Protocol for a co-design study for the development of a chronotherapeutic mobile health behaviour change intervention targeting light exposure among older adults.

Through its wide-ranging effects on human physiology and behaviour, daily light exposure is an important environmental modulator of healthy ageing. Integrating mobile health (mHealth) technology with behaviour change strategies offers a promising approach to optimise light exposure and positively impact sleep, rest-wake cycles, cognitive function, and mood at scale. This study aims to develop the LightSPAN mHealth behaviour change intervention to optimise light exposure across the lifespan. Employing a co-design methodology, the study comprises two distinct workstreams. The first focuses on conceptualising the theoretical framework and implementation strategies through a comprehensive review of light exposure interventions, behaviour change theories, mHealth user personas, and recommendations for designing mHealth interventions for older adults. The second workstream centres on co-designing the intervention, involving consultation with community service providers and engagement with older adults at ageing community centres (≥60 years of age). Community service providers will be consulted through a focus group discussion (target n=5). Older adult participants (n=20) will engage in telephone interviews, focus group discussions and prototyping workshops to explore older adult participants' characteristics, needs, preferences, and mHealth intervention design elements and co-design the LightSPAN mHealth behaviour change intervention. The insights generated in these co-design components will facilitate future implementation of our intervention.