JPH07320513A - Lighting system - Google Patents

Abstract

PURPOSE:To provide a lighting system with high light utilization factor, thin size, and uniform brightness. CONSTITUTION:A lighting system contains a rod-shaped cold cathode fluorescent lamp 1, a light diffusion plate 2 arranged in the front of the fluorescent lamp 1, and a reflecting mirror 3 arranged in the rear of the fluorescent lamp 1. A reflecting surface 3a and a reflecting surface 3b of the reflecting mirror 3 are formed in vertical axis symmetry. When the distance from the intersecting point P of the vertical axis passing the center of the fluorescent lamp 1 to the reflecting mirror 3 to the center 0 of the light source is (s) and the outer diameter of the fluorescent lamp 1 is 2r, angles theta1, theta2 formed by light axes of the reflecting surfaces 3a, 3b and vertical axis satisfy the relation of once 0<theta1 or theta2)<=sin<-1> (r/s).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lighting device used for back lighting of a liquid crystal display device which can be used in personal computer devices, liquid crystal television devices and the like.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 7, a lighting device of this type has a rod-shaped fluorescent lamp 4, a light diffusion plate 5 provided in front of the rod-shaped fluorescent lamp 4, and a rod-shaped fluorescent lamp 4.
It was generally composed of a parabolic reflecting mirror 6 arranged at the rear of the.

In such a parabolic reflector 6 of the conventional lighting device, the light emitted from the rod-shaped fluorescent lamp 4 is reflected toward the light diffusion plate 5 as light parallel to the vertical axis.

[0004]

However, in such a conventional illuminating device, the central part of the illuminating device has a parabolic reflecting mirror 6 in addition to strong direct light from the rod-shaped fluorescent lamp 4 toward the light diffusing plate 5. It becomes bright because it is illuminated by the reflected light parallel to the vertical axis. On the other hand, at the end of the lighting device, the distance from the rod-shaped fluorescent lamp 4 is increased, so that the direct light toward the light diffusion plate 5 is weakened. Further, since the distance between the rod-shaped fluorescent lamp 4 and the reflecting surface of the reflecting mirror 6 becomes long, the light reaching the reflecting surface becomes weak and only weak reflected light can be obtained. Therefore, it becomes dark at the end of the lighting device. As a means for alleviating such an extreme brightness difference between the central part and the end part of the lighting device, that is, brightness unevenness, the light diffusing plate 5 is made of a material having high diffusivity and low transmittance. However, such means has a problem that multiple reflections between the light diffusion plate 5 and the reflecting mirror 6 cause a large loss of light and deteriorate the light utilization efficiency. In addition, in a lighting device having a parabolic reflector, in order to increase the light utilization efficiency, the depth of the reflector 6 is increased and the distance between the light diffusion plate 5 and the rod-shaped fluorescent lamp 4 is increased to obtain a rod-shaped fluorescent lamp. There is a means for reducing the difference between the intensity of direct light from 4 toward the light diffusion plate 5 and the intensity of light reflected by the reflecting mirror 6 and using a light diffusion plate having low diffusivity and high transmittance. This means has a problem that the lighting device becomes thick.

The present invention has been made to solve such a problem, and an object of the present invention is to provide a thin illumination device having high light utilization efficiency.

[0006]

The illumination device of the present invention comprises a line light source, a light diffusing plate provided in front of the line light source, and a reflecting mirror arranged behind the line light source. , The reflecting mirror is parabolic and axially symmetrical with respect to a vertical axis passing through the center of the linear light source, and the optical axis of the reflecting mirror is tilted with respect to a vertical axis passing through the center of the linear light source. There is.

[0007]

In this structure, the difference in brightness between the central part of the lighting device and the end part of the lighting device can be reduced. In addition, the light diffusion plate having a higher transmittance than the conventional one can realize the same degree of brightness uniformity as the conventional one and improve the light utilization efficiency, and can also reduce the depth of the reflecting mirror.

[0008]

1 is a sectional view of an illuminating device according to an embodiment of the present invention.

