A blog by Oliver Stefani
From a nutritional standpoint, much is known about healthy snacks, but defining a LIGHT snack is more complex. We know that higher light intensities during the day, more than what we currently experience indoors, are better for our sleep and health. Light exposure during the day also influences evening light sensitivity, with more light exposure during the day reducing light sensitivity in the evening.
Brown et al. (2022) recommend a minimum of 250 lx mEDI throughout the day. The following thoughts are not based on deductive scientific conclusions, but just playing with numbers. Assuming we sleep for 8 hours and have three hours before bedtime below the recommended 10 lx mEDI, this would be 13 hours at 250 lx mEDI, totaling a minimum recommended daily light exposure of 3,250 lx*h . In a recent study by Schöllhorn et al.(2023) participants were exposed to approximately 33,000 lx*h in summer and 15,000 lx*h in winter on the day before they entered a study on light effects in the evening. This exposure is 5 to 10 times higher than the minimal indoor lighting recommendation.
Photo by: Oliver Stefani
The study examined the extent to which studies on the effects of evening light included seasonal information. The authors concluded that more sleep and circadian studies have been conducted in winter than in summer, and measuring individual light history isn’t standard practice. They found that evening light sensitivity is indeed reduced in summer, likely due to higher daytime light exposure. In summer, the evening light exposure under test had no impact on the time needed to fall asleep. However,, in winter, sleep latency was significant affected by the evening light exposure in their experiment. To draw firmer conclusions and make recommendations about light snacks, measuring individual light exposure history is essential. For now, what this means to me is that “light snacks” during the day are more important in winter than in summer, when we naturally get a full meal of good (day-) light anyway. In winter, stepping out onto the balcony from time to time might be a good light snack.
The Good Light Group recommends taking a daily 2 hour walk outside in natural light. Spending 2 hours outdoors in winter is challenging, even for dog owners. How long should we be out on the balcony? We don’t know but we could play with numbers again: Reykjavik in Iceland has a median diffuse outdoor illuminance of 11.500 lx and Icelanders are one of the happiest nations in the world. As this is daylight, we can estimate 11.500 lx mEDI as well. An outdoor cigarette break is around 5 minutes. That would correspond roughly to 1000 lx*h in Reykjavik. With three – of course non-smoking - cigarette breaks of 5 minutes we could at least achieve the minimum recommended light dose, even if this is only a rough estimate.
In any case, a light LIGHT dinner should not exceed the recommended 30 lx*h mEDI.
Brown et al. (2022): https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3001571
Schöllhorn et al. (2023): https://www.mdpi.com/2624-5175/5/4/44