The Impact of Daytime Lighting Conditions on Sleepiness and Morning/Evening Melatonin Levels

Proper lighting adjustments can reduce energy consumption in buildings, particularly by supporting thermal comfort and minimizing reliance on heating and cooling systems. This study explores the impact of office lighting on sleepiness and melatonin levels, contributing to a broader understanding of lighting’s impacts on human health and wellbeing. Twenty participants were exposed to various lighting conditions over five consecutive working days, with repeated measurements providing insights into the influence of artificial lighting on sleepiness and daily melatonin fluctuations. Results showed that lighting conditions did not significantly affect sleepiness during the experimental period (8:40–15:15). While no immediate melatonin response was observed, longer-term exposure to warm white light for two days resulted in lower melatonin levels at 20:00 and bedtime compared to one-day exposure. Morning melatonin levels decreased throughout the experiment, likely due to the absence of daylight in the office setting.