This application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. JP2005-263081 filed Sep. 9, 2005, the entire content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a lighting device for a non-self-emitting display such as a small-size liquid crystal display used in a cellular phone, a PDA and so on.
2. Description of the Related Arts
In recent years, such a lighting device has employed a light emitting diode (hereinafter abbreviated as “LED”) for a light source thereof.
a and
As shown in
a illustrates a behavior of the light for illumination. A light 15 from the LED unit 64 that has entered the light guide plate 10 advances in the light guide plate 10 while repeatedly bouncing between reflective prisms 62 arranged in the lower surface of the light guide plate and an upper surface of the light guide plate. During the repeated bouncing, an angle of incidence of the light impinging on the upper surface of the light guide plate is gradually made small and finally become smaller than a critical angle, thereby allowing the light to exit upward through the upper surface of the light guide plate. In addition, the light that may exit from the lower surface of the light guide plate is to be reflected by the reflecting sheet 16 and returned to the light guide plate 10. The light exited from the light guide plate 10 may be diffused by the diffusion sheet 70 and then directed toward a non-self-emitting display 74 by the prism sheets 68 and 66 so as to illuminate the display.
It is to be noted that reference numeral 20 designates a flexible printed circuit board serving for establishing an electric connection between the LED unit and an external device.
Referring now to
Further, referring to
b is a diagram representing the directivity of the light emitted from the LED unit as shown in
a is a perspective view of the LED unit 64,
The substrate section 12 comprises a substrate 26 having internal terminals 32 and external terminals 34 which are electrically connected by vias 36 formed in the substrate 26. The emission section 76 comprises a light shielding wall 78 in the shape of a rectangular cylinder and a resin block 80 filling up the interior space in the light shielding wall 78. Within the resin block 80 are embedded a LED chip 28 mounted on the substrate 26 and gold wires 30 connecting the internal terminals 32 with the LED chip 28. The resin block 80 has a front surface 77, which faces to the light entering surface of the light guide plate, and thus, the front surface 77 serves as an emission surface for the light emitted from the LED chip 28 toward the light guide plate.
With reference to
The quantity of the light that cannot be used for illumination may increase or decrease in dependence on a distance L1, between the LED unit 64 and the light guide plate 10 and a thickness T, of the light guide plate as shown in
If the distance L1 is made zero, all of the light could be taken into the light guide plate. However, in actuality, it is impossible to make the distance L1 zero in the lighting device.
In addition, if the thickness T of the light guide plate is made thicker, more light could be taken into the light guide plate to be used for illumination. However, the thickness T is not allowed to be increased for the recent trend of a lower profile of the lighting device, which has been desired in association with the demand for a low-profile, lighter portable device. Actually, it is said that in order to reduce the thickness of the lighting device by 20% to 30%, the thickness of the light guide plate is needed to be reduced by around half.
Unfortunately, as described with reference to
Accordingly, although there is the trend to make the lighting device thinner, it will deteriorate the emission efficiency of the light source, and, therefore, it is impossible to establish the coexistence of “making thinner” and “making brighter” in the lighting device.
In connection with the lighting device with LEDs, there has been a proposal for solving a problem inherent to the lighting device that there appear dark regions or low brightness regions on the light exiting surface of the light guide plate at locations between the LEDs and adjacent to the side edge surface of the light guide plate along which the LED units are arranged. According to the proposal, the upper and lower surfaces of the emission section of the LED unit are mirror-finished or provided with light shielding layers made from material having a high reflectance without subjecting the left and right side surfaces to such treatment (see, for example, Japanese Patent Laid-open Publication No. 2004-127604). The treatments as stated above are not easy but expensive.
An object of the present invention is to provide a lighting device which is of low-profile and inexpensive and has a higher intensity of illumination.
