henry copeland:

Study links night exposure to blue light with breast and prostate cancer: Researchers used images taken by astronauts to evaluate outdoor lighting in Madrid and Barcelona -- ScienceDaily

Results obtained for both cities show that participants exposed to higher levels of blue light had a 1.5 and 2-fold higher risk of developing breast and prostate cancer, respectively, as compared to the less-exposed population.
- www.sciencedaily.com