Even in "sunny" countries, despite the fact that an excess supply of sunlight outside, even during the daytime, windows are darkened and shut because of heat. Thus artificial light is used indoors requiring a high amount of energy. Moreover, these artificial lights are used at a very low level of efficiency only. If windows were left open, too much heat would penetrate through the windows. Thus in buildings, currently, most energy used is for air conditioning! The efficiency of the usual way of transforming solar energy to electricity and then back to light is typically less than 1% (Fig.1), and is always linked with production of unwanted heat, whereas an efficiency of up to 50% depending on the length is achievable by direct use of sunlight e.g. with the Sollektor approach (Poisel et al.). In addition, this light has no heat, and retains the natural spectral distribution that is most beneficial for human performance. The following benefits are linked to the use of this technology: Saving of energy costs through direct use of daylight and eco friendly; Light without heat by splitting off infrared radiation; Non visible part of radiation can be used for energy arvesting; Natural daylight improves human performance and contributes positively to overall human well-being.
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