To quote:

It’s not just animals who are being flummoxed by our efforts to create a permanent daylight. As this month’s National Geographic points out, we’re making an end-run around our own circadian rhythms. Verlyn Klinkenborg writes:

For the past century or so, we’ve been performing an open-ended experiment on ourselves, extending the day, shortening the night, and short-circuiting the human body’s sensitive response to light. The consequences of our bright new world are more readily perceptible in less adaptable creatures living in the peripheral glow of our prosperity. But for humans, too, light pollution may take a biological toll.

Full article here:

http://features.csmonitor.com/environment/2008/12/01/light-pollution-harms-not-just-stargazers/