In the last decade, it has become apparent that light is not only important for vision, but that light responsiveness extends to fundamental aspects of mood, cognition, and performance. Light can be used as an effective and non-invasive therapeutic option with little to no side effects, to improve sleep, mood, and general well-being. However, to utilise the full potential of light to improve mood and well-being and design new interventions, further research is required, starting with determining the relationship between light and mood in human subjects in real-life situations. 

This study's methodology will be the first to offer information into naturalistic light exposure situations and provide insight into its relationship with emotional bias in participants. In total, 25 healthy volunteers are recruited for a 1-week light monitor study. Participants will receive two devices—a light monitor (which measures the gold-standard unit of ambient light exposure, Melanopic-EDI) for daytime use and a Fitbit for continuous sleep and physiology tracking (activity and sleep patterns, heart rate). They are given access to an online questionnaire link. During the week, participants are asked to complete questionnaires, including a baseline questionnaire, which asks for information on sleep health, general health and demographics, in addition to a daily sleep diary and tasks aimed at assessing their current mood status. This includes both repeat subjective mood questionnaires and daily objective cognitive tests of emotional bias, based on using validated tests including the Emotional Categorisation Test (ECAT), Emotional Recall Task (EREC) and Emotional Recognition Memory Task (EMEM). This will also be the first time these objective mood tasks are used across the week, they have been adapted to be conducted on separate days, not just in one sitting. 

Here, we describe the preliminary results of 5 healthy volunteers, which demonstrate the feasibility of the measurements we are collecting. We gathered on average 7.5 days of continuous melanopic EDI data from everyday life, proving the acceptability of our light monitoring protocol. Preliminary results suggest no significant differences between positive or negative bias across days. There were also no significant differences between days and number of incorrect words, suggesting no practice effect for the tasks. Future work will focus on analysing circadian and light exposure impacts on mood regulation. We anticipate that the analysis of the complete dataset will reveal daily rhythmicity of mood, efficacy of objective emotion tasks in detecting mood variations in real-world settings, and relationships between light exposure, physiological variables, and mood in healthy volunteers.