AU595588B2

AU595588B2 - Planar light emitting device

Info

Publication number: AU595588B2
Application number: AU69736/87A
Authority: AU
Inventors: Toshiya Inubushi; Shigeyuki Yoshida
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1986-06-30
Filing date: 1987-03-05
Publication date: 1990-04-05
Anticipated expiration: 2007-03-05
Also published as: GB2192084B; GB2192084A; GB8705784D0; JPS638718A; CA1289534C; AU6973687A; JP2755941B2

Description

5 8 FORM 10 SPRUSON FERGUSON COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: i 7 3 /S7 Class Int. Class Complete Specification Lodged: Accepted: Published: Priority: Related Art: Name of Applicant: MITSUBISHI DENKI KABUSHIKI KAISHA Address of Applicant: 2-3, Marunouchi 2 chome, Chiyoda-ku, Tokyo 100, Japan C t Actual Inventor(s): TOSHIYA INUBUSHI and SHIGEYUKI YOSHIDA SAddress for Service: Spruson Ferguson, Patent Attorneys, S...Level 33 St Martins Tower, 31 Market Street, Sydney, New South Wales, 2000, Australia Complete Specification for the invention entitled: "PLANAR LIGHT EMITTING DEVICE" The following statement is a full description of this invention, including the best method of performing it known to us SBR:eah 291W _I I_ 1.

ABSTRACT

A planar light emitting device for use with, for example, a liquid crystal displaypanel, comprising a body which is formed of a transparent synthetic resin, a light emitting panel which has one surface thereof worked into a prism in correspondence with the liquid crystal displaypanel and which has reflective sheets respectively stuck on slanting surfaces formed on both surfaces thereof, a plurality of light sources which are disposed at positions 1I not opposing to the light emitting panel, and a light guide plate which is thinned in a wedge shape as it C becomes more distant from the light sources.

t I I L asrrrr~~;a~ -2- BACKGROUND OF THE INVENTION This invention relates to planar light emitting devices for use in, for example, the back lights of liquid crystal displaypanels (LCDs) which are installed in portable telephones etc. More particularly, it relates to a planar light emitting device which is thin.

Fig. 5 a and Fig. 6 a are front views showing prior-art planar light emitting devices of the specified type, while Fig. 5 b and Fig. 6 b are vertical sectional 0o views of the respective devices. Numeral 1 designates the planar light emitting device which is provided with a diffusive sheet 6 having a light emitting surface 2 at its front and with a predetermined printed circuit board 5 at i its rear. Inside the planar light emitting device which is comparatively thin, there are formed a diffusion layer 3 made from a diffusant, which diffuses the light of a Splurality of light sources 4 such as light emitting diodes I (LEDs) disposed in the vicinities of the printed circuit j board 5, and slanting surfaces 7a or a slanting surface 7b O which efficiently guide(s) the light of the light sources V 4 to the light emitting surface 2 of the thin planar light emitting device i. In the device shown in Fig. 5 b the rectilinear slanting surfaces 7a flare toward the front i while defining an angle of about 901 therebetween, and in the device shown in Fig. 6 b the slanting surface 7b is made substantially parabolic. In the figures, numerals 8 indicate a plurality of shield walls which are provided near the respective light sources 4 so as to prevent the light of these light sources 4 from rectilinearly propa- 3Q gating directly toward the light emitting surface 2.

Besides, numerals 9 indicate the circular or semicircular fringe patterns of the respective light sources 4 which 3 are directly seen from outside the device through the diffusion layer 3 as well as the light emitting surface 2 because the light emitted from the light sources 4 is not sufficiently diffused by the diffusion layer 3.

Next, Fig. 7 is an exploded perspective view showing part of the casing of, for example, a portable telephone into which the prior-art planar light emitting device described above is assembled. Numeral 23 designates the casing in which a plurality of key buttons 17 are arrayed and which has the planar light emitting device 1 placed on one side thereof. The planar light emitting device 1 is attached to the casing 23 by a holder 22 together with a microconnector 15 and a liquid crystal displaypanel 13.

Shown at numeral 18 is a cover.

