Abstract
Invention of artificial lights has extended human activity time, which has greatly contributed to the development of modern civilization. However, continuous exposure of artificial lights has reduced human sleeping time, which causes a decrease in melatonin production resulting in the side effects such as insomnia, depression, and so on. To prevent the reduction of melatonin by the artificial lights, LED packages helping melatonin generation have been developed. While the commercial LED packages have a high melanopic to photopic ratio (M/P ratio) due to their peak wavelength near the melatonic response around 490nm, those cannot accurately express several colors, that is, give a low R<SUB>9</SUB> or R<SUB>12</SUB> value less than 60 resulting from the peak. Since M/P ratio has a similar formula to that of scotopic to photopic ratio (S/P ratio), the former would have a trade-off relation with color rendering properties as the latter. Therefore, those should be optimized to have values above a certain level by adjusting LED package’s spectral compositions. In this study, M/P ratio and color rendering characteristics were simulated by special combination of 4 blue LEDs and 7 types of phosphors. As a result, the M/P ratios were 0.67, 0.72, 0.78, 0.9, 1.04, 1.14, 1.23, and 1.35 or more. Also, the color rendering properties were R<SUB>a</SUB>≥89, R<SUB>9</SUB>≥75, R<SUB>12</SUB>≥80, R<SUB>9-14</SUB>≥83, and Q<SUB>a</SUB>≥79.
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