JPH0624857Y2 - Backlight device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The backlight device of the present invention will be described according to the following items.

A. Industrial application fields B. Outline of Invention C. Prior art D. Issues to be solved by the invention E. Means for Solving the Problems F. Example [FIGS. 1 to 4] a. Point light source b. Cylindrical lens c. Linear Fresnel lens d. Inclined mirror G. Application Example [FIGS. 5 and 6] G-1. First application example [FIG. 5] G-2. Second Application Example [FIG. 6] Effect of the Invention (A. Industrial Application Field) The present invention relates to a novel backlight device. For more information,
A backlight device for illuminating a transmissive display element from the back side thereof, which aims to provide a novel backlight device which can efficiently use a point light source and can reduce the depth dimension. is there.

(B. Outline of the Invention) In the backlight device of the present invention, a cylindrical lens whose center of the focal line is located at the point light source is arranged in front of the point light source, and the light emitted from the point light source is first made into a parallel light flux in one direction. And a linear Fresnel lens with the center of the focal line located at the point light source is arranged by arranging a number of Fresnel steps extending in the direction orthogonal to the longitudinal direction of the cylindrical lens on the front side of the cylindrical lens In the above, the light made into a parallel light flux is made into a light flux which is also parallel in the other direction orthogonal to the one direction so that most of the light emitted from the point light source contributes to the display of the transmissive display element. To increase the light utilization efficiency, and further to the front side of the linear Fresnel lens with respect to the optical axes of the cylindrical lens and the linear Fresnel lens. The depth dimension, that is, the dimension in the viewing direction of the transmissive display element can be reduced by disposing the inclined mirror and bending the optical path of the parallel light flux.

(C. Prior art) A transmissive type, that is, a display element using a liquid crystal plate, for example, a display element in which display is performed by transmitting light from the back side to the front side is widely used.

For example, a small television receiver is known as a display device using a liquid crystal plate, but such a device requires a backlight device that illuminates the liquid crystal plate from the back side.

As such a backlight device using a linear light source as a light source, conventionally, a U-shaped fluorescent lamp in which a tube is bent into a U-shape is used, and several straight tube fluorescent lamps are arranged in parallel. The ones that are known are known.

(D. Problem to be Solved by the Invention) However, in the above-described conventional backlight device, since the light of each light source enters the transmissive display element as diffused light, the light incident on the transmissive display element is There is a problem that only a part contributes to the visual recognition, and the light utilization efficiency is not good.

Further, there is a problem that a fluorescent lamp is bright at the beginning of use but becomes extremely dark with time.

Therefore, I considered using a point light source with high brightness and durability such as a halogen bulb, a metal halide lamp, and a mercury lamp.

However, a certain optical path length is required to obtain a light flux suitable for a backlight of a transmissive display element, which is a parallel light flux having a certain surface spread using some lenses, and a depth dimension, that is, There is a problem that the size of the transmissive display element in the viewing direction becomes large.

(E. Means for Solving the Problem) In order to solve the above-mentioned problems, the backlight device of the present invention has a cylindrical lens having a focal line center located at the point light source in front of the point light source. A linear Fresnel lens with a large number of Fresnel steps extending in the direction perpendicular to the longitudinal direction of the cylindrical lens is arranged on the front side of the lens, and the center of the focal line is located at the point light source. The lens and the linear Fresnel lens have tilt mirrors tilted with respect to the optical axis.

Therefore, according to the backlight device of the present invention, the light emitted from the point light source is first converted into a light flux parallel to the one direction by the cylindrical lens, and then is converted into the light flux parallel to the one direction by the linear Fresnel lens. Therefore, most of the light incident on the transmissive display element contributes to the visual recognition, and the light utilization efficiency is very good.

Further, since the light passing through the linear Fresnel lens can be bent in the optical path by the tilted mirror, if the transmissive display element is arranged so as to cross the light path bent by the tilted mirror, the depth dimension, that is, the transmissive type is obtained. The size of the display element in the viewing direction can be reduced.

(F. Embodiment) [FIGS. 1 to 4] The details of the backlight device of the present invention will be described below with reference to the first embodiment.

(A. Point light source) 2 is a light bulb as a point light source, and a normal incandescent light bulb, a halogen light bulb, a metal halide lamp, a mercury lamp, or the like can be used.