The prior-art planar light emitting device is constructed as described above. Therefore, the light emitted from the light source 4 is diffused by the diffusion layer 3 made from the diffusant packed inside the device and is diffused again by the diffusive sheet 6 while being reflected in predetermined directions by the Sslanting surfaces 7a or the slanting surface 7b, whereupon it is given forth to the exterior from the light emitting surface 2. Since, however, the planar light emitting device 1 of the specified type is thin, the distance from the light sources 4 to the light emitting surface 2 is very short, and the light of the light sources 4 is not sufficiently diffused within the diffusion layer 3. This incurs the disadvantage that, as shown in Fig. 5 a or Fig. 6 a the circular or semicircular fringe patterns 9 are seen on the light emitting surface 2, and uniform planar light emission is not attained. In addition, even when as shown in Figs. 6 a and 6 b the shield walls 8 4 i are respectively disposed near the light sources 4 so as to prevent the light of the light sources 4 from rectii linearly propagating directly toward the light emitting surface 2, part of the light emergent from each light source 4 turns round the edge of the corresponding shield wall 8 and rectilinearly propagates toward the light emitting surface 2 because the area of the shield wall 8 is small. This incurs the disadvantage that, as shown in Fig. 6 a the semicircular fringe patterns 9 of the I O respective light sources 4 are similarly directly seen from outside the device through the diffusion layer 3 as well as the light emitting surface 2, and the uniform planar light emission is not attained, either. Other disadvantages are that, since the light emitting diodes (LEDs) are inevitably employed in the thin planar light emitting device of the specified type, the printed circuit board 5 for mounting the light sources 4 of these light emitting diodes must be disposed at the rear of the planar light emitting device i, and that the holder 22 is requir- O ed for mounting the planar light emitting device 1 and the Sliquid crystal displaypanel 13 on the casing 23.

C

SUMMARY OF THE INVENTION i c This invention has been made in view of such drawi backs, and has for its object to provide a planar light emitting device which is not limited by the size of a i light source and with which the light of the light source is sufficiently diffused to attain uniform planar light emission even when the device is thin.

The planar light emitting device according to this invention comprises a body which is formed of a transparent synthetic resin, a light emitting panel which i has one surface thereof worked into a prism in correspondence with a liquid crystal displaypanel and which has I reflective sheets respectively stuck on slanting surfaces formed on both surfaces thereof, a plurality of light i sources which are disposed at positions not opposing to said light emitting panel, and a light guide plate which is thinned in a wedge shape as it becomes more distant from said light sources.

In this invention, the reflective sheets stuck on the L0 light emitting panel of the body function to decide the traveling directions of light from the light sources not opposing to the light emitting panel, so that the light may travel toward the light guide plate; the light guide plate functions to prevent lowering in the luminous intensity of the light at positions distant from the light sources; and the prism-worked surface formed at one surface of the light emitting panel functions to efficiently guide the light of the light sources to the light emitting panel, whereby uniform planar light emission is attained.

t tr BRIEF DESCRIPTION OF THE DRAWINGS o 6 Figs. 1 a and 1 b and Figs. 2 a and 2 b all illustrate an embodiment of this invention, in which Fig.

64 1 a is a front view showing a body with a cover, a liquid crystal displaypanel and a microconnector detached therefrom, Fig. 1 a is an exploded vertical sectional view of the body, Fig. 2 a is a perspective view showing the front of the body, and Fig. 2 b is a perspective view showing the rear of the body.

Figs. 3 a and 3 b and Figs. 4 a and 4 b illust- 3~o rate other embodiments of this invention, respectively, in 6 which each of Fig. 3 a and Fig. 4 a is a front view showing a body with a cover, a liquid crystal displaypanel i and a microconnector detached therefrom, and each of Fig.

V 3 b and Fig. 4 b is an exploded vertical sectional view i of the body.

Figs. 5 a and 5 b Figs. 6 a and 6 b and Fig. 7 illustrate prior-art planar light emitting devices of the specified type, in which Fig. 5 a and Fig. 6 a are front views, Fig. 5 b and Fig. 6 b are exploded vertical S sectional views, and Fig. 7 is an exploded perspective view showing part of a casing for assembling the prior-art planar light emitting device therein.

