20. Dewan, Edmond M. “On the possibility of a perfect rhythm method of birth control by periodic light stimulation.” American Journal of Obstetrics and Gynecology 99, no. 7 (1967): 1016–1019; Lin, May C., Daniel F. Kripke, Barbara L. Perry, and Sarah L. Berga. “Night light alters menstrual cycles.” Psychiatry Research 33, no. 2 (1990): 135–138; Rex, Katharine M., Daniel F. Kripke, Roger J. Cole, and Melville R. Klauber. “Nocturnal light effects on menstrual cycle length.” The Journal of Alternative and Complementary Medicine 3, no. 4 (1997): 387–390.