In a previous blog we wrote about a preprint publication of 18 scientist that agreed on recommendations for daytime light and evening light in indoor environments. These recommendations are meant for adults for a better sleep during the night and more energy during the day. The publication is now finalized and published. This news post is a brief summary by one of the authors dr. Luc Schlangen.
The human indoor light environment strongly differs from the natural light-dark cycle outdoors, both in spectrum and amount of light exposure. The ubiquitous availability of electric light enables us to spend large parts of our day indoors, in conditions with limited, or sometimes even without, any natural daylight. Across daytime we therefore expose ourselves to relatively dim light conditions, while during the evening and at nighttime the abundant use of electric light deprives us of natural darkness. Consequently, in our 24/7 society, we experience dimmer days, brighter nights and a much smaller day-night contrast as compared to natural light-dark cycle outdoors. This has negative consequences for our daily mood and functioning, as well as for our sleep, health, and well-being.
Our 24-hour exposure to light and darkness has important influences on our physiology and behaviour. It regulates our circadian rhythms and affects our mood, daytime functioning and nighttime sleep. These effects are mediated by a (melanopsin-based) photoreceptor that is maximally sensitive to the short wavelength portion of the visible spectrum around 480 nm, unlike vision which is dominated by the traditional rod and cone photoreceptors. The spectral sensitivity of the long and medium wavelength sensitive cones defines the units lux and lumen that are commonly used to characterize the brightness of our light environment as experienced by an average human observer. However, for circadian and other non-visual effects of light on physiology and behaviour the traditional units lux and lumen are less appropriate.
Recently an international expert workshop on circadian and neurophysiological photometry, developed a set of recommendations to best support human physiology, sleep and wakefulness in day-active people within indoor settings. The workshop specified bright days and dim nights, not with respect to vision, but for the non-visual functions of light which are typically driven by the melanopsin-based photoreceptor. For this photoreceptor, the brightness of a light condition can be specified in terms of a recently-developed and standardized metric, melanopic equivalent daylight illuminance (melanopic EDI). The recommendations are published in PLOS Biology and specify what daytime, evening and nighttime light exposures are best to support human health and wellbeing.
The recommendations provide highly needed further guidance towards truly integrative lighting solutions, but are not meant to supersede existing guidelines and regulations relating to for instance visual function, comfort and energy consumption.
The expert consensus-based recommendations from the workshop are:
Throughout the daytime, the recommended minimum melanopic EDI is 250 lux at the eye measured in the vertical plane at approximately 1.2 m height (i.e., vertical illuminance at eye level when seated). If available, daylight should be used in the first instance to meet these levels.
During the evening, starting at least three hours before bedtime, the recommended maximum melanopic EDI is 10 lux measured at the eye in the vertical plane approximately 1.2 m height.
The sleep environment should be as dark as possible. The recommended maximum ambient melanopic EDI is 1 lux measured at the eye. In case certain activities during the night-time require vision, the recommended maximum melanopic EDI is 10 lux measured at the eye in the vertical plane.
dr. Luc Schlangen, Eindhoven University of Technology, Eindhoven, The Netherlands