a prism entrance surface on the inner peripheral surface side, and a prism reflecting surface on the outer peripheral surface side are integrally formed in a concentric arrangement. The prism reflecting surface is formed so as to totally reflect incident light from the prism incident surface in a substantially constant direction toward the light emitting surface.

In this surface light source converting optical element, a large number of circular prism portions having a prism reflecting surface for totally reflecting the light emitted from the point light source in a substantially constant direction toward the light emitting surface are arranged concentrically. Since it has an optical element for converting a surface light source, it is possible to reduce the amount of light emitted from the point light source without substantially reducing the amount of light emitted from the point light source, while miniaturizing the optical element at a small distance from the point light source. The light can be emitted from the entire light exit surface of the element. In addition, since the prism entrance surfaces are provided on the inner peripheral surface side of each of the prism portions which are arranged concentrically, the angle of incidence of light emitted from the point light source on each prism entrance surface is determined by the peripheral end of the optical element. Does not increase, and the amount of incident light at the peripheral end of the prism portion does not decrease. Therefore, a substantially uniform amount of light can be emitted from the entire light exit surface, and the entire display panel can be irradiated without uneven brightness.

In the above invention, the rear end of each prism reflecting surface that is separated from each point light source is set on an extension of an incident light beam passing through the front end of the adjacent prism section on each inner side. Preferably, each of the prism reflecting surfaces is formed in a continuous stepwise shape so as to gradually recede in the thickness direction of the optical element as it goes to the center of the surface light source converting optical element.

[0011] Thus, since all of the light beams emitted from the point light source are reflected by the continuous step-like prism reflecting surface, the entire light beam from the light emitting surface of the optical element is directed in a certain direction from the whole. Light can be emitted.

Further, in the above invention, it is preferable that each prism entrance surface is located so as to be located along the direction of the reflected light reflected at the front end portion of the corresponding prism reflection surface.

Thus, each prism entrance surface does not block the light reflected on the corresponding prism reflection surface at all, and all the light rays reflected on the prism reflection surface can be emitted from the light exit surface.

In the above invention, each prism reflecting surface may be a total reflecting surface having an inclination angle for totally reflecting the incident light from the prism incident surface in a substantially constant direction toward the light emitting surface, or a reflecting surface made of an inorganic coating. It is preferable to use either one. This makes it possible to make all the prism reflecting surfaces reflective by easy means.

In the above invention, it is preferable that the surface light source conversion optical element is formed integrally with a light diffusing material, or that each prism reflecting surface is formed as a rough surface. Thus, the optical element serves as an appropriate diffusion light source, so that even if the position of the human eye when looking at the display plate is displaced in an oblique direction with respect to the display plate, the display information on the display plate can be reliably visually recognized. As a surface illumination device using the above-mentioned surface light source conversion optical element, a point light source that emits light and an entire light exit surface on the opposite side to the point light source by reflecting incident light from the point light source are described. And a surface light source conversion optical element that emits light from the surface light source, the surface light source conversion optical element has a circular shape in plan view on the surface on the point light source side, and has a prism entrance surface on its inner peripheral surface side, and A large number of prism portions each having a prism reflection surface on the outer peripheral surface side are integrally formed in a concentric arrangement, and the prism reflection surface directs incident light from the prism entrance surface to the light exit surface. It is preferable that the reflector is formed so as to totally reflect in a certain direction.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing a surface light source conversion optical element according to an embodiment of the present invention and a surface illumination device using the same, and FIG. 2 is a sectional view taken along line II-II of FIG. The surface light source conversion optical element 4 for converting the radiated light of the point light source 1 formed of a light emitting diode or the like into a surface light source includes:
For example, it is integrally formed in a substantially disc shape from a material obtained by mixing a light diffusing material into a transparent plastic material such as acrylic. As shown in FIG. 2, on the surface of the surface light source converting optical element 4 facing the point light source 1, a lens portion 7 having a circular shape in a plan view and having a focal point at a position where the point light source 1 is to be disposed is provided at the center. A plurality of prism portions P1 to Pn having different diameters and having a circular shape in a plan view are formed at equal intervals in a concentric arrangement with respect to the lens portion 7. A flat light emitting surface 8 is formed on the surface light source conversion optical element 4 on the side opposite to the point light source 1.

