Increased exposure to good quality light during the day has been shown to improve sleep, as confirmed by a US study conducted during the pandemic

About study

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Title:	The sleep maths: A strong correlation between more daytime light and better night-time sleep
Author:	MG Figueiro PhD, C Jarboe MS and L Sahin PhD Department of Population Health Science and Policy, Icahn School of Medicine at Mount Sinai, New York, NY, USA Lighting Research Center, Rensselaer Polytechnic Institute, Troy, NY, USA
Date:	11. February 2021
Source:	https://doi.org/10.1177/14771535211005832
PDF:	The sleep maths.PDF

Brief summary

The study examining the impact of reduced light exposure during the day due to the transition from work (school) environments to home during the Covid-19 pandemic confirmed that the more light individuals are exposed to during the day, whether at home, work, or outdoors, the better their subjective perception of sleep quality. The conclusions of the research emphasize the importance of choosing light sources that align with circadian rhythms, thus benefiting sleep, health, and well-being when designing lighting for homes, offices, and schools.

Higher light exposure during the day improves sleep quality

The study confirms that exposure to indoor light or time spent outdoors during the day is highly related to respondents’ subjectively perceived sleep quality. The results show that spending 1-2 hours a day outdoors or in a room with very high luminance (or melanopic equivalent daylight luminance, mEDI, which indicates the biological effectiveness of lighting) improves the quality of sleep at night and reduces the likelihood of sleep disturbances.

Higher light levels during the day improve mood and reduce stress

The authors found that greater exposure to daylight, both indoors and outdoors, was associated with better mental and emotional outcomes for research participants during the COVID-19 pandemic.

Participants in the group exposed to ‘very bright’ indoor light had higher positive affect (feelings of pleasure, joy and happiness) compared to participants in the ‘dim’ and ‘neutral’ light groups. At the same time, participants in the ‘dim’ indoor light group had significantly higher stress and depression scores compared to participants in the other brighter light groups.

Building on their own research and the studies cited above, the authors submit recommendations for improving sleep quality and increasing the sense of well-being. They recommend spending 1 to 2 hours a day outdoors, ideally in the morning after waking up to support the natural circadian rhythm. For people working from home, it is essential to maximise natural daylight indoors and optimise the distribution of light in the room. In the morning and during the day, full-spectrum lighting with maximum circadian effect or maximum melanopic EDI lux is the solution when indoors.
Evening lighting should be warm, dim and placed low and electronic displays should be turned off at least 1-2 hours before bedtime to minimise disruption to the sleep cycle.