The design of indoor environments in hospitals plays a crucial role in patient recovery and staff well-being. Lighting is a critical environmental variable, that influences circadian rhythms, sleep patterns, alertness, and task performance. Hospitals operate around the clock, with indoor environments that serve diverse users (e.g. patients and clinicians) with contrasting needs. Patients need lighting that promote rest and recovery, while clinicians require lighting that supports optimal clinical performance and alertness. Balancing these competing needs makes hospital lighting designLighting design complex, particularly in Intensive Care UnitsIntensive care units (ICUs), where patients are at a high risk of developing delirium. This chapter presents a Human–Building Interaction (HBI) approach for a living-lab case study conducted in a functioning ICU to investigate how bed-space lighting can be designed and evaluated to support both patient recovery and clinicians’ visual tasks. The living-lab context enables in-situ, multi-stakeholder co-creation and iterative testing, while the HBI lens structures the work across three phases: a pre-design investigation to identify needs; a co-designCo-design process with patients/families, architects, and clinicians; and an evaluation phase combining observations, environmental/spectral monitoring, and wearable technologies. While the first two phases have been published elsewhere, this chapter integrates them and emphasises the co-designed evaluation. The outcome is a structured yet flexible framework for evidence-based, human-centred lighting strategies that can be adapted to the complex, user-specific requirements of ICUs.