Little is known about the impact of lighting in rooms designated for critical conversations in counselling or policing contexts, such as therapy, clinical interviewing and police interviews. Lighting may affect bodily stress, discomfort, nervousness, anxiety, mood and self-disclosure. The aim of this study was to map and report research on how illumination affects people’s perception, mood and interaction in healthcare and policing contexts. A scoping review was conducted in which six databases were searched. Twelve studies were included: ten quantitative, one qualitative and one mixed method. The results were presented in two overarching categories: impact of lighting on communication and behaviour. The first category consisted of four sub-categories. The second main category depicted methods and experimental design. The findings indicate that this specific area remains relatively under-researched. The studies were mostly experimental and consisted of small samples. An improved understanding of lighting in contexts for critical and personal dialogue can support professionals, patients and organisations, not least in psychiatric healthcare and other socially vulnerable settings. In addition, our results may inform future design intervention studies and the configuration of rooms designated for conversational and policing environments where critical conversations are conducted.