ABSTRACT Fibromyalgia (FM) is the quintessential nociplastic pain condition and is characterized by chronic widespread pain, mood and sleep disturbance, fatigue, and cognitive dysfunction, and affects >20 million Americans. Underserved individuals feel these impacts more profoundly as symptom burden is heavily influenced by social determinants of health (SDOH). As pharmacological treatments offer only small benefits and numerous adverse effects, guidelines suggest non-pharmacological treatments for FM such as physical therapy/exercise and cognitive behavioral therapy (CBT), although individuals with high SDOH risk have the least access and ability to consistently engage in these therapies. A need exists to develop adjunctive approaches to manage FM symptoms that have optimal treatment effects, minimal side effects, and are easy to implement and readily accessible for all. Morning bright light treatment can reduce depression, improve sleep, and advance circadian timing (more “morningness”), all of which may reduce FM pain. Morning bright light treatment is also non- invasive and self-administered with minimal side effects, making it a potentially accessible and scalable non- pharmacological treatment for FM. We tested a 4-week, 1-hour daily morning bright light versus dimmed light (comparison) treatment in individuals with FM (R21 NR016930), using a commercially available wearable light device. We found the morning light treatment was feasible, reliably advanced and stabilized sleep timing, and significantly improved function, pain, depression, and sleep quality, all with minimal side effects. The improvement in function was similar to that seen after exercise, and double that seen after CBT. However, more research is needed to confirm applicability across diverse sociodemographic groups and identify the separate contribution of sleep timing stabilization and morning bright light. A sociodemographically diverse sample of individuals with FM (n=390) will be randomized to one of three groups: (1) 4 weeks of morning bright light treatment (1 h/day with sleep timing stabilization), (2) 4 weeks of sleep timing stabilization without light treatment, or (3) treatment as usual (TAU), with equivalent study contact (n=103 completed in each group). The study will be conducted remotely with virtual assessments pre- and post-treatment and at 3 month follow up. As per others and our own research, a SDOH risk index will be derived from individual and community level resources. Aim 1 is to compare function and pain outcomes across the three groups of morning bright light, sleep timing stabilization alone, or TAU. Aim 2 is to determine the effect of SDOH risk on baseline symptoms, treatment adherence (engagement) and treatment response. Aim 3 is to explore if improvements in function and pain are partially mediated by improvements in depression, sleep quality and a shift to morningness. Results will reveal the active elements of morning bright light treatment for ...