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Spatial distribution refers to the location from which light is delivered. For example: overhead (ceiling), at the taskplane (table lamp), or low level (pathway lighting or nightlight).
A collection of research studies from the late 1990’s to the early 2000’s showed that light coming from above the horizon has a stronger impact on our circadian rhythms than light coming from below the horizon. The studies also revealed that light coming from below the horizon has almost no effect on melatonin suppression. Additionally, some studies demonstrated that light coming from the side/periphery is just as good as light coming from straight ahead. The findings from these studies tell us that melanopsin containing ipRGCs (which are blue sky seeking sensors in our eyes) are looking for this sky blue signal to come from all different directions above the horizon.
With this data in mind, BIOS has developed a simple method for thinking about where to place circadian lighting for day and night applications – Designers should focus on “lighting the sky” (above the horizon) during the daytime and “lighting the fire” (below the horizon) at night. Circadian lighting design should also be thought of in layers of light. During the day, designers should light vertical surfaces, promoting high vertical brightness and use sources that contain high sky blue frequencies. At night, designers should use warmer color temperature sources with light directed at horizontal planes and tasks below the horizon, such as walkways and on work surfaces like tabletops. Reducing color temperature and focusing light below the horizon will help ensure low vertical brightness and reduce the circadian impact of light at night.