Illumination – Plural light sources – Particular wavelength
Reexamination Certificate
2000-11-13
2003-04-01
O'Shea, Sandra (Department: 2875)
Illumination
Plural light sources
Particular wavelength
C366S076800
Reexamination Certificate
active
06540377
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a full-color light source unit. Particularly, it relates to a full-color light source unit that can exhibit various color tones efficiently freely. Moreover, it relates to an improvement of a unit to be suitably used also as a white light source for back-lighting or front-lighting of a full-color liquid-crystal panel.
The present application is based on Japanese Patent Applications Nos. Hei. 11-320425 and 2000-140772, which are incorporated herein by reference.
2. Description of the Related Art
Use of LEDs emitting three primary colors (RGB) of light as a full-color light source is known generally. In such a general full-color light source, one red LED, one green LED and one blue LED were packed in one package. Such a full-color light source can emit desired-color light as well as white light under suitable control on the respective LEDs.
For example, a surface light source disclosed in JP-A-10-319396 is used as a white light source for a liquid-crystal panel. In the surface light source, a blue LED is used as a light source. The blue LED is arranged in an end portion of a first rod-like light guide plate. The first light guide plate is attached to a light entrance surface of a second panel-like light guide plate. A layer of a color conversion member made of a fluorescent material is formed in a portion of the first light guide plate opposite to the light entrance surface of the second light guide plate. The color conversion member absorbs blue light emitted from the blue LED and emits yellow light. As a result, the yellow light emitted from the color conversion member and the blue light emitted from the blue LED are mixed together to synthesize white light. The white light is made incident into the second panel-like light guide plate. Thus, the second light guide plate serves as a white surface light source for back-lighting of a liquid-crystal panel.
The white light emitted from the white surface light source disclosed in JP-A-10-319396 is, however, a mixture of the blue light emitted from the blue LED and the yellow light emitted from the fluorescent material. Hence, it is difficult to develop red when full-color display is to be achieved by liquid crystal. This is because the white light contains a slight amount of red light component. Moreover, there is a problem in the durability of the fluorescent material because the fluorescent material is apt to change with the passage of time compared with LED. Moreover, 100% of the light emitted from the blue LED does not appear on a light-emitting surface and a conversion loss occurs in the conversion of the blue light into the yellow light because the blue light emitted from the blue LED is mixed with the yellow light due to the conversion of a part of the blue light. Hence, there is also a problem that sufficient light-emitting efficiency cannot be obtained. In addition, the tone of color cannot be changed.
According to a general full-color light source using LEDs with three primary colors (RGB) of light, full-color light containing a sufficient amount of red light component can be generated. If white light developed by such a full-color light source is used for back-lighting of a full-color liquid-crystal panel, red can be expressed sufficiently even in the full-color liquid-crystal panel. Therefore, the inventors of the present invention have made investigation and investigation into a full-color light source using RGB LEDs efficiently and the use of the full-color light source for lighting of a full-color liquid-crystal panel. As a result, the inventors have found the following problem.
In characteristic of currently generally available LEDs, a green or red LED is inferior in the light emission output (Luminance) to a blue LED. For example, in a full-color light source unit having one blue LED, one green LED and one red LED, therefore, it was necessary to suppress the output of the blue LED to balance with the outputs of the green and red LEDs.
Such balance, however, makes efficiency worse because the blue LED cannot emit light with full power. Particularly in a white surface light source to be used in a portable apparatus, such balance is undesirable because high efficiency is required from the point of view of power consumption saving.
Further, another problem which the inventors have found will be described.
JP-A-11-329044 discloses a background-art light-emitting system for back-lighting of a full-color liquid-crystal panel.
The light-emitting system comprises a row of LED chips, and a light guide portion for receiving light from the row of LED chips through an incident surface of the light guide portion and making the light propagate through the inside of the light guide portion to thereby make surface-like back-lighting beams exit from an exit surface of the light guide portion. The row of LED chips are constituted by red (R), green (G) and blue (B) LEDs. Each of the R, G and B LEDs has a narrow-band emission spectrum. Hence, when the R, G and B LEDs are made to emit light, R, G and B light components emitted from the LEDs are mixed to get her so that the liquid-crystal panel can be irradiated with white back-lighting beams.
According to the background-art light-emitting system using light-emitting devices with three colors R, G and B, however, the number of wire-bonding points became so large that the light-emitting devices could not be mounted compactly because each of the G and B light-emitting devices had positive and negative electrodes on the light-emitting surface side. Hence, the distance between adjacent ones of the light-emitting devices became so large that it was difficult to achieve a point light source. Moreover, improvement in color balance was limited. Moreover, when the light-emitting devices were increased in number, the total heating value became so large that the output power is lowered, the life of the light-emitting system is shortened, etc.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a full-color light source unit that can exhibit various color tones efficiently freely.
Another object of the present invention is to provide a light-emitting system in which reduction in size can be made in the case of use of a plurality of light-emitting devices to thereby make improvement in color balance possible.
Still another object of the present invention is to provide a light-emitting device in which lowering of output power and shortening of the life of the light-emitting system can be avoided in the case of use of a plurality of light-emitting devices.
In order to achieve the above objects, according to an aspect of the present invention, there is provided a light-emitting system comprising a plurality of light-emitting devices mounted on a substrate, wherein: the plurality of light-emitting devices include a first group of light-emitting devices and a second group of light-emitting devices, each of the first group of light-emitting devices having first and second electrodes on a light-emitting surface side, each of the second group of light-emitting devices having a first electrode on the light-emitting surface side and a second electrode on a side opposite to the light-emitting surface side; and the first group of light-emitting devices and the second group of light-emitting devices are arranged alternately in a line on the substrate.
According to the aforementioned configuration in which the first group of light-emitting devices each having two electrodes on the light-emitting surface side and the second group of light-emitting devices each having one electrode on the light-emitting surface side and one electrode on the substrate side are arranged alternately on the substrate, the light-emitting devices can be mounted compactly because the light-emitting devices can be connected easily by bonding wires even in the case where the light-emitting devices are arranged densely. Incidentally, the concept “substrate” used herein includes a printed-circuit board in which leads to be connected to
Kaga Koichi
Ota Koichi
Suehiro Yoshinobu
Takahashi Yuji
Negron Ismael
O'Shea Sandra
Pillsbury & Winthrop LLP
Toyoda Gosei Co,., Ltd.
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