Changing color and intensity of LED lighting across the day impacts on human circadian physiology, sleep, visual comfort and cognitive performance

We examined whether dynamic light across a scheduled 16h waking day influences cognitive performance, visual comfort, melatonin secretion, sleepiness and sleep under strictly controlled laboratory conditions of 49h duration. Participants spent the first 5h in the evening under standard lighting, followed by an 8h nocturnal sleep episode at habitual bedtimes. Thereafter volunteers either woke up with static daylight LED (100 lux and 4000 Kelvin) or with a dynamic daylight LED that changed color (2700 to 5000 Kelvin) and intensity (0 to 100 lux) across the scheduled 16h waking day. This was followed by an 8h nocturnal treatment sleep episode at habitual bedtimes. Thereafter, volunteers spent another 12h either under static or dynamic light during scheduled wakefulness. Under dynamic light, evening melatonin levels were less suppressed 1.5hours prior to usual bedtime, and participants felt less vigilant in the evening compared to static light. Sleep latency was significantly shorter in both the baseline and treatment night compared to the static light condition while sleep structure, sleep quality, cognitive performance and visual comfort did not significantly change. Our results support the recommendation of using blue-depleted light and low illuminances in the late evening, which can be achieved by a dynamically changing daylight LED solution.