Evening home lighting adversely impacts the circadian system and sleep

Abstract

The regular rise and fall of the sun resulted in the development of 24-h rhythms in virtually all organisms. In an evolutionary heartbeat, humans have taken control of their light environment with electric light. Humans are highly sensitive to light, yet most people now use light until bedtime. We evaluated the impact of modern home lighting environments in relation to sleep and individual-level light sensitivity using a new wearable spectrophotometer. We found that nearly half of homes had bright enough light to suppress melatonin by 50%, but with a wide range of individual responses (0-87% suppression for the average home). Greater evening light relative to an individual's average was associated with increased wakefulness after bedtime. Homes with energy-efficient lights had nearly double the melanopic illuminance of homes with incandescent lighting. These findings demonstrate that home lighting significantly affects sleep and the circadian system, but the impact of lighting for a specific individual in their home is highly unpredictable.

Figure 1

A new wearable for assessing ambulatory melanopic illuminance. (A) The wearable spectrophotometer is clipped to clothing and records light exposure near eye level. (B) An example of melanopic illuminance across a single waking day, with pop-outs showing recorded spectra at certain times of day.

Figure 2

Home lighting in the context of circadian light sensitivity. Using individual-level dose-response curves for light (A) in combination with home light recordings, we predicted melatonin suppression in each home across the range of individual sensitivity levels (B), with rows sorted by number of homes with > 25% suppression. Predicted responses across individuals are shown as histograms (C) for the dimmest home, average home (median brightness), and brightest home.

Figure 3

Artificial light results in an extended twilight. Changes in melanopic illuminance in the evening for a natural sunset (yellow line), compared with home lighting. Individual homes are shown as gray curves, averaged across nights and smoothed with a 3-h moving average, ending with a gray dot at the individual’s average bedtime. The blue lines show the median (thick solid line), interquartile range (thin solid lines), and the 10th and 90th percentiles (dashed lines) for homes before bedtime.

Figure 4

Energy-efficient lighting is associated with higher melanopic illuminance. (A) Average spectra for each night (3 h up to bedtime) are plotted according to average melanopic illuminance (x-axis position) and melanopic-to-photopic ratio (M:P ratio; y-axis position). Spectra that were classified as predominantly one light source type are colored green (fluorescent), blue (LED), or red (incandescent). Spectra that were unclassified/hybrids of light types are colored gray. (B) Distributions of melanopic illuminance for the three light types.