Reference numeral 3 is a reflecting mirror arranged so as to surround the light bulb 2, and the reflecting surface 3a of the light bulb 2 is formed as a semi-concave spherical surface centered on the light emitting portion 2a of the light bulb 2.

Therefore, the light emitted from the light emitting portion 2a of the light bulb 2 and directed rearward is reflected by the reflecting surface 3a of the reflecting mirror 3 and is returned substantially in the direction of the light emitting portion 2a. Therefore, the light reflected by the reflecting mirror 3 is also reflected by the light bulb 2.
It behaves like light emitted from the front.

(B. Cylindrical Lens) Reference numeral 4 denotes a cylindrical lens, which is arranged on the front side of the light bulb 2 and the center of its focal line is located at the light emitting portion 2 a of the light bulb 2.

Then, the light emitted from the light bulb 2 and incident on the cylindrical lens 4 advances radially as it is in the longitudinal direction of the cylindrical lens 4, but the cylindrical lens 4
The light beams are parallel in the width direction of.

(C. Linear Fresnel lens) Reference numeral 5 denotes a linear Fresnel lens arranged in front of the cylindrical lens 4.

The linear Fresnel lens 5 is composed of a large number of Fresnel steps 6, 6, ...
.. are formed so that the longitudinal direction thereof is orthogonal to the longitudinal direction of the cylindrical lens 4. The center of the focal line of the linear Fresnel lens 5 is at the light emitting portion 2a of the light bulb 2.
Is located in.

Then, the light that has spread radially in the longitudinal direction of the cylindrical lens 4 is the linear Fresnel lens 5
When it passes through, it becomes a parallel light beam.

Therefore, due to the action of the cylindrical lens 4 and the linear Fresnel lens 5, the light emitted from the light bulb 2 becomes a substantially perfect parallel light flux when passing through the linear Fresnel lens 5.

(D. Tilt mirror) 7 is a tilt mirror, which is arranged in front of the linear Fresnel lens 5. The reflecting surface 7a of the tilted mirror 7 is tilted with respect to the optical axis xx of the cylindrical lens 4 and the linear Fresnel lens 5, and the traveling direction of the parallel light flux transmitted through the linear Fresnel lens 5 is substantially the same. It is supposed to change 90 degrees.

In order to change the traveling direction of the light flux transmitted through the linear Fresnel lens 5 by approximately 90 °, if the reflecting surface 7a is a flat surface, it is necessary to incline the optical axis xx by an angle of approximately 45 °. . Therefore, the tilt angle with respect to the optical axis xx (the reflecting surface 7a
In order to increase the incident angle) and reduce the depth dimension, the reflecting surface 7a is formed of a large number of reflecting segments 8, 8, ...
It is better to use the one configured in.

That is, each of the reflective segments 8, 8, ... Is composed of a minute reflective surface extending in the longitudinal direction of the cylindrical lens 4, and each of the minute reflective surfaces 8, 8, ... Is the optical axis xx.
On the other hand, when viewed in the longitudinal direction of the cylindrical lens 4, about 4
It is inclined at an angle of 5 °. Therefore, even if the tilt angle of the tilt mirror 7 with respect to the optical axis xx is increased, the light flux transmitted through the linear Fresnel lens 5 has a traveling direction of about 9 degrees.
The angle of 0 ° can be changed.

An inclined mirror provided with such a large number of reflective segments is disclosed in, for example, Japanese Patent Laid-Open No. 58-125083.

However, an inclined mirror whose reflection surface is a flat surface is used as an optical axis x
Even when arranged at an angle of about 45 ° with respect to −x, the depth dimension can be made considerably smaller than that in the case where the optical path is not bent by using the tilted mirror. It is not absolutely necessary to use the tilting mirror 7 consisting of the reflecting segments 8, 8, ....

Also, the change angle of the optical path is always about 9 with respect to the optical axis xx of the cylindrical lens 4 and the linear Fresnel lens 5.
It doesn't have to be 0 °, it's 80 °
The optical path may be changed more gently such as 60 °.

(G. Application Example) [FIGS. 5 and 6] Next, an application example of the above-described backlight device 1 will be described.

(G-1. First Application Example) [FIG. 5] FIG. 5 shows the backlight device 1 of the present invention applied to a direct-viewing type liquid crystal television receiver 9.

Reference numeral 10 is arranged on the front surface side of the tilt mirror 7 of the backlight device 1 so as to be parallel to the optical axes xx of the cylindrical lens 4 and the linear Fresnel lens 5, that is, to cross the optical path bent by the tilt mirror 7. The liquid crystal panel is driven by a display circuit (not shown).

