0030 Effect of a Simulated Sunset versus Typical Indoor Lighting on Evening Melatonin Levels

Abstract

Introduction: The human circadian clock evolved in the presence of the natural light-dark solar cycle. Exposure to artificial light at night suppresses endogenous melatonin levels and delays the timing of the circadian clock. The advent of tunable LED (light emitting diode) technology presents an opportunity to develop and implement circadian based practices for healthy lighting. Here we determined the influence of a simulated sunset with tunable LED technology on evening melatonin levels. Method(s): Nine healthy adults (3 females, 24.0 +/- 5.3 years) completed a 15-day crossover study comparing typical artificial indoor lighting versus a simulated sunset using tunable LEDs (Acuity Brands-Rubik). After 1 week maintaining an ~8h sleep schedule, participants arrived at the laboratory 6h prior to habitual bedtime. Typical electrical indoor home lighting was <90 lux in angle of gaze until scheduled bedtime (<467 lux maximum at 183 cm in the direction of the ceiling mounted light fixtures; 3,500K). To simulate sunset, a simple least square fit was used to match relative spectral irradiance of the laboratory LED lighting to solar spectral irradiance of a standard mid-latitude summer atmosphere in Boulder, Colorado with solar elevation angles ranging from 3.9 degrees to 0 degrees (sunset). The first 3h30min of the simulation was typical indoor lighting of <90 lux (angle of gaze; 3,500K) followed by a 25 min transition in spectral irradiance and then 2h5min at ~7 lux in the angle of gaze (<38 lux maximum at 183 cm; 2,700K). Result(s): Melatonin levels were initially similar between conditions but were significantly higher (p<0.05) after the sunset transition in the simulated sunset condition compared to the typical electrical indoor home lighting condition. Conclusion(s): These preliminary findings suggest that simulating a sunset transition with tunable LED technology prior to habitual bedtime in the evening has potential to benefit circadian health.