Globe-shaped light fixtures send light in all directions -- including straight up into the sky and streaming through your bedroom window.

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The Dark Side of Light Pollution: Human Effects

We might not wander the wrong way on the beach or crash headfirst into the upper stories of skyscrapers, but that doesn't mean that light pollution -- and an overexposure to light in general -- isn't just as damaging to our bodily functions and overall health.

Regular people also suffer when there's too much light floating around. There are many complex components, but one factor that pops up repeatedly is melatonin: Too much nighttime light equals too little melatonin production. One little hormone might not seem like too big of a loss, but research has consistently proven that low melatonin levels are incredibly detrimental, with sweeping health effects across the body. Light during the nighttime, even at low levels, can seriously impede melatonin production. Less than 40 minutes basking under an incandescent light bulb can reduce melatonin levels up to 50 percent [source: Navara].

Melatonin affects a whole host of bodily processes including metabolism, immune function, and, through the endocrine system, helps balance reproductive, thyroid and adrenal hormones. When you throw into the mix closely related factors such as disrupted circadian rhythms and sleep deprivation, there's a laundry list of the health concerns that have been linked in some degree to an artificially lit world. Among them are obesity, type II diabetes, coronary heart disease, hypertension, insulin resistance, poor metabolism and heart attacks.

Breast cancer and other cancers are another major concern. Melatonin acts as an antioxidant, so combined with all its other key roles, increased cancer risk should come as no surprise -- although the actual figures might. In the developed nations, women are five times more likely to get breast cancer than women in underdeveloped nations [source: Navara]. Shift workers who spend their nights under artificial lights are another group that's highly susceptible to these effects.

It's even been suggested that we've basically been running a massive global experiment, seeing how much we can handle before our addiction to light leads us to a very dark place. Luckily, light pollution is a pretty easy fix with benefits even larger in scope than the improved health of pretty much everything on the planet. Find out what you can do about it on the next page.