The Biology of Darkness

NIKI WILSON – On Science
October 11, 2012

The Jasper Fitzhugh

Photo: Rogier Gruys of Blue Peak Travel Photography

There’s something relaxing about watching a sunset. The blue sky slowly gives way to yellows, and reds. From light to dusk, then dusk to dark. I like to enjoy sunsets with a cold lager in my hand after a good hike. I don’t know if it’s the beer or the exercise, but I often feel a little bit sleepy once the sun dips from view.

Turns out that although the hops and hiking contribute, it’s most likely the light fading that tells my body it’s bedtime. Periods of darkness are crucial for us humans, who’ve spent 3.5 million years taking advantage of the night to rest and repair our bodies. The study of this biological need for darkness is called scotobiology.

Robert Dick is the principal of the Canadian Scotobiology Research Group, and is also a proponent of Dark Sky Preserves through the Royal Astronomical Society of Canada.

Dick explains that humans have evolved to hunt and gather during the daytime hours. “In general, we are adapted to rest at night.”

One of these adaptations is the presence of eye receptors that do not contribute to vision, but are used to detect light with a wavelength in the blue spectrum. Blue light is what we see when the light from the sun is scattered across our daytime sky. These receptors appear to regulate our “sleep/wake” cycles, known as circadian rhythms.

“In the fading light of dusk, [these receptors] detect blue, and they tell your body it is not yet night,” says Dick. “But once the blue fades below a certain threshold, which turns out to be about [the spectrum emitted by] the full moon, then your body says ahh…it’s night time.”

At night, the body’s endocrine system releases hormones such as melatonin, growth hormone and prolactin. These hormones play important roles in our health and development. They are generally made in the late afternoon, in preparation for release at bedtime. Fading blue spectrum light is an important cue for the body to prepare the release of the hormones.

Unfortunately, many of us don’t watch the sun set to black every night, and may not necessarily notice the light fading from the sky. We live in a world full of white light bulbs, a component of which is blue spectrum light. Think of your TV, house lights, and certain streetlights. If you’re like me, you may spend too many night time hours with your laptop screen belting blue spectrum light into your eyes.

“When you have artificial light at night you don’t take advantage of your body’s natural repair systems, and as a result you are not as healthy as you could be,” says Dick.

The deleterious effects of artificial light at night (ALAN) have been studied extensively on shift-workers, whom have been shown to be more vulnerable to hormone-related cancers.

For example, in a landmark study on female nurses, researchers showed that women who worked the graveyard shift at least once in the ten years prior were at an approximately 60 per cent increased risk for breast cancer, compared with those who did not work the graveyard shift. It wasn’t just that the women were sleep deprived, but that they were bathed in artificial light, thus disrupting melatonin release cycles.

Similarly, another study that looked at ALAN exposure across 164 countries found a significant association between high levels of ALAN and prostate cancer in men. Populations experiencing the highest level of ALAN were much more vulnerable to the disease than those experiencing the lowest. This is again likely due to the suppression of melatonin and/or disruption of circadian rhythms.

Animals and plants are also affected by ALAN. In the book The Ecological Consequences of Artificial Outdoor Lighting, editors Catherine Rich and Travis Longcore write: “From nest choice and breeding success of birds to behavioural and physiological changes in salamanders, many organisms are seriously affected by human alterations in natural patterns of light and dark.”

They point to well-publicized cases, like the disorientation of sea turtle hatchlings by beach-front lighting, and the confusion, exhaustion, and collisions experienced by migrating birds when they encounter lighted towers and tall buildings.

Dick adds that impacts on small critters are also of concern: “White light attracts insects and disrupts their night time behaviour. Since they form a base for the food chain, this alters the ecology of the region.”

These are not new problems, although the specific implications for human health and animal/plant welfare are only more recently being studied. As the evidence mounts, some communities are beginning to implement technologies that work toward decreasing the amount and type of light emitted (i.e. replacing unshielded streetlights with fully-shielded, low-pressure sodium lights). While many of the shielded lights still emit some blue spectrum, they are a darker step in the right direction.

Still, Dick says there is substantial resistance to dark sky policy, especially in cities. “We have to demonstrate to the public that [darkness is] not so bad. In fact, it’s kind of nice not to have light in your face all the time.”

Dick says one of the ways to convince people is by creating Dark Sky Preserves (like Jasper National Park), and inviting the public to experience them.

We don’t need complete darkness to be healthy. Most life has evolved to accommodate small amounts of light (like that from stars). However, to be at our healthiest, we need a good chunk of night time free of ALAN. For starters I’ll turn off my son’s night light once he konks out (don’t tell him), and I will try to avoid the 1 a.m. twitchy legs by limiting my screen time before bed. With that in mind, I shall now banish the blue light and bring this to a close. Lights out.