As shown in FIG. 1, the lighting apparatus according to the embodiment of the present invention has a rod-shaped cold cathode fluorescent lamp 1 having an outer diameter of 3 mm, a light diffusion plate 2 covering the front thereof, and a rod-shaped cold cathode fluorescent lamp 1 at the rear. The parabolic reflecting mirror 3 is provided and is composed of a reflecting surface 3a and a reflecting surface 3b which are arranged axially symmetrical with respect to a vertical axis passing through the center O of the rod-shaped cold cathode fluorescent lamp 1. Further, the second quadrant direction of the coordinate axis system which can be the optical axis of the reflecting surface 3a drawn from the intersection P of the vertical axis passing through the center O of the rod-shaped cold cathode fluorescent lamp 1 and the reflecting mirror 3 to the outer wall of the rod-shaped cold cathode fluorescent lamp 1. The angle θ ₁ formed by the tangent line PQ drawn on the vertical axis and the line segment OP on the vertical axis is set to 17 ° with respect to the vertical axis. Further, the angle θ ₂ formed by the tangent line PR drawn in the first quadrant direction of the coordinate axis system, which is the optical axis of the reflecting surface 3b drawn from the intersection P to the outer wall of the rod-shaped cold cathode fluorescent lamp 1, and the line segment OP is the vertical axis. -17
°. The following formula is used as the design formula of the reflecting mirror 3, and the tilt angles θ ₁ = 17 ° and θ ₂ = − of the parabola so that the optical axes of the reflecting surfaces 3a and 3b coincide with the tangents PQ and PR, respectively.
It was set at 17 °.

Y = (X ² / 4f) -f f (focal length) = 5.0 (0,0): Lamp center (focal point) (X, Y): Coordinates of reflecting mirror When the rod-shaped cold cathode fluorescent lamp 1 is turned on, the lighting device of the present embodiment is as shown in FIG.
Since the end of the illuminating device is far from the rod-shaped cold cathode fluorescent lamp 1 and the direct light toward the light diffusion plate 2 is weak, it is illuminated with the light reflected by the reflecting mirror 3. The central portion of the illuminating device where strong direct light is obtained has a configuration in which the contribution of the reflected light from the reflecting mirror 3 is reduced. Note that the direct light is represented by a solid arrow and the reflected light is represented by a dashed arrow. That is, the end of the lighting device is reflected light,
The central portion of the lighting device is configured to be illuminated by direct light. As a result, in the conventional illuminating device having the parabolic reflecting mirror having the optical axis parallel to the vertical axis, the central part of the illuminating device which can obtain the strong direct light from the rod-shaped cold cathode fluorescent lamp 1 is further provided with the reflecting mirror. It is possible to suppress the occurrence of a large luminance difference between the central portion and the end portion of the lighting device, which is caused by the illumination with the reflected light. That is, since the light reflected and condensed in the central part of the lighting device is reflected to the end part of the lighting device, more reflected light is collected at the end part of the lighting device than in the conventional case, and the brightness of the central part and the end part of the lighting device is increased. The difference will be eased. As a result, the same degree of brightness uniformity as that of the conventional art can be ensured by using the light diffusion plate having a lower diffusivity and a higher transmittance than the conventional one, and the light utilization efficiency can be improved. further,
By tilting the optical axis of the reflecting mirror with respect to the vertical axis, the depth of the reflecting mirror can be made shallow, so that the thickness of the lighting device can be made thin.

The solid arrows in the figure represent the direct light, and the broken arrows represent the reflected light. FIG. 3 shows a comparison of the luminance distribution characteristics of the illuminating device to which the light diffusing plate is attached in this example and the conventional example. As is apparent from FIG. 3, the illumination device of the present embodiment can obtain a light diffusion plate surface luminance of about 10% UP more than that of the conventional example with the same lamp input and the same luminance uniformity. I understand. In the figure, a curve A represents the measurement result of the lighting device of this embodiment, and a curve B represents the measurement result of the lighting device of the conventional example.

In the conventional lighting device designed under the following conditions, the lighting range W = 40 in FIG.
The thickness t of the lighting device must be 23 mm in order to secure mm.

Y = (X ² / 4f) -f f (focal length) = 5.0 (0,0): Lamp center (focal point) (X, Y): Coordinate of reflecting mirror Parabolic tilt angle: 0 ° On the other hand, in order to secure the same illumination range W = 40 mm as the conventional example, the thickness of the illumination device of this embodiment can be 13 mm. That is, the lighting device can be made thinner by 10 mm.

