Testosterone levels also went up, from 2.1 ng/ml to 3.6 ng/ml in the light-treatment group. This boost in testosterone is what jump started their sex lives. "In the Northern hemisphere, the body’s testosterone production naturally declines from November through April, and then rises steadily through the spring and summer with a peak in October," the study's lead scientist Andrea Fagiolini said in a press release. "You see the effect of this in reproductive rates, with the month of June showing the highest rate of conception. The use of the light box really mimics what nature does."