Human Centric Lighting (HCL), also called circadian lighting, in KNX automatically modulates the colour temperature (Tunable White, DPT 7.600 K) over the day: cool (5500-6500 K) in the morning to stimulate, neutral (4000-5000 K) at midday, and warm (2700-3000 K) in the evening to support sleep.

HCL aligns artificial light with human circadian (melanopic) rhythms. The scientific premise is that cool, blue-rich light suppresses melatonin and promotes alertness, while warm, blue-poor light favours melatonin secretion and sleep. KNX implementation combines DPT 5.001 (intensity) with DPT 7.600 (Kelvin) on a timed programme: 6500 K at 06:00, 5000 K at 09:00, 4000 K at 12:00, 3000 K at 18:00, 2700 K at 22:00, with smooth transitions. A presence-sensor override handles rare night occupancy. HCL is widely deployed in high-performance offices, schools and care homes.

Limit the maximum colour temperature in late afternoon even if the schedule allows higher: occupants working late under 6500 K light will struggle to wind down for sleep that evening.