1. Field of the Invention
The present invention relates to plane light sources and LCD backlight units having the same, and more particularly, to a plane light source that has high efficiency and can reduce the number of light emitting devices by optimizing the arrangement and pitch of the light emitting devices, and an LCD backlight unit having the same.
2. Description of the Related Art
In general, when a current is applied to a semiconductor light emitting diode (LED), the semiconductor LED can generate light of various colors by recombination of electrons and holes in a p-n junction between p-type and n-type semiconductors. When compared with a filament-based light emitting device, the LED has a longer lifespan, lower power consumption, excellent initial driving characteristics, higher vibration resistance, and higher tolerance for repetitive power switching. Thus, there has been an increasing demand for LEDs. Nowadays, group III nitride semiconductors that can emit light in a short-wavelength region, including blue, have attracted attention.
In the related art, since a cold cathode fluorescent lamp (CCFL), which is used as a light source for an LCD backlight unit, uses mercury gas, environmental contamination may be caused. Furthermore, the CCFL has low response speed and low color reproducibility, and may not allow a reduction in size, thickness, and weight of an LCD panel.
Compared to the CCFL, a light emitting diode (LED) is environment-friendly, has a response speed of several nanoseconds to achieve high-speed response and be effective for a video signal stream, and allows impulsive driving. Further, the LED has a color reproducibility of 100% or more, varies in luminance, color temperature, and the like by controlling the intensity of light of the red, green, and blue LEDs, and can result in a reduction in size, thickness, and weight of the LCD panel. Accordingly, the LED has been widely used as a light source for the backlight unit of the LCD panel or the like.
An LCD backlight using an LED may be divided into an edge type backlight and a direct type backlight according to the position of a light source. In a case of the edge type backlight, a bar-shaped light source having a width larger than its length is positioned at the side thereof and emits light onto a front surface of the LCD panel by using a light guide panel. In a case of the direct type backlight, a plane light source is positioned at a lower part of the LCD panel, and light is directly irradiated onto a front surface of the LCD panel from the plane light source that has almost the same area as the LCD panel.
FIG. 1 is a view illustrating the arrangement of light emitting devices of a plane light source according to the related art.
As shown in FIG. 1, according to the related art, a plane light source 100 that is used in a direct type LCD panel includes a plurality of LEDs 102 that are arranged in rows and columns on a substrate 101. In this case, each four adjacent LEDs 102 of the plurality of LEDs 102 form a rectangle.
In the plane light source 100, the substrate 101 is divided into eight blocks. Eighteen LEDs 102 are arranged in each block, and thus, one hundred forty four LEDs 102 are included in the entire substrate 101. Here, as shown in FIG. 1, the entire substrate 101 is 453×124 mm.
However, the above arrangement requires a larger number of LEDs that are used to cover the same light emitting area than necessary.
Further, an area adjacent to the LEDs 102 has much higher brightness than an area distant from the LEDs 102, that is, the center of the rectangle formed by the four LEDs 102. That is, when a large number of LEDs 102 are arranged, a uniformity of brightness can be achieved. However, when the number of LEDs is reduced to improve the efficiency as described above, the pitch between the neighboring LEDs becomes larger. Thus, a variation may occur in brightness distribution.
Therefore, in terms of a plane light source used in the LCD panel or the like, there is a need for a method of improving the efficiency of the plane light source by reducing the number of light emitting devices used in the plane light source, and achieving the uniformity of luminance, that is, little difference in brightness.
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