Effects of smart lighting actuation delay on the duration and stages of older adults’ simulated night-time bedside task

Residential smart lighting turns light into an event with an arrival time, yet lighting standards for homes and care spaces address the steady-state environment and lack a checkable timing metric for the process from the bed-exit trigger to the moment the key path reaches the required light level. We ran a randomised two-factor mixed experiment in a house-scale laboratory in Hefei with 80 community-dwelling older adults aged 65 and above. Post-detection actuation delay was manipulated within participants at four levels (0.10, 0.70, 1.40, and 2.00 s), and spatial visual contrast was set between participants at two levels. Event timestamps split post-trigger arrival time into detection, movement-initiation, and walking stages, taken as proximal behavioural measures of task performance. Arrival time rose by 0.990 s from the shortest to the longest delay, and the fitted dose-response across the four tested levels was positive and convex. The movement-initiation stage accounted for 84.5% of the stage sum, walking time increased by a smaller amount, and detection showed no difference. At the longest delay most first steps landed before the switch-on command, so lighting response and user movement became less coordinated in time. In a secondary analysis for which the sample size was not planned, enhanced visual contrast was associated with a 0.808-s smaller delay effect. Exploratory analyses found low agreement between reported and measured event order, and satisfaction met the equivalence criterion among participants with observed paired ratings. Response timing should be specified as an end-to-end total delay in performance assessment.