We really underestimate the impact that light has on our bodies. This time of year in the Northern hemisphere brings less exposure to daylight. It is cold/rainy/windy, so we avoid spending time outdoors in the daytime. Most people spend their waking day indoors in their workplace. And due to the shorter days, it is less likely that any of us really encounter much daylight outside before or after work.
But we get plenty of light inside from light bulbs, though. Or from computer screens, phones, e-books, and other electronic devices. This light is less bright than natural sunlight, but much brighter than moonlight. So, let's call this artificial light "medium light."
The body reacts to light all of the time.
Our body produces melatonin and cortisol to create our "circadian rhythm", our cycle of being asleep and being awake. High melatonin levels at night help induce sleep. High cortisol levels in the morning induce wakefulness.
If we lived outside as the animals we are, we would be exposed to much daylight during the day, and only moonlight at night. In our cozy buildings, however, we get this "medium" light consistently throughout the day. This means not enough daylight during the day and too much light in the evening.
During the day, when our cortisol levels are prone to be their highest, we should be exposed to a great amount of light. In particular, the blue spectrum of light (short wavelength), like those obnoxiously bright headlights you see on cars from time to time. If we are exposed to this spectrum of light from 7am to noon, we produce as much as 50% more of the "awake hormone" at this time than we would without this bright light exposure. (1)
Can you imagine being 50% more awake in the morning? Doesn't that sound great?
But exposure to light at night has a negative effect. Exposure to this blue spectrum light in the evening results in a dramatic drop in melatonin production, even in small amounts of light exposure. This means more difficulty getting to sleep, a hard time staying asleep, or lower quality of sleep. (1)
Interestingly, exposure to light in the red spectrum (long wavelength) does not suppress melatonin production like blue light does. According to the research, there is no statistical difference between red light and darkness when it comes to affecting our melatonin levels. (1)
For a wakeful, energetic morning:
For a deeper rest at night:
I have met very few people that don't have any difficulty with sleep AND also feel energetic in the morning. So please don't take light for granted. Some very simple changes in light exposure can make significant changes to your health, especially during the darker months.
1. Mariana G. Figueiro and Mark S. Rea. The Effects of Red and Blue Lights on Circadian Variations in Cortisol, Alpha Amylase, and Melatonin. 2 March 2010. http://www.hindawi.com/journals/ije/2010/829351/