Article

White LED with Excellent Rendering of Daylight Spectrum

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Abstract

In recent years, white LEDs have been increasingly used to replace conventional lighting sources including fluorescent lights. However, in some specific lighting applications, the use of such LEDs to replace halogen and xenon lights can present certain problems, such as in spectral distribution and the color rendering index (CRI).

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... They are often used as daytime running lights in cars but also as dimmed headlights in newer models. The emission spectrum of a LED headlight shows a typical peak at 450 nm (cf. Figure 4) belonging to the blue LED and the yellow color wavelengths belonging to the phosphor [10]. Today there are attempts to invent new phosphor mixtures World Journal of Chemical Education to create an LED with a broad spectrum comparable to the emission spectrum of the sun. ...
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To understand basic principles about the interaction of electromagnetic radiation with matter is often a challenge in chemical education due to the difficult theoretical background of this topic. The present contribution therefore offers an experimental based introduction into the basic principles of UV/Vis spectroscopy following a three-step strategy. The starting point is to construct a simple self-built spectrometer working within the visible range of light. Learners can explore the most important components of such a device and understand their functions without previous knowledge. In a second step, emission spectra of different common light sources are investigated and compared. Finally, spectroscopic experiments are suggested for chemical education such as the qualitative detection of cations and the quantitative analysis of the dye carmine in food. This context-based introduction links chemical applications with the everyday life. It can be presumed that this way, learners are provided an easier access to radiation-matter interaction.
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Die Lehre von physikalisch-chemischen Inhalten in der universitären Lehramtsausbildung und im gymnasialen Chemieunterricht ist herausfordernd. Mögliche Ursachen hierfür sind das teils hohe Abstraktionsniveau und fehlende Messgeräte. Im Rahmen dieser Arbeit wurden kostengünstige Messgeräte entwickelt, mit denen Lernende in typische physikochemische Methoden und deren Anwendungen experimentell eingeführt werden können. Durch offen gestaltete und kontextbezogene Experimente zu Themenfeldern der Spektroskopie, Thermodynamik und Kinetik sollen Lernende einen phänomenologischen Zugang zur physikalischen Chemie finden. Durch eine entsprechende didaktische und experimentelle Aufarbeitung der Konzepte sollen insbesondere Schülerinnen und Schüler ohne größeres Vorwissen für physikalisch-chemische Inhalte im Sinne eines modernen und experimentell orientierten Chemieunterrichts begeistert werden.
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Based on different white OLEDs with the high power monochromatic LEDs matches the solar visible spectrum in 380−780 nm. The correlation index (R²) describes the similarity degree between the matching spectrum and solar visible spectrum. We investigate three different white OLEDs. The optimal algorithm deals with different spectrums of white OLEDs mixing with high power monochromatic LEDs to get different optimal combinations. In the optimal combinations, the subtraction experiments mean that the species of high power monochromatic LEDs are reduced. According to the subtraction experiments, the renew R², correlated color temperature (CCT) and the color-rendering index (Ra) are calculated. As a result, the best OLED, which is the most suitable for matching the solar visible spectrum, is optimized. And the best optimal combination includes a white OLED and 34 species of monochromatic LEDs with the best correlation index of 94.31 %. With deleted monochromatic LEDs species, the R², CCT and Ra are also changed. When the R² is lowest, Ra can still reach 94.0219 with the CCT of 5309 K. It achieves better color rendering when the R² is lowest. This can save a large number of the species and amount of monochromatic LEDs to match solar visible spectrum for comfortable lighting.
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