As shown in FIG. 2, each of the prism portions P1 to Pn has a triangular prism shape having a triangular cross section, and the inner peripheral surface of each of the prism portions P1 to Pn is a prism. The incident surfaces I1 to In and the outer peripheral surface side are prism reflecting surfaces R1 to Rn. Each of the prism reflecting surfaces R1 to Rn is provided with incident light IL1 to I1 from the point light source 1.
Ln is formed at an inclination angle capable of totally reflecting Ln in a direction perpendicular to the light emitting surface 8. The prism reflecting surfaces R1 to Rn may be configured to be a total reflecting surface by coating an inorganic coating material. On the other hand, the prism entrance surface I
1 to In are point light sources 1 in each of the prism portions P1 to Pn.
From the front end on the side, it extends in a direction perpendicular to the light emitting surface 8. In other words, each of the prism entrance surfaces I1 to In is a reflection of the incident light beams IL1 to ILn incident on the front end (hereinafter referred to as the front end) on the point light source 1 side of the corresponding prism reflection surfaces R1 to Rn. Rays RL1-R
It is arranged along Ln.

Further, the prism reflecting surface R1 closest to the center.
, The end of each of the prism reflecting surfaces R2 to Rn apart from the point light source 1 (hereinafter referred to as the rear end) passes through the front end of each of the adjacent prism portions P1 to Pn on the inner side. It is set on the extension of the incident light beams IL1 to ILn, and the rear end of the prism reflection surface R1 is set on the extension of the incident light IL0 passing through the peripheral end of the lens unit 7. Therefore, the prism reflecting surfaces R1 to Rn are successively stepped in a configuration in which the prism reflecting surfaces R1 to Rn are sequentially receded inward in the thickness direction of the surface light source conversion optical element 4 toward the center of the surface light source conversion optical element 4. Is formed.

Since the prism reflecting surfaces R1 to Rn are arranged as described above, light beams other than those radiated from the point light source 1 and transmitted through the lens unit 7 while traveling straight through the lens unit 7 are incident on each prism incident surface. After being incident on I1 to In, all of them are reflected in the direction perpendicular to the light emitting surface 8 by the continuous step-like prism reflecting surfaces R1 to Rn. For example,
All the light beams between the two light beams IL7 and ILn emitted from the point light source 1 are incident on the prism entrance surface In, are totally reflected by the prism reflection surface Rn, and are emitted from the light exit surface 8 in a direction perpendicular thereto. Then, the display panel 3 is irradiated. Similarly,
All of the light beams between the two light beams IL6 and IL7 emitted from the point light source 1 are incident on the prism entrance surface 17, are totally reflected by the prism reflection surface R7, and are emitted from the light exit surface 8 in a direction perpendicular thereto. Then, the display panel 3 is irradiated. Similarly, the ray bundle between two adjacent rays among the rays IL0 to IL6 is totally reflected by the corresponding prism reflecting surfaces R1 to R6, and is emitted from the light emitting surface 8 in a direction perpendicular thereto and displayed. The plate 3 is irradiated. Therefore, the light exits from the light exit surface 8 in a direction perpendicular to the entire surface.

As described above, in addition to emitting light in a direction perpendicular to the entire light exit surface 8, each of the prism entrance surfaces I 1 to In is disposed in a direction perpendicular to the light exit surface 8. Therefore, the angle of incidence of the light emitted from the point light source 1 on each of the prism entrance surfaces I1 to In does not increase even in the peripheral portion, so that the amount of incident light on the prism portions P5 to Pn in the peripheral portion does not decrease. Furthermore, each prism entrance surface I1
In indicates that the incident light beams IL1 to ILn on the front ends of the corresponding prism reflection surfaces R1 to Rn correspond to the prism reflection surfaces R1 to Rn.
Since they are arranged so as to match the reflected light rays RL1 to RLn reflected by Rn, the corresponding prism reflecting surfaces R1 to Rn
There is no blocking of the reflected light reflected by the. Therefore,
From the light emitting surface 8, a uniform amount of light can be emitted from the entire surface, and the entire display panel 3 can be irradiated without uneven brightness. In addition, actually, the incident lights IL0 to IL0
While n is refracted in the prism portions P1 to Pn and reflected on the prism reflecting surfaces R1 to Rn, FIG. 2 does not show a state in which light is refracted for ease of explanation.

Next, the reflection of light on the prism reflecting surfaces R1 to Rn will be described with reference to FIG. FIG.
Shows an enlarged view of a part of FIG.
The prism reflecting surface R7 will be described as an example. The incident light IL7 to the front end of the prism reflecting surface R7 is totally reflected in the direction perpendicular to the light emitting surface 8 by the prism reflecting surface R7, but the reflection point on the prism reflecting surface R7 is separated from the point light source 1 on the rear side. The reflected light RL71 to RL73 inclines outward as the light travels. Therefore, the reflected light beam reflected by one prism reflecting surface R7 also includes a light component having a direction component inclined outward from a direction perpendicular to the light exit surface 8. Looking at the entire light exit surface 8 of the surface light source conversion optical element 4, the luminous flux reflected from each of the prism reflecting surfaces R 1 to Rn is shifted from a component perpendicular to the light exit surface 8 in a direction perpendicular to the light exit surface 8. On the other hand, the light emitting surface 8 is a ring including a component inclined in the outward direction, and the entire light exit surface 8 can be regarded as a disk formed by gathering a large number of rings.