As described above, according to the present embodiment, the optical axis of the conventional parabolic reflector is tilted with respect to the vertical axis and the shape is made to be vertically axisymmetric, so that the conventional reflector has the center of the illuminator. It is possible to condense the light reflected by the reflecting mirror, which has been one of the factors that deteriorated the brightness uniformity, by increasing the brightness of only the part, at the end of the lighting device. As a result, the illuminating device according to the present invention can reduce the difference in brightness between the central part and the end part of the illuminating device. Brightness uniformity can be obtained. That is, the light utilization efficiency can be improved by about 10% as compared with the conventional case.

The inclination θ of the optical axis of the reflecting mirror in the illuminating device is θ = θ ₁ (1) θ> θ ₁ ... Except when the optical axis of the reflecting mirror coincides with the vertical axis in FIG. (2) Three cases of 0 <θ <θ ₁ (3) can be considered. The relationship between the optical path by the reflecting mirror and the luminance distribution when the light diffusion plate having the same transmittance is used in these three cases are shown in FIGS. 4, 5 and 6, respectively.
The vertical axes in FIGS. 4, 5, and 6 show the relative luminance with respect to the central luminance when θ = 10 °. In the case of the formula (3), when θ ₁ = 17 ° and θ = 10 °, as shown in FIG. 6, the reflected light from the reflecting mirror is added to the direct light from the rod-shaped cold cathode fluorescent lamp 1 in the central part of the lighting device. To be However, since the amount of reflected light at the central portion of the illuminating device is smaller than that of the conventional reflecting mirror, the brightness value at the central portion becomes smaller than that of the conventional one. On the other hand, since the amount of light reflected toward the end of the lighting device is large, the brightness uniformity of the entire lighting device is improved as compared with the prior art. Next (2)
In the case of the equation, when θ ₁ = 17 ° and θ = 22 °, FIG.
As shown in, there is a boundary where the direct light from the rod-shaped cold cathode fluorescent lamp 1 is weak, and at the same time the reflected light from the reflecting mirror is hardly obtained, and there is a valley of the brightness on the brightness distribution curve, so that the brightness uniformity is impaired. Be done. In the case of formula (1), θ ₁ = 17 °
Then, as shown in FIG. 4, the rod-shaped cold cathode fluorescent lamp 1
The intensities of the direct light from and the reflected light from the reflecting mirror are balanced, and the valley of the brightness on the brightness distribution curve does not exist.
Therefore, as compared with the cases of the formulas (2) and (3), high brightness uniformity can be obtained with the same light diffusion plate. At this time, the depth of the illumination device for obtaining the same illumination range can be reduced as θ is increased.

That is, (0 <θ <θ ₁ ) → (θ = θ ₁ ).
→ The depth of the lighting device becomes smaller in the order of (θ> θ ₁ ).
Further, the brightness of the central portion of the lighting device is (0 <θ <θ ₁ ) → (θ =
It becomes smaller in the order of θ ₁ ) → (θ> θ ₁ ).

Therefore, from the above results, it is understood that θ for obtaining an illumination device having a smaller depth than that of the conventional illumination device and good brightness uniformity can be set to 0 <θ ≦ θ ₁ .
At this time, since θ ₁ = sin ⁻¹ (r / s) can be expressed from FIG. 1, (0 <θ ≦ θ ₁ ) is 0 <θ ≦ sin ⁻¹ (r / s).
Becomes The distance of the line segment OP is s, and the radius of the rod-shaped cold cathode fluorescent lamp 1 is r. Here, when a reflecting mirror is created by using this relationship, θ may be approximated to sin ⁻¹ (r / s) when importance is attached to the depth and brightness uniformity of the illumination device. Further, when importance is attached to the brightness of the central portion, θ may be brought close to 0.

As described above, according to this embodiment, the optical axis of the parabolic reflector is 0 <θ ≦ sin ⁻¹ (r
/ S), the depth of the lighting device can be reduced by 10 mm as compared with the conventional lighting device having a parabolic reflecting mirror, and at the same time, the light utilization efficiency is about 10 °. % Can be improved.