According to the present invention, a lighting device comprises:
Compared to a conventional LED unit with the reflective member formed on an overall circumferential surface of the emission section of the LED unit, an LED unit according to the present invention can be inexpensive. In addition, since the leak light upward from the emission section can be reflected and returned to the light guide plate, light can be effectively supplied to the light guide plate. Further, since light can be emitted from a left side and a right side of the circumferential surface of the emission section of the LED unit according to the present invention, dark regions or low brightness regions emerging on the light exiting surface of the light guide plate between the LEDs at adjacent area to the side edge surface of the light guide plate can be prevented. Specifically, the reflective member may have a width at least as wide as that of the emission section.
Preferably, the lighting device comprises a reflective plate disposed beneath and adjacent to the bottom surface of the light guide plate and extending toward the substrate of the LED unit under the emission section of the LED unit, thereby utilizing the light from the LED unit more effectively.
The reflective member may be made of a reflective sheet. This may reduce the cost to form the reflective layer.
In addition, the reflective member may have a surface on which an array of reflective prisms are formed so that the reflective prisms facing the emission section deflect light exiting from the circumferential surface of the emission section toward the front surface side of the emission section. Thus, this can reduce a number of bouncing of the light in the emission section, thereby enabling the light to be more effectively supplied to the light guide plate.
Further, the lighting device may comprise a flexible printed circuit board that is attached to and the electrically connected to the LED chip through the substrate, the flexible printed circuit board extending toward and in parallel with the top surface of the light guide plate, wherein the reflective sheet is disposed between and in contact with the flexible printed circuit board and the LED unit.
Still further, the reflective member facing the LED unit may be formed on a surface of the flexible printed circuit board.
Thus, according to the present invention, even if the light guide plate is made thinner, the light from the LED unit can be still effectively supplied to the light guide plate for illumination, and the light can be additionally emitted from the left and the right of the emission section of the LED unit, so that it can prevent the dark regions or low brightness regions from emerging between the LED unit, in an area of the light exiting surface of the light guide plate adjacent to the LED unit. In addition, since the reflective layer is provided separately from the LED unit, it can be inexpensive.
a is a partial sectional view illustrating a lighting device of a first embodiment of the present invention;
b is a partial sectional view illustrating a variation of the device of
a shows a lighting device of a second embodiment of the present invention;
b shows a lighting device of a third embodiment of the present invention;
a is a perspective view illustrating an LED unit used in the present invention;
b shows a light exiting surface of the LED unit of
c is a sectional view taken along the X-Z plane of the LED unit of
d is a back view of the LED unit of
a is a schematic view for illustrating how a light is emitted in case an LED unit, used in the present invention, is applied to a conventional lighting device;
b is a diagram illustrating an emission angle characteristic of a LED unit as shown in
a is a plan view of a conventional lighting device;
b is a side view of the lighting device of
a is a schematic view for illustrating a behavior of an illumination light in the lighting device as shown in
b is a diagram illustrating a directivity of a light from an LED unit of the lighting device of
a is a schematic diagram for illustrating coordinate axes used in the present specification;
b is a diagram for illustrating an emission angle “θ” of a light emitted from an LED unit and directed toward an light guide plate, with respect to the coordinate axes shown in
a is a perspective view illustrating an LED unit with a shading wall provided on an overall circumferential surface of the emission section of the LED unit;
b shows a light emitting surface of the LED unit of
c is a sectional view taken along the X-Z plane of the LED unit of
d is a back view of the LED unit of
a is a schematic side view of the lighting device for explaining a problem associated with the device; and
b is a diagram for illustrating the problem associated with the lighting device of
Embodiments of the present invention will be explained below with reference to the accompanying drawings.
LED unit shown in
As illustrated, the LED unit 13 comprises a substrate section 12 and an emission section 14. The substrate section 12 comprises a substrate 26 on which a LED chip 28 is mounted, internal terminals 32 disposed on an inner surface of the substrate 26, and external terminals 34 on an outer surface of the substrate 26. The internal terminals 32 and the corresponding external terminals 34 are interconnected by vias 36, respectively. At least one LED chip 28 is mounted on the substrate, and gold wires 30 for connecting the internal terminals 32 with terminals of the LED chip 28.