By the way, since the brightness of the surface is the integral amount of the light beam radiated in a certain direction, the prism reflection surface R
The reflected lights RL71 to RL inclined with respect to the vertical direction of 1 to Rn
73 needs to be reduced as much as possible. This inclined reflected light R
The inclination angles a of L71 to RL73 with respect to the vertical direction along the prism entrance surfaces I1 to In are prism reflection surfaces R1 to Rn.
Becomes smaller as the number increases, and if the number of prism reflecting surfaces R1 to Rn is increased as much as possible, most of the reflected light can be directed to a direction close to the vertical direction of the light emitting surface 8.
As a result, most of the light rays emitted from the point light source 1 are emitted from the light emitting surface 8 in a direction perpendicular thereto, and
Can be illuminated brightly without uneven brightness.

FIG. 4 is an explanatory view showing a display device to which the surface illumination device of the present invention is applied. Normally, the film-like display plate 9 for displaying the operation status of the device has a pattern in which a plurality of rectangular display pixels 3a to 3e are arranged in a line as shown in FIG. When illuminating the display panel 3 as described above, the disc-shaped surface light source conversion optical element 4 shown in FIG. 1 is cut into a square corresponding to the size of the display pixels 3a to 3e. Are used in an array corresponding to the display panel 3.

The square surface light source conversion optical element 4 as described above was manufactured, and the emitted light amounts of the optical element 4 and the conventional light diffusion plate 2 shown in FIG. 6 were measured and compared. Here, five locations, that is, the central portion M1 of the quadrangular shape and the corners M2 to M5 of the four corners were selected as the light intensity measuring portions. In the conventional light diffusing plate 2, M1 = 275.4, M2 = 81.39, M3 =
92.9, M4 = 77.13, M5 = 115.8,
In the surface light source conversion optical element 4 of the present invention, M1 = 2637, M
2 = 716, M3 = 1185, M4 = 1661, M5 = 799 were obtained. The unit of the above numerical value is (Cd / m ² ). As is clear from the results of the actual measurement, the optical element 4 for converting a surface light source according to the present invention was able to remarkably suppress a decrease in the amount of light, particularly at peripheral portions.

In such a display device, the position of the human eye when looking at the display panel 3 is determined by the position of each of the display pixels 3a to 3e.
Are not always fixed directly above the display pixels 3a to 3
In many cases, it is obliquely shifted from 3e. Therefore, when irradiating the display panel 3 as described above, it is desirable that the display panel 3 be an appropriate diffusion light source. Therefore, although not shown, in the present invention, the surface light source converting optical element 4 is formed of a material having a diffusive property as described above, or the prism reflecting surfaces R1 to Rn are roughened to diffuse light. I do.

FIG. 5 is a partial sectional view showing a surface illuminating device according to another embodiment of the present invention.

The basic shape of the surface light source converting optical element 4 in the surface illuminating device of this embodiment is the same as that of one embodiment. That is, the rear end of each prism reflecting surface except for the prism reflecting surface closest to the center is set on the extension line of the incident light passing through the front end of each adjacent prism portion on each inner side, The rear end of the prism reflecting surface is set on an extension of the incident light beam passing through the peripheral end of the lens unit. Next, a shape different from that of the embodiment will be described.

Each of the prism portions has the same shape. Now, the prism portion P7 will be described as an example. The prism reflecting surface R7 of the prism portion P7 is set to have an inclination angle that allows the light RL70 reflected by the prism reflecting surface R7 of the incident light beam IL70 incident on the central reflection point thereof to be reflected in the direction perpendicular to the light emitting surface 8. I have. Prism reflecting surface R
The light ray RL71 reflected by the prism reflecting surface R7 of the incident light beam IL71 incident on the front end of the optical element 4 is inclined inward toward the center of the optical element 4 with respect to the perpendicular to the light emitting surface 8. The reflected light RL72 of the incident light IL72 incident on the rear end of the prism reflecting surface R7 and reflected by the prism reflecting surface R7 inclines outward with respect to the perpendicular to the light emitting surface 8. The prism entrance surface I7 of the prism section P7 is set to coincide with the above-mentioned reflected light beam RL72.