PREFERRED EMBODIMENTS OF THE INVENTION 1 r Figs. 1 a and 1 b and Figs. 2 a and 2 b illustrate one embodiment of this invention. Referring to the figures, numeral 1 designates a body which is made of a transparent synthetic resin. Numeral 2 designates a light emitting panel which is formed with a prism-worked surface 2a being, for example, roughened at the front thereof in StfS3 correspondence with a liquid crystal displaypanel 13 that is placed on the front at the stage of assemblage, and which has a reflective sheet 10b stuck on a slanting S surface 7b that is formed at the rear of the panel. A reflective sheet 10a is stuck on a slanting surface 7a which is formed on one side of the front of this light emitting panel 2. Also, the body 1 formed with the slanting surface 7b is formed with a light guide plate 12 which i: thinned in a wedge shape as it becomes more distant from light sources 4 to be described later. Shown at numerals 11 are recesses which correspond to the plurality of light sources 4 such as light emitting diodes _I 1_1~_~1 7 (LEDs) disposed at the predetermined positions of a printed circuit board 5 that is placed and mounted on the rear surface of the body 1, and which receive the light sources 4 when the printed circuit board 5 is placed. An accommodating chamber 14 for receiving the liquid crystal displaypanel 13 is formed in the body 1 in correspondence with the light emitting panel 2, and a plurality of ribs 14a and 14b for positioning the liquid crystal displaypanel 13 are formed at the peripheral wall of this it accommodating chamber 14. A through hole 16 is provided on one side of the accommodating chamber 14, and receives S;Oo a microconnector 15 for electrically connecting the liquid .O 6 crystal displaypanel 13 and the printed circuit board A plurality of key buttons 17 are disposed in the body 1 01 o oo so as to protrude out of a cover 18, a plurality of 0000 0°o° 0 spacers 19 serve to fill up the gaps between the liquid So° crystal displaypanel 13 and the cover 18, and a plurality of reflectors 20 are disposed on the other side of the printed circuit board 5 in order to reflect the light of °oS2D the light sources 4 toward the liquid crystal displaypanel 0 00 0 13.

The planar light emitting device of this invention is constructed as described above. Therefore, the light emergent from the light sources 4 is led toward the light 0 00 o4o o* guide plate 12 by the larger slanting surface 7b as well as the smaller slanting surface 7a formed in the part of the body 1 and the larger reflective sheet 1Ob as well as the smaller reflective sheet 10a stuck thereto, and it is efficiently diffused within the light guide plate 12 while 3 repeating irregular reflections. The light of the light sources 4 is further diffused so as to become uniform planar light emission by means of the prism-worked surface 2a which is formed at the front of the light emitting

_L

I~-i-iciC rr*r- 8 panel 2.

i Figs. 3 a and 3 b, and Figs. 4 a and 4 b illusti rate other embodiments of this invention, respectively.

Fig. 3 a or Fig. 4 a is a front view showing the body from which the cover, the liquid crystal displaypanel and i the microconnector are detached, while Fig. 3 b or Fig.

r 4 b is an exploded vertical sectional view of the body.

The embodiment of Figs. 3 a and 3 b is such that the plurality of key buttons 17 explained in the foregoing S embodiment are omitted, and that the light sources 4 are held within the recesses 11 provided in the body i. On the other hand, the embodiment of Figs. 4 a and 4 b is such that the plurality of light sources 4 are held within the recesses 11 and 11 which are formed on both the sides of the accommodating chamber 14 for the liquid crystal displaypanel 13 as formed in the body i, while the printed circuit board 5 in the foregoing embodiment is omitted, thereby to reduce the thickness of the planar light emitting device still more. The functional effects of the ji~ embodiments are quite the same as those of the foregoing i embodiment.

.e e iI As set forth above, the planar light emitting device according to this invention is constructed of a body which is formed of a transparent synthetic resin, a light I emitting panel which has one surface thereof worked into a i prism in correspondence with a liquid crystal displaypanel Sand which has reflective sheets respectively stuck on slanting surfaces formed on both surfaces thereof, a plurality of light sources which are disposed at positions ?0 not opposing to said light emitting panel, and a light guide plate which is thinned in a wedge shape as it becomes more distant from said light sources. Therefore, II 9 the reflective sheets stuck on the light emitting panel of the body function to decide the travelling direction of light so that the light from the light sources not opposing to the light emitting panel may travel toward the light guide plate, and the light guide plate functions to efficiently diffuse the light from the light sources while repeating irregular reflections, thereby to prevent lowering in the luminous intensity of the light at positions distant from the light sources, and the prism-worked surface is formed at one surface of the light emitting panel, hereby to guide the light of the light sources to i the light emitting panel with the very thin structure and at high efficiency, to produce the excellent effect that uniform planar light emission is attained. Besides, this invention produces the effect that the light sources received in the recesses within the body formed of the transparent synthetic resin can serve also for illuminating key buttons mounted in the body.

IE

Claims

4. A planar light emitting device as defined in Claim 1, further I ,comprising an accommodating chamber adapted to receive said liquid crystal display panel, said accommodatingvhamber being formed in said body in Shcorrespondence with said light emitting panel. A light emitting device substantially as described herein with reference to rIGS. la, lb, 2a and 2b or FIGS. 3a, 3b, 4a and 4b of the accompanying drawings. DATED this SIXTEENTH day of JANUARY 1990 Mitsubishi Denki Kabushiki Kaisha a Patent Attorneys for the Applicant SPRUSON FERGUSON JMR/096 pidp I longitudinal ~~~~ax.fsi oy adwdesae eto eraigi