The emission section 14 comprises a transparent resin block 80, and, the LED chip 28, and gold wires 30 connecting the internal terminals 32 with the LED chip 28 which are embedded in the transparent or translucent resin block 80, which protects all the elements embedded therein and controls the illumination color. The emission section 14 is configured such that in operation, the light can exit not only from a front surface of the resin block 80 facing to light guide plate but also from a top side 14-4, a bottom side 14-5, a left side 14-3 and a right side 14-2 of the same, while the back surface 14-6 is covered by the substrate 26 fixedly attached thereto. As shown in
As apparent from the comparison of
As a result of measurement, it has been found that this configuration of the present invention can increase a total volume of light emitted from the emission section by a multiple of 1.3 to 1.4 over the conventional LED unit 64 that has employed one of the six surfaces of the emission section. Incidentally, it has also been found that when the LED unit of
If the LED unit 13 is applied to a lighting device having the conventional configuration as stated above, however, the quantity of light entering the light guide plate could decrease as explained below.
Similarly to
The present invention intends to achieve a low-profile lighting device with LED units 13 as shown in
a is a partial sectional view of a lighting device according to a first embodiment of the present invention.
In this lighting device, a light guide plate 10 having reflective prisms formed on a bottom surface thereof is provided, in this illustration, on the right side with respect to LED units 13 arranged as in
It should be noted that the reflective plate 16 lies below the entire bottom surface of the light guide plate and extends to the underside of the substrate section 12. It is important that the reflective plate 16 lies below the bottom surface of the emission section 14.
Further, a length, L3, of the reflective sheet 18 is set longer than a length, L2, of the emission section 14 in the longitudinal direction of the light guide plate. Specifically, the length L3 is at least two times as long as the length L2. This allows larger quantity of light to be collected, which would otherwise leak without entering or out of the light guide plate 10.
With this configuration, the light 38 as shown in
Accordingly, the lighting device according to the present invention can accomplish significant superiority in the efficiency in using the light, or the brightness, and the cost performance as well.
Since the lighting device of the present invention can increase the efficiency in using the light in this manner, even if the thickness of the light guide plate is reduced by around half, the lighting device can still illuminate at substantially the same level as that achieved by the conventional device and thus can realize the low-profile, bright lighting device with low production cost.
In
a shows another aspect of a lighting device according to the present invention. This lighting device is different from that shown in
b shows a lighting device according to another embodiment of the present invention, which comprises terminals 46 and 48 on an bottom surface of a flexible printed circuit 21, wherein the terminal 46 is adapted to be connected with the LED chip and the terminal 48 is adapted not to be connected with the LED chip but has a reflective layer 50 formed thereon. This can reduce a number of parts required for assembling the device. The terminals 46 and 48 may be constructed as a single unit, and the reflective layer 50 may be formed over the both terminals 46 and 48.
Although the present invention has been described in terms of specific embodiments, it is anticipated that alternations and modifications thereof will no doubt become apparent to those skilled in the art. It is therefore intended that the following claims be interpreted as covering all such alternations and modifications as fall within the true spirit and scope of the invention.
Number | Date | Country | Kind |
---|---|---|---|
2005-263081 | Sep 2005 | JP | national |
Number | Name | Date | Kind |
---|---|---|---|
5769521 | Osawa et al. | Jun 1998 | A |
5786665 | Ohtsuki et al. | Jul 1998 | A |
5883684 | Millikan et al. | Mar 1999 | A |
6508564 | Kuwabara et al. | Jan 2003 | B1 |
7040794 | Bernard | May 2006 | B2 |
7123316 | Yang et al. | Oct 2006 | B1 |
7182499 | Chen et al. | Feb 2007 | B2 |
20020001192 | Suehiro et al. | Jan 2002 | A1 |
20040061440 | Imai et al. | Apr 2004 | A1 |
20070008739 | Kim et al. | Jan 2007 | A1 |
20070121343 | Brown | May 2007 | A1 |
20070139961 | Cheah et al. | Jun 2007 | A1 |
20070274095 | Destain | Nov 2007 | A1 |
20080007963 | Hsieh | Jan 2008 | A1 |
Number | Date | Country | |
---|---|---|---|
20070058392 A1 | Mar 2007 | US |