In the surface light source conversion optical element 4, the prism reflecting surface R7 converts the light RL70 reflected by the prism reflecting surface R7 of the incident light beam IL70 to the central reflection point thereof into the light emitting surface 8
, The angle of inclination b between the light ray RL71 reflected by the prism reflection surface R7 of the light ray IL71 incident on the front end of the prism reflection surface R7 and the vertical line of the light exit surface 8 because of the inclination angle b. The inclination angle c between the light ray RL72 of the light ray IL72 incident on the rear end of the prism reflection face R7 and the perpendicular ray of the light emission face 8 formed by the reflection light ray RL72 of the prism reflection face R7 becomes equal. Thus, the inclination angles b and c of the reflected lights RL71 and RL72 at both ends of the prism reflection surface R7 with respect to the perpendicular to the light exit surface 8 are inclined in directions opposite to each other with respect to the perpendicular and are set to the same angle. By balancing on both sides, the size becomes much smaller than when the balance is not made, and the perpendicular component of the reflected light beam to the light exit surface 8 increases accordingly.

When the prism reflecting surface R7 is viewed from the direction perpendicular to the light emitting surface 8, the width D of the prism incident surface I7 is much smaller than the width X of the prism reflecting surface R7. Since it is a non-reflective surface, it is visually recognized as black zones by human eyes.

Therefore, the width D of the prism entrance surface I7 is desirably set to a resolution substantially equal to the resolution seen from a clear viewing distance so as not to be visually recognized as a black band.

[0032]

As described above, according to the surface light source conversion optical element and the surface illumination device using the same according to the present invention, the light emitted from the point light source is totally reflected in a substantially constant direction toward the light emitting surface. Since it has a configuration including a surface light source conversion optical element in which a large number of circular prism portions having a prism reflecting surface are concentrically arranged, a compact configuration in which the optical element is opposed to a point light source at a small interval is adopted. However, the light emitted from the point light source can be emitted from the entire light emitting surface of the optical element without substantially reducing the light amount. In addition, since the prism entrance surfaces are provided on the inner peripheral surface side of each of the prism portions which are arranged concentrically, the angle of incidence of the light radiated from the point light source on each prism entrance surface is around the optical element. Also, the incident light amount at the peripheral portion of the prism portion does not decrease. Therefore, a uniform amount of light can be emitted from the entire light exit surface, and the entire display panel can be irradiated without uneven brightness.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a surface illumination device according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along line II-II of FIG.

FIG. 3 is an enlarged view of a part of FIG. 2;

FIG. 4 is an explanatory diagram of a display device to which the above device is applied.

FIG. 5 is a sectional view of a main part showing a surface illumination device according to another embodiment of the present invention.

FIG. 6 is a partial cross-sectional view showing a conventional surface illumination device.

[Explanation of symbols]

 1 point light source 3 display plate 4 surface light source conversion optical element 8 light emitting surface P1 to Pn prism unit I1 to In prism incident surface R1 to Rn prism reflecting surface IL1 to ILn incident light

Claims (7)

[Claims] 1. A surface light source conversion optical element that reflects incident light emitted from a point light source that emits light and emits the light from the entire light exit surface opposite to the point light source, comprising: A large number of prism portions each having a prism entrance surface on the inner peripheral surface side and a prism reflecting surface on the outer peripheral surface side are integrally formed in a concentric arrangement, An optical element for converting a surface light source, wherein the prism reflecting surface is formed so as to totally reflect incident light from the prism incident surface in a substantially constant direction toward the light emitting surface. 2. A rear end of each prism reflecting surface, which is separated from each point light source, is set on an extension of an incident light beam passing through a front end of each adjacent prism portion on each inner side. 2. The surface light source conversion device according to claim 1, wherein each of the prism reflecting surfaces is formed in a continuous stepwise shape so as to gradually recede in a thickness direction of the surface light source conversion optical element as it goes to the center of the surface light source conversion optical device. Optical element. 3. The optical element for converting a surface light source according to claim 1, wherein each of the prism entrance surfaces is located in an arrangement along a direction of the reflected light reflected at a front end portion of the corresponding prism reflection surface. 4. Each prism reflecting surface is formed of a total reflecting surface having an inclination angle for totally reflecting incident light from the prism incident surface in a substantially constant direction toward the light emitting surface, or a reflecting surface made of an inorganic coating. An optical element for converting a surface light source according to claim 1. 5. The surface light source conversion optical element according to claim 1, wherein the surface light source conversion optical element is integrally formed of a light diffusing material. 6. The optical element for converting a surface light source according to claim 1, wherein each prism reflecting surface is formed in a rough surface. 7. A point light source that emits light, and a surface light source conversion optical element that reflects incident light from the point light source and emits the light from the entire light exit surface opposite to the point light source. The surface light source converting optical element includes a plurality of prisms each having a circular shape in a plan view on a surface on the point light source side, a prism incident surface on an inner peripheral surface side, and a prism reflecting surface on an outer peripheral surface side. The part is integrally formed in a concentric arrangement, and the prism reflecting surface is formed so as to totally reflect incident light from the prism incident surface in a substantially constant direction toward the light emitting surface. Characteristic surface lighting device.