Light pollution's effects #4:
Environmental & Biological Consequences
Humans, animals, and plants are all attuned to our planet’s 24-hour cycle.We've all experienced how "jet lag" from a long-distance flight can disrupt the human body's circadian (day-night) cycle. Wildlife and fish also become disoriented when there's too much artificial light at night. It can affect their mating, migration, sleep, and finding food.
For example, many species of birds migrate or hunt at night, which makes them extremely vulnerable to bright lights in areas that are naturally dark. Birds can be drawn to light sources, especially while migrating. Not wanting to fly back into the dark, they continue to fly in the light’s beam or wander off course until they are exhausted, fall, or become prey. An estimated 40,000,000 birds die this way each year.
Reptiles are likewise affected by light pollution. For example, female sea turtles like to nest on remote and very dark beaches. Coastal lights interfere with sea-turtle hatchlings, which crawl instinctively toward the ocean because its reflection of the moon and stars. Artificial lights can confuse the hatchlings and cause them to crawl onto roads or into communities, often leading to fatal exhaustion or dehydration.
Humans are not immune from the negative effects of light at night. When in deep sleep, a small gland in our brain produces a compound called melatonin that helps maintain our immune system and general well being. But our brain won't produce melatonin if it isn't dark — in fact, the eye contains a light sensor, unrelated to vision, that appears to tell the brain that it's dark enough to make the stuff.
Just how much light at night inhibits melatonin production isn't known. However, evidence is mounting that women have greater risk of developing breast cancer if they work at night or live in brightly lit urban areas. And last year the International Agency for Research on Cancer, the cancer arm of the World Health Organization, added overnight shift work as a probable carcinogen. One likely cause? Reduced melatonin production caused by exposure to light during sleep.