Working toward legislation to curb light pollution in Illinois.

Illinois Coalition for Responsible Outdoor Lighting

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Lighting and Human Health Concerns

In just the past century, electric lighting technology has offered us brilliant sources of artificial light, allowing mankind to change the face of the night on a widespread scale for the first time. Where we want "day", we can make day. While for eons the night was a natural time for rest and sleep, we are no longer bounded by daylight's schedule, and can re-arrange the hours as we please. Our modern "darkness-free" nights spread over larger areas, and grow brighter, month after month.

But are our bodies prepared to be taken from a natural, regular day-night cycle, and subjected instead to random periods of light and dark, or no dark at all? This question is more serious than it might sound; research is beginning to show the existence of patterns in the occurences of a diverse assortment of disorders and diseases which indicate ties between illness and the disruption of the day/night cycle.

The Circadian Rhythm

To suggest that nighttime lighting might have adverse health effects on humans, we need to look for a mode of causality, an understanding of any mechanisms which might link light to health. The circadian rhythm, a diverse set of physiological, biochemical and behavioral fluctuations which occur on a 24-hour cycle in a wide variety of living organisms, has been demonstrated to occur in numerous forms in human beings1. In people, there are a number of separate "clocks" within different internal systems, and they are all synchronized by a "master clock" located in the hypothalamus2. The "master clock" is then set by signals from the eyes, which simply tell the brain whether the environment around the body is light or dark, regardless of whether the eyes are open or closed, and even in some people who are otherwise blind3.

Removing darkness from people's daily schedule may cause disease.  
What happens when we disrupt the functioning body's internal clocks? The undesirable results in the short run can include sleep disorders, fatigue, digestive problems, mood swings, depression and irritability. With prolonged disruption of the circadian rhythm, obesity, rheumatoid arthritis, duodenal ulcers, and heart ailments are among the list of diseases which become more likely than they are in people with stable rhythms. Such health consequences have been well documented in workers who face a rotating shift schedule which keeps their body clocks from stabilizing4,5,6. Some initial studies have indicated ties between circadian rhythm disruption from shift work and increased occurence of cancer7. While research remains to be done, a link between light, daily cycles, and cancer is becoming evident8.

Stray nighttime illumination might be making us sick.

Are our darkness-free nights making us sick?

What about the members of the population who live with nighttime light, but don't face the magnitude of disruption which shift workers do; could lack of darkness be effecting our health, too? The disorders and diseases which are noted to increase in workers with rotating shifts certainly are also common in the general population. Some of them have increased in rate of occurence over the past century (over which artificial nighttime illumination has skyrocketed). Those facts, however, do not demonstrate any clear link between light and disease. But some recent studies are showing tantalizing hints of possible negative effects that lack of darkness might be having on the general population. A recent study from Israel showed a significant statistical correlation of incidence of breast cancer to the general nighttime illumination ("light pollution") in the localities where women live9. A study of college students showed a statistical increase in the development of myopia (near-sightedness) in students who were exposed to less darkness (whether asleep or awake) than the group which experienced longer actual dark time on a daily basis10.

Light pollution poses a potential health hazard to many people.Many more studies will need to be done to define the rolls which environmental lighting play in human health and disease. But it is difficult to conduct scientific studies on human beings; we cannot raise generations of people in cages, controlling their environment scientifically. History shows that demonstrating environmental causes for human health problems is a long, drawn-out process. Assembling convincing evidence took decades when it came to establishing the health hazards caused by having materials like lead, asbestos, mercury, and PCBs in the environment. Studies of potential health hazards caused by excessive nighttime illumination are just beginning. The question is: Do we wait for decades, and the outcome of more long-term studies (if such studies receive a share of the dwindling funding which many fields of scientific inquiry face), or do we act in a more timely manner?

Unlike lead, asbestos, mercury, and PCBs, stray nighttime lighting serves no purpose. We won't face potential economic hardship from having to find a replacement for it; we just need to stop creating it. As far as intentional nighttime illumination is concerned, we need to seriously analyze the "when, where, and how much" factors much more; as pointed out on other pages of this website, we already need to do that sort of analysis from an energy consumption standpoint, anyway. But our health is nothing to ignore. Lighting practices simply must progress past the primitive attitude of "more must be better". The light seeping in through your bedroom window at night may be doing more than making it hard to get a good night's sleep.

Additional Resources:

  The article How Bright the Night? Light and Human Health on this website delves into these issues in greater depth.  

There are many articles and studies availble on the Internet about light and health. Below, we give links to some which we find to be well-written synopses of some of the topics touched upon on this page; you will find many more on the Resources> Links page of this website.

1Wikipedia has a good introduction to the circadian rhythm.     2A Boston Globe article (8/20/07) with a good synopsis on the human internal clocks.     3A Salk Institure press release (1/27/05) on the discovery of the primitive light/dark sense cells in the human eye.     4A Workers Health & Safety Centre (Canada) report (2004) on shift work.     5A Science News article (8/5/07) on shift work and sleep disorders.     6A Science News article (4/11/08) on shift work and organ disease.     7News story (12/3/07) on World Health Organization statement linking shift work as cancer cause.     8Science News article (10/17/98) on cancer and nighttime illumination.     9Washington Post article (2/20/08) on excess nighttime illumination and breast cancer.     10Report on study (5/02) on development of myopia.

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