Patent number 8526825 is assigned to
The following quote was obtained by the news editors from the background information supplied by the inventors: "Recently, a white LED has been actively developed and spread into diverse fields, such as illumination, vehicle mounted lamps, liquid crystal backlights, and the like. This white LED, for example, has the characteristic that its on/off-switching response speed is very high in comparison to that of a white light source such as a fluorescent light or the like. Accordingly, a visible light communication system in which the illumination light of a white LED has a data transmission function using white LED light as a data transmission medium has been proposed (see Patent Document 1 below). That is, the luminescence intensity of the white LED is modulated in accordance with the transmission data, and the receiving side converts the intensity of the light into an electric signal through an optical-electrical converter (0/E converter), such as a photodiode (hereinafter referred to as a 'PD') or the like, to realize data transmission.
"The white LED, as described in Non Patent Document 1 below, for example, may be mainly classified into three kinds in accordance with the luminescence scheme.
"(1) Blue-light-excitation-type white LED: this is obtained by combining a blue LED with a phosphor that emits mainly yellow light. That is, a phosphor that is represented by a YAG (Yttrium Aluminum Garnet) group is arranged around a blue LED, and this arrangement is accommodated in a single package. In this structure, the surrounding phosphor is excited by the blue light output from the blue LED arranged in the center, and the light (mainly yellow) that is mainly complementary to blue is output from the phosphor. A pseudo-white light is obtained by mixing the yellow fluorescence output from the phosphor and the blue light output from the blue LED.
"The blue-light-excitation-type white LED has the following advantages: (1) in comparison to other types, it has high energy use efficiency, and high illumination is easily obtained, and (2) due to its simple construction, it can be inexpensively manufactured. On the other hand, the disadvantage of this white LED is that it has bad color rendering. Color rendering indicates the characteristics of color appearance of an object under illumination, and the closer its color is to that perceived under natural light, the better the color rendering.
"(2) Ultraviolet-light-excitation-type white LED: This is obtained by combining an ultraviolet light with phosphors that emit three primary colors of R (Red), G (Green), and B (Blue), respectively. That is, phosphors that emit three primary colors of R, G, and B are arranged around an ultraviolet LED, respectively, and this arrangement is accommodated in a single package. In this structure, the surrounding phosphors are excited by the ultraviolet light output from the ultraviolet LED arranged in the center, and the light of three primary colors of R, G, and B is output from the phosphors, respectively. A white light is obtained by mixing the R, G, and B lights.
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