Since the light transmitted through the liquid crystal plate 10 is a substantially perfect parallel light flux, almost all of it contributes to the visibility from the front side of the liquid crystal plate 10.

(G-2. Second Application Example) [FIG. 6] FIG. 6 shows an example in which the backlight device 1 of the present invention is applied to the rear projector 11.

Reference numeral 12 denotes a condenser lens disposed on the front surface side of the tilt mirror 7 of the backlight device 1, which once narrows the parallel light beam reflected by the tilt mirror 7 and then makes the parallel light beam.

Reference numeral 13 denotes a liquid crystal plate arranged on the front side of the condenser lens 12, which is driven by a display circuit (not shown) so that the collimated light beam converged by the condenser lens 12 is incident on the rear surface thereof. It has become.

Reference numeral 14 denotes a condenser lens arranged on the front side of the liquid crystal plate 13 and has a function of narrowing down the parallel light flux transmitted through the liquid crystal plate 13.

15 is a projection lens disposed in front of the condenser lens 14,
Reference numeral 16 denotes a screen arranged in front of the projection lens 15, and the light flux narrowed down by the condenser lens 14 is projected from the rear surface of the screen 16 by the projection lens 15 to screen the image projected on the screen 16. 1
6 can be seen from the front.

(H. Effect of the Invention) As is apparent from the above description, the backlight device of the present invention is a backlight device that illuminates a transmissive display element from the back side, and includes a point light source and a point light source. It is arranged on the front side of the cylindrical lens, which is arranged on the front side and the center of the focal line is located on the point light source,
It consists of a number of Fresnel steps extending in the direction orthogonal to the longitudinal direction of the cylindrical lens arranged in the longitudinal direction of the cylindrical lens, and the center of the focal line is arranged in the linear Fresnel lens located at the point light source and in front of the linear Fresnel lens. , And a tilt mirror arranged to be tilted with respect to the optical axes of the cylindrical lens and the linear Fresnel lens.

Therefore, according to the backlight device of the present invention, the light emitted from the point light source is first converted into a light beam parallel to the one direction by the cylindrical lens, and then the light beam parallel to the one direction is also converted by the linear Fresnel lens. Therefore, most of the light incident on the transmissive display element contributes to the visual recognition, and the light utilization efficiency is very good.

Further, since the light passing through the linear Fresnel lens can be bent in the optical path by the tilted mirror, if the transmissive display element is arranged so as to cross the light path bent by the tilted mirror, the depth dimension, that is, the transmissive type is obtained. The size of the display element in the viewing direction can be reduced.

In the above description, two application examples of the backlight device of the present invention are shown, but the application examples of the present invention are not limited to these, and a transmissive display element is illuminated from the back side thereof. The backlight device can be widely applied.

[Brief description of drawings]

1 to 4 show an embodiment of the backlight device of the present invention. FIG. 1 is a schematic perspective view thereof, FIG. 2 is a schematic enlarged sectional view, and FIG. 3 is III of FIG. -III sectional view, FIG. 4 is an enlarged sectional view showing the tilted mirror portion, FIG. 5 is a sectional view showing a first application example of the backlight device of the present invention, and FIG. 6 is the present invention It is sectional drawing which shows the 2nd application example of a backlight device. DESCRIPTION OF SYMBOLS 1 ... Backlight device, 2a ... Point light source, 4 ... Cylindrical lens, 5 ... Linear Fresnel lens, 6 ... Fresnel step, 7 ... Inclined mirror, xx ... Cylindrical lens 4, Optical axis of linear Fresnel lens 5, 10 ... Transmissive display element, 13 ... Transmissive display element

Claims (1)

[Scope of utility model registration request] 1. A backlight device for illuminating a transmissive display element from the back side, comprising a point light source, a cylindrical lens arranged in front of the point light source and having a focal line center located at the point light source, and a cylindrical lens. Is arranged on the front side of the cylindrical lens and extends in a direction orthogonal to the longitudinal direction of the cylindrical lens, and is arranged in the longitudinal direction of the cylindrical lens.The linear Fresnel lens with the center of the focal line located at the point light source and the linear Fresnel lens A backlight device, comprising: a tilted mirror that is arranged on the front side of the lens and that is tilted with respect to the optical axes of the cylindrical lens and the linear Fresnel lens.