It may be down to how much light you’re exposed to at night. Researchers at Ohio State University, and the Salk Institute for Biological Studies found late-night exposure to everything from light bulbs to the blue light from electronic screens does more than disturb sleep. It throws off the internal clock in the area of the brain that manages emotion, which can reduce happiness. But increasing your light exposure during the day, and decreasing it after dark, synchronizes your body clock, and is proven to boost moods. So, turn off extra lights, and dim your electronic screens, at least two hours before bed. Not just so you sleep better, but for your mood too.