[Answer] What hormone is produced in response to darkness?
…When darkness falls, the suprachiasmatic nucleus in your brain tells the pineal gland to increase production of the hormone melatonin. Melatonin works with your circadian rhythm, the body’s internal clock, to induce drowsiness to help you sleep. Since it’s triggered by darkness, bright lights close to bedtime (such as from electronic screens) can inhibit production and disrupt your day-night cycle.
What hormone is produced in response to darkness?