In this study, the effect of light wavelength on growth rate and lipid production of Synechocystis was investigated. Continuous cultivation system was used to have uniform cell density and avoid self-shading in order to obtain more precise results. Based on previous studies, red light is more efficient than other colors in the visible spectrum for cultivation of Synechocystis; however, the optimum wavelength in red light spectrum remains still unknown. In order to determine the most efficient wavelength of red light, five different wavelengths including 600, 635, 660, 670, and 730 nm were used for growing Synechocystis in a chemostat setup. The results revealed that 635 nm was the most efficient wavelength for cultivation of Synechocystis in terms of both biomass production yield and growth rate. These findings can be attributed to the existence of phycocyanin, the principal lightharvesting supercomplex in Synechocystis, which absorbs maximally at around 620 nm. The results also indicated that cell size and fatty acid profile of Synechocystis were almost the same for different light wavelengths; however, the maximum light was absorbed at 635 nm.

Background: It has been shown that short-wavelength blue component of the visible light spectrum can alter the circadian rhythm and suppress the level of melatonin hormone. The short-wavelength light emitted by smartphones’ screens can affect the sleep quality of the people who use these devices at night through suppression of melatonin. Objectives: In this study, we examined the effects of covering the screens of smartphones with different filters (changing the effective wavelength of the light) on sleep delay time in 43 healthy students. Materials and Methods: Volunteer students were asked to go to bed at 23: 00 and to use their mobile phones in bed for watching a natural life documentary movie for 60 minutes. No filter was used for one night while amber and blue filters were used for other 2 nights. Photospectrometry method was used to determine the output spectrum of the light passing through the filters used for covering the screens of the mobile phones. The order for utilizing amber or blue filters or using no filter was selected randomly. After 1 hour, the participants were asked to record their sleep delay time measured by a modified form of sleep time record sheet. Results: The mean sleep delay time for the “ no-filter” night was 20. 84± 9. 15 minutes, while the sleep delay times for the nights with amber and blue filters were 15. 26± 1. 04 and 26. 33± 1. 59 minutes, respectively. Conclusion: The findings obtained in this study support this hypothesis that blue light possibly suppresses the secretion of melatonin more than the longer wavelengths of the visible light spectrum. Using amber filter in this study significantly improved the sleep quality. Altogether, these findings lead us to this conclusion that blocking the short-wavelength component of the light emitted by smartphones’ screens improves human sleep.