I often advise clients who have difficulty sleeping to be mindful of their levels of light exposure throughout the day. The reason is that our bodies have an internal circadian biological clock, which responds to light exposure, that regulates sleep and alertness throughout the day.
When light enters our eyes, specialized cells (i.e., suprachiasmic nucleus) in the brain send signals to orchestrate changes that lead to wakefulness, such as increase in body temperature, cortisol release, and delaying release of a hormone called melatonin, which is involved in promoting sleep onset.
Hence, to promote wakefulness, it is a good idea to get exposed to light, ideally natural light, first thing in the morning and during the day (even on a cloudy Vancouver day). In the early evening, to encourage sleepiness and melatonin release, limit light exposure by turning off or dimming lights and limiting screen time from devices such as computers, tablets and smart phones. Blue light emitted from these devices can be especially disruptive to sleep.
Recent research suggests that pre-bedtime screen time, compared to reading a printed book, is associated with reduced sleepiness, suppressed melatonin levels, and decreased alertness the next morning (even after sleeping eight hours).