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The Lighting Research Center (LRC) at Rensselaer Polytechnic Institute has published new guidance documents for designing circadian-effective lighting in K-12 classrooms and hospital patient rooms while avoiding increased energy use.
The guidance documents provide background information and summaries of recent research into the benefits of lighting for circadian entrainment for K-12 students and hospital patients. The primary aim of the publications is to offer guidance for achieving effective, healthy lighting solutions in both applications while limiting increased energy use to the greatest extent possible.
For circadian entrainment and improvements in sleep quality and psychological health, high daytime light levels at the eye are necessary, followed by low evening/nighttime light levels in order to achieve a robust 24-hour light-dark pattern. However, the recommended light levels in K-12 classrooms and for general (non-exam) lighting in hospital patient rooms are generally too low for daytime circadian stimulation. Providing the necessary light levels using design strategies typically intended to deliver illuminance to the horizontal workplane (as opposed to vertical illuminance at the eye) can have the unwanted result of increasing energy use compared to lighting installations designed with only visual performance in mind.
To avoid increased energy use, designers should employ luminaires and luminaire locations that maximize the vertical-to-horizontal illuminance ratio while also avoiding discomfort glare, especially in patient rooms. Designers can also increase the circadian-effectiveness of the overhead lighting by increasing overall light levels to 500 lux on the workplane for at least 2 hours during the daytime and using a CCT of 3500K or higher. The most energy-efficient technique for designers to consider, however, is the addition of a supplemental layer of narrowband short-wavelength (blue) light in conjunction with typical overhead lighting. This method can avoid increasing overall light levels or using very cool CCTs while providing effective circadian lighting and only minimally increasing energy use.
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