When the rod-shaped cold-cathode fluorescent lamp 1 is turned on, the light traveling from the rod-shaped cold-cathode fluorescent lamp 1 toward the reflecting mirror 3 is reflected toward the end portion of the illuminating device by the reflecting mirror 3 whose optical axis is inclined with respect to the vertical axis. It With a conventional reflecting mirror having an optical axis parallel to the vertical axis, the direct light effect is great because direct light is radiated directly above the rod-shaped cold cathode fluorescent lamp 1, that is, in the central part of the lighting device. The difference in brightness between the end portion and the central portion of the lighting device becomes large. In the present invention, since the light that has been reflected only in the direction directly above the conventional rod-shaped cold cathode fluorescent lamp is reflected in the direction of the end of the lighting device by the reflecting mirror whose optical axis is tilted with respect to the vertical axis, the central part of the lighting device. Only strong irradiation will stop. Therefore, the difference in brightness between the central portion of the lighting device, which is directly above the rod-shaped cold cathode fluorescent lamp 1, and the end portion of the lighting device is reduced. As a result, a light diffusion plate having a low diffusivity and a high transmittance as compared with the conventional one can realize the same degree of brightness uniformity as the conventional one, so that the light utilization efficiency is increased. Furthermore, by tilting the optical axis of the reflecting mirror with respect to the vertical axis, the depth of the reflecting mirror can be made smaller than that of a conventional parabolic reflecting mirror whose optical axis is parallel to the vertical axis.

In the above embodiment, Y = (X ² / 4f) -f was used as the design formula of the parabolic reflector, but in the present invention, the reflector has a parabolic (elliptic) shape, and one focus of the parabola is used. The same effect can be obtained by any other design formula as long as the rod-shaped light source is located at the position.

[0021]

As described above, the present invention provides an illuminating device including a line light source, a light diffusing plate provided in front of the line light source, and a reflecting mirror arranged behind the line light source.
The reflecting mirror is parabolic and axially symmetrical with respect to a vertical axis passing through the center of the linear light source, and the optical axis of the reflecting mirror is inclined with respect to a vertical axis passing through the center of the linear light source. As a result, since the reflected light can be condensed at the end portion of the illumination device, which has conventionally lacked the light amount as compared with the central portion of the illumination device, it is possible to suppress the occurrence of uneven brightness due to the difference in luminance. In addition, a light diffusion plate with a higher transmittance than before can realize brightness uniformity to the same extent as in the past, improve light utilization efficiency, and reduce the depth of the reflector so that the illumination device is compact. Thus, it is possible to provide a lighting device having an excellent effect that the realization can be realized.

[Brief description of drawings]

FIG. 1 is a sectional view of a lighting device according to an embodiment of the present invention.

[Figure 2] Similarly optical path diagram

FIG. 3 is a brightness distribution comparison diagram between the present embodiment and a conventional example.

FIG. 4 is an optical path diagram of the illumination device when θ = θ ₁ in the present embodiment.

FIG. 5 is an optical path diagram of the illumination device when θ> θ ₁ in this embodiment.

FIG. 6 is an optical path diagram of the illumination device when 0 <θ <θ ₁ in the present embodiment.

FIG. 7 is a cross-sectional view of a conventional lighting device.

[Explanation of symbols]

 1 Rod-shaped cold cathode fluorescent lamp 2 Light diffusing plate 3 Reflector

Claims (2)

[Claims] 1. A lighting device comprising a linear light source, a light diffusing plate provided in front of the linear light source, and a reflecting mirror arranged behind the linear light source, wherein the reflecting mirror has a parabolic shape. An illumination device, which is axially symmetric with respect to a vertical axis passing through the center of the linear light source, and in which an optical axis of the reflecting mirror is inclined with respect to a vertical axis passing through the center of the linear light source. 2. The distance from the intersection of the vertical axis passing through the center of the linear light source and the reflecting mirror to the center of the linear light source is s, from the intersection of the vertical axis and the reflecting mirror to the outer wall of the linear light source. When the angle formed by the vertical axis and the tangent line that can be the optical axis of the drawn reflecting mirror is θ and the outer diameter of the linear light source is 2r, 0
The lighting device according to claim 1, wherein the relationship <θ ≦ sin ⁻¹ (r / s) is satisfied.