Up to 90% of people with Alzheimer's disease and related dementias (ADRD) experience at least one behavioral and psychological symptom of dementia (BPSD). Agitation is among the most common and challenging BPSD, especially in nursing home (NH) residents with ADRD. Thus, identifying an effective, non-pharmacological intervention to reduce agitation and other BPSDs is critical. Lighting is important for people with ADRD, especially those living in NHs, as they are not exposed to sufficient daylight. Lighting interventions (LIs) work to regulate suprachiasmatic nuclei, maintain a stable circadian rhythm and reduce agitation. LIs are not invasive and have minimal adverse effects, making them ideal interventions for persons with ADRD. Evidence has reported that LIs show improvement in agitation and other BPSDs for persons with ADRD. However, LIs have not been widely implemented in "real world" care settings. Traditional methods using light boxes that required persons with ADRD to sit and keep their eyes oriented toward a bright light led to compliance and workload issues. A more efficient approach to delivering LIs is necessary. Interest has arisen in designing NHs with the capability of providing LIs via ambient LIs. While a few studies have reported positive effects of ambient LIs on agitation, these studies were conducted in settings with window shades closed to minimize daylight. To establish ambient lighting as a feasible and effective intervention, a few fundamental gaps need to be addressed: 1) a feasible implementation approach to ambient LIs, and 2) intervention fidelity (ensuring the lighting received by participants meets the targets). This proposed study seeks to develop a smart ambient bright light (SABL) intervention to provide auto-controlled, consistent indoor lighting that incorporates natural daylight. This SABL includes tunable LED lights, photosensors, and controllers. The SABL system has a pre-programmed 24-hour control schedule for illuminance settings to mimic the natural bright-dark cycle. It will automatically adjust the lights to accommodate the daylight effect to minimize staff burden and maximize the LI effect. The SABL will be installed in participants' bedrooms and designated areas in the dining rooms and activity rooms for four weeks. Each participant will wear a personal light monitor to measure the lighting dosage each participant receives. This study will address three aims: 1) pilot test the effect of SABL on reducing agitation in persons with ADRD, 2) evaluate the fidelity of the SABL delivery, and 3) evaluate the feasibility of implementing the SABL. The study will be conducted in two NHs in Pennsylvania. For aims 1 and 2, the investigators will use a crossover, cluster randomized control trial (RCT) and will enroll residents with ADRD and agitation. For aim 3, the investigators will use a mixed methods design and will interview NH stakeholders to evaluate the acceptability, feasibility, and appropriateness of the intervention. This is the first study that incorporates daylight in ambient light interventions and the first study that addresses the measurement, feasibility, and fidelity of lighting interventions. Findings will establish evidence-based implementation strategies and the best design for SABL to reduce agitation for persons with ADRD in NHs.