This article linked below gives me a new nudge to go to sleep when the sun goes down and get up when the sun comes up. It's only natural. For lighting at night, I like to use candles, which are not bright enough to interfere with melatonin production. And I have to keep reminding myself to turn off the blasted computer screen when the sun goes down.
Mercola points out (in link) that cancer incidence is directly related to longitude...folks near the equator don't get much cancer. He believes this is due to vitamin D levels. He discourages sunblock usage because many of the sunblocks available are toxic. Here's his take: http://v.mercola.com/blogs/public_blog/How-to-Reduce-Your-Risk-of-Cancer-By-50--8790.aspx
And here's a post about electric lighting and the relationship to cancer:
Electric Light may pose Cancer Risk
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