The circadian rhythm is set by external cues of light and darkness. Light increases wakefulness hormones, like cortisol, and darkness is necessary for production of sleep hormones, like melatonin. The amplitude of this hormonal fluctuation is important: you want your wakeful hormones to go way down at night and your sleep hormones to go way up. The greater the fluctuation the easier it is to reach the deepest most restorative phases of sleep. You can help strengthen this rhythm by getting plenty of daylight during the day. Get outside on your lunch break, walk to work, keep the blinds open. If you battle with Seasonal Affective Disorder during the low-light months of winter, then use a full-spectrum lamp at least 30 minutes a day. Conversely, don’t sit under bright lighting at night. Avoid looking at backlit screens like a computer, laptop, TV, tablet or smartphone for long periods in the evening when your eyes should be absorbing in cues from the darkness. Blue light is especially disruptive to sleep quality. Consider using software for your devices that blocks blue light. Either way, avoid looking at electronic screens in the last 60-90 minutes before bed.