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The Organic EL lighting panel consists of an organic EL device layer formed on a glass substrate, an encapsulation structure provided with heat transporting and radiating functions, and an optical film that enhances the efficiency of optical outcoupling.
The Organic EL device layer consists of such organic layers as a hole-injection layer, a hole transport layer, a light emitting layer and an electron-injection/transport layer stacked in order of precedence on a transparent electrode such as ITO. On the Organic EL device layer, a metal as aluminum or the like is layered, which become cathode (negative electrode). When the voltage is applied on the positive and negative electrodes, holes and electrons from the electrodes are injected and transported in the respective organic layers and recombine together in the light emitting layer (Charge recombination). The generated energy of the recombination excites molecules in the light emitting layer. When the excited molecules return to their ground state, the energy is released as light, which is a mechanism of light emission.
The expected merits of Organic EL lighting are not merely confined to its unconventional flat shape, but its power-saving function has attracted attention. The energy conversion efficiency of incandescent and fluorescent bulbs has nearly reached their limits, which is respectively 10% and 20%. On the other hand, the efficiency of the Organic EL lighting is estimated over 70% as a theoretically possible value.
In addition, its spectrum of light is very wide, and closer to one of natural light. Unlike a line-sharp spectrum of fluorescent bulb, the Organic EL lighting can recreate more genuine and natural appearance and colors. Since the Organic EL lighting doesn't include ultraviolet, it is really soft to our eyes, and protects clothes and printed matter from discoloration. It has another merit of preventing insects from coming near.
The fact that the Organic EL lighting contains no harmful substance such as mercury also brings in no concern about environment pollution.
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The light source for lighting fixtures can be broadly divided into a directional light source and a diffused one. The typical directional light source is a spotlight that is a mirrored incandescent bulb, and a LED got to be a main stream of the directional light source in these days. It is used for directly illuminating a limited area, which casts shadows. On the contrary, a ceiling light, an milk white covered fluorescent bulb which is used for general lighting, represents the diffused light source. It is appropriate to provide even brightness over a wide area to some extent. In addition, there are other diffused light sources such as a stand or bracket light, incandescent bulbs with shade. Being a surface emitting illuminator, the Organic EL has a diffused light source itself, and can be the diffused light source without extra structures, for example semi-transparent diffuser plates.
Both the directional and diffused light sources are necessary for lighting, and have been and will be used from now on in various scenes where respective characteristics are suit. In the future, it is expected that the LED will cover the directional light source and the diffused light source will shift to the Organic EL.
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